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FEBRUARY, 1967 THE ANALYST Vol. 92, No. 1091 Techniques in Gas Chromatography Part I. Choice of Solid Supports A Review * BY J. F. PALFRAMAN AND E. A. WALKER (Ministvy of Technology, Labovatory of the Government Chemist, Cornwall House, Stamford Stveet, London, S.E. 1) SUMMARY OF CONTENTS Introduction Diatomaceous supports Types of diatomaceous supports Modified diatomaceous supports Treatment of diatomaceous supports Polar support de-activators Fluorocarbon supports Specialist supports Graphitised carbon Boehmite “Tide’ ’ Glass beads Sterrasters Vermiculite Porous polymer beads (a) Porapak ( b ) Chromosorb 102 (c) Polypak Conclusion Classification of supports THIS review of solid supports has been written as part of a general review of techniques of gas chromatography, which is intended to cover the period since the last general review in the Analyst by Rose1 in 1959.As the period has been one of intense activity in this field (over 7000 papers have been published on various facets of gas chromatography) it would clearly be a difficult task to cover the subject adequately in a single paper, and we therefore intend to produce a series of short reviews, by which means it should be possible to maintain the subject matter at a current level. The column has justifiably been described as the “heart of the gas chromatograph” and in its efficient functioning the solid support plays a vital r61e. However suitable a particular stationary phase may be for a given separation it will accomplish little if insufficient care is paid to the selection, gradation and treatment of the support, and as this is the first step in column preparation it is a good point at which to start this review.The effects of particle size and particle-size distribution were reviewed by Rose,l and apart from reiterating the importance of working with the minimum practicable distribution of particle size, it is not proposed to enter into any discussion of this topic, although some reference will be made to it in the discussion of preparative techniques at a later date. Since 1959 a considerable volume of literature has, however, been published on the treatment and choice of the so-called “inert” solid support. That the support could have a significant influence on such an important parameter as the retention time was acknowledged at the earliest stages of development.2 One has, in fact, only to realise that gas - solid chromatography constitutes a wide field of endeavour to appreciate that the support surface can have significant effects in this respect.Taking an extreme example, we have found that the tendency of carbon dioxide to tail when * Reprints of this paper will be available shortly. For details see Summaries in advertisement pages. 7172 PALFRAMAN AND WALKER: TECHNIQUES IN GAS CHROMATOGRAPHY [Analyst, Vol. 92 chromatographed on silica gel is considerably reduced by the addition of a 1 per cent. coating of SE30 as a stationary phase. The retention characteristics, on the other hand, are not very different from those on the bare silica-gel surface, and are certainly uncharacteristic of a 1 per cent.SE30 column on a normal “inert” type of support. Adsorption and its effect on peak symmetry still frequently remain limiting factors both in the interpretation of retention data, and quantitative evaluation. I t is not surprising, therefore, that considerable effort has been expended in the last few years in the quest for the elusive ideal solid support. DIATOMACEOU s SUPPORTS TYPES OF DIATOMACEOUS SUPPORTS- Ideally the function of the support is simply that of a retentive sponge, capable of holding immobile a relatively large volume of liquid, at the same time exposing a large inert surface area to ensure rapid attainment of equilibrium between solute and solvent. Although many materials have been tried with varying degrees of success, nothing yet has been found to be more satisfactory, in general application, than diatomaceous earths, which have been in use since the early days of James and Martin.3 Natural diatomite (Kieselguhr), which is somewhat fragile, is treated by calcining with a flux of sodium carbonate to 1600” C.This causes the material to fuse and the silica to be converted into crystalline cristobalite, the original grey diatomite becoming white in colour because of the conversion of iron oxide to a colourless complex sodium iron silicate. This flux-calcined material is marketed by Johns Manville as Celite or Chromosorb W. In a variation of the above process, the calcination takes place without the addition of a flux. This causes the mineral impurities to form complex oxides imparting a pink colour to the material, and this is marketed as firebrick or Chromo- sorb P.While neither Chromosorb P nor W may be regarded as ideal, they each fulfil supplementary functions that cover a wide range of applications. Chromosorb P has a greater density than W because of the destruction of the diatom structure in the calcination process, it is less fragile than W and is capable of holding a larger volume of liquid phase before becoming too sticky to flow freely. However, when used with polar solutes severe tailing is often encountered. This arises from adsorptive centres in the support which give rise to non-linear isotherms, an effect which is much less pronounced with the white supports. In a comparison of the pink and white supports Baker, Lee and Wall4 found that the properties varied with respect to surface area and pore-size distribution.The difference in pore size was considered by Otten~tein,~ who reported that the white support had pore sizes of about 9 p while the pink support had a smaller pore size (about 2.0 p). I t was shown that this difference explained the variation in column behaviour of the two supports, Chromosorb W holding the liquid phase in large pools and Chromosorb P in small ones. The column efficiency being controlled by the mass transfer between the liquid and the gas phase, the larger pools of liquid required longer transit times for the solute, and peak broadening was a result. Saha and Giddings6 attempted to correlate the C, terms of the Van Deemter equation with the distribution of pore size, by comparing experimental results with theoretical values.The results obtained for Chromosorb W were satisfactory but those of Chromosorb P were about fifty times too low. Several descriptive technical bulletins are issued by Johns Manville (London) describing the properties and uses of these materials. MODIFIED DIATOMACEOUS SUPPORTS- The realisation of the critical r61e played by the support in gas - liquid chromatography has led manufacturers to prepare and market materials made especially for this purpose. Johns Manville recently introduced Chromosorb G, which is also a diatomite, especially processed for use in gas - liquid chromatography, for which high efficiencies and greatly reduced surface activity are claimed. In our own experience, confirmed by personal com- munications from other workers, it is the most inactive support of its type available on the market, but it is often difficult to obtain good efficiencies by using this material. In a survey of comparative column efficiencies of some common solid supports Saha and Giddings’ showed decreasing potential efficiency through Chromosorb P, Chromosorb W, Gas-Chrom S to a minimum in Chromosorb G.Its physical characteristics differ somewhat from conventional supports, and this factor must be taken into consideration in column preparation. For example, it has a density of about two and a half times that of Chromosorb W, which meansFebruary, 19671 PART I. COMPARISON OF PHYSICAL Free fall density, g per ml . . Packed density, g per ml .. Surface area, m2 per gm . . Surface area, m2 per ml . . pH . . . . . . . . CHOICE OF SOLID SUPPORTS TABLE I PROPERTIES OF 60 TO 80-MESH CHROMOSORBS* Teflon, A P w G 40 to 60 mesh 0.40 0.38 0.18 0.47 0.42 0.48 0.47 0.24 0.58 0.49 2.7 4.0 1.0 0.5 7.8 1.3 1.88 0.29 0.39 - 7 - 1 6.5 8.5 8.5 - 73 TABLE I1 Silica . . . . . . . . Aluminium oxide . . . . Iron(II1) oxide . . .. Titanium dioxide . . . . Calcium oxide . . . . Magnesium oxide . . . . Sodium monoxide + potas- sium monoxide . . . . Moisture . . . . . . TYPICAL CHEMICAL ANALYSES OF CHROMOSORBS~ White Pink r A \ --7--- Non-acid washed, Acid washed, Non-acid washed, Acid washed, per cent. per cent. per cent. per cent. 90.6 91.6 88.9 90.0 4-4 4.1 4.0 3.6 1.6 1-4 1.6 1.4 0.2 0.2 0.2 0.2 0.6 0.4 0.6 0.4 0.6 0.5 0.6 0.5 1-0 0.9 3.6 3.2 0.3 0.3 0.3 0-3 TABLE III* COMPARISON OF WEIGHTS OF LIQUID PHASE IN ~OO-ML OF EACH SUPPORT AT VARIOUS LIQUID LOADINGS Chromosorb I 3 G w P Weight of support, g .. . . . . 58.0 24.0 47.0 Liquid phase a t 1 per cent., g . . 0.58 0.24 0.47 Liquid phase at 2 per cent., g . . 1.18 0.48 0.95 Liquid phase a t 3 per cent., g . . 1.79 0.74 1.45 Liquid phase a t 4 per cent., g . . 2.42 1.00 1.95 Liquid phase at 5 per cent., g . . 3.05 1.26 2.47 TABLE IV* COMPARISON OF SUPPORT FRIABILITY Breakdown, per cent. Mechanical shaking of 30 t o 60-mesh material G IT' I; -60 mesh in 5 minutes . . . . 1.6 19.4 12.0 -60 mesh in 10 minutes . . . . 8.6 53.4 27-6 -60 mesh in 15 minutes . . . . 12.4 75.8 46.0 * Johns Manville technical bulletin. t Ottcnstein.26 that a 5 per cent.w/w loading of liquid phase would be equivalent to a conventional 12 per cent. column. Chromosorb G is particularly useful when low loaded columns are required, as, for example, in steroid and pesticide analysis, where columns of the order of 1 per cent. w/w are necessary in order to minimise retention times. However, because of its low surface area, loadings greater than about 5 per cent. are not recommended. In contrast with this type of support, Chromosorb A, another flux calcined diatomite, was developed for preparative chromatography, where high liquid-phase loadings are required. Like Chromosorb P it has a large surface area, thus allowing a maximum loading of 25 per cent. (compared with 30 per cent. for P) and good mechanical properties, but in its low adsorptive characteristic it is closer to Chromosorb W or G.A summary of the properties of these materials is given in Tables I to IV.74 PALFRAMAN AND WALKER: TECHNIQUES I N GAS CHROMATOGRAPHY [Analyst, Vol. 92 TREATMENT OF DIATOMACEOUS SUPPORTS- Limitations in the reliability of the support imposed by the effects of solute adsorption have prompted a number of studies to be made directed at the elimination of the “active centres.” It is generally agreed that these consist of -OH groups associated with silicon, aluminium and iron,* and for this reason many workers have pre-treated the supports by prolonged extraction with various strengths of hydrochloric acid, which is said to leach out surface alumina and iron. For use in the analysis of amines James and Martin,g among others, have treated the neutralised acid-washed support with alkali; however, this treatment is queried by Fales and Pisano,lo who observe that tailing would persist if the compounds being analysed contain -OH or -NH groups.A detailed description of these techniques is given by Burchfield and Storrs.ll As an alternative to the removal of active centres by acid treatment, Omerod and Scott12 sought to cover them by coating the support with silver. The method is expensive and carries the risk of reactions taking place between themetal coating and the solute; it does, however, give surfaces of high thermal stability and the coating may be carried out in situ. Although treatment with acid can be effective in removing active -OH groups associated with surface impurities such as iron and aluminium, it does nothing to mitigate the effects of the silanol (-%OH) groups which still remain.Alkali treatment, as already menti~ned,~ may be used where basic solutes have to be resolved, but for many other compounds there remains an inherent risk of decomposition by residual alkali. Saturation of the silanol groups can also be accomplished by including in the stationary phase a small proportion of a functionally active compound capable of hydrogen bonding with these surface groups. Here again, the technique imposes limitations particularly for low loaded columns when the amount required may constitute a significant proportion of the total phase. An alternative method, which has been used with great success, is the modification of the surface hydroxyl groups by silanisation.A procedure for this, involving the use of dimethyldichlorosilane, was reported by Horning et aZ.13914 and a detailed study of the technique was carried out by Bohemen, Langer, Perrett and P~rne1l.l~ The dimethyl- dichlorosilane (DMCS) is assumed to react with the hydroxyl groups on the silica surface as follows- I I I I I I \ / / \ -Si-0-Si- + SiCI,(CH,),--+ -Si-0-53- + 2HC1. OH OH I 0 I 0 Si CH, CH, As the two adjacent -OH groups are required for complete reaction it is unlikely that all of the reactive sites are removed. A single -OH group might leave an undesirable Si-C1 linkage as follows- I I 1 I -Si-O-Si- + SjCI2(CH,), + -Si-O-Si-O-SiCl(CH,), + HC1. I AH I I As successful silanisation by means of DMCS has usually been followed by removal of hydrochloric acid by methanol it appears that the Si-C1 reacts with the methanol to form a methoxy compound- OCH, I 1 I I / I I I I \ -Si-0-Si-OSiCl(CH,), + CH,OH + -Si-0-Si-0-Si-CH, + HC1.CH, An alternative reagent, hexamethyldisilazane (HMDS) was used by Boheman, Langer, Perrett and Purnell15 to modify a pink support; this reacts quantitatively with single -OH groups forming a non-reactive linkage- I I I I 1 I I 1 -5-0-Si- + Si,(CH,),NH --+ -Si--0--Si- + NH,. OSi(CH,), OSi(CH,), OH OHFebruary, 19671 PART I. CHOICE OF SOLID SUPPORTS 75 In another paper Perrett and PurnelP compared HMDS-treated white and pink supports, and concluded that the surface of each was reduced by this treatment. As some reactive sites still remain, Littlewoods suggested that not all adsorption is associated with -OH groups.In another critical study of silanisation in which Chromosorb W was treated with various reagents, Kirklandl’ concluded that acid washing was the first essential in the production of a silanised material of minimum activity. A master batch of this support was, therefore, prepared and separate portions reacted with each of the silanising agents. From these supports 20 per cent. Apiezon L columns were prepared and used to separate the same polar test mixture. Although the separations gave similar retention times and efficiencies for each constituent of the test mixture there were pronounced differences in peak shape. Thus the peak asymmetry factorls for the DMCS-treated support was found to be the least, and that of TMCS (trimethylchlorosilane) was greatest, while severe tailing was found when an un- treated support was used.It is interesting to note that the surface area of the DMCS-treated support was considerably less than that of the other two. Kirkland’s views also received support from Fales and Pisano,lo who expressed preference for the DMCS treatment. Pro- cedures for silanisation have also been described by Supina, Kruppa and Henly,lg Purnel120 and elsewhere.21 In the last publication it was emphasised that the common test, flotation on water, for silane-treated supports is unsatisfactory as it qualifies many unsuitable supports. I t was also claimed that peak tailing is not an infallible guide with which to test supports; a more reliable method was to perform quantitative determinations of a known standard to check adsorption losses.Another approach, the co-polymerisation of hexamethyldisilazane on firebrick by treatment with fifty megarads of gamma irradiation, was discussed by Urone and Parcher,22 who claimed a “higher degree of paraffinic character” to the support than previously obtained. The preparation has been described of A e r ~ p a k , ~ ~ a “highly efficient’’ inert support based on silanised Chromosorb W, in which great emphasis has been given to the removal of “fines” at all stages of preparation. This is claimed to account for the improved efficiency and reduced tailing. In the process of silanisation, the character of the surface is changed from hydrophilic to hydrophobic, making it particularly effective for the retention of non-polar and moderately polar phases.However, the resulting production of a support of low surface energy makes it difficult to coat with polar phases because of poor wetting of the surface,17 and in an attempt to overcome this, Vanden-Heuvel, Gardiner and H ~ r n i n g ~ ~ used a coating of poly(viny1 pyrrolidone) which, they claim, does not act as a liquid phase itself but as a satisfactory support de-activator for use with polar phases. It is particularly suitable when using columns with a low percentage of liquid phase. This coating technique has been used successfully in the Government Laboratory for preparing polar columns for steroid analysis, and a similar technique involving the use of an epikote resin is used for pesticide analysis.Experience has shown that, to prepare a satisfactory column by this technique, it is essential to dry the support thoroughly by heating at 200” C for 4 hours before coating it with poly- (vinyl pyrrolidone) . Occasionally slight differences in retention times have been observed when this technique is used, but it is not clear whether this is due to the poly(viny1 pyrrolidone) itself, or the reduced effect of the support. The maximum temperature of operation of a poly(viny1 pyrro1idone)-treated support is 220” C. POLAR SUPPORT DE-ACTIVATORS- The main forces contributing to adsorption are considered to be weak van der Waal’s forces and stronger hydrogen bonding. Scholtz and Brandt26 suggested that all liquid phases neutralise the weak van der Waal’s forces, but that liquid phases capable of hydrogen bonding are required to de-activate the polar adsorption sites. The hydrogen-bonding sites are of two types; the first arises from silanol (Si-OH) groups, where the support is the proton donor in the hydrogen bond, and the second from siloxane (Si-0-Si) groups, where the support acts as the proton acceptor.Ottenstein26 points out that the siloxane group is much more effective in forming a hydrogen bond than the silane oxygen, and that it is the strength of the hydrogen bond that determines the extent of solute adsorption. Therefore, compounds that form strong hydrogen bonds, e.g., water, alcohols and amines, cause severe tailing, whereas ketones, esters, etc., with less tendency to form hydrogen bonds, cause little tailing.Scholz and Brandt25 saturated the silanol group by adding small amounts of Armeen S.D.,76 PALFRAMAN AND WALKER: TECHNIQUES I N GAS CHROMATOGRAPHY [Afizalyst, vol. 92 a long-chained fatty amine, to a non-polar liquid phase for the analysis of amines. Similarly, James and Martin3 eliminated tailing in the separation of fatty acids by incorporating a small amount of stearic acid in the silicone fluidused as a liquid phase. A ~ e r i l ~ ~ discussed the use of corrosion inhibitors in reducing tailing in packed and capillary columns, and among such compounds investigated were dicarboxylic acids (anionic), long-chain amines (cationic) and esterified polyglycols (non-ionic). He found that the use of these inhibitors allowed polar materials to be analysed on non-polar columns without loss of resolution due to tailing.By this procedure the retention times of the non-polar solutes are increased and those of polar solutes decreased. FLUOROCARBON SUPPORTS Of all supports, fluorine polymers are considered to be the most inert, but it is worth noting that although the properties required of an ideal support suggest the use of a totally inert substance, it must still have sufficient surface energy to be capable of holding the liquid phase. A detailed study of the fluoro-polymers as support materials has been made by Kirkland,17 ,28 in which he compares the properties of Kel-F (polymer of chlorotrifluoro- ethylene) , Fluoropak-80 and Teflon-6 (the last two forms of tetrafluoroethylene).The use of these substances as supports requires a more careful consideration of handling techniques than when the conventional diatomaceous ones are used. The choice of liquid phase for the fluorocarbons can be critical, as surface energies are much lower than those of diatomites and they are not so readily “wetted”; they are also fragile and need cooling below the transition point of 19” C before handling. A summary of the optimum conditions for preparation of Teflon columns is given1’- Optimum percentage Optimum carrier gas Support of liquid phase velocity, cm per second Teflon 6 . . . . . . .. 15 to 20 4 to 5 Fluoropak-80 . . . . . . 2 to 5 2 Kel-F . . .. . . . . 15 t o 20 10 t o 15 Under optimum conditions Kirkland17 claimed the following HETP values obtained when n-butanol was chromatographed- Support HETP, mm Surfacc area, m2 per gni Fluoropak-80 . ... .. 3.6 1.3 Kel-F (50 to 80 mesh) . . . . 2.6 2.2 Teflon 6 (full range) . . .. 2.3 10.9 Teflon 6 (40 to 60 mesh). . .. 