摘要:

Analyst, December, 1979, Vol. 104, p p . 1151-1158 1151 Separation of Bismuth-210 and Polonium-210 from Aqueous Solutions by Spontaneous Adsorption on Copper Foils A. B. MacKenzie and R. D. Scott Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow, G75 OQ U A description is given of factors controlling the adsorption of trace amounts of radioactive bismuth and polonium from aqueous solution on to thin copper foils. Optimum conditions are defined for the selective and quantita- tive adsorption of bismuth-210 and polonium-21 0 from aqueous solution and for a subsequent desorption process to give separation of the extracted bismuth and polonium. The method is demonstrated to be suitable for the preparation of thin sources for a-spectroscopy and for analysis of bismuth-210 and polonium-210 in marine sediments.The kinetics of the adsorption and desorption processes are briefly discussed. Keywords : 210Pb, 210Bi and 210Po analysis ; spontaneous adsorption ; desorp- tion; copper surfaces The spontaneous deposition of polonium from aqueous solution on to surfaces of metals such as silver, copper, platinum and nickel was first observed over 70 years ago and reviews of the development and use of the technique have been presented by Bagnalll and Figgins2 Considerable research has been performed on various aspects of the subject, particularly the adsorption of polonium on silver, but the processes involved are complex and not fully understood. ZloPb is a member of the 238U natural decay series and gives rise to radioactive daughter products 210Bi and 210Po as shown in Fig.1. As a result of its high radiotoxicity and geo- chemical behaviour, concentrations of 210Po have been studied in a diverse range of materials in recent years. Spontaneous deposition of 210Po on to silver foils from acidic solutions containing hydroxylammonium chloride has become established as the most common method of separation and source preparation but considerable variations exist in the conditions used and efficiency of adsorption obtained in different laboratories. Examples of recent applica- tions of this method have been in the analysis of sediments,*-' foodstuffs,s waterg and tobacco.lO As early as 1910, Curie and Debiernell established.that polonium could be separated from lead by spontaneous deposition on to copper, but this technique has not been widely used for separation of zroPo as the source obtained also contains 210Bi.In the course of recent & ~ = 2 1 yr 210 Pb 1 46.5 keV 803 keV 206Pb Fig. 1. Decay scheme for 210Pb, 210Bi and 21OPo (based on data from Lederer et aZ.3).1152 MACKENZIE AND SCOTT: SEPARATION OF B~I-210 AND PO-310 FROM AnaZyst, VOZ. 104 work at this Centre involving the preparation of high-purity sources for L-shell ionisation studies during polonium a-decay,12 it was observed that a t temperatures above 90 "C trace amounts of 210Bi and 210Po are rapidly and efficiently removed from aqueous solution by spontaneous adsorption on to copper foils. Moreover, if the foil is subsequently exposed to a similar solution at room temperature then rapid desorption of 210Bi occurs, leaving a pure source of 210Po on the foil.As a result of difficulties experienced in attempting to find any literature reference defining suitable conditions for source preparation by this techinque and in the apparent absence of any previous description of the bismuth desorption effect a systematic study of the adsorption - desorption system was carried out. Experimental Solutions for adsorption experiments were prepared from 0.1-ml aliquots of an equilibrium solution of 210Pb with its radioactive daughter products 210Bi and 210Po. Each aliquot contained 60 nCi of 210Pb with about 10 pg of stable lead carrier and was added to about 20 ml of demineralised water plus 5 ml of 30% wz/V hydroxylammonium chloride solution.The total volume was made up to 40 ml by addition of demineralised water and hydrochloric acid or sodium hydroxide solution as necessary to give the required pH. Solutions for desorption experiments were similarly prepared but without addition of the 210Pb - 210Bi - 21OPo activity. During adsorption experiments a.t elevated temperatures, constant volume was maintained by topping up the solution with demineralised water at the same tempera- ture. All experiments were performed using normal laboratory glassware. Individual square copper foils of side 12.5 mm were cut from BDH laboratory-grade 0.1 mm thick copper sheet and were firmly fixed to a Mylar backing with adhesive. Immedi- ately before use, the foils were cleaned by brief immersion in approximately 2 M nitric acid followed by rinsing with demineralised water and acetone, after which they were carefully dried with paFer tissue.During adsorption and desorption experiments, the foils were simply suspended in solution using a thin strip of the Mylar backing as a support, with care being taken to prevent the copper surface from touching the side of the beaker. Negligible amounts of activity were found to be taken up on either the Mylar or the reverse face of the copper foil, even under the most extreme conditions used. The relative error on the area of the foils was less than 10% and observed count rates were not corrected for variations in foil area. After the completion of each experiment, the foil was removed from the solution, quickly dried with paper tissue and fixed to the centre of ,a 1 in diameter aluminium planchet giving a fixed geometry source for radioactivity counting;. Beta counting for the determination of 210Bi activity was performed using a Nuclear Chicago, Model 470, gas flow Geiger counter.An automatic sample changer gives close positioning of the source to the counter and the small air gap plus the 150,~gcm-~ window of the detector do not prevent penetration of a radiation into the detector. An additional absorber of 6 mg cm-2 of Mylar was therefore positioned over the detector window to prevent a particles from 210Po decay registering counts. 210Po a spectra were recorded using an Ortec surface barrier detector of depletion depth 60 pm, coupled via pre-amplifier, amplifier and biased amplifier units to a Nuclear Data ND 60 multi-channel analyser. The small depletion depth of the detector makes this system insensitive to ,8 radiation so that counts are not recorded as a result of 210€3i decay.The count rate corresponding to 1000//, adsorption of 210Bi was determined by drying an aliquot of the stock equilibrium solution on a copper foil to give the same source geometry as used in subsequent experiments. The additional PI'Iylar absorber used in these experi- ments prevents the very low energy ,B radiation of 210Pb from entering the detector. Self- absorption as a result of source thickness prevented this technique from being used to assess the count rate corresponding to 100~o adsorption of 210Po. In this instance, a solution containing an aliquot of the stock solution was successively extracted five times for zlOPo by adsorption on copper foils under conditions known to give a high adsorption efficiency.Negliglble 210Po activity was obtained by the fourth and fifth extractions and the count rate corresponding to 100~o adsorption was taken as 1:he sum of the count rates from the first three extractions. A number of factors were found to affect the adsorption and desorption processes and it is convenient to consider the effect of varying each of these individually while other conditions remain constant.December, 1979 AQUEOUS SOLUTIONS BE' SPONTANEOUS ADSORPTION ON COPPER FOILS Adsorption Stirring A magnetic bar stirrer was used to assess the effect of stirring speed on the initial rate of adsorption of 210Bi and 210Po from solutions at pH 1.5 and 22 "C.A linear relationship between percentage deposition and stirring speed was obtained for both nuclides up to a stirring speed of about 950 rev min-l, above which excessive vortex and turbulence effects occur. Fig. 2 compares the percentage adsorption of 210Bi and 210Po as a function of time for solutions of pH 1.5 a t 95 "C without stirring and with a stirring speed of 600 rev min-l. Individual experiments were performed for each deposition time studied rather than by using the same foil and solution with increasing deposition times and intermediate counts. The enhancement of the rate of adsorption by stirring is clearly demonstrated by the fact that a deposition time of 9 h is required to give adsorptions of 90% and 80% for 210Po and ZlOBi, respectively, without stirring, while these values are attained within 2 h at a stirring speed of 600 rev min-I.1153 100 1 90 80 70 .: 60 50 .- m N C Q B W 40 0, 7 30 a W g 20 10 0 100 200 300 400 500 0 100 200 300 400 500 Deposition t ime/mi n Fig. 2. Percentage adsorption of (a) 210Bi and (b) zlOPo as a function of time a t 95 "C: (A) without stirring; and (B) with stirring a t 600 rev min-l. On the basis of these observations, subsequent experiments were carried out using a stirrer speed of 600 rev min-l, giving enhanced adsorption rates without the production of excessive vortex or turbulence effects. Temperature The effect of increasing temperature on the initial rate of adsorption is illustrated in Fig. 3, which shows semi-logarithmic plots of the percentage of 210Bi and 2lOPo adsorbed during the first 10 min of deposition as a function of temperature for solutions of pH 1.5.Preliminary experiments of this type in which stirring was not used gave rise to a more complex graph with an enhanced rate of increase in percentage adsorption between 30 and 50 "C. The latter was attributed to a convective mixing effect and was eliminated by stirring. PH A series of experiments was carried out to characterise variations in the percentage adsorption of 210Bi and zlOPo as a function of time for a range of pH values from 1.0 to 5.5. Individual experiments were performed for each set of conditions studied rather than by using the same foil and solution with increasing deposition times. A solution temperature of 95 "C was used in all instances.Attempts to continue this series of experiments at higher pH values were unsuccessful as a result of excessive corrosion of the copper foils. As shown in Fig. 4, adsorption of 210Po is unaffected by variations in pH within the range studied. In contrast, for 210Bi both the rate of adsorption and equilibrium fraction adsorbed decrease markedly with increasing pH.1154 MACKENZIE AND SCOTT: SEPARATION OF BI-210 AND Po-210 FROM Analyst, VoZ. 104 3- 20 30 40 50 60 70 80 90 100 20 30 40 50 60 70 80 90 100 Temperature/"C Fig. 3. Effect of temperature on percentage adsorption of (a) 210Bi and (b) 210Po during the first 10 min of spontane- ous deposition a t pH 1.5. Desorption Over the range of experimental conditions studied, significant desorption of 2lOPo did not occur ; hence the following description of desorption experiments applies exclusively to 2lOBi.Foils for desorption experiments were prepared by 10-min depositions from solutions at 95 "C. In desorption experiments, each foil was exposed to a solution at 22 "C for pro- gressively longer desorption times with intermediate removal, drying and counting. The total desorption time was taken as the sum of individual immersion times. A stirrer speed of 600 rev min-l was used in all instances. The factors considered below were found to be of dominant importance in the desorption process. Air exposwe time In initial experiments it was observed that 210Bi deposited on to copper foils a t 95 "C could be rapidly desorbed by exposure to an aqueous solution at room temperature.Attempts to quantify this effect yielded apparently inconsistent results until it was realised that the desorption process consists of two components, a very rapid fall-off within the first few seconds of exposure to a cold solution followed by a slower desorption of the residual 210Bi over a period of hours. More importantly, as shown in Fig. 5 , the initial rapid desorption depends on the length of time for which the foil is exposed to air following deposition of the 210Bi. The desorption solution used in these experiments had a pH of 1.5 and a temperature of 22 "C. Similar desorption experiments in which the foils were exposed to different atmospheres for 40 min after deposition of 210Bi indicated that the raDid comDonent of the I 1 50 100 150 Deposition tirne/min Fig.4. Effect of pH on percentage adsorption: (a) 210Po within the pH range 1.0-5.5; and (b) 210Bi a t pH (A) 1.0, (B) 1.5, (C) 2.5, (D) 3.0 and (E) 5.5.December, 1979 AQUEOUS SOLUTIONS BY SPONTANEOUS ADSORPTION ON COPPER FOILS 1155 100 90 .- m o 70 .g 60 Q 50 0 80 N + - L +d a, 7J 0, m a, a, 4o 2 30 : 20 a 10 0 50 100 150 2 00 250 Cu mu la t ive deso rp t ion ti me/s Fig. 5. Effect of increasing air exposure time on desorption of 210Bi: (A) 3-min air exposure; (B) 10-min air exposure; (C) 40-min air exposure; and (D) 16-h air exposure. desorption is almost certainly dependent on some form of oxidation process. The results of these experiments are summarised in Fig. 6. A complication necessarily occurs in these experiments, as the foils are exposed to air during each of the successive counts.The time involved is less than 3 min in each instance but this gives rise to an increasing air exposure time with increasing cumulative desorption time, which will have the effect of increasing the gradient of the desorption curves. I I I 0 50. 