1.7 10-5 1.1 - Chromosorb W . . . . . . From these values it seems that properly prepared Teflon columns have efficiencies similar to those prepared from Chromosorb W. However, other workers have reached different conclusions. Sawyer and Barr29 in a comparative study of a number of support materials (including Fluoropak-80, glass beads, Chromosorb W and carborundum) , found that the fluorocarbon support produced “very poor plate heights.” In a review of solid supports, Ottenstein26 cited several authors who had reported upon the use of Teflon, most of whom had com- mented upon the low efficiencies produced when this material was used as a support. It is, however, inert and has been considered useful in the analysis of aqueous samples.30 Japanese workers, Onaka and 0kamot0,~l have used diatomaceous-earth supports coated with PTFE, and found them useful for the separation of polar materials.Kirkland32 com- pared the performance of these coated supports with Teflon-6. From his survey it appears that the unmodified Teflon-6 produces peaks with less tailing than the PTFE-coated diato- maceous-earth supports, and he suggested that this arises from incomplete coating of the support surface. The coated supports, however, have the better handling properties and unlike the Teflon-6 do not have to be handled at temperatures below 19” C during column preparation.Teflon-6 generally produced columns of higher efficiencies, but unlike the coated support did not produce a linear retention - volume plot with change of liquid-phase loading, due no doubt to its low surface energy. SPECIAL~ST SUPPORTS GRAPHITISED CARBON- Since the time Eggertsen, Knight and Groenning~~~ used Pelletex (a modified carbon black) to separate c6 and C, hydrocarbons, an increasing number of workers have used aFebruary, 19671 PART I. CHOICE OF SOLID SUPPORTS 77 vai-iety of modified adsorbents both as supports and partitioning media. A butoxy-modified silica gel was used by Kirkland17 to separate the components of a Phillips’ hydrocarbon mixture. Perhaps the most interesting advance has been the use of thermally graphitised carbon black. The most serious objection to adsorption chromatography has been the asymmetry of the peaks obtained as a result of the heterogeneous nature of the surface. Graphitised carbon black, which is a thermal carbon black heated to 3000” C, has a moderately homogeneous surface which is also, within limits, reproducible. It, therefore, does not suffer from the same limitations as the more common adsorbents such as silica gel.Its nature and use have been discussed in detail by K i ~ e l e v , ~ ~ $ ~ ~ who also demonstrated a number of useful separations. Spheron-S coated on a polythene moulding powder (100 to 120 mesh) has been used analytically by Pope36 and B r ~ d a s k y , ~ ~ who compared Sterling FT 2700, a graphitised carbon, with the more conventional supports, Chromosorb W, Haloport F and Anakrom.When analysing a mixture of polar compounds (comprising water, alcohol, ketones and amines) on a non-polar phase (Dow Corning, Silicone Oil 200) he found that although adsorption was greater when using the graphitised carbon, it was superior in the prevention of peak asym- metry. Brodasky concluded that the advantages of using graphitised carbon as a support material included the elimination of chemical pre-treatment to prevent tailing, even with low loadings of non-polar stationary phases. High efficiencies were also obtainable, and there is little problem from temperature limitations, the principal disadvantage being the necessity of careful size grading of the coated support. Halasz and H o r ~ a t h ~ ~ reported the use of graphitised carbon as a porous layer on glass beads, with increased resolution in spite of shorter re ten tion times.BOEHMITE- Another versatile adsorbent, finding increasing use in a similar fashion, is Baymal (a fine alumina boehmite), which Kirkland17932,39 has used both for gas - solid and gas - liquid chromatography. This material consists of small crystalline fibrils of colloidal alumina, about 1000 A long and 50 A in diameter, with a high specific surface area of about 275 m2 per g. Because of its high positive surface charge, boehmite has a unique property, vix., ease of deposition from aqueous solutions on to a variety of surfa~es.3~,40~~~ This enables it to anchor to such negatively charged surfaces as carboxylic acids, colloidal silica, proteins, organic chelating agents and anionic surfactants.It has, therefore, great potential as a material for the preparation of “custom” surfaces for specialised separations, as, for example, capillary columns of a highly selective nature. The surfaces prepared from fibrillar boehmite can be further modified by conventional liquid phases or by prior treatment with acetate ions. Kirkland17 used boehmite, modified with stearic acid, to separate a mixture of low boiling fluorocarbons. “TIDE”- A commercial household detergent “Tide” has been used by a number of workers both as a support and a partitioning material. Its use was first reported by Gohlke and M~Lafferty~~ as a general-purpose material, and later by Desty and Harb0u1-n~~ for the separation of hydro- carbon mixtures.Decora and Dinneen44 obtained a porous, inert residue from “Tide” by grinding, sieving and extracting the organic material with 30” to 60” C light petroleum in a Soxhlet apparatus. This was then coated with a silicone oil and used as column packing in the separation of a number of pyridines, which was accomplished without producing tailing peaks. However, in later work45 on more basic nitrogenous samples, a modification (the residue was reacted with potassium hydroxide) had to be made to overcome the tailing. B e n ~ ~ ~ studied the adsorption characteristics of several supports used in gas chromatography including “Tide,” and found that while the elution of hydrocarbons was in the order of the boiling-points, the elution of ketones, acetates and alcohols was not.He was unable to predict the order of elution of oxygenated compounds when using “Tide” as support. Pocaro and Johnston4’ used unmodified “Tide” (although perfume and water had been removed by drying at 110” C) to separate 2-methyl-1-butanol from 3-methyl-1-butanol; previous attempts in which both polar and non-polar stationary phases were used had been unsuccessful in resolving these materials. GLASS BEADS- Glass beads have been used intermittently for a number of years as an alternative support. Callear and Cvetanovits4* used them as long ago as 1955 to reduce tailing, but although78 PALFRAMAN AND WALKER: TECHNIQUES IN GAS CHROMATOGRAPHY [Analyst, Vol. 92 the beads are thought by many to be relatively inactive, Littlew~od~~ has suggested that this is not universally acceptable.One of the main advantages of glass-bead columns is speed of analysis, arising from the low volume of liquid phase involved and improved per- meability due to evenness of packing which is made possible by the use of homogeneous, uniformly sized spherical particles. These factors also made glass beads ideal for theoretical studies on column p e r f o r m a n ~ e . ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ They are, on the other hand, usually much less efficient than conventionally packed columns. Several authorsa 955 have suggested that this is caused by the formation of liquid pools at the contact points between the beads and that it is, therefore, necessary to distribute the liquid thinly and evenly over the surface.An attempt to overcome this by mechanical etching of the beads was U ~ S U C C ~ S S ~ U ~ , ~ ~ but a study of the effect of chemical etching56 with hydrogen fluoride showed some improvement in efficiency, In 1960, Golay5’ suggested that the contact effect could be overcome by coating the beads with a porous inactive layer, a system that would retain the advantages of a solid non-permeable core, and more recently this approach has been given closer attention with some success. Dewar and Maier54 prepared a packing by coating the beads with a stationary phase containing very fine particles of “Super Floss” (a diatomaceous earth) relying upon surface tension for adherence to the beads. HETP values of 0-8 mm were obtained, as compared with 0.6 to 2.0 mm for columns prepared from diatomaceous-earth packings and 4.5 mm for unmodified beads.As already mentioned, graphitised carbon black has been used3* as a coating for micro glass beads giving “porous-layer” glass beads,” the coating of fine particles apparently adhering by van der Waal’s forces. In comparison with conventional columns a %fold reduction in analysis time is claimed. Kirkland59 made a similar approach by modifying glass beads with a thin layer of diatomaceous earth using Baymal (a fibrillar boehmite) as an anchoring agent. With columns prepared from these beads, a HETP value of 0.8 mm was obtained, in agreement with values also reported by D e ~ a r , ~ ~ presumably arising from the homogeneity of liquid-phase deposition over the surface which improved the liquid mass- transfer effects. The modified beads showed no tendency to give asymmetric peaks when chromatographing polar solutes on non-polar solvents.In another the same author prepared glass beads modified by silica gel, again with Raymal as adherent. With this technique he was able to prepare a support of desired thickness and surface area retaining the good packing characteristics of the glass-bead nucleus. The increase in surface area after successive treatment with the Baymal- silica sol is indicated- Untreated . . . . . . . . . . . . 0.02 Methanol - potassium hydroxide cleaned . . . . 0.03 After 1 Baymal- silica treatment . . . . .. 0.05 After 3 Baymal- silica treatments . . . . .. 0.28 Unfortunately, it also exhibited a greater tendency to tail. Condition of the glass beads, 60 to 80 mesh Surface area, m2 per g After 5 Baymal - silica treatments .. .. .. 0.47 STERRASTERS- As a possible alternative support to glass beads the naturally occurring sterrastcrs, obtained from marine sponges, were studied by Webb, Smith and Wells.58 They are mainly spherical in shape with an average diameter of 54.9 p, which is about the optimum size, as calculated, for glass beads.53 The entire surface of the sterrasters is covered with a fine, elevated texture which, acting as a natural etching, causes the liquid phase to be evenly distributed in a thin film. From this material columns with HETP values of 0.6 mm were obtained. As a result of their hard impervious core, sterrasters have the relative inertness to polar solutes characteristic of glass beads, and show little tendency to produce tailing peaks with higher alcohols.VERMICULITE- Another naturally occurring material, vermiculite, has been examined by McKinney.60 This is a hydrated magnesium iron silicate, composed of platelets, about 9.3 A thick, of tetrahedral sheets bonded to a central bivalent sheet of Mg2+ ions. An interesting property of this material is its ability to adsorb water and carboxylic acids which penetrate between the platelets, suggesting its use in the analysis of aqueous samples. However, adsorption is greater and efficiencies lower than with the diatomaceous supports.February, 19671 PART I. CHOICE OF SOLID SUPPORTS 79 POROUS POLYMER BEADS- First described by Lloyd and Alfrey6l962 these materials were used by Moore63 to prepare columns for separating polymers by “Gel-permeation Chromatography.” The bead polymer is synthesised by “suspension p~lymerisation”~~ and by drying the styrene divinyl benzene beads they still retain their wet structure.A detailed description of these beads and their properties when used as a support material in gas chromatography is given by Hollis,G5@ and a summary has also been published.23 Porapak-Five basic materials are marketed under the name of Porapak (supplied by Waters Associates Inc., Massachussetts, U.S.A.) (P, Q, R, S and T) differing in the degree of cross linking of the basic styrene with ethyl vinyl benzene, and some remarkable separations have been achieved by the use of these materials. It appears that the separation of the solute components by direct partition from the gas phase throughout the solid polymer is not just a surface effect as with conventional supports.As adsorption sites are non-existent, highly polar materials are eluted without tailing, and as no liquid phase is normally used, column bleed is not a problem even when temperature programming (the beads are thermally stable to about 250” C). Compounds containing hydroxyl groups (e.g., water, alcohols and glycols) are usually a problem in conventional gas-chromatographic analysis because of the tailing produced by adsorption of these polar compounds by the support. The porous polymer beads are, however, non-adsorptive and hydroxylated materials are eluted with symmetrical peaks, an interesting point being the early elution of water and certain glycols, while less polar materials are retarded.In the Government Laboratory, porous polymer beads have been successfully used to separate components from aqueous alcoholic solutions and promising results are being achieved in the separation of glycols and in the determination of their trace impurities. It is expected that information on this subject will be published shortly. The beads are supplied in the same mesh size as the diatomic supports and columns are prepared from them in a similar manner, although, in this case, packing is facilitated by the more rigid structure of the beads. These columns are capable of producing efficiencies of up to 800 plates per foot, but are easily overloaded and sample sizes of about 0.2 p1 per component are recommended.However, the non-sorptive nature of the beads allows for a rapid recovery of base-line should the column be overloaded, as in the analysis of trace constituents. Chromosorb 102-Prepared from Rohm and Haas Amberlite XAD-2, this material is a resin of high surface area, size graded for use as a packing as a support in gas-liquid chromatography. Polypak-This is a porous polymer developed by F. & M. Scientific Ltd. Its properties and separations are similar to Porapak. Its properties are similar to those of the porous polymer beads. CONCLUSION An “ideal” support must combine apparently conflicting qualities, for it is evident that what may be ideal for one circumstance may be unacceptable in another. Nevertheless, considerable advances have been made in the development of the conventional types of solid supports. In the technology of diatomaceous earths, development is probably approaching a limit, but undoubtedly there still remains room for further advances in the use of porous layer glass beads.Perhaps the ideal is to be found in the development of the various types of solid phases such as the cross-linked polystyrene. This might undoubtedly lead to a vast field of development. Classification of Supports DIATOMACEOUS SUPPORTS THE WHITE DIATOMACEOUS SUPPORTS These are derived from flux-calcined diatomite, and are friable but relatively inert and useful for the analysis of polar samples. They are commercially available in several forms. UNMODIFIED DIATOMACEOUS SUPPORTS- in a number of mesh sizes by J.J. (King’s Lynn). Celite 545-Manuf actured by Johns Manville, and supplied in this country already sieved80 PALFRAMAN AND WALKER: TECHNIQUES I N GAS CHROMATOGRAPHY [Analyst, Vol. 92 Chromosorb W (N.A . W.)-Manufactured by Johns Manville by size grading Celite, and supplied by Perkin-Elmer in a variety of mesh sizes. Gas-Chrom S-Prepared by Applied Science, from Celatom (a Celite type of diatomite manufactured by Eagle Picher Co. from deposits in Nevada). Available in a wide variety of mesh sizes. Gas-Chrom CL-Prepared by Applied Science from Celite. Anakrom U-Prepared by Analab Inc., and distributed in this country by Gas Chromato- graphy Ltd. This support is specially size graded in a 10-mesh range cut claimed to give higher efficiencies. ACID-WASHED DIATOMACEOUS SUPPORTS- These include the previous supports, which have been modified by various acid-washing procedures to remove some of the adsorptive sites. Celite (A.W.)-Washed with hydrochloric acid. Chromosorb W (A. W.)-Washed with hydrochloric acid. Gas-Chrom (A)-Celatom acid washed. Gas-Chrom (CL.A)-Celite acid washed. Anakrom (A)-Acid washed. Size graded. ACID AND ALCOHOLIC-BASE WASHED DIATOMACEOUS SUPPORTS- This technique was developed to reduce tailing when chromatographing basic materials (e.g., amines) . The acid-washed supports are dried, treated with alcoholic potassium hydroxide and washed with methanol. Gas-Chrom P-Celatom, acid and alcoholic-base washed. Anakrom AB-Acid and alcoholic-base washed Anakrom U. Gas-Chroulz CL.P.-Celite, acid and base washed.Diatomite C-Celite prepared by J.J. (can be obtained acid or alkali washed). SILANISED DIATOMACEOUS SUPPORTS- These are recommended for very polar materials and for low loaded columns. supports are incompatible with certain highly polar liquid phases. with dimethyldichlorosilane (DMCS) . For further reduction of active centres many supports are available in a silanised form. Silanised Chromosorb W (A. W.-DMCS)-The acid-washed Chromosorb W that has been treated Gas-Chrom 2-Celatom acid washed and DMCS treated. Gas-Chrom Q-Celatom acid and base washed, and DMCS treated. Gas-Chrom (CL.H)-Celite treated with hexamethyldisilazane. Gas-Chrom (CL.S)-Acid washed and DMCS treated Celite. Anakrom (A .S.)-Siliconised, acid-washed Anakrom U. Anakrom (ABS)-Acid and alcoholic-base washed, and vacuum silanised L4nakrom U.The residual hydrochloric acid is removed by methanol washing. It is inert, suitable for steroid analysis and is available in a wide variety of 10-range-mesh cuts. An inert support prepared especially for steroid analysis. THE PINK DIATOMACEOUS SUPPORTS These are derived from calcined diatomite, without flux, and they have better handling They give greater efficiencies, but are less inert characteristics than the white supports. and not suitable for polar solutes. UNMODIFIED PINK DIATOMACEOUS SUPPORTS- Chromosorb P-Prepared by Johns Manville from firebrick, suitable for hydrocarbon separations. Gas-Chrom R-Prepared by Applied Science from Johns Manville Sil-o-Cel C22 firebrick (smaller surface area and less reactive than the pink supports prepared from calcined diatomite).Anakrom P-Prepared from calcined diatomaceous earth. Available in 10-range mesh cuts. Diatomite S- J. J’s. prepared firebrick.February, 19671 PART I. CHOICE OF SOLID SUPPORTS 81 ACID-WASHED PINK DIATOMACEOUS SUPPORTS- are, however, still unsuitable for polar materials. These are less active than the untreated firebrick, due to removal of surface iron. They Chromosorb P ( A . W.)-Acid-washed Chromosorb P. Gas-Chrom (R. A .)-Acid-washed Gas-Chrom R. Gas-Chrom (R.P.)-Acid and alcoholic-base washed Gas-Chrom R. Anakrom (PA .)-Acid-washed Anakrom P. SILANISED PINK DIATOMACEOUS SUPPORTS- These are the least active of the pink supports but still not as inert as the best white supports. They will make efficient columns for semi-polar materials but are not satisfactory for low loaded columns.Chromosorb P (HMDS)-Hexamethyldisilazane-treated Chromosorb P. Chromosorb P (A. W.-DMCS)-Acid washed and dimethyldichlorosilane-treated Chromo- Gas-Chrom R.2.-Acid-washed and silanised C22 firebrick. Wide variety of mesh cuts sorb P. available. Limited range of mesh cuts available. MISCELLANEOUS DIATOMACEOUS SUPPORTS Chromosorb G-This is specially prepared by Johns Manville as a support for gas chromatography. As it is very inert, robust and dense, it is particularly useful for columns of less than 5 per cent. weight loadings of liquid phase. (Because of its high density this is equivalent to about 10 per cent. with usual supports.) It is available in three mesh sizes 45 to 60, 60 to 80, 100 to 120 and modified as: Chromosorb G, untreated; Chromosorb G (A.W.), acid washed; and Chromosorb G (A.W., DMCS), acid washed and silanised.J.J’s. M-This is similar in property to Chromosorb G, and is available in acid washed and DMCS and HMDS-treated forms. Chromosorb A-This is a flux-calcined diatomite manufactured by Johns Manville especially for preparative columns. It is similar in appearance to Chromosorb P but less reactive. Its high surface area allows it to take up to 25 per cent. liquid loadings. High performance Chromosorbs G and W-These have been developed for steroid analysis and are available in A.W. and DMCS-treated forms. The surface is claimed to be highly inert and capable of HETP values of 0.45 mm. FLUOROCARBON SUPPORTS These supports are very inert, and useful for aqueous or other highly polar samples, but they are very difficult to handle and often produce very inefficient columns.Cool them to 0” C before use; they are fragile. Chromosorb T-This is prepared by Johns Manville from Teflon G and is available in mesh sizes 30 to 60 and 40 to 60. FZuoroport T-This is supplied by Applied Science. It has a wide mesh range, and is derived from Teflon 6. KeZ-F 6051-Chlorotrifluoroethylene manufactured by the Minnesota Mining and Manufacturing Co. Flztoropak-80-Fluorocarbon support produced by the Fluorocarbon Co. Tee-Six-Processed by Analabs from Teflon 6. It is available in a large variety of REFERENCES mesh sizes down to 160 to 170 mesh-cut in 10-mesh-cut ranges. 1. 2. 3. 4. 5.6. 7. 8. 9. Rose, B. A., Analyst, 1959, 84, 574. Graig, B. M., in Noebels, H. J., Wall, R. F., and Brenner, N., Editors, “Gas Chromatography,” James, A. T., and Martin, A. J . P., Biochem. J., 1952, 50, 679. Baker, W. J., Lee, E. H., and Wall, R. F., in Noebels, H. J., Wall, R. F., and Brenner, N., Editors, Ottenstein, D. M., “Progress in Industrial Gas Chromatography,” Volume 1, Plenum Press, New Saha, N. C., Giddings, J. C., Analyt. Chem., 1965, 37, 822. -, -- , Ibid., 1965, 37, 830. Littlewood, A. B., “Gas Chromatography,” Academic Press, New York and London, 1962, p. 213. James, A. T., Martin, A. J. P., and Smith, G., Biochem. J., 1952, 52, 238. Academic Press Inc., New York and London, 1961, p. 37. o p . cit., p. 21. York, 1961, p. 51.PALFRAMAN AND WALKER Fales, H.M., and Pisano, J. J., in Szymanski, H., Editor, “Biomedical Applicationsof GasChromato- Rurchfield, H. P., and Storrs, E. E., “Biochemical Applications of Gas Chromatography,” Academic Ormerod, E. C., and Scott, R. P. W., J . Chromat., 1959, 2, 65, Horning, E. C., Moscatelli, E. A., and Sweely, C. C., Chem. & Ind., 1959, 751. Horning, E. C., Vanden-Heuvel, W. J . A., and Creech, B. G., in Glick, D., Editor, “Methods of Biochemical Analysis,” Volume XI, Interscience Publishing Co. Ltd., New York, 1963, p. 80. Bohemen, J., Langer, S. H., Perrett, R. H. and Purnell, J. H., J . Chem. Soc., 1960, p. 2444. Perrett, R. H., and Purnell, J . H., J . Chromat., 1962, 7, 455. Kirkland, J. J ., in Fowler, L., Editor, “Gas Chromatography,” Academic Press, New York and Staszewski, R., and JanAk, J., Colln Czech.Chem. Commun., 1962, 27, 532. Suppina, W. R., Kruppa, R. F., and Henly, R. S., J . Amer. Oil Chem. SOC., 1965, 42, 459A. Purnell, H., “Gas Chromatography,” John Wiley and Sons Inc., New York and London, 1962, Applied Science Newsletter, 1966, 7, No. 2. Urone, P., and Parcher, J . F., J . Gas Chromat., 1965, 3, 35. Varian Aerugraph Research Notes, Spring 1966. Vanden-Heuvel, W. J. A., Gardiner, W. L., and Homing, E. C., Analyt. Chem., 1963, 35, 1745. Scholz, R. G., and Brandt, W. W., in Noebels, H. J., Wall, R. F., and Brenner, N., Editors, 09. Ottenstein, D. M., J . Gas Chromat., 1963, 1, 11. Averill, W., in Noebels, H. J., Wall, R. F., and Brenner, N., Editors, op. cit., p. 1. Kirkland, J. J., Analyt. Chem., 1963, 35, 2003.Sawyer, D. T., and Barr, J. K., Ibid., 1962, 34, 1518. Landault, C., and Gurochen, G., J . Chromat., 1962, 9, 133. Onaka, T., and Okamoto, T., Chem. Pharm. Bull., Tokyo, 1962, No. 10, 757. Kirkland, J. J., in Goldup, A., Editor, “Gas Chromatography 1964,” Institute of Petroleum, Eggertsen, F. T., Knight, H. S., and Groennings, F., Analyt. Chem., 1956, 28, 303. Kiselev, A. V., Q. Reu. Chem. SOC., 1961, 15, 99. -, in Goldup, A., Editor, op. cit., p. 238. Pope, C. G., Analyt. Chem., 1963, 35, 654. Brodasky, T. F., Ibid., 1964, 36, 1604. HalBsz, I., and Horvath, C., Ibid., 1964, 36, 1178. Kirkland, J. J., Ibid., 1963, 35, 1295. Bugosh, J., U.S. Patent 2,915,475, December, 1959. “Baymal Colloidal Alumina,” E. I. Du Pont de Nemours and Co., Bulletin A 18211, 1961. Gohlke, R. S., and McLafferty, F. W., Paper presented a t the American Chemical Society Meeting, Desty, D. H., and Harbourn, C. L. A., Analyt. Chem., 1959, 31, 1965. Decora, A. W., and Dinneen, G. U., Ibid., 1960, 32, 164. - -- , in Noebels, H. J., Wall, R. F., and Brenner, N., Editors, op. cit., p. 33. Bens, E. M., APzalyt. Chem., 1961, 33, 178. Porcaro, P. J., and Johnston, V. D., Ibid., 1961, 33, 361. Callear, A. B., and Cvetanovits, R. J., Can. J . Chew, 1955, 33, 1256. Littlewood, A. B., “Gas Chromatography,” Academic Press, New York, 1962, p. 210 Hawkes, S. J., Russell, C. P., and Giddings, J . C., Analyt. Chem., 1965, 37, 1523. Littlewood, A. B., in Desty, D. H., Editor, “Gas Chromatography 1958,” Butterworths Scientific Publications, London, 1958, p. 23. Frederick, D. H., Miranda, B. I., and Cooke, W. D., in Brenner, N., Callen, J. E., and Weiss, M. D., Editors, “Gas Chromatography,” Academic Press lnc., New York and London, 1962, p. 27. --- , Analyt. Chena., 1962, 34, 1521. Dewir, R. ’A., and Maier, V. E., J , Chromat., 1963, 11, 295. Giddings, J. L., Analyt. Chem., 1962, 34, 458. Ohline, R. W., and Jojola, R., Ibid., 1964, 36, 1681. Golay, M. J. E., in Scott, R. P. W., Editor, “Gas Chromatography 1960,” Butterworths Publishing Co. Ltd., Edinburgh and London, 1960, p. 139. Webb, J. J,., Smith, V. E., and Wells, H. W., J . Gas Chromat., 1965, 384. Kirkland, J. J., Analyt. Chew., 1965, 37, 1458. McKinney, R. W., J . Gas Chromat., 1965, 388. Lloyd, W. G., and Alfrey, T., Paper presented at the 130th American Chemical Society Meeting, graphy,” Plenum Press, New York, 1964, p. 41. Press Inc., New York and London, 1962, p. 41. London, 1963, p. 77. p. 236. cit., p.7. London, 1965, p. 146. Dallas, Texas, April, 1956. Division of Polymer Chemistry, St. Louis, March, 1961. , , J . Polym. Sci., 1962, 62, 301. -- Moore, J. C., Ibid., 1964, 2, 835. Billmeyer, F. W., jun., “Textbook of Polymer Science,” Interscience, New York, 1962, p. 341. Hollis, 0. L., Analyt. Chew., 1966, 38, 309. Hollis, 0. L., and Hayes, W. V., J . Gas Chromat., 1966, 235. Received August 25th, 1966 82 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66.