100 150 200 2 50 Cumulative desorption timeis Fig. 6. Effect of different atmospheres on desorp- tion of 210Bi: (A) 40-min exposure to vacuum; (B) 40-min exposure to helium; (C) 40-min exposure to nitrogen; and (D) 40-min exposure t o air. w The pH values of both the adsorption and desorption solutions appear to exert an influence The combined effect gives rise to a complex situation, as shown The data shown represent the results of a series of experiments in which foils All Desorption experiments were per- on the desorption process.in Fig. 7. were prepared by adsorption of 210Bi at 95 "C from solutions of pH 1.0, 3.0 and 5.0. foils were exposed to air for 10 min after preparation. formed with solutions at 22 "C and pH values as indicated in Fig. 7.1156 MACKENZIE AND SCOTT: SEPARATION OF HI-210 AND Po-210 FROM Analyst, V O ~ . 104 " 50 100 150 200 250 Cumulative desorption time/s Fig. 7. Effect of pH on desorption of Z10Bi: (a) Zl0Bi deposited at pH 1.0; (b) 210Bi deposited at pH 3.0; and (c) 210Bi deposited a t pH 5.0. pH values: (A) 1; (B) 3; (C) 5 ; and (D) 7. Carrier Desorption of 210Bi was found to be independent of the amount of stable lead carrier in solution, proceeding even into doubly distilled waker.With the presence of 10 pg of stable lead carrier in the desorption solution, the 210Bi can be re-adsorbed on to a new copper foil with the same efficiency as previously described. In the absence of carrier, however, most of the 210Bi was lost by adsorption on the glassware and could not be recovered by re- adsorption on to copper. Efficiency of Separation from 210Pb No adsorption of 210Pb was observed over the range of conditions studied, as verified by the following results : (1) after adsorption of 21013i and 210Po, foils were analysed using a high resolution lithium- drifted silicon detector and the absence of the 46.5-IreV 7-ray indicated that 210Pb was not being extracted ; (2) adsorbed zlOBi decays with the correct unsupported half-life ; (3) experiments using zlzPb tracer (p, t, = 10.6 h) indicated no significant adsorption of lead.Application to Analysis of Marine Sediment successive acid digestions and leachings with 6 M hydrochloric acid. A bulk sample of recent sediment from the Clyde Sea Area was totally dissolved by A sample containingDecember, 1979 1157 the equivalent of 4 g of dried sediment was spiked with an aliquot of the 210Pb equilibrium solution and 5 ml of 30% m/V hydroxylammonium chloride solution were added. The total volume was made up to 40 ml with de-mineralised water and the pH of the solution ad- justed to 1.5. A deposition time of 3.5 h at 95 "C with a stirrer speed of 600 rev min-l resulted in 100% adsorption of both 210Bi and 210Po on a 12.5 mm square copper foil.The method is therefore suitable for the analysis of 210Po in dissolved sediment and with the use of 208Po, as a chemical yield tracer, could be applied in 210Pb dating studies. In a similar experiment without hydroxylammonium chloride, the surface of the copper was highly corroded and while 1 0 0 ~ o adsorption of 210Po was obtained, only 16% of the 210Bi was deposited. Corresponding experiments using spiked demineralised water without hydroxylammonium chloride did not result in corrosion of the copper or a decrease in the amount of 210Bi adsorbed. These effects can therefore be attributed to the presence of some species dissolved from the sediment, the effect of which is inhibited by the presence of hydroxylammonium chloride. Source Thickness Typical sources produced during these experiments gave a full width a t half-maximum resolution of 25 keV in the cc spectrum, which is the nominal energy resolution of the surface barrier detector.Therefore, while low-energy "tailing" in the o( spectrum indicates that the sources produced are thicker than vacuum-deposited sources, they are thin enough to ensure that the energy resolution of the detector is the limiting factor in o! spectroscopic applications, except perhaps in the extreme instance of the search for a very weak component in the scatter- ing tail of a much more intense line. AQUEOUS SOLUTIONS BY SPONTANEOUS ADSORPTIOK ON COPPER FOILS Discussion The foregoing results indicate that this technique is suitable for the quantitative separation of zlOBi and 210Po from aqueous solution and that the method is a t least as good for the analysis of 210Po in dissolved sediment as the more conventionally used silver adsorption process.The method is therefore suitable for application in 210Pb dating studies and the quantitative adsorption of 210Bi provides the additional possibility of detailed investigation of the geochemical characteristics of the 210Pb - 210Bi - 210Po system. Optimum conditions for the adsorption are a temperature of 95 "C, pH 1.0-1.5 and a stirrer speed of 600 rev min-1. Hydroxylammonium chloride should be present in the analysis of dissolved sediment to prevent corrosion of the copper. Using these conditions, with a solution volume of 40 ml and copper foil of area 160 mm2, total adsorption of 210Bi and 210Po is achieved within 3.54.0 h.Separation of the extracted bismuth and polonium is readily achieved by repeatedly exposing the foil to air for 40 min followed by immersion for 10 min in an aqueous solution at pH 1 and 22 "C containing about 10 pg of stable lead carrier. The desorbed bismuth can be recovered from the combined desorption solutions by re-adsorption on to another copper foil. A detailed investigation of the reaction mechanisms and kinetics involved in the adsorp- tion and desorption processes is beyond the scope of the present work, but a number of comments can be made. The enhanced rate of adsorption with increased stirring can be regarded as arising simply from an increased number of collisions between ions in solution and the copper surface. Hashimoto13 observed a similar effect for adsorption of ZlOPo on silver.In this instance a deposition time of 2 h was used and, for those samples which had not reached the equilibrium adsorption of about 90% within this time, an enhanced rate of deposition was obtained with increased stirring speed. The results shown in Fig. 4 indicate that at a fixed temFerature, adsorption of 210Po follows first-order kinetics. Thus, the fraction F of *loPo originally in solution that is adsorbed after a deposition time t is given by F = 1 -exp(-kt) A t 95 "C and for the experimental conditions defined above, the constant K has a value of 0.019 min-l. The results shown in Fig, 3 indicate an exponential increase in the rate of adsorption of 210P~ with increasing temperature. Variations of adsorption rate in direct proportion to the1158 MACKENZIE AND SCOTT foil area and in inverse proportion to the solution volume in this type of process are well established1 and in this instance were verified but not studied in detail.Thus a more general expression for the rate of adsorption of 210Po is where N = number of ions in solution, T = temperature, A = surface area of foil, S = stirrer speed, V = solution volume and k’ and k’,’ are constants. At pH values between 1.0 and 1.5, adsorption of 210Ri also follows first-order kinetics and under the optimum conditions defined above again gives a value for k of 0.019 min-1. At higher pH values, adsorption of 210Bi does not fo1l.o~ first-order kinetics and the equilibrium fraction adsorbed decreases with increasing pH.This indicates that at higher pH values a desorption process competes with the adsorption reaction and the turning points in the graphs for pH values of 2.5 and 3.0 in Fig. 4(b) indicate an even more complex situation with at least one more process operating along with the adsorption and desorption reactions. The adsorption of 210Bi on copper can therefore be regarded as an acid-catalysed reaction, which, at low pH, reaches a limiting condition in which the reaction follows the same kinetics as the 210Po adsorption process. The most efficient desorption occurs as a result of oxidation, giving rise to an initially very rapid removal of bismuth from the copper surface on exposure to cold aqueous solutions. After desorption of the oxidised component, a slower desorption of the remaining 210Bi occurs.In all instances studied, the initial rapid desorption is most efficient into solutions of pH 1, while the slower desorption is most efficient into solutions of pH 3. On the basis of the results obtained, the desorption process is therefore shown to vary in a complex manner as a function of air exposure time and the pH values of both the adsorption and desorption solutions. The oxidation reaction giving rise to the initial rapid desorption is selective to bismuth and does not affect polonium. Therefore, it is probable that the mechanism involved is either direct oxidation of the bismuth without oxidation of the polonium or oxidation of the copper surface giving rise to a bond with bismuth, which is readily broken by acid-catalysed hydrolysis, whereas the bond with polonium is relatively stable.The processes involved are therefore complex and would require more rigorous investi- gation before they could be accurately described. This study is a t present being extended by an investigation of the adsorption and desorption reactions of 210Bi and 210Po with other metals and the determination by particle-track -methods of the distribution of the radio- nuclides on the metal surface. In 210Bi desorption, two distinct processes occu:t-. 1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. References Bagnall, K. W., “Chemistry of the Rare Radioelements Polonium - Actinium,” Butterworths, London, 1957. Figgins, P. E., “The Radiochemistry of Polonium,” National Academy of Sciences Nuclear Science Series NAS-NS 3037, Office of Technical Services, Department of Commerce, Washington, D.C., 1961. Lederer, C. M., Hollander, J. M., and Perlman, I., “Table of Isotopes,” Sixth Edition, John Wiley, New York, 1968. Flynn, W. W., Analytica Chim. Acta, 1968, 43, 221 Robbins, J. A., and Edgington, E. N., Geochim. Cosmochim. Acta, 1975, 39, 285. Eakins, J. D., and Morrison, R. T., Int. J . Appl. Rzdiat. Isotop., 1978, 29, 581. Mackenzie, A. B., Baxter, M. S., McKinely, I. G., Swan, D. S., and Jack, W. J . Radioanalyt. Chem., Khandekar, K. N., Hlth Phys., 1977, 33, 148. Schnell, W. R., Geochim. Cosmochim. Acta, 1977, 41, 1019. Singh, D. R., and Nilekani, S. R., Hlth Phys., 1976, 31, 393. Curie, M., and Debierne, A., C . R. Hebd. SE‘anc. Acad. Sci., Paris, 1910, 150, 386. Scott, R. D., J . Phys. G., 1978, 4, 1353. Hashimoto, T., Radiochim. Radioanalyt. Lett., 1971, 1, 25. 1979, 48, 29. Received M a y lst, 1979 Accepted July 9th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401151

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, December, 1979, Vol. 104, @p. 1159-1164 1159 Determination of Mercury in Smelter Flue Dusts by Acid Digestion Methods Chung H. Chiu and John C. Hilborn Chemistry Division, Environment Canada, A i r Pollution Technology Centre, River Road, Ottawa, Canada, K1A 1C8 In order to develop a mercury digestion method suitable for flue dust from non-ferrous and secondary lead smelters, seven acid digestions, two in a closed system and five in an open system, were studied. Closed systems were less convenient to use and had no real advantage over open systems. We conclude that the use of aqua regia in open systems is the most effective digestion method. A 96% recovery for spiked mercury(I1) sulphide and mercury(I1) oxide and a 98% recovery for mercury(I1) chloride were obtained. Keywords : Mercury determination ; acid digestion ; j l u e dust ; non-fewous smelter An inventory (1970) of mercury emissions from Canadian zinc and copper smelters estimated these to be 8.68 tons or 10% of the total mercury emissions in Canada.l A high percentage of the mercury emitted is particulate. Therefore, a method for determining the mercury in particulate form is important to a total mercury emission study.Several papers2-10 indicate that mercury in rocks, soils, sediments and biological materials can be determined successfully by acid digestion, although some workers have reported losses of mercury during acid digestion of organicll and biological materials.12 Iskandar et aL2 reported that the complete recovery of organomercury compounds from sediments and soils can be achieved by wet digestion with a sulphuric acid-nitric acid mixture at 60 "C and subsequent oxidation with potassium permanganate and potassium persulphate.However, this method is inadequate for quantitative recovery of mercury( 11) sulphide. The addition of a small amount of hydrochloric acid to the extraction medium was proposed by Agemian and C h a ~ . ~ This modification improved the recovery of mercury from geological samples that contained large amounts of sulphide and also yielded complete recovery of mercury in cinnabar (HgS). Other report^^-^ have suggested the use of aqua regia as the oxidising agent. Jonasson et aL7 claimed that excessive hydrochloric acid caused mercury loss due to the volatilisation of mercury( 11) chloride.They recommended digesting rock samples with nitric acid - hydrochloric acid (20 + 1) at 90 "C. The combination of perchloric acid, nitric acid and sulphuric acid has been used for wet ashing organics for the determina- tion of m e r c ~ r y . ~ ~ ~ A cold-digestion method has also been developedLo for the extraction of mercury from ores and mill products. The decomposition of solids under pressure in closed systems for the determination of heavy metals13 can also be applied to mercury determination. Because, in a closed system, the loss of volatile mercury can be eliminated and the activity of mineral acids increases, resistant mercury compounds can be more easily dissolved. Omang and PamL4 digested geological materials in a PTFE-lined decomposition bomb with a hydrofluoric - nitric acid mixture at 120 "C.Methods with similar types of bombs using hydrofluoric acid - aqua regia mixtures for multi-element determinations in rocksL5 and mercury determination in sedi- ment@ have been published. In this paper, seven digestion methods, two in a closed system and five in an open system, are compared for the determination of mercury in flue dust samples. Red mercury(I1) sulphide (cinnabar) is the chief form in which mercury exists in the natural state17 and is resistant to some acids.7 Mercury oxides and various mixed oxides are undoubtedly formed during the processing or roasting and smelting of ores. Therefore, both mercury(I1) sulphide (HgS) and mercury(I1) oxide (HgO) were used as spiked mercury compounds for recovery studies.1160 CHIU AND HILBORN: DETERMINATION OF MERCURY I N Analyst, V d .104 Experimental Apparatus digestions. of 25-ml volume were used for the closed-system digestions. oven (Precision Scientific Co.) was used for heating the digestion bombs. was employed for the analysis. detected using a wavelength-dispersive X-ray spectrometer (Siemens SRS-1). A temperature-controlled water-bath (Fisher Scientific Co.) was used for the open-system Four acid digestion bombs (Parr Instrument Co.) with PTFE-lined inner cups A precise temperature-controlled A cold vapour atomic-absorption spectrophotorneter (Coleman Mercury Analyzer MAS-50) The mercury remaining in residues after digestion was Reagents The reducing agents tin(I1) chloride (10% m/V) and hydroxylammonium chloride (1.5% m/V) were purchased as mercury-free reagents from Coleman Instruments.Sulphuric, nitric and perchloric acids were certified to contain less than 1 p.p.b. (1 part per lo9) of mercury. Certified reagent-grade chemicals were used for all analyses. Dust Samples except for three samples from secondary lead smelter baghouses. samples are indicated in Table I. All samples used originated from either the stack or the flue system of non-ferrous smelters The sources of dust TABLE :[ SOURCES OF THE SMELTEE;: DUSTS ANALYSED Code I DS-4 DS-7 DS-8 DS-10 DS-15 DS-20 DS-21 DS-26 DS-27 DS-38 DS-40 DS-43 DS-45 90. Source .. .. .. . . .. . . .. . . .. .. .. .. .. .. .. .. . . . . .. .. . . . . .. . . .. .. Baghouse dust Baghouse dust Stack dust Baghouse dust Nickel sulphide dust Reactor dust Cottrell reverb dust Cottrell converter dust Cottrell reverb dust Stack dust Stack dust Stack dust Stack dust Type of smelter Secondary lead Secondary lead Copper - zinc Secondary lead Nickel Copper Copper Copper Copper Nickel Copper - zinc Copper - zinc Copper - zinc Procedure Glassware was cleaned by washing with a solution of 35ml of saturated potassium dichromate in 1 1 of concentrated sulphuric acid and rinsed with 1 + 1 nitric acid solution followed by de-ionised water.( A ) Open-system acid digestions Dust samples weighing approximately 0.5 g were transferred into 125-ml Erlenmeyer flasks and not more than 3 ml of de-ionised water were allowed for sample wetting. The samples were then treated with each of four acid mixtures as follows.Mixture I-sulphuric, nitric and hydrochloric acids (8 + 4 + l ) . 3 After the addition of 16 ml of sulphuric acid and 8ml of nitric acid to the sample flask, the contents were mixed by swirling and cooled in an ice - water bath for several minutes. Hydrochloric acid (2ml) was then added very slowly to the flask and the cooling was then continued for a further several minutes because of the heat released by the highly exothermic reaction. The flask was then placed in a hot water-bath for digestion for 2 h at 60-65 "C. The flask was then removed and the contents were diluted with 25 ml of de-ionised water and cooled to room temperature. The sample was filtered through a glass-fibre filter into a 100-ml cali- brated flask to remove any residue. The sample flask was rinsed twice with 0.05% potassium (i)December, 1979 SMELTER FLUE DUSTS BY ACID DIGESTION METHODS 1161 dichromate in 1% sulphuric acid, which was also filtered and collected in the 100-ml cali- brated flask.The residue was air dried and the mercury content was measured by X-ray fluorescence spectrometry. The Lcc radiations of mercury were measured and concentra- tions were calculated from net intensities using the thin-film approximation and calibration constants taken from Giauque et a1.18 After the addition of 18 ml of hydrochloric acid and 6 ml of nitric acid to the sample flask, the contents were mixed, digested and filtered as described in (i). (iii) After the addition of 15 ml of nitric acid, 5 ml of sulphuric acid and 5 ml of perchloric acid to the sample flask, the contents were mixed, digested and filtered as described in (i).Mixture IV-sulphuric, nitric and hydrochloric acids (6 + 6 + 1). After the addition of 12 ml of sulphuric acid, 12 ml of nitric acid and 2 ml of hydrochloric acid to the sample flask, the contents were mixed, digested and filtered as described in ( i ) . (v) Mixture V-hydrochloric and nitric acid mixture. After the addition of 20 ml of hydrochloric acid, the sample flask was allowed to stand covered overnight at room tempera- ture. Then 20ml of nitric acid were added and the sample flask was allowed to stand covered for a further 24 h. The filtered digests from mixtures (I) and (IV) were preserved with 5 ml of 5% potassium dichromate solution. The filtered digests from mixtures (11), (111) and (V) were preserved with 1 ml of 5% potassium dichromate solution.The solutions were finally diluted to volume { 100 ml) with de-ionised water. The detection limit is 3 pg of mercury. (ii) Mixture 11-aqua regia. Mixture III-nitric, sulphuric and perchloric acids (3 + 1 + 1). (iv) The sample was then filtered as described in (i). (B, Closed-system acid digestions To each PTFE cup containing 0.1 g of dust sample, 6 ml of aqua regia were added and the cup was sealed tightly in a stainless-steel vessel. The sealed bomb was then placed in an oven that had been pre-heated to 110 "C. After digestion for 2 h, the bomb was cooled in an ice - water bath for 30 min. The solution was transferred into a 50-ml calibrated flask and 0.5 ml of 5% potassium dichromate solution was added as a preservative.HydroJuoric acid + aqua regia.15 A representative 0.5-g sample of dust was trans- ferred into the PTFE cup and 6 ml of hydrofluoric acid and 1 ml of aqua regia were added. The sealed bomb was heated in the oven at 110 "C for 2 h. After digestion, the bomb was cooled in an ice - water bath and the solution was transferred into a PTFE beaker containing 5 g of boric acid.lg To this were added 40 ml of de-ionised water and the mixture was stirred to dissolve the boric acid. (i) Aqua regia. (ii) Filtration was then carried out as described in ( A ) (i) above. ( C ) Analysis The analyses of all aqueous samples were carried out by the cold vapour atomic-absorption technique.20 To an aliquot of each sample (0.5-50m1, depending on the mercury con- centration of the sample), 5 ml of hydroxylammonium chloride were added in order to reduce the excess of dichromate.De-ionised water was added to adjust the volume of all samples to 100ml. Mercury was then reduced to the elemental state by the addition of 5ml of tin(I1) chloride, which was aerated from solution in a closed system. (D) Recovery To study the recovery efficiency of the methods, 3-6 mg of mercury(I1) sulphide powder or mercury(I1) oxide powder were weighed to the nearest 0.01 mg on a small piece of cellulose filter-paper, then both filter-paper and mercury were transferred into a flask that contained 0.1-0.5 g of dust sample. The digestions were then performed by the procedures described in each method. Mercury(I1) chloride, because of its volatility, was also used here to accentuate any mercury loss during the acid digestion. When pure mercury(I1) chloride solution was used no dust sample was added. ( E ) Filter and reagent blanks with mixtures (I) and (11).The content of mercury in the glass-fibre and cellulose filters was examined by digestion Reagent blanks were treated using the sample procedures.1162 Digestion The results of the seven digestion procedures are presented in Table 11. Whereas the results from most digestion procedures are in good agreement, the procedure using hydrofluoric acid in a digestion bomb yielded lower mercury values from some samples. Owing to the large amount of residue remaining after digesting with method (B) (ii), it is reasonable to conclude that aqua regia is a more effective digesting mediu.m than a 6 + 1 mixture of hydrofluoric acid and aqua regia.Ideally, digestion conducted in a closed system under high pressure should digest the dust more efficiently and should prevent any loss of mercury from volatilisation. CHIC; AND HILBORN : DETERMINATION OF MERCURY IN AnaZyst, vol. 104 Results and Discussion The mercury level in the dust samples varied from less than 0.1 p.p.m. to 1.9%. TABLE I1 COMPARISON OF MERCURY RESULTS (pg g-l) for SEVEN DIGESTION METHODS Digestion bomb: 2 h a t 110 "C Open system: 2 h a t 60 "C Cold digestion method, Dust sample KO. HKa-a =(I)- Mixture (11) *Mixture (111) Mixture (IV) mixture (V) DS-4 . . . . . . DS-7 .. . . .. DS-10 . . .. .. DS-15 . . .. .. DS-38 . . . . . . DS-20.. .. ..DS-21 . , . . . . DS-26 . . . . . . DS-27 . . .. . . DS-40 . . . . . . DS-43 . . .. .. DS-45 . . . . . . DS-8 . . .. . . 3.10 9.75 9.70 7.47 9.7 9.65 3.44 4.33 4.55 <0.1 <0.1 < 0.1 - <0.1 <0.1 0.36 0.34 0.29 2.93 3.15 2.91 - <0.1 < 0.1 - 1.19 1.15 99 10.5 105 149 149 151 - 129 128 - 19.1 x 1 0 3 18.6 x 103 I 9.75 9.45 4.48 <0.1 < 0.1 < 0.1 104 152 131 9.3 X 103 0.33 2.94 1.13 9.70 9. 60 9.50 9.80 9.45 9.45 4.63 4.55 4.77 < 0.1 < 0.1 < 0.1 < 0.1 t 0 . 1 - 0.34 0.31 < 0.1 3.19 2.79 3.06 - <0.1 - 0.76 - - 104 103 102 152 154 151 130 - - 15.0 x 1 0 3 18.9 x 103 19.0 x 10s The results in Table I1 confirmed that the amounts of mercury extracted in open systems are in good agreement with the results conducted by digestion bombs using 6 ml of aqua regia. The results from the cold-digestion method ( A ) (v) also agree well with the values from most other methods, except for some samples containing mercury at low concentrations, such as DS-20 and DS-27.For sample DS-8, containing extremely large amounts of mercury, complete recovery of mercury was not obtained using mixture (111) in the open system. Unextracted mercury was found in the residue by X-ray fluorescence spectrometry. When the residues remaining after extraction of some other samples, such as DS-40, DS-43 and DS-45, were examined by X-ray fluorescence spectrometry, no mercury was found (detection limit 3,ug). From the agreement between results using mixtures (I) and (IV) in Table 11, one can conclude that slight changes in the proportions of sulphuric and nitric acids are not critical.Recovery from Spiked Samples The average of four replicate analyses listed in Table I11 shows that no loss of mercury chloride results from any of the acid digestion procedures used. The recoveries of mercury from mercury(I1) oxide are better than 96% and from mercury(I1) sulphide are better than 95%, except for the 93% recovery obtained by the cold-digestion method. I t seems that heating is required in order to decompose mercuiry (11) sulphide completely. TABLE I11 FRACTION OF MERCURY RECOVERED BY DIFFERENT DIGESTION METHODS Each value is the mean of four replicates and all precision values are within 1 5 % . Digestion bomb: 2 h at 110 O C Open system: 2 h a t 60 O C Cold digestion Form of mercury ,-- A , method, added H F + aqua regia Aqua regia Mixture ( I ) Mixture (11) Mixture (111) Mixture (IV) mixture (V) HgCI, (10 pg) .. 0.99 1.02 1.00 0.99 0.97 1 .oo 1.00 IzgqI,'(I ph') . . . . 