ISSN:0003-2654    

DOI:10.1039/AN9679200071

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, February, 1967, Vol. 92, pp. 83-90 83 The Component of Commercial Titan Yellow Most Reactive towards Magnesium: Its Isolation and Use in Determining Magnesium in Silicate Minerals BY H. G. C. KING AND G. PRUDEN (Rothamsted Experimental Station, Harpanden, Herts.) The component of Titan yellow most reactive towards magnesium has been isolated from the acetone-extracted dye by adsorption chromatography on Sephadex G-10. I t is so reactive that i t can be used at a concentration as small as 0.008 per cent., a t which concentration the response is linear between 20 and 15Op.g of magnesium. Values found for the magnesium content of silicate minerals agree with those obtained by spectrographic and gravimetric methods. TITAN yellow, variously described in the literature as Clayton yellow, Thiazole yellow, Acridingelb 5G and Azidingelb 5G, was first used by Kolthoff1y2 to determine magnesium.The chemical constitution of the dye, which is synthesised by coupling a molecule of a sulphonic acid of dehydrothio-9-toluidine with a molecule of its diazonium salt, is usually given as- H 3 C y - J q 5 3 N=N-HN /(---3&UCH3 ’,4 3 / 6L5’ - \N / -t S03Na Na03S t N (The positions of the sulphonate groups are uncertain.) There are inconsistencies in the published formulation of Titan yellow, particularIy in the positions of the sulphonate groups; some authors state that it differs from Clayton y e l l ~ w , ~ whereas others* find no specific differences between any of the compounds named above, At least one manufacturer uses the names Titan yellow and Clayton yellow synonymously.* Samples of commercial Titan yellow, Clayton yellow and Thiazole yellow were first shown to differ in their reactivity towards magnesium by Mikkelsen and Toth,B who found that Thiazole yellow was the most active, the inference being that the dyes tested were of different composition. Bradfield5 analysed four samples of Titan yellow and found variable, and often large, amounts of sodium chloride (55 per cent.for one). He demonstrated by paper chromatography that Titan yellow was a mixture, and separated a contaminant that did not react with magnesium, and under ultraviolet light, gave the blue - violet fluorescence characteristic of a dehydrothio-p-toluidine sulphonate. Recently Hall, Gray and Flynn’ confirmed the complexity of fourteen commercial Titan yellow samples by using paper and thin-layer chromatography, and showed spectrophotometrically that, at the wavelength of maximum absorption, the optical densities of equal concentrations of the dyes have a wide range of values.They also isolated the active component on a micro scale by thin-layer chromatography. The presence of variable amounts of sodium chloride in Titan yellow is largely responsible for the observed differences in optical densities, and perhaps explains earIier inconsistent results in magnesium determination because the amount of magnesium t o be determined may sometimes have exceeded the reactivity of Titan yellow. Some workers have attempted * Kolthoff1p2 and Hirschfelder and Searles3 show formulae for Titan yellow inconsistent with the chemical consitutions described in their texts.Kalthoff also describes the dye as a derivative of dehydro- thio-p-toluidine sulphonate. Bradfield5 gives the formula as a 3’-disulphonate, as does Sandell,O although he describes i t as a 2’-disulphonate; Hall et a1.’ describe Titan yellow as a 2’-disulphonate.84 KING AND PRUDEN: THE COMPONENT OF COMMERCIAL [Artalyst, vol. 92 to overcome the variability of Titan yellow by using the reagent at a standard optical density. However, this is unsatisfactory, because the criterion of reactivity is not the optical density of the mixture of components of different reactivity, but of the proportion of the most reactive component in the dye. We find that the colours of alkaline blanks of the magnesium-reacting components differ in optical density, and that the blank of the most active component has the least colour.The use of the most active component thus ensures greatest sensitivity in determining magnesium. By the use of the dextran gel Sephadex G-10 we have prepared enough of the active component for several hundred magnesium determinations. The blue - violet fluorescing contaminant was largely removed by extracting the dye with acetone, and the remaining components were separated on Sephadex G-10, by using the gel not as a molecular sieve, but by making use of its property of adsorbing differentially the main components with water, followed by aqueous acetone, as eluent. This procedure has enabled us to assess the relative amounts of the active components in a commercial sample of Titan yellow and to prepare amounts of a standard, reproducible fraction that has been used for the routine determination of magnesium in silicate minerals.EXPERIMENTAL Eastman Kodak’s Titan yellow, P4454, a grade also studied by Mikkelsen and Toth,* was used for the detailed examination and preparation of the most active component, It contained 374 per cent. of sodium chloride. A sample of Hopkin and Williams’ Titan yellow (Clayton yellow) containing 42.0 per cent. of sodium chloride was examined by paper chromatography only. SPECTROPHOTOMETRY- Ultraviolet and visible absorption spectra of Titan yellow and its fractions, at concen- trations of 1.5 to 2.5 mg in 100 ml of water, were measured with a Unicam SP500 spectro- photometer, with quartz cells of light path 1 cm.The spectrum of an aqueous solution of commercial Titan yellow between 200 and 500 mp showed two maxima, one at 325 mp (Eke% = 152) and the other at between 405 and 410 mp (Elc$ = 348). Because the optical densities of the maxima vary inversely with the amount of sodium chloride mesent. the molecular extinction coefficient of Titan yellow cannot be obtained directly. Bradfieldg found the maxima to be 330 mp gave only the higher wavelength maximum, as 405 mp. I 200 300 400 500 Wavelength, mu Fig. 1. Ultraviolet and visible absorption spectrum of Eastman Kodak’s Titan yellow, P4454 (2.1 mg in 100 ml of water) and 405 mp, and Hall et aZ.7 PAPER CHROMATOGRAPHY- The descending method was used with Whatman No. 1 paper and aqueous ethanol, 80 per cent., as solvent.(This simple solvent gives as good resolution of the components as more complex combinations of butanol, ethanol, ammonia solution or acetic acid, although none of the solvent mixtures examined gave satisfactory resolution of the components between the origin and the head of the most active component [R, about 0.36 in aqueous ethanol].) Fluorescent areas were marked out under ultraviolet light (366 mp, Wood’s glass filter).February, 19671 TITAN YELLOW MOST REACTIVE TOWARDS MAGNESIUM 85 Papers were dipped in aqueous magnesium sulphate solution (2 per cent.), suspended in a current of air until almost dry, and dipped in alcoholic sodium hydroxide solution (2 per cent.). The relative activities of the reactive areas should be assessed as soon as possible, because the less active components begin to fade within 25 minutes.Paper chromatography did not reveal some of the minor fluorescent compounds described by Hall et aZ.,' who used thin-layer chromatography, but confirmed the presence of the main components. TABLE I PAPER CHROMATOGRAPHIC PROPERTIES OF COMPONENTS OF TITAN YELLOW Component RF Colour in daylight Colour in ultraviolet light . . 0.32 (head) Yellow Yellow 1 (= Band 1) . . 0-00 (tail) 0.20 (tail) 2 (= Band2) . . . . 0.36 (head) Bright yellow 1~e110~ 3 . . , . .. . . 0.49 Colourless Bright blue - violet 4 .. . . . . . . 0.40 Colourless Faint violet 5 . . . . . . . . 0.00 Pale yellow Yellow Only bands 1 and 2 reacted with magnesium to give the characteristic red colour in With band 1 the colour began to fade in 25 minutes, the presence of sodium hydroxide.but the colour obtained with band 2 was stable for 45 minutes. PRELIMINARY FRACTIONATION OF TITAN YELLOW- Titan yellow was extracted with acetone in a Soxhlet apparatus. The solvent was removed from the extract by vacuum distillation and the extracted Titan yellow dried in air. The acetone extract, 6.3 per cent. of the starting material, consisted of a yellow coni- ponent (25 per cent.) whose chromatographic behaviour was similar to band 1, and the colour- less component 3 (75 per cent.). The latter was isolated by passing an aqueous solution of the acetone-soluble extract down a column of Solka Floc (powdered cellulose) with 6 per cent. acetic acid as eluent. The yellow component was immobile in this system.SMALL-SCALE SEPARATION OF COMPONENTS OF EXTRACTED TITAN YELLOW ON SEPHADEX G-10 Twenty grams of Sephadex G-10 (Pharmacia Ltd., Uppsala), particle size 40 to 12Op, were allowed to swell overnight in 0.1 M sodium chloride solution. The supernatant liquid was then poured off and the gel was stirred with three successive 100-ml portions of water, decanting any fine material after each stirring. The gel was poured as a slurry into a glass chromatographic column, 25 x 2.25 cm diameter, having at its lower end, as a support for the gel, a sintered-glass plate of porosity 3, i.e., pore size less than 40 p. (For the large-scale preparation of the most active fraction of Titan yellow 75 g of Sephadex G-10 and a column, 32 x 3.25 cm diameter, were used.) When the gel had settled, a filter-paper disc was placed on its surface and the column was washed with water until free from sodium chloride.The water in the prepared column was allowed to drain to the level of the filter-paper disc, then 2.5 ml of an aqueous solution containing 2.5 mg of acetone-extracted Titan yellow 0 Wavelength, mu Fig. 2 . Ultraviolet and visible absorption spectra of fractions of Titan yellow isolatcd by gel filtration and chromatography on powdered cellu- lose: A, band 1 ; B, band 2 ; and C, blue - violet fluorescing component86 KING AND PRUDEN: THE COMPONENT OF COMMERICAL [Analyst, VOl. 92 was introduced. The column was eluted with water at a flow-rate of about 1 ml per minute. Sodium chloride was eluted first, followed by the first yellow band (band 1).The solvent was then changed to 50 per cent. aqueous acetone, and the column washed until the effluent was colourless (band 2). The acetone was distilled from the band 2 effluent, and band 1 and band 2 solutions were diluted to 100 ml with water for spectrophotometric examination. The acetone-insoluble fraction, fractionated on the small Sephadex column, gave the ratio 1/0.86 for the optical density of band 1 (salt-free) to that of band 2. The optical densities of bands 1 and 2 were 51.0 per cent. and 45.3 per cent., respectively, of the optical density of the unfractionated Titan yellow, measured at 410 mp. The remaining 3.7 per cent. of the absorption at 410 mp is accounted for by the acetone-soluble fraction, and a trace of yellow material held at the top of the Sephadex column.Fig. 2 shows the ultraviolet and visible absorption spectra of the Titan yellow fractions. DETERMINATION OF THE REACTIVITY WITH MAGNESIUM OF TITAN YELLOW FRACTIONS- For these measurements band 1 and band 2 fractions were prepared in larger amounts 2.s described below. Fifteen ml of standard magnesium chloride solution (equivalent to 150 pg of magnesium) were added to the stabilising colloid mixed reagent solution,1° followed by 5 ml of a solution of the Titan yellow fraction under examination and 5ml of aqueous, 30 per cent. sodium hydroxide. Concentrations of Titan yellow fractions ranging from 0.02 per cent., by steps of 0.001 per cent., to a final concentration of 0.001 per cent. were used. The volume was made up to 100 ml with water and the optical density of the solutions measured at 545 mp, with glass cells of light path 4 cm, against a blank of the corresponding Titan yellow fraction treated with sodium hydroxide.The point at which magnesium was in excess of Titan yellow was found by plotting the optical density of the latter against its concentration. The optical density at 545 mp of each blank was also measured against water and again the optical density was plotted against concentration of the Titan yellow fraction. Titan yellow fraction, per cent. Titan yellow fraction, per cent, Fig. 3. Reactivity of Titan yellow fractions Fig. 4. Variation of optical density of re- with 150 pg of magnesium: A, band 1 ; B, band agent blank concentration of Titan yellow : A, 2 ; C, acetone-soluble fraction ; and D, unfraction- band 1 ; B, band 2 ; C, acetone-soluble fraction; ated Titan yellow and D, unfractionated Titan yellow Figs.3 and 4 show the least concentration of each Titan yellow fraction reacting with magnesium chloride - sodium hydroxide ; and with sodium hydroxide alone. The relative activity of the fractions is measured by the minimum concentration of each that reacts with the given amount of magnesium. The difference in the reactivity of bands 1 and 2 is apparent from the curves. METHOD Fractionation of Titan yellow-Extract 1.0 g of Titan yellow with AnalaR acetone in a Soxhlet apparatus for a total of 12 hours. Dry the extracted dyestuff in air, and dissolve 0.5 g of it in 25.0 ml of water. Introduce the aqueous solution into the top of the Sephadex column and allow the liquid to drain to the surface of the gel, applying a little suction if necessary.Elute the column with water to wash out sodium chloride and the less activeFebruary, 19671 TITAN YELLOW MOST REACTIVE TOWARDS MAGNESIUM 87 component (band 1). When the effluent is colourless, change the eluent to 50 per cent. aqueous acetone and wash out the more active component (band 2). Distil the solvent under vacuum and dry the residue over phosphorus pentoxide. ANALYSIS OF SILICATE MINERALS The solution of the silicate mineral to be examined is prepared by Meyrowitz's method,lo with the acidity adjusted to be about 1.2 N with respect to sulphuric acid. REAGENTS- Acid blank solution-About 1.2 N sulphuric acid.Standard magnesium solution-Dissolve 500 mg of pure magnesium ribbon in 15 ml of 6 N hydrochloric acid. Evaporate off excess of the acid, dissolve the residual magnesium chloride in water and make up the solution to 500ml. Ten ml of this solution, diluted to 1 litre gives a working standard containing 1Opg of magnesium per ml. Complexing solution-Dissolve 16 g of potassium cyanide in 100 ml of water. Add 100 ml of triethanolamine, and mix the solution. Sodium hydroxide solution, 30 per cent.-Dissolve 60 g of sodium hydroxide pellets in about 50 ml of water. Dilute the solution to slightly less than 200 ml. Cool, dilute to 200 ml and transfer the solution to a polythene bottle. Titan yellow reagent solution, 0.008 per cent.-Dissolve 8 mg of Titan yellow band 2 in 100 ml of water.Mixed reagent s0lutio.n-Add 100 mg of poly(viny1 alcohol) to 150 ml of water in a 600-ml beaker. Place the beaker on a hot-plate and heat gently with constant stirring until the temperature of the solution is 60" C. Heat at 60" to 70" C, with constant stirring until the solution is clear. Add, with mixing after each addition, 300 ml of water, 5 ml of 9 N sulphuric acid, 750 mg of hydrated aluminium nitrate, Al(NO,),.SH,O, and 20 g of hydroxyl- ammonium chloride. Cool the solution and dilute it to 500 ml. Filter with a fine filter-paper. DETERMINATION OF MAGNESIUM- Dilute to 250ml with water and mix well. Transfer 5 ml of acid blank solution to a 100-ml calibrated flask. Transfer 2, 4, 6, 8, 10, 12 and 14ml of working standard magnesium solution (20 to 140 pg of magnesium) to seven 100-ml calibrated flasks.Add to the flasks containing the standard magnesium solution, 5 ml of acid blank solution. Transfer to the 100-ml calibrated flasks 2 to 5 ml (containing no more than 140 pg of magnesium) of the sulphuric acid solution of the mineral (about 1.2 N). Add to each of the flasks enough acid blank so that the volume of sample solution taken together with the added amount of acid blank is 5 ml. Introduce 5 ml of the mixed reagent, 45 ml of water and 2 ml of complexing solution to each flask, mixing after each addition. Add to the first of the flasks 5 ml of Titan yellow reagent solution. Immediately add 5 ml of 30 per cent. sodium hydroxide, swirling the contents of the flask. Dilute the solution to the mark and mix.Follow this sequence systematically through the 10 Wavelength, mp Fig. 5. Visible absorption spectra: A, Titan yellow band 2 - magnesium complex against water as blank; B, reagent blank against water blank; and C, Titan yellow band 2 - magnesium complex against reagent blank88 [AnaZyst, Vol. 92 whole series of flasks. Allow the solutions to stand for at least 20minutes. Determine the optical density at 545mp, relative to the reagent blank, with 4-cm absorption cells. The wavelength at which the Titan yellow - magnesium complex is measured has been reported variously as 530 mp,497 545 mpl0 and 550 r n p 5 We find that when the coloured complex is set against the blank, with the optimum concentration of Titan yellow band 2 found above, the wavelength of maximum absorption is at 545mp.However, this is not the wavelength of maximum absorption with water as blank, but is the wavelength that gives the greatest difference between the optical densities of the complex and the blank, i.e., the wavelength at which the method has the greatest sensitivity (Fig. 5 ) . KING A-ND PRUDEN: THE COMPOYENT OF COMMERCIAL Table I1 shows results for some typical silicate minerals. TABLE I1 MAGNESIUM CONTENT (AS MAGNESIUM OXIDE) OF SILICATE MINERALS Mineral Granite (G-1) . . . . .. .. Diabase (W-1) . . . . .. .. Granite (G-2) .. .. .. Peridotite (PCC-1) . . . . . . Dunite (DTS-1) . . . . . . .. Basalt (BCR-1) . . .. .. . . Granodiorite (GSP-1) . . .. . . Andesite (AGV-1) . . .. . . Biotite quartz monzonite, Keller Peak, San Bernarclino Mts., California Biotite quartz monzonite, Rattlesnake Mt., Pluton, San Bernardino Mts., California .. . . . . . . Biotite granodiorite, Mt. Edna, San Jacinto Mts., California . . . . Woodson Mt., granodiorite, Jarupa Hills, Riverside County, California .. Lakeview Mt., tonalite, Lakeview Mts., Homeland, California . . . . La Sierra, tonalite, La Sierra, California Standard sample, sulphide ore-1 . . Granite (GH) . . . . . . .. Granite (GA) . . . . .. .. Basalt (BR) . . . . . . . . . . BY Titan yellow 0.41 6.70 0-73 1-48 43.55 49-09 3.46 0.96 0.46 1.09 1.25 0.41 3.27 1.86 3-85 0.03 0-88 12.61 Spectrographic Gravimetric 0.35 - 6.58 - 0.76 - 1.53 - 43.4 to 44.6 43.86 48.2 to 49.7 49.40 3.48 - 0.93 - 0-52* 1*09* 1-25* 0-48* 344* 1-89* 3.71 t o 4.49'3 0.0313 0*9513 1 2*6013 * Secondary chemical standards determined by X-ray methods. Results supplied by Prof.A. I<. Baird, Pomona College, Claremont, California, U.S.,4. DISCUSSION Although the structure of Titan yellow is uncertain, it seems that the commercial dye is essentially a mixture of two compounds that react differently with magnesium; in the sample studied these two components account for at least 90 per cent. of the total active material. The amounts of these components vary from sample to sample, and sodium chloride is always a major impurity. Standardisation of Titan yellow is made difficult by the fact that all of the components are water-soluble. Removing sodium chloride and the blue - violet fluorescing compound from different samples of Titan yellow gives products of different reactivity with magnesium, although the spectra and optical densities at the wave- lengths of maximum absorption are closely related. The difference in activity is shown in the greater colour developed by the less active component (band 1) in the presence of alkali.With a fixed amount of magnesium and different concentrations of dyestuff components, the optimum concentration of the more active fraction (band 2) is about one-third of that of our unfractionated Titan yellow. At this concentration the intensity of the colour of the blank is minimal, whereas the colour of the magnesium complex develops strongly. With unfractionated Titan yellow, interference caused by the blue - violet fluorescing component (about 5 per cent. of the starting material in our sample) is negligible.Bradfields considers that this compound is the 7-sulphonate of dehydrothio-P-toluidine, some of which remains unreacted during the synthesis of Titan yellow, but this is at variance with Bradfield's own formulation of the dye as a 3'-disulphonate. We have confirmed Bradfield's finding that Titan yellow can be degraded to a blue - violet fluorescing compound that exhibits theFebruary, 19671 TITAN YELLOW MOST REACTIVE TOWARDS MAGNESIUM 89 L Weight of magnesium, pg Fig. 6. Calibration for magnesium in silicate materials same behaviour on paper chromatograms and to ultraviolet light as the contaminant seen on paper chromatograms of the unfractionated dye. Bradfield degraded Titan yellow with an acid - sodium dithionite mixture; we degraded the band 2 component with 2 N sulphuric acid, neutralising the hydrolysate with sodium hydrogen carbonate.It is unlikely that such treatment would cause the sulphonate groups to migrate, and the fluorescent compound is probably a 3’- or 2’-sulphonate of dehydrothio-P-toluidine. The ultraviolet spectrum of the compound has a maximum at 332 mp (E:,2 = 93), significantly different from the shorter wavelength maximum of Titan yellow. We do not attribute the shorter wavelength maximum of Titan yellow to contamination by the blue - violet fluorescing compound (contrast Brad- fieldg) but to the contribution of the chromophoric groups of the active components to the spectrum of the dye. Traces of the fluorescent compound are found after fractionation in bands 1 and 2, possibly because of slight hydrolysis on the Sephadex column, but the ratio of the 405 to 410 mp maximum to that at 320 to 325 mp is almost constant in unfractionated Titan yellow band 1 and band 2, with values of 2-30, 2.47 and 2-43, respectively.Paper chromatography has confirmed that acetone removes all but a trace of the blue -violet fluorescing compound from Titan yellow, but this does not increase the ratio of Titan yellow maxima given above. By using model compounds we have confirmed that Sephadex G-10 has a molecular weight exclusion limit of 700. It would be expected that Titan yellow (estimated molecular weight 696) would also be excluded within the void volume of the column. However, the active components of Titan yellow are adsorbed differentially whereas the sodium chloride, behaving as expected with Kd = 1, appears when a volume of water equal to the void volume (V,) and the column internal volume (Vi) has passed through the gel.Presumably the behaviour of bands 1 and 2 indicates a structural difference, which, in view of the similarity of their spectra, may be no more than a difference in the positions of the sulphonate groups. The evidence does not allow us to say whether or not bands 1 and 2, which are mobile in water and in aqueous acetone, respectively, are single compounds or mixtures of isomers. An improved solvent system for paper chromatography would probably resolve this question. Bands 1 and 2 do not separate into further components when passed down the Sephadex column a second time.The most active Titan yellow fraction (band 2) gives excellent results in the determination of magnesium in silicate minerals. With Meyrowitz’slO procedure, in which the samples are prepared at a constant acidity, it is unnecessary to buffer the solution when developing the Titan yellow - magnesium complex’ because the final alkalinity is the same for each sample, pH 13.2. As such small amounts of sample are needed for the determination, inter- ference by other metals is usually negligible in the analysis of silicate minerals. By using the active fraction at a concentration of 0-008 per cent. instead of the usual 0.02 per cent., the calibration can be extended down to 20 pg of magnesium, while the high upper level of 150pg is maintained. For the determination of magnesium in other materials, e.g., soil, the Titan yellow method may need to be modified, see, e g ., Hall et aL7 With the technique described above, a reproducible, highly active fraction, salt-free and relatively uncontaminated by other less active components, can be isolated from com- mercial Titan yellow. The sodium chloride content of the starting material and the amount90 KING AND PRUDEN of less active material present may vary within wide limits; in our sample the amount of the most active fraction, recovered quantitatively from the Sephadex column, was 28.5 per cent. of the original dyestuff. We thank Dr. Francis J. Flanagan, United States Geological Survey, Washington, D.C., Professor A. K. Baird, Pomona College, Claremont, California, and Dr. K. Govindaraju, Centre de Recherches Pktrographiques et Geochimiques, Nancy - Vandoeuvre, France, for samples of analysed silicate minerals. REFERENCES 1. 2. 3. 4. 5. 8. 7 . 8. 9. 10. 11. 12. 13. Kolthoff, I. M., Biochem. Z., 1927, 185, 344. -, Chem. Weekbl., 1927, 24, 254. Hirschfelder, A. D., and Searles, E., J . Bid. Chem., 1934, 104, 635. van Wesemael, J. Ch., Analytica Chirn. Acta, 1961, 25, 238. Bradfield, E. G., Analyst, 1960, 85, 666. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Third Edition, Interscience Publishers Ltd., London, 1959, p. 591. Hall, R. J., Gray, G. A., and Flynn, L. R., Analyst, 1966, 91, 102. Mikkelsen, D. S., and Toth, S. J., J . Amev. SOC. Agron., 1947, 39, 165. Bradfield, E. G., Analytica Chim. A d a , 1962, 27, 262. Meyrowitz, R., Amer. Minev, 1964, 49, 769. Fleischer, M., Geochim. Cosmochim. Actn, 1965, 29, 1263. Webber, G. R., Ibid., 1965, 29, 229. Roubault, M., de la Roche, H., and Govindaraju, K., Sciences Terve, 1962-1963, 9, 339. Received J u l y 19th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200083