0.99 1.01 1.00 0.98 1.00 1.01 0.99 Hgb (3-6 :rig + dust*) 0.!37 0.96 0.96 0.96 0.95 0.95 0.93 HgO (3-6 mg + dust*) 0.98 0.96 0.95 0.96 0.98 l.iJ0 0.95 * Dust sample DS-38.December, 1979 SMELTER FLUE DUSTS BY ACID DIGESTION METHODS 1163 Choice of Digestion Method Of the seven digestion methods, the open system with mixtures (I), (11) and (IV), and the closed system with aqua regia, are equally effective. There are several disadvantages in the use of a digestion bomb, including limitation of the amount of sample and acid and the time consumed in the procedures of cooling, sealing and unsealing.The adoption of the open-digestion procedures for routine analysis is therefore preferred. Comparing the three open-system digestion methods [(I), (11) and (IV)], method (11) appeared to be the most effective because the least residue remained after digestion. Results obtained using methods (I) and (IV) did not indicate any advantage in having sulphuric acid in the digestion mixture. Therefore, method (11), the open-system method using aqua regia, was the preferred method for extraction of mercury from the flue-dust samples. Oxidation State of the Mercury I t is necessary to oxidise unstable lower oxidation states of mercury to mercury(I1) in order to stabilise the mercury in the final solution. To check the completeness of oxidation of dust samples, 5ml of 5% potassium persulphate solution21p22 were added to samples DS-4, -7, -10, -27, -40, -43 and -45, previously digested using mixture (11) and left overnight at room temperature.There was no indication of any increased recovery of mercury as a result of the use of potassium persulphate as an oxidising agent. This suggested that oxidation of mercury in the digestion procedure was essentially complete. Reliability The precision was calculated for the preferred method, the open-system digestion pro- cedure using mixture (11), on four dust samples. The relative standard deviations for samples with mercury concentrations of 150, 104, 1.1 and 0.3 pg g-l are 4, 3, 11 and 19%, respec- tively (Table IV). The minimum determinable amount of mercury (defined as the smallest TABLE IV PRECISION VALUES WITH MIXTURE (11) 7 DS-20 0.40 0.29 0.16 0.26 0.36 0.22 0.32 0.29 0.37 0.30 0.34 0.32 0.29 0.36 Mercury contentlpg g-I A DS-27 DS-40 1.30 101 1.16 106 1.22 103 0.94 106 1.06 103 0.94 104 1.08 110 1.10 107 1.02 113 0.90 110 0.96 102 0.98 102 1.16 103 1.10 104 7 DS-43 151 149 152 158 140 154 140 158 152 154 150 144 148 154 Mean .. . . . . 0.31 1.07 105 150 Standard deviation . . 0.06 0.12 3.6 5.7 Relative standard deviation 19% 11% 3% 4% amount for which a precision figure has been determined) is 0.3 pg g-l with a standard deviation of 19%. An inaccuracy as great as 5% may arise from incomplete recovery. References 1. 2 . 3. “National Inventory of Sources and Emissions of Mercury (1970),” Report APCD, 73-6, Environment Iskandar, I.K., Syers, J . K., Jacobs, L. W., Keeney, D. R., and Gilmour, J . T., Analyst, 1972, 97, Agciniaxi, H., and Chau, A. S. Y., Analyst, 1976, 101, 91. Canada, Ottawa, 1973. 388.1164 CHIU AND HILBORN 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 16. 16. 17. 18. 19. 20. 21. 22. Jacobs, L. W., and Keeney, D. R., Envir. Sci. Technol., 1974, 8, 267. Bishop, J . N., Taylor, L. A., and Neary, B. P., “The Determination of Mercury in Environmental Samples,” Ministry of the Environment, Ottawa, Canada, 1973. “Method for Chemical Analysis of Water and Wastes,” US Environmental Protection Agency Report EPA-625-/6-76-003a, 1976, pp. 134-138. Jonasson, I. R., Lynch, J. J., and Trip, L. J., Geol. Surv. Can., Report No. 73-21, Energy, Mines and Resources, Ottawa, 1973. Fedlman, C., Analyt. Chem.. 1974, 46, 1606. Pillay, K. K. S., Thomas, C. C., Sondel, J. A., and Hyche, C. M., Analyt. Chem., 1971, 43, 1419. Donaldson, E. M., “Method for the Analysis of Ores, Rocks and Related Materials,” Mines Branch Rains, T. C., and Menis, 0. J., J . Ass. Off. Analyt. Chem., 1972, 55, 1339. Stuart, D. C., Analytica Chim. Acta, 1978, 96, 83. Sulcek, A., and Povondra, P., CRC Crit. Rev. Analyt. Chem., 1977, 6, 256. Omang, S. H., and Paus, P. E., Analytica Chim. 14cta, 1971, 56, 393. Buckley, D. E., and Cranston, R. E., Chem. Geol., 1971, 7, 273. Agemian, H., Aspila, K. I., and Chau, A. S. Y . , Analyst, 1975, 100, 253. Friberg, L., and Vostal, J., “Mercury in the Environment,” CRC Press, Cleveland, Ohio, 1972. Giauque, R. D., Goulding, F. S., Jaklevic, J . M., and Pehl, R. H., Analyt. Chem., 1973, 45, 671. Bernas, B., Analyt. Chem., 1968, 40, 1683. Hatch, W. R., and Ott, W. L., Analyt. Chem., 1968, 40, 2085. El-Awady, A. A., Miller, R. B., and Carter, M. J., Analyt. Chem., 1976, 48, 110. Melton, J. R., Hoover, W. L., and Howard, P. A., Soil Sci. SOC. Am. PYOC., 1971, 35, 850. Monograph 881, Energy, Mines and Resources, Ottawa, 1974. Received February 2 lst, 1979 Accepted May 18th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401159

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, December, 1979, Vol. 104, p p . 1165-1170 1165 High-performance Liquid Chromatographic Determination of Acrylic Acid Monomer in Natural and Polluted Aqueous Environments and Polyacrylates L. Brown School of Environmental Sciences, Plymouth Polytechzic, Drake Circus, Plymouth, Devon, PL4 8A A A procedure is described for the determination of acrylic acid monomer in natural and polluted waters and polyacrylates. Polyacrylates are extracted using a mixture of methanol and water prior to analysis, but no preparation is required for water samples. Separation from interferences is achieved by high-performance liquid chromatography and quantification by ultraviolet detection. A detection limit of 0.05 mgl-1 and a precision of 8% at 1.17 and 10 mg 1-1 of acrylic acid have been achieved using water samples.Samples tested included river, sea and estuarine waters, sewage and china clay works effluents and potable waters. Acrylic acid can be detected at levels in excess of 0.0005~0 of monomer in the polymer with a precision of 8% a t levels of 0.05% and 0 . 0 0 3 ~ 0 of monomer. Keywords : A crylic acid determination ; aqueous solutions ; polyacrylates ; high-performance liquid chroinatography ; environmental pollution Polyacrylates are used extensively as dispersants for emulsion paints and as boiler-scale inhibitors, and copolymers of acrylic acid and acrylamide are used to aid water clarification at water treatment works1s2 and for the treatment of coal tailings.2 The manufacture of such polyelectrolytes could leave a small residue of unpolymerised acrylic acid monomer.1s2 Certain marine phytoplankton (Phaeocystis sp.) secrete acrylic acid, killing many less resistant phytoplankton in their v i ~ i n i t y .~ , ~ Euphausia sp. feeding on Phaeocystis sp. concentrate acrylic acid, which may cause changes in the bacterial activity in the gut of certain penguin^.^^^ A sensitive method for the determination of acrylic acid is required for aquatic environ- ments and polymers. Acrylic acid may be separated by gas -liquid chromatography and detected by flame ionisation using direct water injections on to a Chromosorb 101 column, but the method may suffer from interferences1 This paper reports a routine method of analysis using high-performance liquid chromatography (HPLC) . Experimental Apparatus A Perkin-Elmer Series 2 liquid chromatograph, fitted with a Whatman PXS 10/25pm PAC column (250 x 4 mm i.d.), a variable-wavelength Perkin-Elmer LC55 spectrophoto- meter and a Perkin-Elmer 023 recorder were used.A Rheodyne, Model 7105, injection valve with a 175-pl sample loop was employed to inject the sample on to the analytical column. A Scientific Glass Engineering syringe (100 p1) was used to inject the sample. A Sonicor ultrasonic bath was employed to deaerate the solvents used as the eluents. Samples were agitated during the extraction procedures with a Labline Junior Orbit shaker. Perkin- Elmer and Spherisorb silica columns, Spherisorb octadecylsilane (ODS) and nitrile (CN) columns and a Whatman strong anion-exchange column (SAX) were also examined for the analysis of acrylic acid but were found to be unsatisfactory.Reagents All standards and solvents were of AnalaR or Nanograde quality unless otherwise stated. Solvents. Concentrated orthophosphoric acid, sp. gr. 1.75. Eluent, 0.01 yo VlV orthophosplzoric acid in distilled water. AcryZic acid, 99% pure. Isopropanol, hexane and methanol (Fisons HPLC grade). Aldrich Chemical Co. Ltd. ,4 solution of acrylic acid was prepared by weighing to constant mass a 25-ml calibrated flask containing approximately1166 BROWN: HPLC DETERMINATION OF ACRYLIC ACID MONOMER IN Analyst, VoZ. 104 20 ml of distilled water, adding two drops of acrylic acid and weighing to constant mass followed by filling to the mark. Appropriate dilutions were made in order to achieve suitable concentrations.Interferents tested were formic, acetic and propionic acids, acrylonitrile and acrylamide. Heated at 600 "C. for 24 h, dried and stored in a grease-free desiccator. For analysis using a Whatman SAX (strong anion exchange) column, de-ionised water, doubly distilled in glass under a nitrogen atmosphere and stored in glass under nitrogen, was used. Interferents. Anhydrous sodium suZPhate. Distilled water. For general use, singly distillled water was used. Glassware dried at 110 "C. All glassware was soaked in a chromic acid bath, washed with distilled water and oven Determination of Acrylic Acid Monomer in ,Qqueous Solutions Samples were collected in glass-stoppered bottles (250 ml) and stored in a refrigerator. Boiling prior to storage to prevent bacteriological degradation was carried out if the time that elapsed between collection and analysis was longer than 16 h.Boiling caused no signific- ant loss of acrylic acid but prolonged storage under non-sterile conditions led to the loss of acrylic acid from solution (Table I). Each sample was filtered through Whatman GF/F filters. An aliquot (12 p1) of the sample was injected into the liquid chromatograph's Rheodyne valve and chromatographed under the following conditions : column, Whatman PXS 10125 pm PAC (250 x 4 mm i.d.) ; mobile phase, 0.01% V/V orthophosphoric acid in distilled water; flow-rate, 4 ml min-l; pressure, I3000 lb in-2; detector wavelength, 195 nm; chart speed, 0.5 cm min-l; and absorbance scale, 0.02. According to the sensitivity required, duplicate aliquots of the sample (1-100 pl) were injected.For maximum sensitivity the absorbance scale was set to 0.01. Peak heights of less than three times the base-line noise were not considered detectable. TABLE I EFFECT OF BOILING ON THE CONCENTRATION OF ACRYLIC ACID I N SPIKED AQUEOLS SOLUTIONS Boiling for 3 min and rapid cooling had no significant effect on the acrylic acid concentration, but it did limit the possibility of biodegradation. Acrylic acid concentration/ mg 1-' Acrylic acid concentration in boiled sample/mg 1-' Spiked acrylic acid I------*---- 7 7-A- 7 Sample concentration/mg 1-' After 12 h After 400 h After 12 h After 400 h River water . . Sea water . . Distilled water . . 5.0 4.9 > 0.05 5.0 4.7 . . 5.0 5.0 - 5.1 - . . 5.0 4.9 - 4.9 - Determination of Acrylic Acid Monomer in Polyacrylates and Acrylic Acid Co - p ol y rners A known mass of polymer (500 mg) was added to a methanol - distilled water mixture (1 + 1, 50 ml) and allowed to stand overnight to complete the extraction of the monomer from the polymer.Various mixtures of methanol and distilled water (range 1 + 99 to 99 + 1, 50 ml) were added to the polymer for 1, 2, 8 and 24 h. The above procedure was found to be most satisfactory. The extract was injected into the liquid chromatograph's Rheodyne valve and chromatographed as above (Figs 1 and 2; Table 11). Preparation of Calibration Graphs Standard solutions of acrylic acid (0, 0.05, 0.117, 0.5, 1.17, 3.5, 4.0, 5.0, 7.0, 8.0, 10.0, 11.7 and 14.0 mg 1-I) were treated in the same manner as the samples described previously.The slope of the calibration graph of absorbance (peak height) versus concentration did not change by what was considered an appreciable amount for an eluent flow-rate of 4 ml min-I over the period studied (Fig. 1).December, 1979 NATURAL AND POLLUTED AQUEOUS ENVIRONMENTS AND POLYACRYLATES 1167 200 190 180 170 .- TJ 160 x 150 I=" 140 $ 130 ," 120 : 110 c" 100 ; 90 2 80 n ((I 70 60 ; 50 - 40 30 20 10 0 - 1 1 1 I I 1 1 1 I I 0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Concentration of acrylic acid/mg I-' Fig. 1. Stabilitv of the HPLC acrvlic moo 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 acid calibvation graph. _I Chromatographic c&ditions : column, Whatman PXS 10/25 p m PAC (250 x 4 mm i.d.) ; eluent, 0.01% V / V orthophosphoric acid in distilled water; flow-rate, 4 ml min-'; chart speed, 0.5 cm min-'; wavelength, 195 nm; absorbance scale, 0.01 a.u.f.s.= 100 units; response, 1.0 s. Absorbance was calculated for a 100-pl injection. A, Concentration range 0- 15 mg 1-'; and 0, concentration range 0-1.5 mg 1-'. The samples were: 0, 0.05, 0.5, 5.0 and 10.0 mg 1-I unspiked and spil-ed river water (20.3.79); 0, 0.117 and 11.7 mg 1-1 unspiked and spiked sea water (20.3.79); 0 and 1.17 mg 1-' unspiked and spiked estuary water (20.3.79); 0 and 4.0 mg 1-1 unspiked and spiked sewage effluent (22.3.79); 0 and 8.0mg1-1 unspiked and spiked china clay effluent (22.3.79); 0, 3.5, 7.0 and 14.0 mg 1-1 unspiked and spiked potable water (23.3.79). Various other environmental samples and industrial effluents were spiked with 1.17 and 10 mg1-I of acrylic acid.The ranges of values are shown in the figure. Calculations 100-pl injection on an absorbance scale of 0.01 a.u.f.s., i.e., mean absorbance of concentrate volume of concentrate injected The concentration of acrylic acid in a sample was calculated from the absorbance of a absorbance scale 0.01 Total absorbance = - x 100 x The concentration of acrylic acid was found by comparison with a previously prepared calibration graph of total absorbance uersus original acrylic acid concentration (Fig. 1). Interferences acrylic acid was not detected did not interfere. sea water, river water, sewage and china clay effluents and potable waters. The levels of inorganic and organic UV-absorbing molecules present in samples in which The samples tested included estuarine and Formic, acetic1168 BROWN : HPLC DETERMINATION OF ACRYLIC ACID MONOMER IN Analyst, VoZ.104 and propionic acids, acrylonitrile and acrylamide at concentrations of less than 100 mg 1-1 did not interfere. Acrylic acid could be detected in standard solutions of distilled water or methanol (Fig. 2). No significant loss of acrylic acid was noted between a sample stored overnight and another aliquot of the same sample heated to boiling, rapidly cooled and stored overnight (Table I). 90 ~ 85 80 75 70 65 60 55 50 al fl 4 8 45 40 35 30 25 20 15 10 5 C 0 .- - 25 8 " Methanol Acrylic acid I Act- ac I nj J I Inorganic ions Acrylic acid Inj. Jnknowr I nj 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Timeimin Fig.2. Resolution of acrylic acid from interferences using a Whatman PXS 10/25 pm PAC column and eluting with 0.01 yo V / I/ orthophosphoric acid in distilled water. Chromatographic conditions : column, Whatman PXS 10/25 pm PAC (250 x 4 mni i.d.); eluent, 0.017; V / V orthophosphoric acid in distilled water; flow-rate, 4 ml min-'; chart speed, 0.5 cm min-l; wavelength, 195 nm; absorbance scale, 100 units = full-scale deflection; and response, I s. A, 50-p1 injection of acrylic acid spiked distilled water (1.07 mg l-l), absorbance scale 0.02 a.u.f.s.; B, 100-p1 injection of acrylic acid spiked river water (0.05 mg l-l), absorbance scale 0.01 a.u.f.s.; C, 23-p1 injection of acrylic acid spiked river water (5.0 mg 1-l) t o which formic, acetic and propionic acids, acrylonitrile and acrylamide (at concentrations of 100 mg 1-l) have also been spiked, absorbance scale 0.02 a.u.f.s.; D, 8-pl injection of the extract of the polymer Crosfloc CFA 70, absorbance scale 0.02 a.u.f.s.; and E, 100-p1 injection of the extract of the polymer Magnafloc 155, absorbance scale 0.01 s.u.f.s.No peak with the retention time of acrylic acid was found in unspiked samples. Results and Discussion Selection of Liquid Chromatographic Colunin and Wavelength Perkin-Elmer and Spherisorb silica columns and Spherisorb octadecylsilane (ODs) and nitrile (CN) columns were unable to resolve acrylic acid from interferents. The Whatman SAX column was able to resolve acrylic acid in the absence of formic, acetic and propionicDecember, 1979 NATURAL AND POLLUTED AQUEOUS ENVIRONMENTS AND POLYACRYLATES 1169 TABLE I1 DETERMINATION OF ACRYLIC ACID MONOMER IN COMMERCIAL POLYMERS A known mass of polymer (500 mg) was added t o a mixture of methanol and distilled water (1 + 1, 50 ml) and allowed to stand overnight to complete the extraction of the monomer.An aliquot was injected into the rheodyne valve and chromatographed. Fig. 1 shows the calculation of the con- centration of acrylic acid in the extract media. Fig. 2 shows the trace for two extracts. Sample Magnafloc 155* . . . . .. Magnafloc 156* . . . . . . Crosfloc CFN l o t . . . . . . Crosfloc CFN 20t. . . . . . Crosfloc CFA 4 0 t . . . . . . Crosfloc CFA 7 0 7 . . . . . . Polyacrylate CPA5Nt . . . . Acrylic acid concentration/ mg 1-' (Fig.1) 0.05 5.2 0.10 0.35 1.7 7.5 0.32 R/lass/mg per 500 mg of polymer (50 ml of methanol - water) 0.002 5 0.26 0.0050 0.0175 0.085 0.375 0.0160 Concentration of acrylic acid monomer in the 0.000 5 0.05 0.001 0.003 0.017 0.075 0.003 polymer, % * Manufacturer: Allied Colloids Ltd., Bradford, Yorkshire. t Manufacturer : Crosfield Polyelectrolytes, Joseph Crosfield and Sons Ltd., Warrington, Lancashire. acids. The elution of acrylic acid from this column was dependent on ionic strength; 0.000 25 M sodium sulphate in deaerated, doubly distilled water adequately resolved acrylic acid from most interferents. This method was susceptible to carbon dioxide changing the pH of the unbuffered distilled water and hence the retention time. The determination of acrylic acid in the presence of formic, acetic or propionic acids was not possible as these acids cause changes in the retention time.No buffering system (pH 3.0-7.0) at the low ionic strength necessary to prevent elution after the void space could solve this interference. Distilled water, distilled water - isopropanol mixtures, isopropanol, isopropanol - hexane mixtures and hexane were unable to elute acrylic acid from the Whatman PXS 10/25 pm PAC column, presumably as it became strongly bonded to the amino groups. Elution using 0.5% V/V orthophosphoric acid in distilled water caused acrylic acid to be eluted after the void space, as the orthophosphoric acid blocked the adsorption sites. Dilution of the orthophosphoric acid to O.Olyo V/V allowed the resolution of acrylic acid from all of the interferents tested.The wavelength of 195 nm was chosen for maximum sensitivity, although Table I11 shows that acrylic acid can be determined with detectors which scan to 206 or 210nm. These wavelengths will cause a 47% and 74% loss of sensitivity, respec- tively. TABLE I11 EFFECT OF DETECTION WAVELENGTH ON THE SENSITIVITY OF THE METHOD Many detectors do not possess the ability to scan a t 195 nm. I t can be seen that the analysis could be achieved a t 206 nm although the sensiti\-ity would be approximately halved. Loss of sensitivity relative to that a t 195 nm, yo Detection wavelength/nm 195 0 198 7 202 27 204 38 206 47 210 74 Analysis of Water Samples and Polymers for Acrylic Acid Monomer Spiked natural and polluted environmental samples were analysed with an accuracy of 8% for concentrations of 1.17 and 10.0 mg 1-1 of acrylic acid monomer (Fig.1). No method was available to check the accuracy of the results for polymers of low monomer content. The results were, however, in agreement with the concentrations expected from the manu- facturing procedure.lJ The analysis of samples in triplicate (Magnafloc 156 and Crosfloc CFN 20, Table 11) gave results with a precision of 8%.1170 BROWN Conclusion The proposed technique was found to be capable of detecting acrylic acid in aqueous solutions at concentrations in excess of 0.05 mg 1-1 and in polymers at levels in excess of 0.0005% of monomer. The assay was found to have several significant advantages over gas - liquid chromatography with flame-ionisation detection, including speed of determina- tion, extended linearity and stability of the calibration graph and the absence of significant interferences. If lower levels of detection in aqueous media are required, it is suggested that concentration can be achieved by passing suitable volumes (over 11) through pellicular Whatman PAC columns (dry packed) and eluting with a small volume of 0.5% V/V orthophosphoric acid in distilled water. Research is continuing into the chemical and biological degradation of acrylamide and acrylic acid and their adsorption on to sediment:;. The author thanks Dr. M. M. Rhead and Dr. K. C. C. Bancroft of Plymouth Polytechnic, the South West Water Authority, Mr. R. Lisle of Allied Colloids, Dr. P. Sykes of Crosfield Polyelectrolytes and Mrs. C. Stone of Whatman Laboratory Sales. The work in this paper was carried out under contract from the Departiment of the Environment and publication is with their permission. References 1. 2. 3. 4. 5 . Lisle, R., Allied Colloids, Bradford, personal communication, 1979. Sykes, P., Crosfield Polyelectrolytes, Warrington, personal communication, 1979. Sieburth, J. McN., Science, N.Y., 1960, 132, 676. Guillard, R. K. L., and Hellebust, J . A., J. Phycol., 1971, 7, 330. Sieburth, J . McN., J. Bact., 1961, 82, 72. Received April lBth, 1979 Accepted July 16th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401165

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, December, 1979, Vol. 104, p p . 1171-1175 1171 Determination of Ochratoxin A in Pig's Kidney Using Enzymic Digestion, Dialysis and High-performance Liquid Chromatography with Post-column Derivatisation D. C. Hunt, Lesley A. Philp and N. T. Crosby Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, SE1 9NQ A method for the determination of ochratoxin A in pig's kidneys is described. The detection limit is less than 1 pg kg-l. By using enzymic digestion con- currently with dialysis and by controlling the pH conditions, the sample is extracted and interfering co-extracts removed without the use of column chromatography. The final determination employs reversed-phase high- performance liquid chromatography with either a phthalimidopropylsilane or a C,, (docosyl) bonded column, and the sensitivity of the fluorescence detector is increased ten-fold by the formation of a post-column derivative with ammonia solution.Keywords : Ochratoxin A ; high-fierformance liquid chromatography ; enzymes ; dialysis Ochratoxins are highly toxic mould metabolites produced by several species of fungi of the Aspergillus ochraceus group and also by Penicillium viridicatum. Ochratoxin A is claimed by Chul to be the most toxic of the ochratoxins. It has been found as a natural contaminant in corn, wheat, oats, barley, peanuts and mixed grain feed.2-5 It is a potent nephrotoxin, and tissues of farm animals may contain residues of ochratoxin A at slaughter. In a survey carried out in Denmark, ochratoxin A was found in the kidneys of pigs whose carcasses had passed meat inspection; levels as high as 68 pg kg-l were encountered.6 A number of methods for determining ochratoxin A in cereals by thin-layer chromato- graphy have been publi~hed.~-l~ Ochratoxin A has also been determined in tissue using a thin-layer chromatographic method,13 and by high-performance liquid chromatography following a preparative thin-layer chromatographic clean-up.14 There is a need for a method of determining this mycotoxin in tissues that is economical in labour and both sensitive and quantitative. Enzymic digestion and dialysis combined with high-performance liquid chromatography and post-column derivatisation should meet these requirements. Development of the Method Extraction was carried out in the presence of an enzyme in order to ensure the release of any ochratoxin A present in the matrix. Osselton and c o - ~ o r k e r s l ~ ~ ~ ~ have shown that both acidic and basic drugs, which can accumulate in target areas such as the liver, may be bound to protein but they can be released by enzymic digestion.Boley et al.17 have used enzymes in order to release food dyes from various foodstuffs. The extracting medium was an alkaline water - methanol mixture maintained at 50 "C in order to keep any fat in the liquid state, and to ensure the partitioning of ochratoxin A from the fat into the aqueous solvent. The dialysis clean-up stage has been used previously for ochratoxin A as part of a general screening method for a number of different mycotoxins in animal feeding stuff,ls but using a different solvent and with recoveries of only 50% at the milligram per kilogram level.Following the digestion and dialysis stage, the ochratoxin A was partitioned from the diffusate into dichloromethane by adjusting the pH with formic acid. A technique for the determination of the mycotoxin using high-performance liquid chromatography on a reversed- phase column was developed that uses an acidic water - acetonitrile mobile phase. The spectral behaviour of ochratoxin A in different solvents has been reported,lg and the detection of this mycotoxin has been improved on thin-layer chromatographic plates by exposure to Crown Copyright.1172 HUNT et al. : DETERMINATION OF OCHRATOXIN A IN PIG'S Analyst, Vol. 104 ammonia fumes.20 Using the same principle, a post-column system was developed, in which the eluate was reacted with ammonia solution before it passed into a fluorescence detector.Experimental Reagents All reagents were of analytical-reagent grade. Methanol. Dichloromethane. Formic acid. Ammonia solution, sp. gr. 0.880. Sodium sulphate, anhydrous, granular. Enzyme. obtained from Fisons Ltd., Loughborough. Subtilisin A, obtained from Novo Enzymes Products Ltd., Windsor, or papain Apparatus Dialysis. Homogeniser. Ilado homogeniser, X l0/20. High-performance liquid chrovnatogra9h. Visking tubing 24/32, obtained from Scientific Instrument Centre, London. Column, stainless steel, 20 cm x 4.6 mm i.d., maintained at 40 "C; packing, either phthalimidopropylsilane on Partisil 5, as prepared by Hunt et aLJ2l or C,, Supergrade on Partisil 5 from Magnus Scientific, Sandbach, Cheshire; injector, Rlieodyne 7120 with a 20-4 loop; pumps, Waters Associates, 1 4 6000; mobile phase, acetonitrile - water - acetic acid (57 + 41 + 2) at 1.3 ml min-l; post-column, 107; V/V ammonia solution (sp.gr. 0.880) in water at 0.7 rnl min-l; post-column connection, Cheminert T-piece with 1.5-mm PTFE microbore tubing; detector, Aminco Fluorohlonitor with Corning 7-60 excitation filter and Wratten 98 fluorescence filter. Method The dialysis tubing was prepared by soaking a 75 cm length in warm running tap water for 1 h, then rinsing in de-ionised water. A 600-ml aliquot of the extracting solvent was prepared by mixing 300 ml of methanol with 300 in1 of water and adjusting the pH to between 9 and 10 by the addition of a few drops of ammonia solution.A 10-g finely chopped representative sample of pig's kidney was weighed into a 250-ml tall-form glass beaker; 80 ml of the extracting solvent and 55 mg of the enzyme were added, and the contents homogenised for 1 min. A knot was tied in one end of the dialysis tube then, using a funnel, the homogenised mixture was poured into the tube. The beaker, homogeniser and funnel were rinsed with 50 ml of extracting solvent, which was then added to the contents of the tube. The top of the tube was squeezed to expel air and then knotted. After blotting with a tissue to remove the excess of water, the dialysis tube was inverted several times to mix the contents, then coiled into