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, February, 1967, Vol. 92, pp. 91-97 9L The Determination of Dicumyl Peroxide in Polystyrene Materials BY J. A. BRAMMER, S. FROST AND V. W. REID (“Shell” Research Limited, Central Laboratories, Egham, Surrey) A method has been developed for the determination of dicumyl peroxide in polystyrene plastic materials that may contain other organic peroxides. The dicumyl peroxide is extracted from the plastic with acetone and separated from the other additives present by thin-layer chromatography on silica gel. The silica gel in the area that contains the dicumyl peroxide is transferred to a small reaction flask and the peroxide determined by a micro-titration procedure. Formulations containing 0-25 to 0-5 per cent. w/w of dicumyl peroxide have been analysed by this method with a precision of f 12 per cent.of the determined value. Other organic peroxides commonly used in polystyrene formulations do not interfere. DICUMYL peroxide (DCP), which imparts a considerable degree of fire resistance to self- extinguishing grades of polystyrene and is often included in fire-resistant formulations, has the structural formula- CH, CH3 I I CH3-C-0-0-C-CH3 I I To maintain good self-extinguishing properties it is important that the DCP content of the product should not be materially reduced below the original level, either by the manu- facturing process or by subsequent conditions of usage. To investigate the stability of DCP in commercial products during processing and storage, a method for its determination in polystyrene was required. The method should be capable of application in the presence of other organic peroxides used in the formulation.Dicumyl peroxide is one of the most unreactive of the organic peroxides, and is not readily reduced by chemical or electrochemical methods. The only analytical method we have noted that has a specific application to DCP is the assay method used by the Hercules Powder C0mpany.l This is a titrimetric procedure, similar to that published by Mair and Graupner,2 and depends upon the liberation of iodine when refluxed with a sodium iodide - glacial acetic acid mixture. This procedure would be open to interference from other peroxides, however, which would also liberate iodine under the conditions used. It was expected that low molecular weight polystyrene, which is always present to some extent in polystyrene products, would also interfere.Separation of the DCP from the other additives would thus be a necessary pre-requisite to the determination. Thin-layer chromatography was used as a separation procedure, and a micro-titration procedure was then developed to determine the small amounts of DCP separated by this technique. EXPERIMENTAL DEVELOPMENT OF A SEPARATION PROCEDURE- Knappe and Peteri3 have published a method for the separation and detection of a number of organic peroxides by thin-layer chromatography. They used siIica gel as substrate and developed the chromatogram with a toluene - carbon tetrachloride solvent. Peroxide spots were detected by spraying with a solution of NN‘-dimethyl #-phenylenediamine dih ydrochloride.92 BRAMMER, FROST AND REID: DETERMINATION OF [A?th?bSt, Vol.92 This method was examined with respect to the separation of the peroxides that may be present in self-extinguishing grades of polystyrene, for example, dicumyl peroxide, t-butyl perbenzoate, benzoyl peroxide and cumene hydroperoxide (associated with the dicumyl peroxide). Solutions of these peroxides in carbon tetrachloride were applied to a thin-layer plate coated with silica gel, and developed according to the Knappe and Peteri method. Application of the spray reagent to the dried plate failed to reveal the position of the DCP, however, although the other peroxides were rendered plainly visible. The same separation procedure was carried out on plates coated with silica gel which embodied a fluorescent indicator, Merck Kieselgel GF254, and the dried plates were viewed by ultraviolet light at a wavelength of 254 mp.The DCP, t-butyl perbenzoate and benzoyl peroxide appeared as dark spots on a green fluorescent background. Only the cumene hydroperoxide spots remained invisible. By applying both methods of rendering the spots visible, a good separation was achieved for each of the compounds, as shown in Table I. TABLE I DETECTION OF PEROXIDES AFTER SEPARATION BY THIN-LAYER CHROMATOGRAPHY Visual indication r 1 NN’-Dimethyl GF254 plates Additive p-phenylenediamine and ultraviolet light RF values Dicumyl peroxide .. .. negative positive 0.55 t-Butyl perbenzoate . . .. positive positive 0.15 Benzoyl peroxide .. .. positive positive 0.30 Cumene hydroperoxide .. . . positive negative 0.05 Having established the conditions for separating the DCP from the other peroxide additives, the procedure was applied to the analysis of a sample of expanded polystyrene board containing 0.2 per cent. w/w of DCP. A solution of this sample in chloroform was applied to a prepared fluorescent plate, which was developed as before. Examination of the plate by ultraviolet light revealed that the polystyrene present in the solution had streaked badly and had obliterated most of the peroxide spots. A procedure was required, therefore, to enable the additives to be extracted from the polystyrene before separation of the DCP from the other peroxides. EXTRACTION OF THE ADDITIVES FROM THE POLYSTYRENE- A 25-g sample of the same polystyrene containing 0.2 per cent.w/w of DCP was extracted several times with 50-ml portions of acetone, and the separate extracts were reduced in volume to 10 ml. Aliquots of each extract were spotted on to a plate coated with the fluorescent silica- gel adsorbent, and the plate was developed and inspected under ultraviolet light. By com- paring the spots produced with those resulting from known weights of DCP, it was possible to estimate the amount of peroxide in each extract. The chromatogram obtained showed no visible DCP spot on the eighth extract. It was shown that if 1 per cent. of the original DCP had remained in this extract, then a visible spot would have appeared. A minimum of eight extractions was thus used in the developed procedure. Some polystyrene was visible near the starting line on this plate, but the streaking effect had been sufficiently reduced by the pre-extraction procedure to ensure that the small amount of polystyrene remaining in the acetone extract would not interfere with the DCP determination.DETERMINATION OF THE SEPARATED DICUMYL PEROXIDE- In view of the relatively small amounts of material that can be effectively separated by thin-layer chromatography, an attempt was made to determine the isolated DCP by a colorimetric procedure. Trials were made with two methods for the colorimetric determination of organic peroxides. In the first method, Vioque and Vioque4 used NN’-dimethyl p-phenylene- diamine dihydrochloride as the colour producing agent. In the second method (Eiss and Giesecke5) zirconium naphthenate and benzoyl leuco methylene blue were used. ’These reagents failed to produce a colour with DCP.Titrimetric procedures based on the liberation of iodine were then examined, particularly the procedures used by Mair and Graupner and the Hercules Powder Co. In these proceduresFebruary, 19671 DICUMYL PEROXIDE IN POLYSTYRENE MATERIALS 93 the sample is refluxed with a glacial acetic acid solution of sodium iodide, and the liberated iodine titrated with sodium thiosulphate solution. These titrimetric methods were designed for the determination of about 0.3 g of DCP, so that it was necessary to use a modified pro- cedure in order to determine the smaller amounts of peroxide separated by thin-layer chromatography. The volume of the apparatus was scaled down by a factor of ten, and an Agla micrometer syringe was used as the titration burette.This micro-scale procedure proved to be satisfactory after eliminating certain causes of high blank values. For example, it was found that the xylene, which was used as a solvent in the preparation of standard DCP solutions, contained trace amounts of peroxide impurities. These impurities could be removed by passing the solvent through an activated alumina column, as proposed by Dasler and Bauer.6 Also, the nitrogen used to displace air from the flask while refluxing and titrating contained oil and other impurities that liberated iodine. These were removed by passing the nitrogen through a tube packed with molecular sieves and cotton-wool. The micro-titration procedure was then applied to synthetic solutions of DCP in xylene that contained between 0.4 and 1.2-mg amounts of the peroxide.The recoveries obtained are shown in Table 11, where it may be seen that good recovery of peroxide, together with a reasonable degree of reproducibility, is obtained when the amount of DCP titrated is about 1 mg. A t this level, the blank values normally obtained were in the region of 3 to 5 per cent. of the sample titre. The method published by the Hercules Powder Co. introduces a correction factor based on the assumption that there is 93 per cent. reaction of dicumyl peroxide with sodium iodide. This factor was not applied in calculating the results shown in Table 11, and has not been included in the final procedure. TABLE I1 MICRO-TITRATION OF DCP WITH SODIUM THIOSULPHATE DCP present, mg 1.205 1.205 1-205 1-174 1.174 1.174 0.782 0.782 0.782 0.391 0.391 0.391 0.02 N Thiosulphate titre (less blank), 410 425 420 430 420 425 270 280 275 145 130 140 P*.1 DCP found, DCP recovery, mg per cent.1.11 92 1.15 95 1.14 95 1.16 99 1.14 97 1.15 98 0.73 93 0-76 97 0.74 95 0.39 100 0.35 90 0.38 97 We then examined the possibility of transferring the adsorbent containing the DCP spot to the reaction flask and subsequently titrating it by the micro-procedure. The silica-gel adsorbent gave negligible blank values when the procedure was applied in the absence of sample. We then applied known solutions of DCP in xylene to thin-layer chromatographic plates coated with Merck Kieselgel GF,,, adsorbent, and the chromatograms were developed with toluene - carbon tetrachloride solvent as before.When the plates were dried, the DCP zones were marked out under ultraviolet light and the silica gel from each zone was quanti- tatively transferred to separate reaction flasks. The peroxide content of each zone was then determined by the micro-titration procedure. The results obtained are shown in Table 111, which includes values for the amount of sample and the lengths of the sample stripes applied to the plate. At the 0.6-mg level, 12 pl of DCP solution applied evenly along the starting line for a distance of 5 cm gave good recovery of the peroxide; 1.2 mg distributed along a 7.5-cm length gave recoveries of about 80 per cent. When the amount of DCP separated was about 1 mg, and the sample was applied to a 15-cm length of the starting line, good recoveries were obtained.This last procedure was therefore adopted.94 BRAMMER, FROST AND REID: DETERMINATION OF [Analyst, Vol. 92 DCP solution (strength, normal), mg per ml 50 50 50 50 50 5 5 5 5 5 TABLE I11 RECOVERY OF DCP FROM THIN-LAYER CHROMATOGRAPHIC PLATES Volume of solution on TLC plate, 12 12 12 25 25 300 300 300 200 200 P1 Length of sample stripe on TLC plate, cm 5 5 5 7.5 7-5 15 15 15 15 15 Sodium Weight of thiosulphate DCP present, titre (less blank), mg E.1 0.578 220 0.578 215 0.578 205 1.205 335 1.205 345 1.174 420 1.174 425 1.174 415 0.782 285 0.782 300 DCP recovery, per cent. 103 101 96 75 78 97 98 96 99 104 The extraction, separation and titration steps were then combined into one procedure, which was applied to samples of polystyrene products in the form of beads and expanded boards. METHOD APPARATUS- Thin-layer chromatography (TLC) equipment-This consists of TLC plates, 20 x 20 cm, plate coating equipment (any commercially available equipment is suitable), drying oven, desiccator, chromatographic tank capable of holding the TLC plates and a TLC spotting template.Ultraviolet lamp-The lamp used should give maximum emission at 254 mp. Reaction and titration equipment-This is assembled, together with the nitrogen purifica- Micro-reaction flask-This consists of a 25-ml round-bottomed flask with B 14/23 neck, Agla micrometer syringe-This is fitted with a glass capillary delivery tube and mounted Magnetic stirrer-This is fitted with a plastic-coated stirrer bar, 15mm in length. tion train and micro-reaction flask, as shown in Fig.1. fitted with a capillary side-arm, as shown in Fig. 1. on a retort stand. REAGENTS- All reagents should be of analytical-reagent grade, unless otherwise stated. Kieselgel GF,,, (Merck)-TLC silica gel with binder and fluorescent indicator. A cetone. Toluene. Carbon tetrachloride. Dicumyl peroxide-Technical grade (obtainable from Hercules Powder Co., Hercules Acetic acid, glacial. Sodium iodide. Sodium thiosulphate solution, 0.02 N-Prepare a 0.1 N solution of sodium thiosulphate. Tower, Wilmington 99, U.S.A.). Dilute 20 ml of this solution to 100 ml. PROCEDURE- Preparation of TLC equipment-Coat a batch of 20 x 20-cm TLC plates with Kieselgel GF,,, to give a layer thickness of 0-25 mm.Allow the layer to set, then dry the plates at 110" C for 30 minutes. Store the prepared plates in a desiccator. Prepare the developing solvent by mixing two volumes of toluene with one volume of carbon tetrachloride. Pour sufficient of the mixed solvent into a TLC tank to give a depth of liquid of about a & inch. Line the inside of the tank with filter-paper, replace the lid and allow the tank to stand for at least 4 hours to enable the atmosphere to become saturated with solvent vapour.February, 19671 DICUMYL PEROXIDE IN POLYSTYRENE MATERIALS 95 EXTRACTION OF THE ADDITIVES- sample as indicated in Table IV. (;) Treatment of expanded boards-Weigh to the nearest 0.1 g a suitable amount of TABLE IV OPTIMUM SAMPLE WEIGHTS FOR LEVELS OF DCP UP TO 1 PER CENT.DCP content, Sample weight, per cent. g 0 to 0.25 25 0.25 to 0.5 10 0.5 to 1.0 5 Before weighing cut the sample into pieces 3 x 1 x 1 inches. Introduce the weighed pieces, one at a time, into a 250-ml beaker containing about 100 ml of acetone. The pieces will immediately collapse to form a rubber-like mass on making contact with the acetone. Pummel the mass for 5 minutes with a glass rod flattened at the end, and then decant as much of the acetone as possible into a clean 100-ml beaker. Evaporate the acetone solution to about 10 ml. Add a further 30 to 40 ml of acetone to the polystyrene sample, repeat the extraction procedure and decant the excess of acetone into the same 100-ml beaker. Carry out a total of eight extractions in this way, reducing the acetone volume in the beaker to 10 ml each time.Finally, reduce the volume of acetone solution to less than 10 ml, quantitatively transfer this solution to a 10-ml calibrated flask and make up to the mark with acetone. After mixing the solution, allow the flask to stand until any emulsion formed has subsided. The solution is then ready to be applied to the TLC plate. (ii) Tyeatment of polystyrene beads-Weigh a suitable amount of sample (Table IV) into a 250-ml beaker and add 100 ml of acetone. Pummel the beads until the sample has com- pletely softened to a rubbery mass. Carry out eight extractions with acetone to produce a 10-ml volume of acetone solution as described above. CHROMATOGRAPHIC SEPARATION OF DCP- Take a prepared TLC plate and apply 0-2 ml of the acetone extract along a starting line, 2.5 cm from the bottom edge of the plate, either by applying a series of small (5 p1) drops, or by using sample striping equipment.Whichever method of application is used, it is essential that the correct volume of solution be applied as uniformly as possible along a 15-cm length of the starting line. Parallel with the starting line, and 15 cm away from it, draw a line through the adsorbent to mark the limit of travel of the developing solvent. Allow the acetone solvent to evaporate from the plate, and then develop the chromatogram in the pre-saturated tank. This process should take about 45 minutes. Remove the plate from the tank, transfer it to a fume cupboard and completely evaporate the solvent in a stream of dry nitrogen. Place the plate under an ultraviolet lamp that is emitting light at 254 mp, The DCP will then be visible as a dark zone against the green fluorescent background, and will normally be located nearest the solvent front.Should any difficulty be experienced in locating the correct zone, a solution of DCP in acetone may be used as a marker. Draw round the DCP zone, leaving sufficient margin to include adsorbent that may contain traces of DCP not visible under the ultraviolet light. Transfer quantitatively the adsorbent within the marked area to a small test-tube, in readiness for the determination of the DCP. DETERMINATION OF THE SEPARATED DCP- Transfer by pipette 5 ml of glacial acetic acid into the micro-reaction flask and add a few anti-bumping granules. Connect the nitrogen line to the side-arm and adjust the flow of nitrogen so that a slight dimple is produced on the surface of the liquid.Assemble the reaction apparatus as shown in Fig. 1 and pass a steady flow of tap water through the condenser jacket. Increase the nitrogen flow to a steady stream as indicated by the water bubbler, and then heat the flask contents to boiling. Reflux for 5 minutes to remove dissolved air.BRAMMER, FROST AND REID: DETERMINATION OF [AutabSt, VOl. 92 A = Molecular sieves B = Cotton-wool C = PVC tubing D = Capillary side-arm, 6mm o.d., Imm i.d. E = Condenser (I50mm) F = Reaction flask, 25:ml (Quickfit and Quartz Ltd., FR 25/15) = Water Fig. 1. Apparatus for the reaction of DCP with sodium iodide After refluxing, increase the nitrogen flow further, and cool the flask by immersing it in water.Ensure that the gas flow-rate is sufficient to prevent air being sucked back into the flask. Remove the flask from the condenser, add 0.6g of sodium iodide and swirl the flask to dissolve it. Transfer by pipette 0.3 ml of distilled water into the flask and mix the liquid phases. Momentarily turn off the nitrogen supply and quickly pour the silica gel powder, on which the DCP sample is adsorbed, into the flask. Again attach the flask to the condenser and reflux the contents for 15 minutes, with a steady nitrogen flow. Cool the flask contents as before, then remove the flask from the condenser, add 10 ml of water and introduce a small magnetic-stirrer bar. Clamp the flask over a magnetic stirrer and adjust the stirring-rate so that a shallow vortex is produced.By using an Agla syringe burette titrate the contents of the flask with 0.02 N sodium thio- sulphate to a colourless end-point. Carry out a blank titration as described above with 5 ml of glacial acetic acid, 0.6 g of sodium iodide and 0.3 ml of water. Do not include silica gel in the blank titration. CALCULATION- The percentage by weight of DCP in the sample is given by- (Ts - TB) x N x 270.4 x 100 - (Ts - T B ) x N x 676 - 2 x 1000 x 0.02 x w W where Ts = millilitres of sodium thiosulphate solution used for the sample, TB = millilitres of sodium thiosulphate solution used for the blank, W = the weight in grams of polystyrene taken, and N = the normality of the sodium thiosulphate solution. RESULTS The procedure has been applied to samples of polystyrene in expanded board and in bead form.The results obtained on ten determinations carried out on the board, which had been prepared by the addition of 0-5 per cent. w/w of DCP* during manufacture, are shown in Table V (sample No. 1). * The technical DCP used contained 98 per cent w/w of dicumyl peroxide.February, 19671 DICUMYL PEROXIDE IN POLYSTYRENE MATERIALS TABLE V DETERMINATION OF DCP IN EXPANDED POLYSTYRENE BOARD { 3 0.5 0.25 0.25 12 Sample DCP added, Sample weight, DCP found, per cent. w/w 0.43 0.51 0.46 0.47 0.47 0.44 0.51 0.45 0-45 0.47 Mean . . 0.47 0.20 0.20 25 0-17 0.20 Mean . . 0.19 0.19 25 0.18 No. Der cent. w/w g Mean . . 0.185 97 These results are reasonabl 7 reprodi cible and close to the known addition, the average result being 0.47 per cent.with a spread of k0-04 per cent. The standard deviation is 0.03 per cent., which represents 95 per cent. confidence limits of some k12 per cent. of the JXP content in single determinations. The reproducibility at the 0-25 per cent. w/w level (sarr ples Nos. 2 and 3) is of a similar order. The results obtained at similar DCP levels, when the sample was in the form of :mall polystyrene beads, are shown in Table VI. Here again, satisfactory agreement was obta ined, the DCP content determined being of the same order as the amount of DCP added i i the bead formulation. TABLE VI DETERMINATION OF DCP IN POLYSTYRENE BEADS Sample DCP added, Sample weight, DCP found, per cent. w/w g per cent. w/w 0.43 0.46 4 10 0.44 0.48 Mean . . 0.45 No’ { 0.5 0.20 0.19 0.20 I Mean . . 0.20 The results obtained on both board and bead samples are slightly lower than the amount of DCP added during manufacture; this is to be expected as some DCP would be lost during processing. CONCLUSION 5 [ 0.25 25 0.20 A method has been described for the determination of dicumyl peroxide in polystyrene, either in the form of expanded boards or beads. The reproducibility of the method is of the order of k12 per cent. of the determined value at the 0.25 and 0-5 per cent. w/w level. Good recovery of dicumyl peroxide has been obtained in the analysis of formulated products. REFERENCES 1. 2. 3. 4. 5. 6. “Assay Analyses for Dicumyl Peroxide,” Technical Data Bulletin PR-107, Hercules Powder Co., Mair, R. D., and Graupner, A. J., Analyt. Chein., 1964, 36, 194. Knappe, E., and Peteri, D., 2. analyt. Chem., 1962, 190, 4, 386. Vioque, A., and Vioque, E., Grasas Aceit., 1962, 13, 5, 203. Eiss, M. l., and Giesecke, P., Analyt. Chem., 1959, 31, 1558. Dasler, W., and Bauer, C. D., I n d . Engng Chem. Analyt. Edn, 1946, 18, 52. Hercules Tower, Wilmington 99, Delaware, U.S.A. Received June 30th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200091

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

98 Analyst, February, 1967, Vol. 92, $9. 98-102 The Amperometric Titration of Submillinormal Concentrations of Hexacyanoferrate (111) with Mercury (I) Perchlor ate BY JOHN T. STOCK AND R. J. MERRER (Department of Chemistry, The Universit3. of Connecticut, Stows, Connecticut 06268, U.S.A .) Although quite precise under rigidly controlled conditions, the mercury (I) amperometric titration, a t a rotating platinum electrode, of submillinormal concentrations of hexacyanoferrate(II1) in sodium hydroxide - potassium iodide medium gives results that vary with the concentrations of alkali, iodide and hexacyanoferrate (111). Dependence upon solution composition is small in perchloric acid - potassium thiocyanate medium. In this medium, the titration of 5 x to 1 3 - 3 ~ hexacyanoferrate(II1) is precise and accurate to within k1.5 per cent.N hexacyano- ferrate(II1) is precise to about 5 per cent. The titration of 5 x THE mercury(1) perchlorate potentiometric titration of approximately 0.01 N hexacyano- ferrate(II1) in sodium hydroxide - potassium iodide medium is stated to be satisfact0ry.l The titration can also be carried out in acidified potassium thiocyanate m e d i ~ m , ~ , ~ in which precise results for hexacyanoferrate(II1) concentrations of approximately 0.004 to 0.023 N are r e p ~ r t e d . ~ The present work concerns the amperometric mercury( I) titration of sub- millinormal concentrations of Eiexacyanoferrate(II1) ion by methods similar to those used for iron (I I I) ,4 copper (I I)5 and iodine. EXPERIMENTAL VOLTAMMETRY- The voltammetry of mercury(1) and mercury(I1) in acid thiocyanate and acid thio- cyanate - iodide media has already been de~cribed.~?~ In 0.01 N perchloric acid - 0.5 N potas- sium thiocyanate, the limiting current of hexacyanoferrate(III), measured at a fixed potential within the range +0.1 to -0.1 volt (all potentials are with respect to the saturated calomel electrode, S.C.E.), was found to be proportional to concentrations of this ion when these were not greater than about 8 x 1 0 - 4 ~ .A linear relationship between the current and the concentration of hexacyanoferrate(III), at a fixed potential in the same range, was also obtained in N sodium hydroxide - 0 . 4 ~ potassium iodide. Hexacyanoferrate( 11) is not electroactive in either medium over this potential range.Fig. 1 shows current - voltage curves obtained at various stages in the amperometric titration of 5 x N hexacyanoferrate(II1) in alkaline iodide medium with mercury(1) perchlorate solution. A similar group of curves obtained in acid thiocyanate medium is shown in Fig. 2. AMPEROMETRIC TITRATIONS- All titrations were run at zero potential and at room temperature (in the range 24" to 27" C). End-points in acid media were located by procedures (A) and (B) (below) and by the L-curve m e t h ~ d . ~ 9' In alkaline-media titrations, which were carried out by similar methods, clogging resulted when the tip of the microburette containing mercury( I) perchlorate solution was immersed in the solution being titrated. The tip was therefore placed a few millimetres above the solution and each addition of titrant was rinsed down with four successive drops (a total of 0-2ml) of water.STOCK AND MERRER 99 METHOD REAGENTS- Use analytical-grade reagents and distilled or de-mineralised water throughout.Mercury ( I ) perchlorate, approximately 0.1 N in N Perchloric acid-Prepare, dilute as required with N perchloric acid, and standardise by the dichromate - iodide method, as described by Berka, Vulterin and Zyka.* Store over metallic mercury and shake the solution thoroughly before use. Potassium hexacyanoferrate(II1) , approximately 0.1 N-Dilute as required and standardise iodimetrically . Perchloric acid, approximately 0.02 N. Potassium thiocyanate, approximately N. Use conventional apparatus for amperometric titration at a rotating platinum electrode that is maintained at zero potential.5 Clean and pre-condition the electrode as de~cribed,~ but use potassium hexacyanoferrate(II1) as the substance titrated. The platinum electrode used in the present work was rotated at 600 r.p.m.It then had a sensitivity of 0-0298 pA per micromole of hexacyanoferrate(II1) per litre, measured at zero potential in de-oxygenated 0.5 N potassium thiocyanate - 0.01 N perchloric acid at 25" C. . +0I -0.1 -0.2 -03 Potential, volts Fig. 1. Current - voltage curves at stages in the titration of 5 x N hexacyanoferrate(II1) in N sodium hydroxide - 0 . 4 ~ potassium iodide. Percentage equivalent of mercury( I) perchlorate added: curve A, 0 ; curve €3, 50; curve C, about 100; curve D, 150 f U C t! 3 U +03 + 0 2 +O.I 0 -0.1 4 2 Potential, volts Fig. 2.Current - voltage curves a t stages in the titration of 5 x 1 0 - 6 ~ hexacyanoferrate(II1) in 0 . 0 1 ~ perchloric acid - 0-5 N potassium thio- cyanate. Percentage equivalent of mercury( I) perchlorate added: curve A, 0 ; curve B, 50; curve C, about 100; curve D, 150 PROCEDURE- ( A ) Transfer 50 ml of 0.02 N perchloric acid and 50 ml of N potassium thiocyanate to the titration cell. Insert the platinum electrode and salt bridge, de-oxygenate with a stream of nitrogen, then stop the gas stream. Inject 0.01 N potassium hexacyanoferrate(II1) so that the amount introduced is about 30 per cent. of that contained in the sample solution. After 2 minutes, note the current reading, P, then inject the sample solution. Read the current after a further 2 minutes, then titrate with 0-01 to 0.1 N mercury(1) perchlorate until the current has fallen nearly to zero.Allow an interval of 1 minute between a titrant addition and the reading of the current. Find the end-point graphically as the intersection of the linear portion of the titration curve and the line: current = P. (B) Proceed as in ( A ) up to the stopping of the gas stream. Note the residual current, R, then at once inject the sample and titrate as in ( A ) . Find the end-point graphically by producing the linear portion of the titration curve to cut the line: current = R.100 STOCK AND MERRER: AMPEROMETRIC TITRATION OF [ArtaZyst, Vol. 92 RESULTS TITRATIOK IN ALKALINE IODIDE MEDIA- N hexacyanoferrate(II1) ion in sodium hydroxide - potassium iodide media.The actual normality of the titrant was 0.0932. Although the results are fairly precise, they are noticeably influenced by the com- position of the medium. Such an effect is not necessarily intolerable in routine titrimetry. Table I gives the results obtained in triplicate titrations of TABLE I EFFECT OF HYDROXIDE AND IODIDE CONCENTRATION IN THE TITRATION OF 10-4 N HEXACYANOFERRATE(III) Hydroxide concentration, 0.1 0.5 1.0 1-5 2.0 4.0 1.0 1.0 1.0 N Iodide concentration, 0.4 0.4 0.4 0.4 0.4 0.4 0.1 0.6 0.9 N Apparent mercury( I) normality Procedure ( A ) 0.088 * 0.002 0-089 & 0.002 0*093,& 0.001," 0.100 * 0.001 0.102 & 0.005 0.128 0-002 0.087 * 0.001 0.105 f 0.002 0.192 0.004 * 30 runs. L-curve 0.087 f 0.002 0.086 f 0.002 0.088, j: 0.002," 0.098 & 0.001 0.100 & 0.006 0.126 0.008 0.085 f 0.001 0.101 & 0.003 0.185 f 0.003 1 Procedure (B) 0.088 0.002 0-087 f 0.003 0-090, & 0.001,* 0.100 & 0.002 0.101 f 0.005 0.128 & 0.007 0.086 & 0.001 0.102 & 0.002 0.185 5 0.003 However, the results obtained in N sodium hydroxide - 0.4 N potassium iodide are accurate only at a hexacyanoferrate(II1) concentration of about 10-4~ (Table 11).An alkaline iodide medium cannot therefore be recommended for the mercury( I) titration of submillinormal concent rations of hexacy anof errat e (I I I) ion. TABLE I1 TITRATION OF HEXACYANOFERRATE(III) IN N SODIUM HYDROXIDE - 0.4 N POTASSIUM IODIDE Hexacyano- ferrate (I 11) concentration, (1.N 10 20 50 100 200 500 1000 Number of runs 6 4 9 30 3 3 6 Apparent mercury(1) normality L-curve I h 3 Procedure ( B ) 0.116 f 0.030 0.097 f 0.009 0.108 & 0.012 0.103 & 0.006 0.098 & 0-008 0.102 & 0.008 0.093, & 0.001 0.088, f 0.002, 0.090, * 0.001, Procedure ( A ) 0.092 & 0.004 0.089 & 0.004 0.093 & 0-004 0.078 & 0.002 0.077 5 0.002 0.077 & 0.002 0.081 & 0.001 0.082 4: 0.002 0.081 f 0.001 0.085 0.002 0-084 0.002 0-084 f 0.002 TITRATION IN ACID THIOCYANATE MEDIA- The normality of the mercury(1) perchlorate solution used for titrations in acid thio- cyanate media was 0.1017.Table I11 lists the results obtainedin triplicate runs at a hexacyano- ferrate(II1) concentration of N. Although it needs to be fairly high, the concentration of thiocyanate can be varied without noticeable effect upon precision or accuracy.Runs made in 0.01 N perchloric acid - 0.5 N potassium thiocyanate, which gave optimum results at a hexacyanoferrate concentration of N, showed that this medium is also satisfactory for the titration of both higher and lower concentrations of this ion (Table IV). Procedure ( A ) is precise and accurate to within 1.5 per cent. for hexacyanoferrate(II1) concentrations of from 5 x to 10-3 N, or to within 1 5 per cent. for concentrations down to 5 x 10-6 N. Procedure (B) is a little less precise than procedure (A) and is less accurate. However, procedure ( B ) becomes satisfactory if it is also used for the actual standardisation of the titrant. The results obtained by the L-curve method are decidedly inaccurate and are generally more erratic than the results given by procedures ( A ) and (B).Procedure (B) is useful when the sample is presented as a highly dilute solution. The sample is made 0.01 N in perchloric acid, de-oxygenated, made 0-5 N in potassium thiocyanate,February, 19671 SUBMILLINORMAL CONCENTRATIONS OF HEXACYANOFERRATE(III) 101 TABLE I11 TITRATION OF N HEXACYANOFERRATE(III) IN ACID THIOCYANATE MEDIA Thiocyanate concentration, 0-05 0.2 0.25 0-3 0.5 0.5 0.5 0.5 0.8 1.0 1.5 3.0 N Perchloric acid concentration, 0.02 0.02 0.02 0.02 0.01 0.02 0.05 0.08 0.02 0.01 0.01 0.01 N TITRATION OF Hexscyano- ferrate( 111) concentration, PN 1 5 10 50 100 1000 Apparent mercury(1) normality Procedure ( A ) 0.098 f 0.002 0.098 f 0-002 0.095 f 0.002 0.099 -+ 0*002* 0.101 & 0.001 0.100 f 0.001 0.099 f 0.001 7 0.101 f 0.001 0.100 f 0.001 0.101 f 0.002 0.100 f 0.001 * 6 runs.t Medium decomposc :d. L-curve 0.094 f 0.002 0.090 f 0.002 0.090 f 0.004 0.091 f 0*002* 0.097 f 0.001 0.096 f 0.001 0.092 f 0.002 t 0.100 f 0.001 0.094 & 0.002 0.094 f 0.001 0.097 f 0.001 Procedure '(B) 0.093 f 0.003 0-092 f 0.002 0.092 f 0.002 0-093 f 0.002* 0.099 f 0.001 0.096 f 0.001 0.094 f 0.001 t 0.103 f 0.001 0.097 f 0.001 0.096 5 0.001 0.098 f 0-001 TABLE IV HEXACYANOFERRATE(III) IN 0.01 N PERCHLORIC ACID - 0.5 N POTASSIUM THIOCYANATE Number of runs 3 6 6 6 10 6 Apparent mercury(1) normality f 1 Procedure ( A ) L-curve Procedure ( B ) 0.0145 & 0.0009* 0-0094 f 0.0006* 0.0101 -+ 0.0004* 0.0102 f 0*0004* 0.0087 f 0-0005* 0.0092 f 0.0004* 0.0098 & 0*0002* 0.0078 f 0*0003* 0.0086 & 0*0004* 0.1011 f 0.0004 0.0967 f 0.0004 0.1005 f 0.0009 0.1005 & 0.0011 0.0953 f 0.0019 0.0980 f 0.0016 0.1028 0.0011 0.0990 f 0.0007 0.1002 f 0.0004 * Titrant diluted 10-fold.de-oxygenated for 5 to 10 minutes longer, and then titrated. A separate 0.01 N perchloric acid - 0-5 N potassium thiocyanate solution is used for residual-current determination. Three results thus obtained with N hexacyanoferrate(II1) were precise and accurate to within 5 per cent. With the availability of a suitable ultramicroburette, the volume of hexacyanoferrate(II1) solution required for titrationlo could probably be reduced by a factor of at least 50. DISCUSSION Titrations in alkaline medium (Tables I and 11) give apparent mercury(1) normalities that are high when the concentrations of hydroxide, iodide and hexacyanoferrate( 111) are high, high and low, respectively.The normalities are low when the concentrations of hydroxide or iodide are reduced, or when the concentration of hexacyanoferrate(II1) is in- creased. These trends suggest the occurrence of side reactions that cause the destruction of the substance being titrated and of the titrant. Accurate results in the titration of N hexacyanoferrate(II1) in N sodium hydroxide - 0.4 N potassium iodide probably arise from mutual compensation of these sources of error. The spontaneous destruction of hexacyanoferrate( 111) in alkaline iodide media was noted by Burriel-Marti, Lucena-Conde and Arribas- Jimen0.l In the present work, measurements of the limiting currents of N hexacyanoferrate(II1) in N sodium hydroxide - 0.4 N potassium iodide made 1, 10, 20 and 30 minutes after injection of hexacyanoferrate(III), were found to be in the ratio 100: 91 : 84: 78, respectively.As from 10 to 15 minutes must elapse in the amperometric titrations of submillinormal concentrations of hexacyanoferrate(III), the effect is an obvious source of error. At high ionic strength, the formal potentials of the hexacyanoferrate(II1) - hexacyano- ferrate(I1) and iodine (or tri-iodide) - iodide couples are probably not very different.l1,l2 An incipient liberation of iodine will be favoured by increasing the concentrations of potassium102 STOCK AND MERRER iodide and sodium hydroxide. The kinetic aspects of the hexacyanoferrate - iodide reaction in neutral solutions have been extensively studied.The moderately slow reaction is speeded by increasing the iodide concentration or the ionic strength, and by the presence of metallic p1atin~m.l~ In alkaline medium, iodine rapidly passes into hypoiodite and iodide ions. Hypoiodite then disproportionates at a measurable rate into iodate and iodide ions,14 so that the over-all effect is loss of hexacyanoferrate(II1). In the present work, the introduction of approximately N hexacyanoferrate(II1) in N sodium hydroxide - 0.4 N potassium iodide did not change the limiting current or the volume of titrant needed. When made alkaline] mercury(1) perchlorate disproportionates and a precipitate of mercury(I1) oxide and metallic mercury is the final re~u1t.l~ Although this effect may not occur when hexacyanoferrate(II1) is titrated in the presence of much iodide, it should become significant as the iodide concentration is reduced.The erratic behaviour at comparatively high hexacyanoferrate(II1) concentrations (Table 11) may be caused by high local concen- trations resulting from larger titrant additions. N hexacyanoferrate(II1) ion in 0.01 N perchloric acid - 0.5 N potassium thiocyanate was found to be unchanged after ageing for 30 minutes. High titrant normalities are therefore not to be expected. Disproportionation of mercury(1) ion in thio- cyanate medium is po~sible,~ and may account for the somewhat low titrant normalities observed at thiocyanate concentrations of less than 0-5 N. This work was carried out with the partial support of the United States Atomic Energy Commission (Contract AT(30-1)-1977). M potassium iodate into The limiting current of 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. REFERENCES Burriel-Marti, F., Lucena-Conde, F., and Arribas- Jimeno, S., Analytica Chim. Acta, 1954, 10, 301. Tarayan, V. M., and Arutyunyan, A. A., Izv. Akad. Nauk Armyan. SSR, Fiz-Mat. Estestven. Lucena-Conde, F., and Bellido, I. S., Talanta, 1958, 1, 305. Stock, J. T., and Heath, P., Analyst, 1965, 90, 403. Stock, J . T., Ibid., 1966, 91, 27. -, Ibid., 1966, 91, 280. --, “Amperometric Titrations, ” Interscience Publishers, a division of John Wiley and Sons Berka, A., Vulterin, J., and Zyka, J., Chemist-Analyst, 1963, 52, 122. Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” Third Edition, Stock, J. T., 09. cit., p. 108. Willard, H. H., and Manalo, G., I n d . Engng Chem. Analyt. Edn, 1947, 19, 462. Laitinen, H. A., “Chemical Analysis : An Advanced Text and Reference,” McGraw-Hill Book Co. Spiro, M., and Ravno, A. B., J . Chem. SOG., 1965, 78, and references cited. Morgan, K. J., Q. Rev. Chew. SOG., 1954, 8, 123. Lingane, J . J . , “Analytical Chemistry of Selected Metallic Elements,” Reinhold Publishing Corp., Received August 16th, 1966 i Z’ekh. Nauki, 1950, 3, 651. Inc., New York, London and Sydney, 1965, chapter 1, p. 8. Macmillan Co., New York and London, 1952, p. 595. Inc., New York, Toronto and London, 1960, pp. 290 and 393. New York, 1966, p. 79.

ISSN:0003-2654    

DOI:10.1039/AN9679200098

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, February, 1967, Vol. 92, $9. 103-106 103 Spectrsphotometric Determination of Aluminium in Soil Extracts with Xylenol Orange BY D. T. PRITCHARD (Soil Survey of England & Wales, Rothanzsted Experimental Station, Havpenden, Herts.) A spectrophotometric method for determining aluminium in soil extracts with xylenol orange a t pH 3.8 is described. Various extraction reagents can be used. Interference of iron(II1) and iron(I1) is eliminated with EDTA. Rectilinear calibration covers a range of 0 to 60pg of aluminium. Typical results are shown for an iron - humus podzol. Recovery of added aluminium and levels of interference of anions and cations relevant to soil analysis are shown. The practicability of the method in contrast with “lake” methods is emphasised. MOST conventional spectrophotometric methods for the determination of aluminium depend on the adsorption of coloured dyes on colloidal aluminium hydroxide.Sandelll commented on the unsatisfactory nature of these “lake”-forming methods (exemplified by aluminon) and deplored the necessity for their use. Korbl and Pi-ibi12 prepared xylenol orange as a metallo- chromic indicator that forms a soluble coloured complex with aluminium. Otomo3 examined this reaction in detail, and Budeshinsky4 used the reagent to determine aluminium in uranium. Although xylenol orange is not specific for aluminium, only iron is likely to cause serious interference in soil extracts, and this is eliminated in the proposed method by the use of EDTA. METHOD REAGENTS- All reagents, except xylenol orange, were of AnalaR quality.Tamm’s reagent-Dissolve 24.9 g of hydrated ammonium oxalate and 12-6 g of hydrated Bupeer solation, pH 3.8-Dissolve 136 g of hydrated sodium acetate in water, adjust to oxalic acid in water and dilute to 1 litre. pH 3.8 with hydrochloric acid and dilute to 1 litre. APPARATUS- measurements. A Rausch and Lomb colorimeter (Spectronic 20) was used for spectrophotometric PROCEDURE- Preparation of soil extracts-Shake overnight 2-00 g of soil (crushed to pass a 2-mm sieve) with 100.0ml of Tamm’s reagent and spin it in a centrifuge. Take a 25-ml aliquot and destroy organic matter with 40-volume hydrogen peroxide. Add 10 ml of 9 N sulphuric acid and evaporate to fuming. Cool the solution, dilute it, adjust to about pH 2 and dilute t o 100ml.S$ectrophotornetry-Transfer an aliquot of the soil extract containing 0 to 60 pg of a h - minium into a 100-ml calibrated flask. Add 25 ml of buffer solution (pH 3-8) and 10.0 ml of 0.15 per cent. aqueous xylenol orange. Place the flask in a water-bath at 40” C for 18 hours. Cool the solution, add 5 ml of 0.05 M EDTA (disodium salt), dilute to 100 ml and allow it to stand at room temperature for 1 hour. Measure the optical density at 550mp. RESULTS AND DISCUSSION In the absence of EDTA, the colour produced by the aluminium - xylenol orange complex is stable for several days. The colour develops slowly at room temperature and the rate of development is further retarded by the presence of iron. The temperature chosen (40” C) ensures that a stable, coloured product is obtained in 18 hours.Higher temperatures cause a more intense colouration, but reduce its stability, even in the absence of EDTA.104 PRITCHARD : SPECTROPHOTOMETRIC DETERMINATION OF [A ?Zdy.St, VOl. 92 I I 60 I20 Time. minutes Fig. 1. Rates of colour fading clue to EDTA: curve A, 50 pg of aluminiumplus 1000 pgof iron(II1) plus xylenol orange; curve B, 50 pg of aluminium plus xylenol orange Both iron(II1) and iron(I1) react with xylenol orange to give coloured solutions that react similarly in all respects, and absorb strongly in the region of maximum absorption of the aluminium - xylenol orange complex. The method depends on the difference caused by EDTA in the rates of fading of the colours produced by iron and aluminium with xylenol orange (Fig. 1).It can be seen that the colour produced by 1000 pg of iron fades completely within 1 hour, whereas that produced by the aluminium fades slowly enough to allow repro- ducible readings to be made. Theoretical considerations suggested that ascorbic acid or mercury(I1) - EDTA might mask the iron - xylenol orange reactions without affecting the aluminium - xylenol orange colour. However, under various conditions, neither reagent was wholly satisfactory. Fig. 2 shows the absorption spectra of a solution containing aluminium and xylenol orange, and of xylenol orange alone, which indicate a wavelength of maximum absorption of 550 mp for the aluminium - xylenol orange complex. Wavelength, mp Fig. 2. Absorption spectra: curve A, 100 p g of aluminium #Zus 2 ml of 0.15 per cent.xylenol orange; curve B, xylenol orange aloneFebruary, 19671 ALUMINIUM IN SOIL EXTRACTS WITH XYLENOL ORANGE 105 Fig. 3 illustrates the variation of optical density at 550 mp of the aluminium - xylenol orange complex, and of xylenol orange alone, as a function of pH. The graph is horizontal at pH 3.2 and 3.8, and both points are therefore suitable for measuring the optical density. At pH 3.8, there is some loss of sensitivity, but this pH value was chosen for use because Beer's law is obeyed over a wider range of aluminium concentration than it is at pH 3.2. A rectilinear calibration is obtained over the range 0 to 60 pg of aluminium. Molar absorp- tivity is 11,000 under the conditions described. It is not necessary to include standards with each batch of samples, nor to re-calibrate when using fresh solutions of xylenol orange.2.0 3.0 4.0 PH Fig. 3. Variation of optical density as a func- tion of pH: curve A, 50 pg of aluminium plus 10 ml of 0.15 per cent. xylenol orange; curve B, xylenol orange alone Organic anions such as citrate, oxalate and acetate are common constituents of extraction reagents for soils, and are readily destroyed in the normal course of treatment to oxidise soil organic matter. Hydrofluoric acid, which is used as a soil extractant, particularly for aluminium, can be easily removed. Pyrophosphate extracts can also be analysed after hydrolysis to orthophosphate. TABLE I IRON AND ALUMINIUM VALUES IN ALIQUOTS OF ORIGINAL SAMPLE, RECOVERY OF ADDED ALUMINIUM AND RECOVERY OF ALUMINIUM AFTER ADDING IRON Original aliquot Experiment I Experiment I1 v Iron Aluminium r-- e- Clg pg mg per cent.* Pg t-G Iron Aluminium found, Aluminium Aluminium present, & added, found, added, found, 52 7.5 15 20 26-5 800 8.0 12 5.4 11 20 24.5 so0 5.7 24 7.5 16 20 26.5 800 8.0 40 26.0 52 20 46.5 800 26.0 268 34.0 136 20 54-7 so0 34.0 180 26.2 105 20 46.7 800 26.2 * Concentration of aluminium expressed as a percentage of the soil. A typical extraction procedure with Tamm's reagent was carried out with samples taken from six horizons of an iron - humus podzol profile. Separate aliquots were taken for the determination of iron with thioglycollic acid, and for the determination of aluminium by the proposed method. The results obtained are shown in Table I, which also shows the recovery of added aluminium (Experiment I), and the aluminium found after adding 800pg of iron106 PRITCHARD (Experiment 11). Table I1 shows the order of interference of anions and cations relevant to soil analysis.The results shown in Tables I and I1 indicate that the method can be successfully applied to the determination of aluminium in the amounts usually occurring in soil extracts. TABLE I1 LEVELS OF INTERFERENCE OF ANIONS AND CATIONS RELEVANT TO SOIL ANALYSIS Aluminium present, 50 pg Cation or anion added, pg Aluminium found, pg Iron (Fe) 1000 .. .. 50.0 Titanium (Ti) 50 . . .. 55.0 Calcium (Ca) 5000 . . Magnesium (Mg) 5000 . . :} 50.3 Silicate (SiO,) 500 . . . . 50.3 Citrate 1000 .. . . 47.0 Oxalate 1000 .. .. 11.7 Pyrophosphate (P) 1000 . . .. 15.8 Manganese (Mn) 1000 . . . . Fluoride (F) 50 . . . . 47.3 Phosphate (P) 1000 .. .. 49.7 Phosphate (P) 10,000 . . .. 49.3 REFERENCES 1. 2. 3. 4. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Third Edition, Interscience Korbl, J., and Pfibil, R., Chemist-Analyst, 1956, 45, 162. Otomo, M., Bull. Chem. SOC. Japan, 1963, 36, 809. Budeshinsky, B., Zh. Analit. Khim., 1963, 18, 1071. Publishers Ltd., London, 1959, p. 227. Received July 7th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200103