a large 2-lb Kilner jar containing 470 ml of the extracting solvent, and the jar was sealed and placed in an oven at 50 "C overnight.The next morning, after cooling to room temperature, the tubing was removed. The diffusate was thoroughly mixed and the pH was checked to ensure that it was still alkaline. A 300-ml aliquot of the diffusate was transferred into a 500-ml separating funnel and 45 ml of 5% m/V sodium sulphate solution were added; 100 ml of dLcliloromethane were added to the separating funnel, which was then shaken. The lower, dichloromethane layer was transferred into a 250-ml separating funnel and shaken with 40 ml of 5% ?n/V sodium sulphate solution and one drop of ammonia solution. The cliffusate in the 500-ml separating funnel was washed a second time with 100 ml of dichloromethane, and this in turn was added to the 250-ml separating funnel containing the alkaline sodium sulphate solution, and shaken.The dichlorometliane layer was discarded and the alkaline sodium sulphate solution was transferred into the 500-ml separating funnel containing the diffusate. The diffusate was made acidic by the addition of 2 ml of formic acid and the mycotoxin was then extracted by shaking with two 100-ml portions of dichloromethane. The dichloro- me thane extracts were dried by passing through f!O g of anhydrous sodium sulphate contained on a filter-paper in a funnel. The extract was concentrated to 1 ml using a rotary evaporator on a water-bath at 60 O C , taking care not to let the extract dry completely. The residue was The lower dichloromethane layer was discarded.December, 1979 KIDNEY USING ENZYMIC DIGESTION, DIALYSIS AND HPLC 1173 transferred quantitatively into a small glass vial with dichloromethane.The extract was evaporated just to dryness with a stream of nitrogen and re-dissolved in 200 p1 of acetonitrile using slight warming to aid the process. The resulting solution was ready for injection on to the high-performance liquid chromatography system. High-performance liquid chromatography Aliquots of the final extracts and the mycotoxin standards were injected separately on to the column using a 2 0 - 4 loop. The temperature of the column was maintained at 40 "C and the acidic mobile phase, after passing through the column, was met by a stream of 10% ammonia solution before passing into the fluorescence detector.The system that was used is shown diagrammatically in Fig. 1. Loop injector Water-jacket at 40 "C Cheminer T-piece 't + Waste Fig. 1. Diagram of the high-performance liquid chromatography system. Results and Discussion As the final volume of 200p1 is equivalent to 5 g of the original sample, the sensitivity for a 20-4 injection is 0.5pgkg-l. The reproducibility of the system for 5 ng of ochratoxin A was satisfactory, with a coefficient of variation of 1.9% for ten injections. The recovery of ochratoxin A from pig's kidney spiked at the 5 and 20 pg kg-l levels is shown in Table I. The recovery experiments were carried out over a 3-week period and The system, as described, can detect 0.25ng of ochratoxin A. The method gave a linear response from 1 to 20 ng of ochratoxin A.TABLE I RECOVERY OF OCHRATOXIN A FROM SPIKED PIG'S KIDNEY Spiking level/ Standard Coefficient of Pg kg-l Kccovcry, v/o Mcan, yo dcviation, 94, variation, :h 5 76, 88, 74, 74, 78 78.0 5.8 7.5 20 85, 75, 77, 74, 7 3 76.8 4.8 6.31174 HUNT et al. : DETERMINATION 'OF OCHRATOXIN A IN PIG'S Analyst, VoZ. 104 resulted in mean figures of 78.0 and 76.8% fo'r the 5 and 20 pg kg-l levels, respectively. The use of enzymes did not significantly increase the recovery of ochratoxin A from spiked samples when compared with recoveries without enzymes, but results were doubled for some naturally contaminated samples, containing 0.5 pg kg-l of ochratoxin A, when the enzyme was used. Simple spiking may not truly reproduce the natural state of association of ochratoxin A in kidneys in vivo.Both phthalimidopropylsilane and C,, Supergrade on Partisil 5 gave good separations of ochratoxin A from other co-extracts but a C,, stationary phase on Partisil 5 gave less satisfactory results. Under acidic conditions, however, ochratoxin fluoresces a pale green - blue, but under alkaline conditions the fluorescence is a bright blue. Advantage has been taken of this behaviour by introducing 10% ammonia solution into the column eluate by means of a second pump and a T-junction before the fluorescence detector. The pH shift produces a ten-fold increase in sensitivity and is very rapid, so that the PTFE reaction tube can be as short as 10 cm, resulting in very little peak broadening. These features are reflected in the sensitivity of the system, which enables 0.25 ng of ochratoxin A to be detected, and in the efficiency of the column, where 20 p1 of ochratoxin A with a k' value of 3.1 gives an HETP of 0.027 mm.By repeating the injection without the post-column pump acting, the disappearance or diminution of the ochratoxin A peak can be used as confirmation of identity. Fig. 2 shows a chromatogram obtained for a naturally contaminated kidney and the effect upon both the sample and the standard of turning off the post-column pump. It may be possible to replace The mobile phase must be acidic in order to elute the mycotoxin as a sharp peak. + E + Standard w V X w E w I, itandard +Post column working++ Post column stopped -+ LIIIIIIIII -- 0 2 4 6 0 2 4 6 8 1 0 0 2 6 8 1 0 0 2 4 6 Tirne/min Fig.2 . High-performance liquid chromatogram of 20-pl injections of an ochratoxin A standard (2.5 ng) and a naturally contaminated kidney extract on a C,, column, showing the post column working and the post column stopped. Other conditions are as stated in the text. the present post-column pump with one of simpler design, as the ammonia solution meets the mobile phase at the low pressure end of the column. We thank the Government Chemist for permission to publish this paper.December, 1979 KIDNEY USING ENZYMIC DIGESTION, DIALYSIS AND HPLC References 1175 1 . 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. Chu, F. S., Crit. Rev. Toxicol., 1974, 2, 499. Scott, P. M., van Walbeek, W., Harwig, J , , and Fennel, D. I., Can. J . Plant Sci., 1970, 50, 583. Shotwell, 0 .L., Hesseltine, C. W., Goulden, M. L., and Vandegraft, E. E., Cereal Chem., 1970, 47, Shotwell, 0. L., Hesseltine, C. W., Vandegraft, E. E., and Goulden, M. L., Cereal Sci. Today, 1971, Scott, P. M., van Walbeek, W., Kennedy, B., and Anyeti, D., J . Agric. Fd Chem., 1972, 20, 1103. Krogh, P., Nord. VetMed., 1977, 29, 402. Stoloff, L., Nesheim, S., Yin, L., Rodricks, J. V., Stack, M., and Campbell, A. D., J . Ass. Off. A~zalyt. Eppley, R. M., J . Ass. Off. Analyt. Chem., 1968, 51, 74. Nesheim, S., Hardin, N. F., Francis, 0. J., Jr., and Langham, W. S., J . Ass. Off. Analyt. Chew&., Egon Josefsson, B. G., and Moller, T. E., J . Ass. Off. Analyt. Chem., 1977, 60, 1369. Wilson, D. M., Tabor, W. H., and Trucksess, M. W., J . Ass. Off. Analyt. Chem., 1976, 59, 125. Balzer, I., Bogdanic, C., and Pepeljnjak, S., J . Ass. Off. Analyt. Chem., 1978, 61, 584. Krogh, P., Axelsen, N. H., Elling, E., Gyrd-Hansen, N., Hald, B., Hyldgaard-Hensen, J., Larsen, A. E., Madsen, A., Mortensen, H. P., Mraller, T., Petersen, 0. K., Ravnskov, U., Rostgaard, M., and Aalund, O., Acta Path. Microbiol. Scand., Sect. A , Suppl. No. 246, 1974. 700. 16, 266. Chem., 1971, 54, 91. 1973, 56, 817. Hunt, D. C., Bourdon, A. T., Wild, P. J., and Crosby, N. T., J . Sci. Fd Agric., 1978, 29, 234. Osselton, M. D., J . Forens. Sci. SOG., 1977, 17, 189. Osselton, M. D., Shaw, I. C., and Stevens, H. M., Analyst, 1978, 103, 1160. Boley, N. P., Crosby, N. T., and Roper, P., Analyst, 1979, 104, 472. Roberts, B. A., and Patterson, D. S., J . Ass. Off. Analyt. Chem., 1975, 58, 1178. Golinski, P., and Chelkowski, J., J . Ass. Off. Analyt. Chem., 1978, 61, 586. Tenk, H. L., and Chu, F. S., J . Ass. Off. Analyt. Chem., 1971, 54, 1307. Hunt, D. C., Wild, P. J., and Crosby, N. T., J . Chromat., 1977, 130, 320. Received April 9th, 1979 Accepted July 2nd, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401171

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

1176 Analiyst, December, 1979, Vol. 104, pp. 1176-1180 Preparation and Stability of Dilute Insecticide Analytical Standards for Gas Chromatography* D. L. Suett, G. A. Wheatley and C. E. Padbury National Vegetable Research Station, Wellesbourne, Waraiick, C V35 9EF A convenient and economical procedure for preparing and storing accurately measured amounts ( 1 .OO mg) of insecticide analytical standards is described. The validity of the method was evaluated in a 2-year study of the storage stability of carbofuran, chlorfenvinphos, diazinon, dichlorvos (DDVP), stability of carbofuran, chlorfenvinphos, diazinon, dichlorvos, disulfoton and disulfoton sulphone. Solutions ( 1 nig ml-I) of each insecticide were prepared in hexane, toluene or acetone and aliquots sealed in glass ampoules were stored at -20, 1 and 20 "C.After 0.25, 0.5, 1.0 and 2.0 years the mean concentra- tions of all compounds, except dichlorvos, were within 0.90/, of fresh solutions of the original standards; dichlovos was 3.6% greater. Neither the type of solvent nor the storage temperature had significant ( P = 0.05) effects on the concentrations but there were large differences in purity between different batches of primary standards of all the organophosphorus insecticides. Keywords 1 Insecticide analytical standards ; inse,:ticide residues ; chromato- PPJZY The continually increasing number of pesticides and their residues that are likely to occur in agricultural and environmental samples present the residue analyst with the problem of maintaining an expanding range of reliable analytical reference standards.For pesticide- residue analysis, working standard solutions of low concentrations (1 ,ug ml-l) are commonly prepared by sequentially diluting a primary standard with volatile solvents suitable for subsequent gas - liquid chromatography1p2 but evaporation of the solvent can severely limit the useful life of the working standard solution. Several successive working standards can usually be prepared from a secondary solution of intermediate concentration but, for reliable analysis, the secondary solution must soon be replenished by directly weighing a fresh portion of the primary standard. As many pesticide primary standards are difficult to obtain and/or are available only in small (less than 100 mg) amounts the demands of good analytical practice cannot always be readily reccnciled.A convenient procedure has therefore been devised for preparing and storing dilute solutions of insecticide standards, which seems not only to fulfil the rigid requirements of quantitative residue analysis but also offers considerable economy of time and material. The method was used for several years with organochlorine insecticides and has more recently been adopted for other less stable compounds. Its validity has now been evaluated in a 2-year study of the storage stability of one carbamate and five organophosphorus insecticides. Experimental Nomenclature and Concentrations of Standard Solutions summarised in Table I. The nomenclature used to distinguish standard solutions of different concentrations is Procedure for Preparing Standards Use only grade A calibrated glassware and high-purity organic solvents refined specifically for pesticide-residue analysis.Alternatively, solvents can be purified by refluxing and/or double distillation3 and then stored over anhydrous calcium sulphate. Accurately weigh about 55 mg of the primary insecticide standard into a 50-ml calibrated flask. The amount required is determined by th'e purity of the standard and the certificated volume of the calibrated flask at 20 "C and should be sufficient to ensure a final solution * Presented (in part) at the IVth International Congrcss of Pesticide Chemistry (IUPAC), Zurich, 1978. While the standards are being prepared, maintain the laboratory at 20 & 0.5 "C.SUETT, WHEATLEY AND PADBURY TABLE I NOMENCLATURE OF STANDARD SOLUTIONS 1177 Standard Concentration Primary .. . . . . >90% pure Secondary . . . . 1 mg ml-1 Stock . . . . . . 20.0 pg ml-1 Working . . .. . . 