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Anal-yst, February, 1967, Vol. 92, $$. 107-111 107 The Determination of Phosphate and Calcium in Feeding Stuffs BY C. B. STUFFINS ( J . Bibby & Sons Ltd., Nutrition Research and Advisory Departments, “ Weatherstones,” Neston, Wirral, Cheshire) Procedures are described for the determination of phosphate and calcium in the Kjeldahl-digestion solution. PULSS~ y 2 described a procedure for the determination of phosphate in the Kjeldahl-digestion solution. A similar technique is adopted for the determination of phosphate, and also a procedure for the determination of calcium in the same digestion solution. The usual procedure adopted for the determination of protein, phosphate and calcium involves three main preliminary stages, vix., the weighing of at least two portions of the sample, i.e., one for protein and the other for phosphate and calcium determination; Kjeldahl digestion ; and dry-ashing.The following procedure eliminates one weighing in addition to a considerable amount of manipulative work connected with the dry-ashing technique, and also the use of crucibles and muffles. The elimination of much manipulative work will be appreciated in laboratories in which many of these analyses are carried out and to which the cost of an AutoAnalyzer would not be economically justified. To carry out the investigation, a feed mixture containing no added minerals was obtained, and known amounts of dicalcium orthophosphate were added to it. Five standard mixings were prepared. The phosphate and calcium contents of the “blank feed’’ were obtained by the proposed The dicalcium orthophosphate was first dissolved in hydrochloric acid before procedures.aliquots were taken for the determination. PKOPOSED PROCEDURE FOR PHOSPHATE DETERMINATION REAGENTS- Ammonium va?zadomoZybdate compZex3-Dissolve 40 g of ammonium molybdate in 400 ml of water at 50” C. Dissolve 1 g of ammonium vanadate in 300 ml of boiling water. Cool, add to the solution 200 ml of AnalaR nitric acid. Mix both solutions together and make up the volume to 1 litre. Standard Phosphate sohiion-Dissolve 0.4394 g of potassium dihydrogen orthophosphate, KH,PO,, in 1 litre of distilled water. (1 ml of solution == 0-2 mg of phosphorus pentoxide.) CALIBRATION OF GRAPH FOR PHOSPHORUS PENTOXIDE- Transfer by pipette 5, 10, 15, 20 and 25-ml aliquots of the standard phosphate solution into 100-ml calibrated flasks.Add 30ml of the ammonium vanadomolybdate reagent to each flask in turn with continuous shaking of the flask. Make the solution up to the mark with distilled water. Allow the flasks to stand for 1 to 2 hours. Measure the optical density at 436mp with a Unicam SP600 operated at maximum sensitivity (or any other similar instrument), against a distilled water - reagent blank. Draw a graph of optical densities against milligrams of phosphorus pentoxide. DETERMINATION- Transfer by pipette 5 ml of the Kjeldahl-digestion solution” into a 100-ml calibrated flask. Add 1 to 2 drops of phenolphthalein and make the solution just alkaline with 30 per cent. * This solution is obtained from the normal Kjeldahl digestion, with a catalyst containing potassium sulphate and copper sulphate; the digest is transferred to the calibrated flask by washing with distilled water.108 STUFFINS : DETERMINATION OF PHOSPHATE [Analyst, Vol.92 sodium hydroxide; then, with 10 per cent. sulphuric acid adjust the solution to neutral or faintly acidic. Add 30 ml of vanadate reagent (shake the flask continuously during addition). Make up to the 100-ml mark with distilled water. Allow the solution to stand for 1 to 2 hours and measure the optical density at 436mp. PROPOSED PROCEDURE FOR CALCIUM DETERMINATION REAGENTS- Potassium permanganate, N. Ammonia solution, 50 per cent. v/v. Sulfihuuric acid, 8 per cent. v/v. Hydrochloric acid, 2 N. Ammonium oxalate, (saturated a d hot). Methyl red.PROCEDURE- Add about 50ml of distilled water and 2 to 3 drops of methyl-red solution. Make the mixture just alkaline with 50 per cent. ammonia solution, then by adding 2 N hydrochloric acid just acid again. Dilute the solution to about 150 ml with distilled water, and bring it to the boil. While stirring add slowly 10ml of hot saturated oxalate solution. If the solution becomes yellow - orange add 2 N hydrochloric acid until it becomes pink. Allow to stand for 1 hour. Filter the mixture through a Whatman No. 44 filter-paper. Wash the filter-paper with warm water. After dissolving the precipitate in 8 per cent. sulphuric acid carry out the normal procedure for determining calcium by titration with permanganate. When these procedures were applied to the “blank feed’’ and dicalciuni orthophosphate they were found to contain- Transfer by pipette 40 ml of the Kjeldahl-digestion solution into a 250-ml beaker.Phosphorus Calcium oxide, pentoxide, per cent. per cent. “Blank feed” . . .. .. . . 0.35 0.18 Dicalcium orthophosphate . . .. 30.35 34.6 The five standards thus contained the following amounts of added and total phosphate and calcium- Added Total ----A- 17------7 Calcium Phosphorus Calcium Phosphorus Standard oxide pentoxide oxide pentoxide A 0.30 0.34 0.65 0.52 B 0.595 0.678 0.945 0.858 C 1.167 1-33 1.517 1.51 D 1-718 1.96 2-068 2-14 E 6.0 6-85 6-35 7.06 PHOSPHATE DETERMINATION EXPERIMENTS- Four procedures were followed in the determination of phosphate in the five standard samples by combining two methods of sample preparation, vix., dry-ashing and Kjeldahl digestion, with two finishes : colorimetric determination with vanadate reagent,3 and with reduced molybdate reagent .4 95 $6 The results shown in Table I indicate that lower recoveries are obtained with the dry- ashing technique.The possibility of losing phosphoric acid when dry-ashing has been known generally for some considerable time. It is suggested in the Fertiliser and Feeding Stuffs Regulations 1955, that a nitrate should be added before incineration of the sample, to avoid loss of phosphoric acid.February, 19671 AND CALCIUM IN FEEDING STUFFS TABLE I THE EFFECT OF TWO METHODS OF SAMPLE PREPARATION 109 (a) Kjeldahl digestion- Vanadate P,O, found, Recovery, Standard per cent. per cent. A r 1 A 0.49, 0.50, 0.52 96.6 B 0.83, 0-85, 0.87 99.1 C 1.42, 1.40, 1.47 94-6 D 2.05, 2.03 95.3 E 6-88, 6.86 97.3 (b) Dyy-ashing- Vanadate , 3 P,O, found, Recovery, Standard per cent.per cent. A 0.48, 0-48 91-7 B 0.62, 0-73, 0-73 80.8 C 1.22, 1-15, 1.27 80.1 D 1.76, 1.56, 1.67 77.6 E 6.86, 6-90 97-4 Reduced molybdate P,O, found, Recovery, per cent. per cent. 0.53, 0-56 104-8 0.88, 0-90 103.7 1-51 100.0 2.12, 2.08 98.1 6-64, 6.68 94.3 A 7 7 Reduced molybdate P,O, found, Recovery, per cent. per cent. 0.51, 0.47 94-2 0.73, 0.72 84.5 1-21, 1.18 79.5 1.58 73.8 6-62, 6.62 93-8 r A \ Some experiments were carried out to ascertain the effect of adding an oxidising agent before dry-ashing, on the loss of phosphoric acid. This technique adopted here may not have been suitable because the recoveries of phosphoric acid were by no means satisfactory.(See Table 11). However, an interesting observation in connection with the loss of phosphoric acid on dry-ashing was obtained later. (See Table I11 and the comments). TABLE I1 THE EFFECT OF TWO METHODS OF OXIDATION BEFORE DRY-ASHING ( a ) Addition of nityic acid- Vanadate Reduced molybdate A I > f A \ P,O, found, Recovery, P,O, found, Recovery, Standard per cent. per cent. per cent. per cent. C 1.58, 1-44 100.0 1-15, 1.26 79.5 D 2.08 97.2 1.47, 1.54 70-6 (b) Addition of fiotassium nityate- Vanadate Reduced molybdate r----A-- 7 7-p P,O, found, Recovery, P,O, found, Recovery, Standard per cent. per cent. per ccnt. per cent. A 0.51 98.1 B 0-77 89.7 C 1.32 87.4 D 1.78 84.1 0.4G 0.74 1-15 1.34 88.4 86.2 7G.1 62.6 It will be seen from Table I that reasonably accurate results are obtained when the Kjeldahl-digestion solution is used for the phosphate determination either by the vanadate or reduced molybdate procedures.Whereas the vanadate procedure produces slightly low results (96 per cent.) the reduced molybdate figures are slightly high (101-6 per cent.). Because the vanadate procedure requires less manipulative work and involves less time, it is the recommended technique. To obtain a more comprehensive picture of the variations expected by the adoption of the recommended procedures, further work was carried out on samples containing various levels of calcium and phosphate.110 STUFFINS DETERMINATION OF PHOSPHATE [Analyst, Vol. 92 The following levels of phosphate and calcium were taken- (a) Four poultry food samples containing 4 to 5 per cent.of calcium oxide and 1.5 to 2.0 per cent. of phosphorus pentoxide (laying foods). (b) Four poultry food samples containing 2 to 3 per cent. of calcium oxide and 1.5 to 2.0 per cent. of phosphorus pentoxide (growing foods). (c) Two samples of fish meal containing about 6 per cent. of calcium oxides and about 6 per cent. of phosphorus pentoxide. (d) Two samples of meat meal containing about 9 per cent. of calcium oxide and about 7 per cent. of phosphorus pentoxide. The results of this work are shown in Table 111. TABLE I11 DETERMISATION OF VARIOUS LEVELS OF CALCIUM AND PHOSPHATE FOR STANDARD AKALYSIS Kjeldahl digestion Dry-ashing Vanadate Molybdate Vanadate Mol ybdate A r A 7 r 7 Sample CaO P20, P20, P20, P205 CaO P205 P205 P205 P205 A { i::; 1.58 1.60 1-69 1.62 { t::: 1.58 1.69 1.61 1.76 L { ::? 1.85 1.85 1-95 1.90 {::!: 1.83 1.84 1.97 1.99 11 { E::8 1-82 1.77 1-94 1-83 {:::: 1.89 1.88 1.97 1-91 S {::is 1-50 1.54 1.59 1-53 {::A: 1-51 1-49 1.63 1.71 40 { i::: 1-87 1.83 1-92 1.83 { i:;: 1.73 1-78 1.51 1.60 3743 { t:;: 1.97 1.91 1.98 1.88 { i::; 1.76 1.82 1.54 1-58 3744 {E::! 1-65 1-69 1-69 1-70 { i::: 1.63 1.60 1.50 1.54 3746 { i::: 1.66 1.66 1.61 1-71 {E:; 1.64 1.64 1-56 1.56 Xeat meal { ::i: 6-70 6-78 6.74 7.10 { i::: 6.70 6.40 6.72 6-98 Meat meal { :::: 6.56 6.99 6.50 7-18 { ::i6 6.70 6.56 6.86 7.08 Fish meal { :::: 5.90 6.01 5.9G 6.06 { :::! 5-80 5.70 5.68 5.98 Fish meal { :::: 5-68 5.60 5.90 5.83 { ::;: 5.68 5.64 5.68 6-14 The following statistical analysis was obtained from the results in Table III- Calcium determination- Kjeldahl digestion (means) Material KD Growing foods .. . . 2.29 Animal protein.. . . 7.09 Laying foods . . .. 4.47 P7aosphate determination- Kjeldahl digestion (means) Material KD Laying foods . . . . 1.72 Crowing foods . . .. 1.78 -Animal protein.. .. 6.34 Least Dry- significant ashing difference (means) (mean of 8) D h p = 0.05 Significance 4.39 0.19 Not significant 2.51 0-19 Significant (p = 0.05) KD < DA 7.54 0.19 Significant (p = 0.01) KD < DA Least Dry- significant ashing difference (means) (mesnof 16) DA p = 0.05) Significance 1-77 0.09 Not significant 1.62 0.09 Significant (p=O.Ol) DA < KD 6.26 0.09 Not significantFebruary, 19671 AND CALCIUM IN FEEDING STUFFS 111 In Table I11 further confirmation is obtained of the observation made earlier in this paper with reference to the loss of phosphoric acid on dry-ashing (Table I).The samples 40, 3743, 3744 and 3746 contain similar amounts of calcium and phosphoric acid as the standards C and D of Table I where similar results were obtained. However, the other results in Table I11 do not indicate any loss of phosphoric acid when the calcium content is at least twice that of the phosphoric acid. The vanadate procedure can tolerate 1000 p.p.m. of copper and 100 p.p.m. of iron without interference. Neither of these two elements is likely to be present to this extent in the aliquot taken for the determination. Manganese and zinc do not interfere. With the calcium determination, however, we have the reverse effect of that which takes place with phosphate.For samples 40, 3743, 3744 and 3746 higher recoveries are obtained on dry-ashing. This latter observation is further illustrated in the investigation of the recommended method for calcium, in which a similar pattern of work was carried out on the standards to that adopted for the phosphate. These results are shown in Table IV. TABLE IV THE EFFECT OF TWO METHODS OF SAMPLE PREPARATION (a) ICjeldahl digestion 7- - I CaO found, Recovery, Sample per cent. per cent. A 0.65, 0.64 99.2 B 0.98, 1.0, 0.92 102.3 C 1.50, 1-50 98.9 D 2-08, 2.03, 2-16 101.1 E 6.06, 6.14 96.1 (b) Dry-asliing CaO found, Recovery] per cent. per cent. 0.69, 0.71, 0.71 106-1 0.99, 1.02 106.3 1-55, 1.57 102.8 2.11, 2-13 102-5 6.41, 6.48 101.5 The adoption of the recommended technique enabled these laboratories to carry out the determination of protein, calcium and phosphate on the same Kjeldahl-digest solution. The protein determination required only a small aliquot of the digest solution, and, conse- quently, sufficient solution remains for the determination of calcium and phosphate. The gravimetric method for phosphate has not been considered in this work because the colorimetric procedures are much less tedious but equally accurate. The adoption of the recommended procedures enabled the 2-fold aim of the investigation to be achieved, namely: speed-up of analyses; and elimination of the need of apparatus such as muffles and crucibles. I thank the Directors of J. Bibby & Sons Ltd. for their permission to publish this paper. REFERENCES 1. 2. 3. 4. 5. 6. Pulss, G., Landw. Forsch., 1961, 14, 38. - , 2. analyt. Chem., 1960, 176, 412. Kitson, R. E., and Mellon, M. G., Ind. Engng Chem. Analyt. Edn, 1944, 16, 379. Finzade, C. H., Ibid., 1935, 1, 227. Gerritz, H. W., J . Ass. Off. Agvic. Chem., 1940, 23, 321. Schricker, J., and Duncan, I?., Ibid., 1939, 22, 167. Received June 1st. 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200107

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

112 Analyst, February, 1967, Vol. 92, $9. 112-114 The Determination of Calcium in Biological Samples by X-Ray Fluorescence BY K. P. CHAMPION AND R. N. WHITTEM (Australian Atomic Energy Commission Research Establishment, Sutherland, New South Wales, Australia) An X-ray fluorescence method is described for the rapid determination of calcium in ashed biological samples. Samples are digested in nitric acid, and calcium is determined in the extract. The results are comparable with those obtained by a conventional titrimetric method. THE determination of calcium in biological samples, such as ashed milk, vegetation, oysters, etc., by an X-ray fluorescence technique is complicated by the presence of high levels of potassium and chlorine, both of which exhibit strong absorption effects for calcium K, radi- ation.Methods which might be used to overcome this difficulty include- Lithium borate fusion technique (as used by Rose, Adler and Flanaganl for siliceous rocks)-This has the disadvantage that the buffer used (lanthanum oxide) does not materially assist in overcoming the potassium and chlorine interference, so that each of these elements must be determined and corrections made to the calcium intensity. Thus the analysis becomes quite complex. Internal standard methods-The best internal standard line2 is tin L,, and this offers good correction for absorption effects. However, in the Philips spectrometer it is not sufficiently resolved from the calcium K, line to be useful over a reasonable range of calcium concentrations, unless the tin content is varied to suit each sample type.Further, particle-size effects3 are likely to be important in this wavelength region, so that thorough grinding and mixing of the internal standard material are essential. Aqueous solzdion methods4-These appear attractive as particle-size effects have no significance, and also because accurate dilutions can be made, thus reducing absorption effects to acceptable levels, provided, of course, that adequate sensitivity is available. The use of aqueous solutions was therefore investigated, and a method was developed for the rapid determination of calcium in the ash of milk, oyster shells and flesh, and of vegetable matter. EXPERIMENTAL APPARATUS- The apparatus and experimental conditions used are as follows. Spectrometer” .. X-ray tube . . Detector* .. Crystal . . . . Collimator . . Pulse height analyser Counting strategy Sample holder . . .. . . Philips PW1520 . . . . . . Sealed proportional counter, PW1965/10 . . . . Lithium fluoride .. . . 320-p spacing .. . . . . Fixed counts, generally 10,000 . . . . Chromium target, type 25718/61, operating a t 40 kV, 20 mA . . . . Set to 90 per cent. of Ca I<, counts Plastic holder PW1527/10, fitted with 6 - p thick “Melinex” window * If available, the all-vacuum instrument, PW1540, with flow proportional counter, offers greater sensitivity. SAMPLE PREPARATION- Weigh between 0.25 g and 1 g of sample (w,), depending on expected calcium content, and place it in a 100-ml beaker. Add 5 ml of analytical-reagent grade nitric acid (sp.gr. 1-42), and evaporate it on a hot-plate to about 1 ml.Allow to cool, add about 30 ml of water, cover the beaker, and boil the solution for 5 minutes. Cool and filter the solution into a lOO-ml,CHAMPION AND WHITTEM 113 weighed calibrated flask. Wash the beaker and filter-paper three times with 10 ml of hot 0-5 N nitric acid. Make up to the mark with water, cool, mix, and weigh (net weight = W,). PREPARATION OF STANDARDS- Dissolve 2.497 g of analytical-reagent grade calcium carbonate by adding dropwise dilute nitric acid (1 + 2) and dilute with water to 1 kg. This stock solution contains 0-1 per cent. w/w of calcium and lower concentration working standards can be made by dilution. In general, only one working standard is necessary, as linear calibrations in the range 0 to 0.1 per cent. w/w are obtained.PROCEDURE- Fit the sample holder with a "Melinex" window (6 p thick) that has been well rinsed to remove calcium contamination. Pour about 5 ml of sample solution into the cell and measure the time for 10,000 counts. If the counting time exceeds 200 seconds, errors may occur owing to the formation of bubbles on the window surface. If this happens, stop the count, refill the cell, and then resume the count. Measure the count-rate of a suitable Concentration of standard, and also the count-rate of water as a blank. Set the spectrometer to the calcium K, line at 3-360 A. CALCULATIONS- equation- Calculate the percentage of calcium in the original ash sample from the following ?%x - %, w, Percentage of calcium = C, - .- n S - nB w X where C , is the concentration of the standard expressed as per cent.w/w, W , is the weight of the sample solution, wx is the weight of sample taken, "rzx is the count-rate of the sample, 12, is the count-rate of the standard, and n, is the count-rate of the blank. The standard deviation of the result can be simply calculated from the count-rates and the number of counts accumulated for sample, standard and blank5 RESULTS AND DISCUSSION A selection of samples was analysed by the present method, and also by a conventional chemical method. Some difficulty was experienced in choosing a chemical method that would suit the range of samples, as co-precipitation of many elements frequently occurred in conventional oxalate methods. The A.O.A.C. method 20.027,6 modified so that the phos- phate separation was performed at pH 4.4 instead of pH 4, was adopted.This modification eliminated the co-precipitation of zinc from the oyster samples. The results are shown in Table I and indicate excellent agreement between the two methods. The result on the NBS limestone indicates the accuracy. TABLE 1 COMPARISON* OF X-RAY FLUORESCENCE AND CHEMICAL RESULTS X-ray fluorescence method, Sample per cent. w,/w Limestone NBS l a t . . . . 29.4 Grass ash 64/221 .. .. 2.S5 Grass ash 65/33 . . . . . . 6-02 Milk ash 65/76 . . . . . . 15.1 Oyster-flesh ash 65/29 . . . . 10.5 Milk ash 65/79 . . . . . . 15.5 Oyster-flesh ash 65/131 . . . . 5.s3 Chemical method, per cent. w/w 29.3 2.82 5.97 15.3 15.4 10.5 5-90 * Based on the means of four analyses.t Certificate analysis 29.52 per cent.114 CHAMPION AND WHITTEM The speed of analysis is worthy of comment. Sample preparation takes about 4 hours for a batch of 10 to 20 samples. Instrument time is about 2 minutes per sample (with the PW1540 instrument, counting times of about 10 seconds are adequate). It should be stressed that it is essential to make up the sample solutions on a weight basis, as their specific gravities generally lie in the range 1.02 to 1.05. Thus, if a weight per volume technique is used, systematic errors of 2 to 5 per cent. can occur. Recent work with the all-vacuum instrument PW1540 has shown that this method can be extended to the simultaneous determination of potassium, chlorine and sulphur. We gratefully acknowledge the help of Mrs. B. McAllister for the titrimetric analyses. REFERENCES 1. 2. 3. 4. 5. 6. Rose, H. J., Adler, I., and Flanagan, P. J., Appl. Spectrosc., 1963, 17, 81. von Hevesy, G., “Chemical Analysis by X-rays and its Applications,” McGraw-Hill, New York, Claisse, F., and Samson, C., Adv. in X-ray Analysis, 1962, 5, 335. Gunn, E. L., A.S.T.M. Special Technical Publication No. 349, 1964, p. 70. Mack, M., and Spielberg, N., Spectrochim. Acta, 1958, 12, 169. Horwitz, W., Editor, “Official Methods of Analysis of the Association of Official Agricultural Chem- ists, ” Ninth Edition, Association of Official Agricultural Chemists, Washington, D.C. ~ 1960, Method 20.027, p. 268. Received November 22nd, 1966 1932, p. 161.