0.1-1.0 pg ml-1 concentration of 1 .OO-1.10 mg ml-l. After diluting to volume with hexane, calculate the precise volume containing 1.00 mg of insecticide; ideally, this should be 0.95-0.98 ml. Transfer this volume into acetone-washed 2-ml glass ampoules (Baird and Tatlock Ltd.) using a securely mounted 1-ml graduated pipette operated with a 2-ml glass syringe. Carefully rinse the necks of the ampoules with hexane to give a final volume of about 1.5 ml, deftly heat-seal them with a needle flame from a town gas - oxygen glass-blowing torch and store them at -20 "C.The number of ampoules obtained from each 50-mg weighing is usually limited to 30 to minimise errors induced by progressive evaporation of the solvent. Subsequently, prepare stock standard solutions containing 20 pg ml-l as required, by diluting the contents of one ampoule to 50ml in a calibrated flask. Prepare appropriate concentrations of working standards, or mixtures of standards, by further diluting the stock standards. Changes in concentrations of the stock and working standard solutions due to solvent evaporation are minimised by using narrow-neck screw-capped amber-glass bottles, the rims of which have been ground smooth on an oil-stone. The wax-disc insert in the cap must be covered with aluminium foil. Solvent leakage through the seals is then less than occurs from ground glass stoppered flasks and the amber-glass bottles reduce possible photolytic degradation.Gas - Liquid Chromatography The organophosphorus insecticides were chromatographed in a Philips PV4000 Research Chromatograph equipped with a caesium bromide thermionic detector and a glass column containing 4% OV-101 on Chromosorb W-HP. Carbofuran was chromatographed in a Perkin-Elmer F-11 chromatograph fitted with a rubidium silicate thermionic detector and a glass column containing 6% OV-210 plus 4% OV-101 on Chromosorb W-HP.4 Isothermal column temperatures were adjusted to give retention times of 2-3 min and 2 - 4 aliquots were injected by a single operator. Analyses of variance were performed on peak-height data after converting sample peak heights into percentage of freshly prepared standard. Reproducibility of Preparations Using the above procedure, eight diazinon solutions of 20 pg ml-l were prepared from eight separate weighings and dilutions, by a single operator at intervals during a 7-h period and using eight separate sets of glassware.The eight solutions were each chromatographed four times in a random sequence. Stability of Dilute Solutions Organophosphorus insecticides were selected to encompass a wide range of polarities. Primary standards of carbofuran, disulfoton and disulfoton sulphone (Bayer UK Ltd.), chlorfenvinphos and dichlorvos (Shell Chemicals UK Ltd.) and diazinon (Fisons Ltd.) were obtained from the manufacturers. Using the above procedure, secondary standard solutions of the insecticides were prepared in hexane, toluene and acetone and 1.00-mg amounts were dispensed into ampoules that were then heat-sealed.Carbofuran was insufficiently soluble in hexane and solutions of this insecticide were prepared in toluene and acetone only. It was necessary to dissolve disulfoton sulphone in about 2 ml of acetone before diluting to volume with hexane. After 0.25, 0.5, 1.0 and 2.0 years, four replicate ampoules of each solution were diluted to 50.0 ml with hexane The sealed ampoules were stored in the dark at -20, 1 and 20 "C.1178 SUETT et al. : PREPARATION AIiD STABILITY OF DILUTE Analyst, Vol. 104 and analysed by gas - liquid chromatography, and compared with solutions that had been freshly prepared from the original respective primary standards.Each stored sample was injected twice in a fully randomised sequence within a systematic design of one injection of standard after every third sample. Variability of Primary Standards At the end of the 2-year storage study, fresh primary standards of all the insecticides, except diazinon, were obtained from the manufacturers and compared with the original primary standards that had been used throughout the experiment. For each insecticide, solutions of both standards were injected ten times in a random sequence. Results and Discussion Reproducibility of Preparations There was a small, significant (P = 0.05) downward trend in the concentrations of solutions prepared during a day but the over-all coefficient of variation was still only 1%. The experiment confirmed that the ampoule preparation procedure was very reproducible when performed carefully under the stated laboratory conditions.The results for eight replicate diazinon solutions are summarised in Table 11. TABLE 111 REPRODUCIBILITY OF PREPARATIONS Variance of eight replicate diazinon standard solutions (as a percentage of the grand mean). Replicate (in order of preparation Percentage of mean . . . . 100.7 100.2 100.5 100.7 99.5 100.2 99.3 98.9 during 7-h period) . . .. 1 2 31 4 5 6 7 8 Coefficient of variation = 1.1 % . Stability of Dilute Solutions fresh standard solution that was prepared on each sampling occasion. Results of the 2-year stability study (Table 111) were calculated as a percentage of the Each result is the TABLE I11 STORAGE STABILITY OF DILUTE INSECTICIDE SOLUTIONS Results expressed as a percentage of freshly prepared primary standards.Solvent f A -7 - 20 "C 1 "C 20 "C Storage ,-*--\ ,---------A-, ,--A-\ LSD Insecticide time/years Hexane Toluene Acetone Hexane Toluene Acetone Hexane Toluene Acetone (P = 0.05) Carbofuran . . . . . . 0.5 - 1 .0 - 2.0 - Chlorfenvinphos , . . . 0.25 100.4 0.5 99.6 1.0 104.0 2.0 100.2 Diazinon . . . . . . 0.25 i00.8 0.5 99.9 1 .0 88.4 2.0 99.x Dichlorvos . . . . . . 0.25 102.5 0.5 104.7 1.0 107.4 2.0 104.8 Disulfoton . . . . . . 0.25 100.3 0.5 99.6 1.0 103.6 2.0 100.1 Disulfoton sulphone . . . . 0.25 99.7 0.5 100.9 1.0 100.7 2.0 98.6 99.9 101.7 98.8 97.6 99.6 102.3 100.4 102.0 99.5 101.0 103.3 105.4 99.6 101.9 99.3 100.4 99.0 99.7 86.9 87.8 100.0 101.2 101.5 104.3 104.3 105.0 107.2 107.4 111.0 102.8 100.7 102.5 98.6 100.0 102.6 104.5 100.9 100.2 100.0 107.6 97.7 99.5 100.0 100.9 99.6 102.4 - 99.5 102.1 - 100.1 - 99.9 101.9 - 101.6 - 98.7 99.8 - 98.0 102.3 101.7 103.1 100.9 101.6 99.2 100.2 100.8 101.7 100.8 104.0 102.9 103.9 105.7 104.4 99.8 99.0 101.6 100.5 100.0 100.4 98.9 100.4 100.9 99.8 99.9 98.7 96.9 100.1 98.9 89.7 88.6 89.1 91.7 93.1 100.9 99.6 100.4 99.8 99.1 102.4 102.8 103.6 102.7 103.0 103.2 103.1 103.5 103.3 102.8 107.2 107.3 107.7 114.8 106.8 106.4 113.1 101.3 104.6 108.5 100.5 102.2} 3.52 100.4 :!\!} 1.96 101.9 94.5 102.8 100.3 98.3 105.2 87.0 J 701.5 100.9 101.9 101.6 101.2 102.1 99.1 99.6 99.2 100.1 98.7 100.0 103.1 102.9 103.4 102.7 102.4 99.3 100.6 100.7 100.9 100.8 100.4 100.8 99.7 99.2 105.0 100.0 100.2 99.7 99.9 101.6 100.3 98.3 99.4 97.5 101.0 99.4 99.4 98.7 100.3 101.8 97.0 98.9 106.03December, 1979 INSECTICIDE ANALYTICAL STANDARDS FOR GAS CHROMATOGRAPHY 1179 mean of eight analyses, i.e., duplicate injections of four replicate solutions.Least signifi- cant differences (LSDs) for comparing any two individual means were determined at the 95:4 confidence level; because of the structure of the statistical analysis, two LSD values were obtained for each insecticide but only the larger value is expressed in Table 111. The sampling date was the principal source of variation for all the organophosphorus compounds, except disulfoton sulphone. Most of this variation was caused by anomalies in the 1-year samples, subsequently traced to an intermittent fault in the analytical balance used on that occasion to weigh the fresh primary standards.When the 1-year values were omitted from the statistical analyses, the amended grand means for all insecticides, except dichlorvos, were between 100 and 101% (Table IV). Even with dichlorvos the grand mean was less than 105y0, although the increase in variation with increased storage time suggested that the change was mainly due to its inherent instability rather than to solvent or tempera- ture effects. The close agreement between the ampouled solutions and the freshly prepared standard solutions also confirmed that heat-sealing the ampoules did not lead to any detectable loss of insecticide. TABLE IV STORAGE STABILITY OF DILUTE INSECTICIDE SOLUTIONS Insecticide Carbo- Chlor- Disulfoton' furan fenvinphos Diazinon Dichlorvos Disulfoton sulphone Grand mean of all samples .. . . 100.3 101.7 97.5 104.6 101.0 100.4 No. of observations . . . . . . 144 288 288 288 288 288 Grand mean excluding 1-year samples 100.2 100.9 100.0 103.6 100.5 100.6 No. of observations . . . . . . 108 216 216 216 216 216 Neither solvent type nor storage temperature induced any consistently significant changes in the concentrations of the insecticides during the 2-year storage period. Nevertheless, when the data from the 1-year samples were omitted, between-sample variability was smallest in samples stored in hexane at -20 "C (Table 111). There was no detectable oxidation of the parent organophosphorus compounds to their respective oxygen analogues, or with disulfoton to its sulphoxide or sulphone; their stability, even under the most rigorous storage combination of acetone at 20 O C , therefore suggested that hexane solutions stored in ampoules at -20 "C should be quantitatively reliable for considerably longer than the 2-year period of this study.Variability of Primary Standards Only with carbofuran, a crystalline solid, was there no significant difference (P < 0.01) between the final fresh primary standard and those used during the experiment (Table V). The differences were most marked with dichlorvos and disulfoton sulphone, the pure liquids apparently deteriorating by 30 'and ISYO, respectively, in 2 years. The deterioration of dichlorvos was partly evident in the higher concentrations in the dilute ampouled solutions, suggesting that degradation was slower in these than for the pure primary standard.With disulfoton sulphone, there was a large difference between the original and fresh standards, TABLE V VARIABILITY OF PRIMARY STANDARDS Insecticide Observed purity of fresh standards, percentage of the original standard . . Carbo- Chlor- Disulfoton furan fenvinphos Dichlorvos Disulfoton sulphone . . 99.6 92.0 130.5 93.8 118.01180 SUETT, WHEATLEY AND PADBURY contrasting markedly with the stability of the dilute solutions. The solutions prepared from fresh standards of chlorfenvinphos and disulfoton contained 8 and 6% less insecticide than solutions prepared from their respective original primary standards. With all the insecticides, except dichlorvos, t’he similarity between the dilute ampouled solutions and the original primary standards during the %year experiment suggested that the dilute solutions were very stable when stored; they were unlikely to have degraded at identical rates to the pure compounds irrespective of storage temperature or solvent. The differences between the original and fresh primary standards, therefore, most likely reflect discrepancies between the original and the later primary standards themselves.Although some deterioration during storage cannot be entirely discounted, the relatively large dis- crepancies suggested that the purities of some of the standards as received from the manu- facturers differed appreciably from those stated, possibly through deterioration during transit. As batches of ampoules need only be prepared very infrequently in comparison with the more widely used procedures the technique affords several advantages.There is less frequent need to maintain precise laboratory conditions, thereby minimising inconvenience. Many primary standards can, if desired, first be calibrated against the certified reference materials available from national agencies. The risk of contaminating the primary standards is greatly reduced and the ready availability of precisely measured amounts in ampoules ensures an immediate supply of a wide range of reliable, freshly prepared working standards at all times. Conclusions The experiments showed that dilute solutions of insecticides could be accurately and economically prepared in hexane, toluene or acetone, dispensed into ampoules and, after heat-sealing, stored for long periods at -20 to 20 “C. The dilute solutions of the insecticides studied were then at least as stable as the pure primary standards from which they were prepared. It seems likely that many other insecticides would store satisfactorily as dilute standards, particularly in hexane solutions at -20 “C. References 1. 2. 3. 4. McLeod, H. A., and Ritcey, W. R., Editors, “Ana,lytical Methods for Pesticide Residues in Foods,” Department of National Health and Welfare, Ottawa, 1973, Section 13. Thompson, J. F., in Coulston, F., and Korte, I?., Editors, “Environmental Quality and Safety, Supplement,” Volume 111, Georg Thieme, Stuttgart, 1975, p. 47. Vogcl, A. I., “A Text Book of Practical Organic Chemistry,” Second Edition, Longmans, London, 1951, p. 47. Williams, I. H., and Brown, M. J., J . Agvic. Fd Chem., 1973, 21, 399. Received May 2nd, 1979 Accepted June 8th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401176