ISSN:0003-2654    

DOI:10.1039/AN9679200112

出版商:RSC    

年代:1967

数据来源: RSC

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Analyst, February, 1967, Vol. 92, p p . 115-117 115 Determination of Sulphate in the Presence of Soluble Silicate BY M. AZEEM (Pakistan Atomic Energy Commission, P.O. Box No. 31 12, Karachi, Pakistan) A method is described ior determining sulphate in the presence of soluble silicate. The sulphate was precipitated as barium sulphate in an acidic medium, after adding dimethylformamide. The formation of a stable complex between Si (OH), and dimethylformamide is considered. DURING an investigation of the SiF, - SF, system, an ethereal solution of dimethylformamide (DMF) was used for separating the sulphur tetrafluoride from the mixture; silicon tetra- fluoride was absorbed in the solution thereby producing solid SiF4.2DMF.l ,2 However, sulphur tetrafluoride is slightly soluble3 in ether, and can be determined in solution by precipitation of barium sulphate. The ethereal solution and the complex SiF4.2DMF were first hydrolysed with ice-cold water, and then made alkaline with sodium hydroxide solution.The solution, containing the sulphite, silicate, fluoride and sodium ions and dimethylform- amide, was treated with hydrogen peroxide and then analysed for sulphate. For the gravi- metric determination of sulphate in the presence of soluble silicate the logical procedure would be to separate silica in the first stage, and then precipitate barium sulphate from the filtrate and the washings. When the recommended procedures4~5 were used for precipitating silica from the alkaline sulphate - silicate solution containing dimethylformamide, the yield of silica was found to be abnormally low.Therefore, an excess of dimethylformamide was added to a standard solution of sulphate - silicate, followed by the addition of an excess of hydrochloric acid. The solution was boiled, evaporated to one quarter of its original volume and then diluted. The solution was crystal clear. The acidified solution was then placed on a steam-bath for 48 hours. At the end of this period the solution was clear and colourless. This showed that dimethylformamide acts as a hold-back carrier for the silicate, and barium sulphate can be precipitated directly from the solution. METHOD REAGENTS- All reagents should be of analytical-reagent quality. Potassium sulphate. Sodium sul9hate. Sodium silicate, Na2Si03.9H20, su$$lied by Fislzev Scienti$c Company.Dimethyl f ovmamide. PROCEDURE- A standard solution of potassium sulphate containing an equivalent amount of sodium silicate was prepared. To a 25-ml portion of the solution, 1 to 2 ml of dimethylformamide were added. The solution was then diluted to 250 ml and acidified with hydrochloric acid. The solution was heated to boiling, and an excess of 5 per cent. barium chloride solution was added slowly with constant stirring. The solution was heated on a steam-bath for a few hours to granulate the precipitate. The supernatant liquid was decanted through a Whatman No. 42 filter-paper. The precipitate was washed, transferred to the filter-paper and then ignited in a weighed silica crucible to a constant weight, as described in the recom- mended p r o c e d ~ r e .~ , ~ The results of the analysis are given in Table I.116 AZEEM: DETERMINATION OF SULPHATE [Analyst, Vol. 92 TABLE I RESULTS OF THE GRAVIMETRIC DETERMINATION OF BARIUM SULPHATE I N THE PRESENCE OF SOLUBLE SILICATE Weight of K,SO, in 25 ml of the solution containing Na,SiO,, g 0.2438 0.2438 0.2438 0.2438 0.2438 0-2204 0.2204 0.2204 0.2204 0.2204 Weight of BaSO, calculated in 25 ml of the solution, g 0,3265 0-3265 0.3265 0.3265 0.3265 0.2952 0.2952 0.2962 0.2952 0.2952 Weight of BaSO, found in 25 ml of the solution, g 0-3258 0.3252 0.3271 0-3280 0.3269 0.2950 0.2945 0.2961 0.2965 0.2958 In another series of experiments a 25-ml aliquot of a standard solution of sodium sulphite containing an equivalent amount of sodium silicate was treated with 2 ml of 30 per cent.hydrogen peroxide to oxidise the sulphite ions. The solution was heated to decompose excess of the peroxide and then analysed for sulphate according to the above procedure. The results of the analysis are given in Table 11. TABLE I1 DETERMINATION OF SULPHITE BY PRECIPITATION OF BARIUM SULPHATE I N THE PRESENCE OF SOLUBLE SILICATE Weight of Na,SO, in Calculated weight of Weight of BaSO, Amount of Na,SO, 25 ml of the solution containing Na,SiO,, the solution, the solution, BaSO, found, BaSO, from 25 ml of found in 25 ml of calculated from g g g g 0.1637 0.3032 0-3025 0.1633 0.1637 0.3032 0.3047 0.1645 0.1637 0.3032 0.3042 0.1642 0-1637 0.3032 0-3035 0.1639 0.1637 0.3032 0.3020 0.1635 0.1450 0.2685 0.2672 0.1443 0.1450 0.2685 0.2700 0.1457 0.1450 0-2685 0.2692 0.1453 0.1450 0.2685 0.2888 0.1451 0.1812 0.3357 0.3352 0.1810 0.1812 0.3357 0.3365 0.1817 0.1812 0.3357 0.3370 0.1s19 The purity of the solid sodium sulphite was checked by the iodimetric m e t h ~ d .~ , ~ It was observed that short exposure of the compound to the atmosphere, as experienced in weighing, does not appreciably affect its purity (Table 111). TABLE 111 DETERMINATION OF THE PURITY OF SODIUM SULPHITE Weight of iodine coiisumed by b" g g 0.1552 0- 1548 0.3128 0.1465 0.2954 0.1466 0,2692 0.1336 0.1335 0.1282 0.2579 0.1280 Weight of Na,SO, calculated from Weight oE Na,SO, taken, Na,SO,, the amount of iodine consumed, RESULTS AND DISCUSSION The gravimetric values for barium sulphate are within k0-5 per cent. of the theoretical value.The concentration of either sulphate or silicate ions does not appear to affect the results. The values in Table I1 show that this method can be used satisfactorily for determining sulphite in the presence of silicate. From the above observations and results it is concludedFebruary, 19671 I N THE PRESENCE OF SOLUBLE SILICATE 117 that the soluble silicate forms a very stable complex with dimethylformamide, which is not affected by strong acids. It is suggested that hydrochloric acid reacts initially with the aqueous silicate forming Si(OH), which in turn interacts with dimethylformamide, a strong electron donor. Presumably the complex is of the type Si(OH),(DMF). (where x = 1 or 2), and is analogous to SiF,(DMF),.1,2 This work was carried out at the McMaster University, Hamilton, Ontario, Canada. I thank Dr. R. J. Gillespie for providing the laboratory facilities and for his encouragement. REFERENCES 1. 2. Muetterties, E. L., Ibid., 1960, 82, 1082. 3. 4. 5. Piper, T. S., and Rochow, E. G., J . Amer. Chem. SOL, 1954, 76, 4318. Azeem, M., “The Structures of SF,.BF, and Some Related Compounds,” Ph.D. Thesis, MchIaster Vogel, A. I., “A Text Book of Quantitative Inorganic Analysis,” Third Edition, John Wley Scott, W. W., Editor, “Standard Methods of Chemical Analysis,” Fifth Edition, D. Van Nostrand Received January 31st, 1966 University, Canada, 1965. & Sons, New York, 1961; pp. 370, 464 and 583. Co. Inc., New York, 1939; pp. 127, 803 and 926.

ISSN:0003-2654    

DOI:10.1039/AN9679200115

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

118 Analyst, February, 1967, Vol. 92, $$. 118-123 The Determination of Antimony, Cadmium, Cerium, Iridium and Silver in Biological Material by Radioactivation BY H. J. M. BOWEN (Chemistry Department, T h e University, Reading, Bevks.) A method for determining antimony, cadmium, cerium, iridium and silver simultaneously in a sample of biological material is described. The method involves radioactivation to long-lived radionuclides by using thermal neutrons from a reactor, and has a high sensitivity. The technique has been used to measure these five elements in a standard biological material. THE elements studied in the present work are all rare constituents of plants and animals that defy the ingenuity of the analyst. While methods of analysis are available for traces of these elements at the microgram level, they are insufficiently sensitive for determinations at the milli-microgram or micro-microgram level.Methods that are capable of determining these elements in natural biological materials are set out in Table I, with an indication of their minimum sensitivity. TABLE I SEXSITIVITY OF DETECTION OF SILVER, CADMIUM, CERIUM, IRIDIUM AND ANTIMONY, GRAMS Element r Method Ag Cd Ce I r Sb ’ Activation1* . . .. 5 x 10-9 10-9 10-9 10-11 10-10 Colorimetry2 . . . . 10-7 10-8 2 x 10-7 2 x 10-6 3 x 10-8 Mass spectrometry3 . . 2 x 10-6 3 x 10-8 4 x 10-8 9 x 10-7 Polarography4 95 .. - 1.5 x 10-G - Spectroscopy2 9 6 . . .. 10-7 5 x 10-9t 5 x 10-7 5 x 10-6 4 x 10-6 X-ray fluorescence7 . . 2 x 9 x 10-8 10-7 5 x 10-8 1.2 x 10-7 - 10-7 * Assuming a flux of 1012 neutrons cm-2 second-l.t After chemical concentration. It is clear that activation analysis is the most sensitive method available for determining these elements. It also has the advantage of avoiding contamination by reagents. Activation analysis has already been used to measure all five of the elements discussed here in biological materials, as follows- Antimony-In soft mammalian tissues8 y 9 ; in bloodlo; and in urine.ll Cadmium-In bone12; in soft tissue^^,^; and in blood.1° Cerium-In soft t i s ~ u e s . ~ , ~ ~ Iridiuwz-In soft Silver-In soft tissues.8,9 However, a full radiochemical procedure has been reported only for antimony, the other determinations being based wholly or partly on y-ray spectrometry. In this work an attempt has been made to devise a separation procedure after activation that will yield all five elements in a radiochemically pure state, and to apply the procedure to a standard biological material.NUCLEAR RESULTS *All five elements are activated to long-lived radionuclides when exposed to thermal neutrons. ,4ntimony--On activation this gives a good yield of antimony-124 (half-life 60 days), together with much antimony-122 (half-life 2-8 days) wliicli soon decays away. The 0.60-MeV y-ray of antimony-124 is convenient for counting. Tellurium and iodine are too Some characteristics of these radionuclides are as follows.BOWEN 119 rare in most biological material to interfere, although iodine in thyroids could generate antimony-124 by an (n,a) reaction. Cadmium-On activation this gives a moderate yield of cadmium-1 15m (half-life 43 days) together with cadmium-115 (half-life 2.3 days).The decay is complex and involves indium- 115m (half-life 4-5 hours). In practice, the y-rays from cadmium-115m are of low intensity and P-counting is best for its determination. Iridium and tin are too rare to interfere by com- peting nuclear reactions. Standard solutions must be very dilute to avoid self-shielding. Cerium-This gives a moderate yield of cerium-141 (half-life 32.5 days), together with cerium-143 (half-life 33 hours) which decays via praseodymium-143 (half-life 13.7 days). The 0.145-MeV y-ray of cerium-141 can be used for counting (praseodymium-143 is a pure p-emitter). Uranium could interfere as cerium-141, cerium-143 and cerium-144 (half-life 284 days) are all fission products produced with a yield of 4 to 6 per cent.(nuclides of silver, cadmium and antimony are also fission products with yields of GO-04 per cent.). Iridium-This gives an excellent yield of both iridium-192 (half-life 74 days) and iridium-194 (half-life 19 hours). The former has an 0.32-MeV y-ray, which is useful for counting. Gold and platinum are too rare to interfere by competing nuclear reactions. The iridium standard solutions must be dilute to avoid self-shielding. Silver-This gives an excellent yield of silver-1 10m (half-life 253 days) together with some short-lived activities. Indium and cadmium are too rare to interfere by competing nuclear reactions. BEFORE ACTIVATION- Samples of standard kale14 were ashed at 450" C in silica crucibles in a furnace lined with silica.The ash was thoroughly mixed with a plastic spatula, and weighed aliquot parts of about 0.7 g were placed in small silica tubes capped with aluminium foil. The silica tubes were cleaned by boiling with nitric acid, and then washed with water until no sodium could be detected in the rinsings with a flame photometer sensitive to about lO-7g of sodium. The ashing procedure could have resulted in changes in the antimony and cadmium contents of the material as these elements have volatile derivatives that could distil into, or out of, the samples at the temperature concerned. Adsorption losses might also have occurred, although the ash did not adhere to the crucible walls. Ashing before activation is an undesirable step.In this work it was necessary because of the high operating tem- perature of the reactor. Standards were prepared by dissolving weighed amounts of Johnson Matthey Specpure silver nitrate, cadmium oxide, cerium( IV) oxide, ammonium iridmm chloride [ (NH,) JrC16] and antimony in water or concentrated or dilute hydrochloric or nitric acids, distilled from a silica still, to make solutions as follows- 0.4 mg of silver per ml; 50 pg of cadmium per ml; 0.5 mg of cerium per ml; 1 pg of iridium One or two drops of each solution were then weighed into a silica tube by using a polythene transfer pipette. Alternatively, the drops were weighed on to squares of aluminium foil. The water was evaporated off at about 60" C and the tubes were capped with aluminium foil. Four samples, and two standards per element, were activated for 28 days in a flux of about 1-5 x 1012 neutrons cm-2 second-l in the Harwell reactor BEPO.REAGENTS- The 0.66-MeV y-ray is convenient for counting. METHOD per ml; and 50 pg of antimony per ml. All reagents were of recognised analytical grade. Ammonia solution, 18 N. Ammonium acetate, 30 per cent. w l v . Ammonium oxalate, 4 per cevzt. w/v. Ammonium reinzeckate, 4 per cent. W/LL (fyeshly prepared). Ammoniwn sulphide, yellow. Iron(III) nitrate, 10 per cent. w/v. Formic acid, 100 pev cent. Hydrochloric acid, 12 and 2 N. Hydrogen peroxide, 30 $ev ceiqt. w / i ~ . Iodic acid, 50 pev cmt. X J / I ! .120 BOWEN : DETERMINATION OF ANTIMONY, CADMIUM, CERIUM, [Ana,@St, VOl. 92 Yitric acid, 16 and 6 N. Sodium bronzate, saturated solution.Sodium hydroxide, 40 per cent. w l v . Sodium hypochlorite, 10 per cent. w / v . Sodium sulphite, 10 per cent. w/v. Sulphuric acid, 36 and 2 N. Teepol, 1 per cent. wIv. Thiourea, 5 per cent. v / v . Zinc acetate, 10 per cent. w / v . Zirconium nitrate, 10 per cent. w/v in dilute nitric acid. Isopropyl ether. Silver nitrate carrier solution-Prepare a 3.15 per cent. w/v solution of silver nitrate in water. 1 ml of solution = 20 mg of silver. Cadmium acetate carrier solution-Prepare a 4-74 per cent. w/v solution of cadmium acetate, Cd(C,H,O,) ,.2H,O, in water. 1 ml of solution = 20 mg of cadmium. Cerium.(IV) sulphate carrier solution-Prepare a 2.885 per cent. w/v solution of cerium(1V) sulphate, Ce(S0,) ,.4H,O in dilute nitric acid. 1 ml of solution = 10 mg of cerium(1V).ammonium chloroiridate, (NH,) ,1rC16, in water. A mmonium chloroiridate carrier solution-Prepare a 2.289 per cent. w/v solution of 1 ml of solution = 10 mg of iridium. ,4 ntimony trichloride carrier solution-Prepare a 3.545 per cent. w/v solution of antimony trichloride in dilute hydrochloric acid. 1 ml of solution = 20 mg of antimony. RADIOCHEMICAL SEPARATION SCHEME SAMPLES- Step 1-Transfer each activated sample into a 50-ml centrifuge tube and dissolve it in a few millilitres of 12 N hydrochloric acid. Add 1 ml each of antimony, cadmium, cerium, iridium and silver carrier solutions in that order, and dilute to about 3 N. Spin to collect the silver chloride precipitate and wash it twice with water. For treatment of the precipitate see step 5.Step 2-Add 1 ml of Teepol solution to the supernatant liquid, and pass hydrogen sulphide through it. Dilute the solution with water and continue to pass hydrogen sulphide until both the antimony and cadmium sulphides are fully precipitated. Spin to collect sulphides and wash the precipitate twice with 2 N hydrochloric acid. For treatment of the precipitate, see step 9. Step 3-Transfer the solution to a 150-ml beaker, add 5ml of ammonium acetate and 5 ml of formic acid, and boil for 10 minutes to precipitate iridium. Transfer the suspension to a clean centrifuge tube, spin it and wash the collected precipitate once with 12 N hydro- chloric acid and three times with water. Transfer the precipitate to a weighed counting tray, dry and weigh. Step 4-Add ammonia solution to the supernatant liquid until it is alkaline, spin to collect the cerium(II1) hydroxide and wash it twice with water.Discard the supernatant liquid. For treatment of the precipitate, see step 12. Step 5-Dissolve the silver chloride from step 1 in hot ammonia solution, add 1 drop of iron( 111) nitrate solution and spin to collect iron(II1) hydroxide. Reject the precipitate. Step 6-Pass hydrogen sulphide through the solution for 1 minute, spin to collect silver sulphide and wash it twice with 2 N sulphuric acid. Step 7-Dissolve the silver sulphide in hot 16 N nitric acid, dilute with water and add excess of sodium hydroxide. Discard the supernatant liquid. Step 8-Dissolve the silver oxide in hot 36 N sulphuric acid, dilute with water and add 0-5 ml of iodic acid solution.Spin to collect silver iodate and wash it three times with water. Transfer the precipitate to a weighed counting tray, dry and weigh. Reject the supernatant liquid. Reject the supernatant liquid. Spin and wash the collected silver oxide with water.February, 19671 IRIDIUM AND SILVER I N BIOLOGICAL MATERIAL 121 Step 9-Extract the sulphide precipitate from step 2 twice with hot ammonium sulphide, spinning to collect cadmium sulphide each time. For treatment of the supernatant liquid, see step 16. Step 10-Dissolve the cadmium sulphide in hot 12 N hydrochloric acid and boil out hydrogen sulphide. Dilute the solution to N, add 2 ml of thiourea solution, 1 drop of zinc acetate and 2.5 ml of ammonium reineckate. Spin, collect the cadmium reineckate and wash it with water.Step 11-Dissolve the precipitate in hot 16 N nitric acid, dilute the solution to N and pass hydrogen sulphide. Spin to collect cadmium sulphide and wash it twice with water. Transfer the precipitate to a weighed counting tray, dry and weigh. Step 12-Dissolve the precipitate from step 4 in 2 N hydrochloric acid and add ammonia solution until the solution is neutral. Reject the supernatant liquid. Step 13-Dissolve the precipitate in 6 N nitric acid, add 1 drop of hydrogen peroxide [to reduce any cerium(IV)], 1 drop of zirconium nitrate and 1 ml of iodic acid solution. Spin to separate zirconium iodate and discard it. Step 14-Add 1 ml of sodium bromate to the solution, boil and spin to collect cerium(1V) iodate. Reject the supernatant liquid.Step 15-Dissolve the precipitate in 12 N hydrochloric acid, and add 1 ml of sodium sulphite, 2 ml of ammonium oxalate and ammonia solution until the pH is about 6. Spin to collect cerium(II1) oxalate and wash it twice with water. Transfer the precipitate to a weighed counting tray, dry and weigh. Step 16-Add 12 N hydrochloric acid slowly and carefully to the thioantimonate solution from step 9 until it is acidic, then pass hydrogen sulphide through the solution and spin to collect the antimony sulphide. Cool, add an equal volume of water and 1 ml of sodium hypochlorite solution. Transfer the solution to a 50-ml separating funnel and extract three times with di-isopropyl ether. Reject the aqueous phase. Step 18-Add 2 N hydrochloric acid to the di-isopropyl ether and cautiously evaporate off the ether.Pass hydrogen sulphide through the solution, spin to collect antimony sulphide and wash it twice with water. Transfer the precipitate to a weighed counting tray, dry and weigh. Reject the supernatant liquid. Discard the supernatant liquid. Spin to collect cerium(II1) hydroxide. Discard the supernatant liquid. Discard the supernatant liquid. Step 17-Dissolve the antimony sulphide in hot 12 N hydrochloric acid. STAKDARDS- carrier, and hydrogen sulphide was used to precipitate antimony sulphide. carrier, and hydrogen sulphide was used to precipitate cadmium sulphide. carrier, and ammonium oxalate at pH 6 was used to precipitate cerium oxalate. carrier, neutralised with ammonia and boiled with formic acid to precipitate iridium.carrier. was finally precipitated as silver iodate. The antimony standards were dissolved in hydrochloric acid containing 1 ml of antimony The cadmium standards were dissolved in hydrochloric acid containing 1 ml of cadmium The cerium standards were dissolved in hydrochloric acid containing 1 ml of cerium The iridium standards were dissolved in hydrochloric acid containing 1 ml of iridium The silver standards were dissolved in water and nitric acid containing 1 ml of silver Silver chloride was precipitated and dissolved in ammonia solution, and the silver TESTING THE RADIOCHEMICAL PROCEDURES- The radiochemical procedures were tested by carrying out each operation with anti- mony-124, cadmium-1 15m, cerium-1 14, iridium-194 or silver-ll0m so as to estimate the chemi- cal yields and the losses involved in each step.In addition, some decontamination factors were measured by using iron-59, phosphorus-32, sulphur-35 and zinc-65 as tracers, as these are the main activities in activated biological material that has been allowed to decay for a week or so. The results of these tests can be summarised as follows. A ntimony-Chemical yield, 86 per cent. ; phosphorus-32 carried through procedure, 1.4 x Iron and zinc are removed by the precipitation of sulphides in acidic solution. per cent. The main loss of antimony occurs in the solvent extraction, step 17.122 BOWEN : DETERMINATION OF ANTIMONY, CADMIUM, CERIUM, [Analyst, Vol. 92 Cadmium-Chemical yield, 93 per cent. ; phosphorus-32 carried through procedure, 2 x Iron and zinc are not precipitated as reineckates or as sulphides in acid solution.Cerium-Chemical yield, 86 per cent. ; phosphorus-32 carried through procedure, 0-0625 per cent. The main loss of cerium occurred by adsorption on the zirconium iodate precipitate. Iridium-Chemical yield, 57 per cent. ; phosphorus-32 carried through procedure, 0.03 per cent. The most likely radioactive contaminants are other platinum metals that might be precipitated by boiling formic acid. The main loss of iridium occurred at this stage. Silver-Chemical yield, 87 per cent. ; phosphorus-32 carried through procedure, 8.3 x per cent.; zinc-65 carried through procedure, 2.7 x The main loss of silver occurred in the precipitation of silver oxide. per cent. Iron, zinc and other lanthanides are not precipitated as iodates.per cent.; sulphur-35 carried through procedure, <2.7 x per cent. RESULTS The method was used to determine the elements in four samples of standard kale powder, with the following results, expressed in terms of p.p.m. of dry kale tissue- Antimony . . . . . . 0.0930, 0.0972, 0.0976, 0.1101 mean 0.0995 Cadmium . . .. . . 0.347, 0.386, 0.392, 0.410 mean 0.384 Cerium . . . . . . 0.379, 0.430, 0.507, 0.510 mean 0.457 Iridium . . . . . . 0.0098, 0.0101, 0.0171, 0.0162 mean 0.0133 mean 0-0295. Silver . . .. . . 0.0264, 0.0235, 0-0386, There are few comparable results in the literature; results from unpublished work by F. Girardi, H. D. Livingston, H. P. Yule, J. F. C. Tyler and K. Samsahl are available for this material- Antimony .. 0-059 and 0.065 p.p.m. by activation analysis. Cadmium . . Iridium . . . . <0.021 p.p.m. and <0.0006 p.p.ni. by y-ray spectrometry after activation. Lanthanum . . Silver . . . . 0.50 p.p.m. and (0-45 p.p.m. by y-ray spectrometry after activation. 1-0 p.p.m. by polarography and 0-63 p.p.m. by activation analysis. 0.08 p.p.m. by activation analysis ; the terrestrial cerium-to-lanthanum ratio is about 3. The reasons for the discrepancies must await further analysis, preferably by other techniques. The y-ray spectrometric results are not reliable, so that the main discrepancies occur for antimony and cadmium, both of which may have been affected by the ashing procedure. DISCUSSION OF THE METHOD The method described appears to be quite satisfactory for antimony and silver,l5 especially in view of the excellent decontamination from radioactive phosphorus.For cadmium, it is advisable to repeat steps 10 and 11 in the radiochemical separation at least once, to remove traces of phosphorus-32, if the cadmium is to be determined by p-count ing . The method is not altogether satisfactory for cerium in view of the relatively poor decontamination from phosphorus-32 and the untested decontamination from other radio- active lanthanides, such as neodymium-147, europium-152, europium-154, terbium-160, dysprosium-159, erbium-169, thulium-170 and ytterbium-169. These impurities can be neglected if the sample is shielded from the counter by 3 mm of aluminium to eliminate 13-rays from phosphorus-32 and by using a scintillation spectrometer focused on the 0.14-MeV y-ray of cerium-141.Among the long-lived lanthanide radionuclides, ytterbium-169 has a 0.13-MeV y-ray and neodymium-147 a 0-16-MeV y-ray which might interfere. The method is not ideal for iridium, but more work must be carried out on the radio- chemistry of this element before a really satisfactory procedure can be evolved.16 In this. work it was expected from a study of the literature that iridium would be precipitated by silver (as AgJrCl,) and by hydrogen sulphide, but only 2-3 per cent. and 4-8 per cent., respectively, of the iridium present was lost from solution during these precipitations. Tracer studies showed that most of the small amount of iridium precipitated as sulphide was soluble in yellow ammonium sulphide solution; less than 1 per cent.of this iridium was extracted from 6 N hydrochloric acid by isopropyl ether; and less than 1 per cent. of iridium in solution co-precipitated with cerium(II1) hydroxide (step 4).February, 19671 IRIDIUM AND SILVER IN BIOLOGICAL MATERIAL 123 REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Bowen, H. J. M., and Gibbons, D., “Radioactivation Analysis,” Oxford University Press, 1963. Meinke, W. W., Science, 1955, 121, 177. Wolstenholme, W. A., Nature, 1964, 203, 1284. Cholak, J., and Hubbard, D. M., Ind. Engng Chem. Analyt. Edn, 1944, 16, 333. Goodwin, L. G., and Page, J . E., Biochem. J . , 1943, 37, 198. Mullin, J. B., and Riley, J. P., J . Mar. Res., 1956, 15, 103. Gofmann, J. W., de Lalla, 0. F., Johnson, G., Kovich, E. L., Lowe, O., Piluso, D. L., Tandy, Samsahl, K., Rrune, D., and Wester, P. O., Aktiebolaget Atomenergi Report A E 124, 1963. Wester, P. O., Actu Med. Scund. Suppl., 1965, 439, 7. Brune, D., Samsahl, K., and Wester, P. O., Atompruxis, 1963, 9, 368. Howie, R. A., Molokhia, M. M., and Smith, H., Analyt. Chem., 1965, 37, 1059. Soremark, R., and Bergman, B., Actu Isotopica, 1962, 27, 5. Koch, R. C., and Roesmer, J., J . Fd Sci., 1962, 27, 309. Bowen, H. J. M., i n Shallis, P. W., Edito~, “Proceedings of the SAC Conference, Nottingham, Morris, D. F. C., and Killick, R. A., Talantu, 1960, 4, 51. Leddicotte, G. W., U.S. Atomic Energy Commission Report, NAS-NS-3045, 1961. R. K., and Upham, F., Adv. Biol. Med. Phys., 1962, 8, 1. 1965,” W. Heffer & Sons Ltd., Cambridge, 1965, p. 25. Received June 9th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200118

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

124 Analyst, February, 1967, Vol. 92, pp. 124-131 Comparative Elemental Analyses of a Standard Plant Material BY H. J. M. BOWEN (Chemistry Defiartment, The U?ziversity, Reading, Bevks.) Results are reported by 29 laboratories for the analytical determination of 40 elements in standard kale powder. Consistent results were obtained by more than one laboratory for Au, €3, Ba, Br, Ca, C1, Co, Cr, Fe, Ga, I, Mn, Mo, N, P, Rb, S, Sc and W. Small differences between results obtained by different techniques were found for Cu, K, Mg, Na, P, Se, Sr and Zn. Of these, the most significant were: that flame photometry gave high results for Na; that activation analysis without chemical separation was unreliable for determining K and Mg ; and that atomic-absorption spectrometry gave high results for Cu and Sr.Gross discrepancies were found in the results reported for Al, As, Hg, Ni and Ti. Similar anomalies have been reported in analyses of mammalian blood. Where possible, the precisions of different analytical techniques were compared, INTER-LABORATORY comparison of a standard material is a good method for assessing the accuracy and, incidentally, the precision of analytical techniques. This paper describes the results of elemental analyses of a standard consisting of dried kale powder, whose production has already been described.1 Quantitative results have been obtained for 40 elements by submitting batches of the powder to 29 laboratories listed in an Appendix. A statistical review of the results obtained reveals numerous inconsistencies, but shows that certain techniques give consistently high or low results.The results received for 19 elements are consistent enough for the sample to be used as a standard for assessing the accuracy of analytical methods for these elements in biological materials. OUTLINE OF METHOD OF COMPARISON Each laboratory was asked to determine as many elements as possible in the kale powder, and to report at least four replicate determinations together with the method used. The results were set out in the form of a table for each element studied, and any sets of results differing greatly from the mean were noted. It soon became clear that when a few grossly aberrant results were omitted, the differences between techniques were usually larger than the differences between individual laboratories in which the same technique was used.Wherever sufficient results were available, means and standard deviations were calculated for each technique, and Student’s t-test was applied to find the probability that the difference between means was caused by chance. The t-test was also used to reject a few aberrant results and to justify the pooling of results from different laboratories. Results were rejected when the probability that their mean and the grand mean were the same was less than 1 per cent. A grand mean and standard deviation were usually calculated for each element, but in some cases differences between techniques were so large that it seemed better to quote two or even three different means, where these means differ significantly by the t-test.The standard deviation calculated from the results of several laboratories, obtained by using a given technique, is a measure of the precision of that technique. The accuracy of a technique can only be assessed by its degree of consistency with other techniques, and where several means are quoted the accuracy of all techniques concerned is still in doubt. It is hoped that further work on this material will clear up these inconsistencies. AS only four or fewer results were reported for each element by most laboratories it was not possible to make a reliable comparison of inter-laboratory and intra-laboratory precisions. DRY I NG- The kale powder is slightly hygroscopic and contained about 5 per cent. of water when despatched to the laboratories. Different workers used different drying conditions, which may have led to errors of up to 1 per cent.in their reported results. The effect of dryingBOWEN 125 kale powder at 60", 75", 90" and 100" C is shown in Fig. 1. In future work with this material, it is recommended that an aliquot of the material be dried for 20 hours at 90" C for the deter- mination of dry weight. Hours in oven Fig. 1. Loss in weight by kale powder as a function of drying time CONVENTIONS USED- symbols to individual laboratories will not be given here. Each laboratory has been assigned a symbol (A-2, AA, etc.), but the code relating these Each technique is referred to by a three-letter symbol, as follows- act = activation analysis ata = atomic-absorption spectroscopy cat = catalytic technique col = colorimetry fla = flame photometry vol = volumetric analysis flu = fluorescence analysis gra = gravimetry pol = polarography spe = spectrometry tur = turbidimetry Means ( M ) , standard deviations ( S ) , and the number of determinations made ( N ) are All means are given in p.p.m.of dry kale powder. The results are summarised under individual elements which are in alphabetical order given in the form M + S ( N ) . RESULTS by symbol. Rejected results are enclosed in square brackets. Element Result Laboratory <Om45 T 0-50 5 0.10 (3) M Ag Technique act act A1 Results inconsistent- 7.35 -J= 1.05 (4) A act (y-ray spectrometry) 78.5 2.5 (2) S act (y-ray spectrometry) 6.4 & 0.7 (3) 0 col * 35.5 -J= 7.3 (16) A, B, C, E col 80.1 -J= 11.9 (9) c, p SPe As Results inconsistent- * 0.127 f 0.029 (16) A, U, BB 1.80 -J= 0.16 (4) 0 Au 0-00222 & 0.00055 (7) Y, cc act col act col col] B 50.9 4.7 (35) A, C, E, J, K, L, R, AX [21.1 (8) B [41.2 (5) P spel Ba 4.38 & 0.54 (12) A act c, p SPe * "Best" mean pending further work.126 Element Br Ca Cd c1 C O Cr CS CU DY F Fe Ga Hg I I r BOWEN : COMPARATIVE ELEMENTAL ANALYSES [Analyst, Vol.92 Result Laboratory Technique A,D, E, L, M, R,T,V, X,AA 24.3 & 1.6 (18) A, M, s, u act 41,400 -J= 2230 (41) 39,350 f 958 (4) M, T act 42,350 f 492 (16) n, L, v, x ata 41,720 f 910 (13) R, AA fla Significant differences between techniques, e.g.- 40,950 f 1050 (2) E col 39,700 f 433 (6) A, E vol The following low results were reported, but have not been used in computing these means- [31,150 (4) C flal [33,320 (5) P SPel 1.0 & 0.1 (4) Q p01 3330 & 1060 (21) A, M, s, T act R vol [29,600 (5) W ata] [25,800 (1) Z ata] 0-0562 & 0.0077 (22) 0.0520 f 0.0082 (8) A, u act A, E, I, K, L, N, U No significant differences between techniques, e.g.- 0.0586 f 0.0066 (14) E, I, K, L, N col The following high results were reported, but have not been used in com- puting means- 10.075 (4) C spel L2.0 (5) P spel 11.6 (5) w ata] 0.331 & 0.155 (13) A, u act C SPe w ata 0.0688 & 0.0071 (6) U act 4-81 & 0.735 (88) Small but significant differences were found between techniques- 4-12 f 0.731 (12) A, G, u act 5.25 f 0-479 (18) V, W, X, 2, AA ata col 20 laboratories 4-65 f 0.518 (44) 5.34 f 0-536 (5) EJ Q p01 5.39 f 1.104 (9) c, P sPe 117 (3) 0 col] L9.4 (5) R col] < 0-024 T act 5.55 0.57 (4) Q vol 119.5 & 19.5 (79) 123.2 f 14.2 (8) M, u act 118.2 & 11-7 (17) V, W, X, AA ata col [59 (1) z ata] C, D, E, I, J, K, L, N, V, AA 17 laboratories No significant differences were found between techniques- 121.0 f 19.4 (45) 111.2 f 32.7 (9) c, p sPe B, C, D, E, J, K, L, 0, R, V 0.045 & 0.020 (6) A, u act 0.150 f 0.008 (9) U, BB act Results inconsistent- 0.0122 f 0.0024 (4) Q col 0.0800 3 0.0234 (12) I, K, N cat <0.021 T actFebruary, 19671 OF A STANDARD PLANT MATERIAL 127 Element Result Laboratory Technique K 24,630 1218 (53) 11 laboratories Three results obtained by y-ray spectrometry after activation were low and have been rejected; otherwise the differences between techniques were not significant- [18,890 & 3318 (11) fif, s, T, act (y-ray spectrometry)] 24,160 f 1377 ( 5 ) x, ata 24,570 f 1222 (43) A , C , D , E , L , R,V,AA fla 25,620 & 427 ( 5 ) P SPe La 0.0767 & 0.0103 U act 1604 & 119 (43) 10 laboratories Results obtained by y-ray spectrometry after activation and by spectro- metry were low, and results obtained by flame photometry were high and have been rejected; otherwise the differences between techniques were not significant- Mg [1350 f 188 (6) S act (y-ray spectrometry)] D, L, V, W, X, Z, AA 1611 f 72 (31) ata 1533 f 142 (8) B, c col [3461 (5) R flal [1140 f 155 (5) P SPel 1700 & 271 (4) E vol Mn 14-9 5 1.8 (83) 20 laboratories A, F, G, M, S , T The differences between techniques were not significant- 14.7 f 1.34 (24) act 15.5 & 1.80 (23) V, W, X, Z, AA ata col 14.6 f 1.92 (36) [29 (4) [25 (5) [lo (5) D, E, G, I, J, K, L, N, V C c01; R col] P SPe! Mo 2-33 & 0.47 (44) 9 laboratories Two spectrometric results were lower and have been rejected ; otherwise there was no significant difference between techniques- 2.36 f 0.856 (9) A, u act 2.33 f 0.320 (35) A , C , E , I, K, L,N,AA col [0-996 2 0.497 (9) c, p spel N 43,102 & 102 (35) 9 laboratories No significant differences between techniques- 43,500 & 806 (2) M act vol 42,460 f 583 (5) P SPe 43,188 f 120 (28) B, C, D, E, L, AA Na Results inconsistent- Grand mean 2594 5 617 (52) 9 laboratories 2168 5 310 (15) M, S, T act 2318 f 332 ( 5 ) x, ata 2837 f 324 (32) A, C, R, AA fla [965 (2) W ata- [1220 f 45 (5) P spe; The results from flame photometry are significantly higher than those: obtained with other techniques .Ni Results inconsistent- 10.98 f 0.85 (4) X ata 2.65 & 1.56 (4) C sPe <1 A col P 4524 & 158 (38) B,C,D,E, L, R,V,AA col [4020 f 84 (5) P SPel Pb 3-21 & 1.61 (21) B, C, H, Q 1.6 (4) B col 3.8 ( 5 ) Q col 5-4 (4) H p01 3.0 (4) Q p01 2.1 (4) C sPe Precision poor ; individual laboratories found- 52.8 6.25 A, u act Rb128 Element S Sb s c Se Si Sn Sr Ti iv Zn BOWEN : COMPARATIVE ELEMENTAL ANALYSES [Analyst, Vol. Result Laboratory Technique 16010 2648 (21) B, AA col R gra C vol [24900 (4) C tur] 0.0653 & 0.0125 (6) U act 0.00835 0.00074 (4) A, M act 0.148 & 0.0137 (20) - Differences between techniques significant at 1 per cent. level- 0.155 f 0.0143 (12) A, u act 0.139 4 0.0040 (8) C, AA flu 242 & 10 (5) M act B col 0-160 & 0.037 (4) C SPe 84-1 & 10.7 (20) A, M, w, x Differences between techniques significant at 1 per cent.level- 74.7 & 4.2 (6) A, M act 88.1 f 10.2 (14) w, x ata [149*6 3.4 (5) P spel 0.330 & 0.050 (4) B col 2.75 f 0.13 (4) C sPe 0.0605 & 0.00123 (8) A, u act 31-88 & 4.82 (77) 32.27 & 1.88 (13) A, G, u act 34-23 & 1.57 (28) ata col Results inconsistent- 19 laboratories Some differences between techniques were significant- D, L, V, W, X, Z, AA 30.71 f 5.49 (24) 24.57 8.00 (7) E, R p01 33-60 & 0.89 (5) P sPe C, E, J, K, N, 0 The polarographic results were significantly low at the 1 per cent. lei with respect to the activation results. TABLE I RESULTS FOR MANGANESE IN KALE Laboratory Ashing method Technique A - Activation analysis F - Activation analysis G - Activation analysis S - Activation analysis T - Activation analysis 31 __ Activation analysis v \v x Z AA C n E G I K L 1; R v J - _ _ - - - Wet Dry Wet Wet Wet Wet Wet 4.z Dry i Atomic absorption Atomic absorption Atomic absorption Atomic absorption Atomic absorption Colorimetry - Colorimetry - Colorimetry (formaldoxime) Colorimetry (permanganate) Colorimetry (permanganate) Colorimetry - Colorimetry (permanganate) Colorimetry (perrnanganate) Colorimetry (perrnanganate) Colorimetry (permanganate) Colorimetry (permanganate) P - Spectrometry Manganese, p.p.rn.* 12.6, 13.4, 13.7 13-2, 13.6, 13.8, 14.1, 14.2, 14.5, 14.6, 14 13.1, 16-1 16.0, 16.9, 16.9, 1’7.8 13.9, 14.0, 14.4, 14.9, 15.2, 15.2 16.0 15.9, 17.2, 19.0, 19.8 13.4, 13.6, 14.0, 14-7, 14.7, 16.2 13.5, 13.9, 14-0, 14-0 15.0 14, 15, 15, 15, 16, 17, 17, 18 26, 26, 30, 34t 13.5, 13.5, 13.8, 13.8, 14.1, 14.8 12.0, 12.0, 12.2, 12.5 14.4, 14.8 15, 17, 17, 19 11, 11, 11, 13 15, 16, 16, 16 15, 15, 15, 15 16, 16, 17, 17 25, 25, 25, 25, 251- 15, 15, 15, 17 9, 9, 10, 11, l l t * A11 results are corrected to p.p.m.of dry weight. As these results are significantly different from the mean of all other results by the t-test, they were rejected as being probably erroneous. $ Method not known.February, 19671 OF A STANDARD PLANT MATERIAL 129 RESULTS FOR THE ELEMENT MANGANESE- The results for the element manganese are given in Table I to illustrate the extent of inter-laboratory and intra-laboratory variation in a typical case.There are no significant differences between techniques, except for the single result by spectrometry. The consistency or accuracy of the results can be summed up as follows. (1) Consistent results were obtained by more than one laboratory with the same technique for Au, B, Br, Ga, I, Rb, Sc and W. (2) Consistent results were obtained by different laboratories with several different techniques for Ba, Ca, C1, Co, Cr, Fe, Mn, Mo, N, P and S. No change in nitrogen content with storage, as reported for citrus leaves by Steyn,2 was found. (3) Small but significant differences between results were obtained with different techniques for Cu, K, Mg, Na, P, Se, Sr and Zn. (4) Gross differences between results were obtained with different techniques for Al, As, Hg, Ni and Ti.The large number of elements in categories (1) and (2) should be a source of satisfaction to the analysts concerned in this programme. It is difficult to account for the small differences in category (3) without detailed knowledge of all the techniques used. The best defined difference was found for sodium, where flame photometry gave significantly higher results than activation analysis or atomic-absorption spectrometry. For copper, activation analysis gave significantly lower results, and atomic-absorption spectrometry significantly higher results, than colorimetry. The differences between techniques for the other five elements in this group, although statistically significant, are felt to be based on too few experimental results to be more than guides to future work with other materials.They include the following provisional findings. K Activation analysis (y-ray spectrometry only) gives lower results than other tech- niques. Mg Activation analysis (y-ray spectrometry only) and spectrometry give lower results than atomic absorption and colorimetry. P Spectrometry gives lower results than colorimetry. Se Fluorimetry gives lower results than activation analysis. Sr Atomic absorption gives higher results than activation analysis. Zn Polarography gives lower results than other techniques. SUMMARY OF RESULTS For category (4) elements, further analyses may resolve some of the discrepancies. It appears likely that high values for aluminium and titanium may have arisen from contamination by dust, and nickel contamination might arise from handling the material with a spatula. Arsenic and mercury are both volatile elements which could readily distil into, and out of, the sample during heat treatment; the activation analysis results are probably the more reliable.COMPARISON OF PRECISIONS The precisions of two techniques can be compared by computing their variance ratio and applying the F-test. This has been carried out for a few elements, for which plenty of experimental results obtained by using more than one technique were received, with the following results. Ca Atomic absorption was more precise than flame photometry (P < 0.02). Co The precisions of activation analysis and colorimetry did not differ significantly (P > 0.05).Cu The precisions of activation analysis, atomic absorption, colorimetry and polaro- graphy did not differ significantly (P > 0.05). Fe Atomic absorption was more precise than colorimetry (P = 0.01) ; activation analysis was intermediate in precision. Mn Activation analysis was more precise than either colorimetry (P > 0.02) or atomic absorption (P < 0.05). Mo Colorimetry was much more precise than activation analysis (P < 0.01).130 BOWEN : COMPARATIVE ELEMENTAL ANALYSES [Analyst, Vol. 92 Na The precisions of activation analysis, atomic absorption and flame photometrg did not differ significantly (P > 0.05). Zn Both activation analysis and atomic absorption were much more precise thar colorimetry or polarography (P < 0.01).DISCUSSION There are comparatively few comparisons of this type reported for biological materials Ward and Heeney3 reported a similar study for calcium, potassium and magnesium in driec plant powders. They found flame photometry the best method for determining potassium but it was unsatisfactory for calcium and magnesium, for which titrimetric techniques werc much more precise. The Agricultural Research Council has published a Report of a grouj on Comparison of Methods of Analysis of Mineral Elements in Plants, in June, 1963. A compilation of values for the elementary composition of mammalian blood4 confirm: several of the findings from the present work. Thus, gross differences were found in value reported for each of the elements aluminium, arsenic, mercury, nickel and titanium in wholc blood by different workers.Activation analysis was found to give lower results for coppe in whole blood than either colorimetry or spectrometry. Flame-photometric results fo sodium in whole blood, but not those in serum or plasma, were somewhat higher than thosc found by other techniques. For phosphorus in blood, spectrometry gave lower results thar either activation analysis or colorimetry. There was no indication of significant difference between techniques used to determine potassium, magnesium or zinc in whole blood, an( there were too few results to test such differences for selenium and strontium. Cook, Crespi and Minczewski5 have carried out a valuable survey of the accuracy an( precision of techniques used to measure chromium, copper, mercury and manganese in ai artificial standard.They obtained consistent results for all four elements from nine labora tories by using activation analysis, colorimetry, polarography and spectrometry. In general the precisions of the first three techniques did not differ significantly, but spectrometry wa significantly less precise. The mercury content of Cook, Crespi and Minczewski’s standarc was 15 p.p.m., so that it was easier to determine than in the kale standard used here. The precision of analytical determinations on standard rocks appears to be much lowe than that attainable for biological standards, judging by the results compiled by Webber. The accuracy and precision for aluminium and titanium, which are present in large amounts were good, but gross differences were found by different workers for some trace constituents such as arsenic and nickel.It appears that flame photometry gives higher results thar spectrometry for sodium in Syenite rock. Appendix Analysts and laboratories (in alphabetical order) who supplied the results that mad Beardsley, D. A., Briscoe, G. B., RtiiiEka, J., and Williams, M., College of Advancec Bowen, H. J. M., Wantage Research Laboratories (A.E.R.E.), Wantage, Berkshire, an( Bradfield, E. G., Long Ashton Research Station, Bristol. Carson, R. B., Department of Agriculture, Ottawa, Ontario, Canada. Cawse, P. A., Wantage Research Laboratories (A.E.R.E.), Wantage, Berkshire. Collier, R. E., National Agricultural Advisory Service, Shadlow Hall, Derby. Cook, G. B., International Atomic Energy Agency, Vienna, Austria.Cuypers, J., and Wainderdi, R. E., Texas A & M University, College Station, Texac David, D. J., C.S.I.R.O., Canberra, Australia. Davies, E. B., and McNaught, K. J., Department of Agriculture, Hamilton, New Zealanc Fricker, D. J., National Agricultural Advisory Service, Ashford, Kent. Girardi, F., Euratom, Ispra, Italy. Heinerth, K. E., 28 Truchsess Strasse, Dusseldorf, Germany. Jackson, E., National Agricultural Advisory Service, Leeds, Yorks. Jewell, E. J., National Agricultural Advisory Service, Starcross, Exeter, Devon. Jones, J. B., Ohio Agricultural Experiment Station, Wooster, Ohio, U.S.A. it possible to write this paper are- Technology, Birmingham. The University, Reading, Berkshire. U.S.A.February, 19671 OF A STANDARD PLANT MATERIAL 131 Lane, J. C., Johnston Castle Agricultural College, Wexford, Ireland. Miettinen, J. K., and Puumala, H., University of Helsinki, Finland. Miller, S. T., and Cotzias, G. C., Brookhaven National Laboratory, New York, U.S.A. Morris, D. F. C., and Gupte, J. C., Brunel College of Technology, London. Pickett, E. E., University of Missouri, Columbia, Missouri, U.S.A. Samsahl, K., Aktiebolaget Atomenergi, Studsvik, Nykoping, Sweden, Sjostrand, B., and Westermark, T., Royal Institute of Technology, Stockholm, Sweden. Teichman, T., Department of National Health and Welfare, Ottawa 3, Ontario, Canada. Tyler, J. F. C., Ministry of Technology, Laboratory of the Government Chemist, Cornwall Ward, G. M., Department of Agriculture, Harrow, Ontario, Canada. Williams, A. M., National Agricultural Advisory Service, Cardiff, Glamorgan. Williams, T. R., National Agricultural Advisory Service, Coley Park, Reading, Berkshire. Yule, H. P., General Atomic, P.O. Box 608, San Diego, California, U.S.A. House, Stamford Street, London, S.E. 1. REFERENCES 1. 2. 3. 4. 5. 6. Bowen, H. J. M., in Shallis, P. W., Editor, “Proceedings of the SAC Conference, Nottingham, Steyn, W. J. A., J . Agric. Fd Chem., 1959, 7, 344. Ward, G. M., and Heeney, H. B., Can. J . PI. Sci., 1960, 40, 589. Bowen, H. J . M., “The Elementary Composition of Mammalian Blood,” U.K. Atomic Energy Research Establishment Report AERE-R 4196, H.M. Stationery Office, London, 1963. Cook, G. B., Crespi, M. B. A, and Minczewski, J., Talanta, 1963, 10, 917. Webber, G. R., Geochim. Cosmochim. Acta, 1965, 29, 229. 1965,” W. Heffer & Sons Ltd., Cambridge, 1965, p. 25. Received February 18th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200124

出版商:RSC    

年代:1967

数据来源: RSC