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, December, 1979, Vol. 104, pp. 1181-1184 1181 Assay of Nicotinamide in Multivitamin Preparations Using an Ammonia Gas-sensing Electrode D. P. Nikolelis, C. E. Efstathiou and T. P. Hadjiioannou" Labovatory of Analytical Chemistry, University of Athens, Athens, Greece A simple potentiometric method for the determination of nicotinamide is described. The sample is subjected to alkaline hydrolysis and the ammonia thus produced is determined with an ammonia gas-sensing electrode. Amounts of nicotinamide in the range 0.5-15 mg have been determined with an average error of about 1.7%. The method has been applied to the analysis of multivitamin preparations. The analytical recovery of nicotinamide was 95-107y0. Keywords : A rnrnonia gas-sensing electrode ; direct Potentiowetry ; nico- Comparison with an official method gave satisfactory results. tinantide determination ; nzultivitamin preparations analysis The official spectrophotometric methods of analysis for the determination of nicotinamide in natural products and multivitamin preparations are based on the Konig reaction of pyridine and its derivatives with cyanogen bromide and an aromatic amine.ls2 These methods are sensitive and relatively free from interferences, but they have the disadvantage of using the extremely toxic cyanogen bromide.Polarographic and microbiological methods have also been used but they are tedious and time consuming.2 Recently, a liquid-membrane nicotinate ion-selective electrode has been developed for the determination of ni~otinamide.~ This paper describes a potentiometric method for the determination of nicotinamide in multivitamin preparations.The sample is treated with 2 M sodium hydroxide solution, nicotinamide is hydrolysed and an' equivalent amount of ammonia is released, which is determined with an ammonia gas-sensing electrode. Amounts of nicotinamide in the range 0.5-15 mg were determined with an average error of about 1.7%. Recovery and comparison studies carried out on pharmaceutical preparations have shown a recovery of 95-107% and good agreement with the official AOAC method. Experimental Apparatus ments were made with an Orion, Model 801, digital pH - millivolt neter. were made at ambient temperature in a 50-ml cell equipped with a magnetic stirrer. When not in use, the electrode was kept in 0.05 M ammonium chloride s ~ l u t i o n .~ An Orion, Model 95-10, ammonia gas-sensing electrode was used and the potential measure- All measurements Reagents All solutions were prepared with de-ipnised, distilled water from reagent-grade materials. All vitamins used were of biochemistry grade. Standard nicotinamide solutions. Prepare a stock solution by dissolving in water 10.000 g of nicotinamide, dried in a vacuum desiccator, and diluting the solution to 1 1 in a calibrated flask. Prepare standard nicotinamide solutions containing 0.100 0, 0.300, 1 .OOO and 3.00 mg ml-l from the stock solution by appropriate dilution. All nicotinamide solutions are stable for at least 1 week if kept in a refrigerator when not in use. Standard ammonium chloride solutions.Prepare a stock solution by dissolving 2.965 g of ammonium chloride in water and diluting the solution to 1 1 in a calibrated flask. This solution contains 1 .OOO mg ml-l of NH,+. Prepare standard ammonium chloride solutions containing 0.01000, 0.0300, 0.1000 and 0.300 mg ml-l from the stock solution by appro- priate dilution. Sodium hydroxide solution, 3 M. Borate bufer solution, pH 10, 0.5 M. Dissolve 30.9 g of boric acid in about 800 ml of water, adjust the pH to 10.0 with 3 M sodium hydroxide solution and dilute the solution to 1 1 with water. * To whom all correspondence should be addressed.1182 Procedure Preparation of the sample Weigh at least 20 tablets (or the content of 20 capsules) of the multivitamin preparation and pulverise them uniformly in a mortar.Weigh an appropriate amount of the pulverised sample, dissolve it in water and dilute the sol.ution to 50.00 ml with water so that the solution contains 0.1-3 mg ml-l of nicotinamide (solution A). If the formulation contains water-insoluble excipients, heat the suspension in a water-bath at 50 "C for 15 min with occasional shaking to ensure complete dissoliition of nicotinamide. Filtration is not necessary and the whole solution is used (solution A). NIKOLELIS et d. : ASSAY OF NICOTINAMIDE I N MULTIVITAMIN Analyst, Vol. 104 Determination of blank To determine the blank due to ammonium salts, transfer into the measurement cell 5.00 ml of standard ammonium chloride solution or solution A and 25.00 ml of borate buffer (pH lo), immerse the electrode in the solution, :;tart the stirrer and read the e.m.f.when it is stabilised to within & O . l mV (in about 2-5 min). Include four ammonium chloride standards in the 0.01-0.3 mg ml-l of NH,+ range. Calculate the ammonium concentration (C) of solution A from a calibration graph of E (mV) vemm log [ammonium concentration (mg ml-I)] and multiply C by the conversion f.actor 6.77 (C,H,NCONH,/NH,+) to obtain the blank value due to ammonium salts, [Niclbl, in milligrams of nicotinamide per millilitre. Determination of nicotinamide Pipette 5.00 ml of standard nicotinamide or unknown sample solution (solution A) and 10.00 ml of 3 M sodium hydroxide solution into 20-ml vials with well fitting stoppers, shake and leave the vials in a water-bath at 50 "C for about 30 min. Cool the vials to room temperature, transfer 5.00 ml of the solution arid 25.00 ml of water into the measurement cell, and proceed as for the determination of the blank.Calculations Calculate the nicotinamide concentration of solution A, [Nic], from a calibration graph of E (mV) veysuus log [nicotinamide concentration (mg ml-')I. The mass of nicotinamide (Mnic) in milligrams per tablet (or capsule) is calculated from Mnic = 50 ([Nic] - [Niclbl) (BIB), where B and Bare the sample mass and the average tablet or capsule content mass, respectively . Results and Dliscussion The rate of hydrolysis of nicotinamide increases with increasing temperature (Fig. 1) and sodium hydroxide concentration. A temperature of 50 "C and 2 M sodium hydroxide solution were chosen as a compromise between speed of hydrolysis and experimental con- venience.100 s aJ- 80 m .- 60 u C .- + In In 0 40 >. TI >. I .- - 2 20 0 20 40 60 80 Time/m i n Fig. 1. Hydrolysis rate of nicotinamide in 2 M sodium hydroxide solution a t : A, 50 "(1; and B, 25 "C.December, 1979 PREPARATIONS USING AN AMMONIA GAS-SENSING ELECTRODE 1183 Results for the determination of nicotinamide in aqueous solutions are given in Table I. It can be seen that amounts of nicotinamide in the range 0.5-15 mg per 5-ml sample solution can be determined with an average error of about &1.7yo.The coefficient of variation for six complete replicate analyses of 1.50 mg was 1.0%. TABLE I RESULTS FOR AQUEOUS NICOTINAMIDE SOLUTIONS Nicotinamide per 5 ml/mg r A 7 Taken Found* E/mV Relative error, % 0.500 0.509 67.9 + 1.8 1.14 1.14 47.5 0.0 2.40 2.36 29.1 - 1.7 5.25 5.46 8.0 +3.8 10.6 10.5 - 8.6 -0.9 15.0 15.3 - 18.1 +2 0 Average: 1.7 * Single measurements.Calibration graph obtained with four standard nicotinamide solutions, each measured once. Regression eqnation, E = -58.211og[Nic] + 10.16; correlation coefficient, -0.999 90. There is a linear relationship between E and log (nicotinamide concentration) in the range 0.1-3 mg ml-l. The proportionality constant, corresponding to the slope of the response of the ammonia gas-sensing electrode, decreases at lower nicotinamide concentrations because the final ammonia concentration approaches the lower limit of the linear response of the electrode. The minimum amount of nicotinamide that can be determined can be reduced by at least one decade with a few minor modifications to the procedure (smaller volumes of sodium hydroxide solution and of added water to the measurement cell, smaller measure- ment cell, etc.).However, such modifications are not necessary for the determination of nicotinamide in multivitamin preparations because they normally contain amounts of nicotinamide that permit the application of the proposed method. Also, such modifications would affect the accuracy of the method. Table I1 shows the effect of various substances (vitamins and excipients) that are usually present in multivitamin preparations with nicotinamide. The results show that all B complex vitamins examined except cyanocobalamin (vitamin B,,), when present with nicotinamide in the proportions 1 + 1, have almost no effect on the nicotinamide assay. Larger proportions of nicotinamide were not tested because all formulations contain larger amounts of nicotinamide than of other B complex vitamins.Cyanocobalamin has six -CONH, .groups per molecule and causes a positive error, but this has almost no effect on the nicotinamide assay because cyanocobalamin is present in much smaller amounts than nicotinamide. A positive error may also arise if desiccated liver is present in the multi- vitamin preparation as a source of natural vitamins. Desiccated liver was found to contain both free ammonium salts and water-soluble substances, probably proteinic in nature, which yield ammonia upon alkaline hydrolysis. An empirical correction factor can be TABLE I1 EFFECT OF VARIOUS SUBSTANCES ON NICOTINAMIDE DETERMINATION Amount of nicotinamide in solution, 5 mg.Substance Relative error, 76 Thiamine.HC1 (vitamin B,)* . . . . . . - 1.7 Riboffavine (vitamin B,)* . . .. . . -0.8 Pyridoxine.HC1 (vitamin B6) * . . . . 1-1.7 Ascorbic acid (vitamin C ) t . . .. .. - 1.2 Glucose7 .. .. . . .. .. - 1.2 Cyanocobalamin (vitamin B,,)* . . . . + l l . S Calcium pantothenate* . . .. .. - 0.4 Desiccated liver? . . .. .. . . +13.2 Starch7 . . .. .. . . . . - 1.7 * 5 mg of substance. t 50 mg of substance.1184 NIKOLELIS, EFSTATHIOU AND HADJIIOANNOU TABLE I11 COMPARISON OF POTENTIOMETRIC AND AOAC METHODS FOR THE DETERMINATION OF NICOTINAMIDE I N MULTIVITAMIN PREPARATIONS Amount of nicotinamide found/ mg per tablet f standard deviation* Average mass A Difference, Sample of tabletlg Proposed method AOAC method % Nicotivit (Chropi) .. . . . . 0.102 51.2 f 1.1 52.5 f 1.2 -2.5 Neo-Multi-B (Chropi) . . . . 0.745 26.8 f 0.2 26.2 f 0.4 +2.3 Multi B + C (Chropi) . . . . 0.682 47.0 f 1.0 48.3 -)= 0.8 -2.7 Surbex-T (Abbott) . . . . . . 1.084 104 f 2 103 f 2 + 1.0 * Average of five determinations for each sample and method applied, if the ratio n = mass of desiccated liver/mass of nicotinamide is known. In this work the amount of nicotinamide found per tablet was decreased by 1.32ny0. Comparative results for the determination of nicotinamide in some multivitamin prepara- tions are given in Table 111. Nicotinamide was determined by both the proposed method and the official AOAC meth0d.l The precisions of the two methods are about the same.There is satisfactory agreement between the results obtained by use of the two methods. In only one instance (Surbex-T) was it found necessary to apply corrections for both the blank due to ammonium salts (equivalent to 1.2 mg of nicotinamide per tablet) and for the desiccated liver (n = 1.5). For the other preparations the blank was equivalent to less than 0.1 mg of nicotinamide per tablet. The accuracy of the proposed method was further checked by means of recovery experi- ments carried out on one representative multivitamin preparation, in which nicotinamide was added to the sample. The results are shown in Table IV. TABLE IV RECOVERY OF NICOTINAMIDE ADDED TO TABLET SAMPLES (MULTI B + C) Amount of nicotinamide/mg per 5 ml r 7 L-- Initially present Added Found* Recovery, yo 0.36 1.50 11.87 101.3 0.52 1.50 :!.07 103.3 0.52 0.75 11.23 94.7 0.69 0.75 1 43 97.3 1.07 0.75 1.87 106.7 1.05 2.25 3.21 96.0 Average : 99.9 * Single measurements. Conclusion The proposed method for the assay of nicotinamide in multivitamin preparations is simple, fast and has a precision and accuracy comparable to those of the more tedious AOAC method. The method cannot be applied to the determination of nicotinic acid but the latter is not generally used in pharmaceutical preparations. References 1. Horwitz, W., Editor, “Official Methods of Analysis of the Association of Official Analytical Chemists,” Twelfth Edition, Association of Official Analytical Chemists, Washington, D.C., 1975, p. 828. Strohecker, R., and Henning, H. M., “Vitamin Assay Tested Methods,” Verlag Chemie, 1965, pp. 195, 201 and 207. Campanella, L., De Angelis, G., Ferri, T., and Gozzi, D., Analyst, 1977, 102, 723. “Ammonia Electrode Instruction Manual,” Form IM 95-10/679, Orion Research Inc., Cambridge, 2. 3. 4. Mass., 1976. Received A p r i l 9th, 1979 Accepted May 30th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401181

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Analyst, December, 1979 SHORT PAPERS 1185 Spectrophotometric Method for the Determination of Residues of Carbaryl in Water S. K. Handa and A. K. Dikshit Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi, India Keywords : Carbaryl residues ; water analysis ; spectrophotonzetry Carbaryl(1-napthyl methylcarbamate) has attained widespread use and acceptance because of its effectiveness and low mammalian toxicity. The oral LD,, of carbaryl to rats is 560 mg kg-l. Currently carbaryl is marketed in wettable powder, bait, dust, liquid and aerosol forms. Among these many types of formulations label guarantees may range from 5 to 80% content of carbaryl. After carbaryl has been applied, residues may be present in aquatic systems via direct treatment of water or by run off from treated areas into lakes, streams and ponds. A rapid and reliable method is therefore required to permit the determination of carbaryl residues and thus to study its persistence and fate in aquatic systems. Spectrophot~metric,~-~ enzymatic5 and chromatographic6-10 methods have been reported for its determination.The spectrophotometric methods reported in the literature require the use of p-nitrobenzene- diazonium fluoroborate. The occasional unavailability of this reagent has necessitated a search for an alternative method. A quantitative colour reaction of vanillin with oc-naphthol in acetic acid has accordingly been developed that forms the basis of a method for the determi- nation of carbaryl. This rapid spectrophotometric method has been found to be satisfactory for the analysis of carbaryl in field water samples. Experimental Perkin-Elmer, Model 402, with 1-cm silica cells.Bausch and Lomb Spectronic 20 with 12 x 100 mm tubes. These were of 30-ml capacity, with B19 sockets and stoppers. Apparatus Spectrophotometer. CoZorimeter. Test-tubes. Reagents Carbaryl. India. Potassium hydroxide solution. VanilZin solution. Orthophosphoric acid. Potassium carbonate solution, 0.1 M. The sample was obtained through the courtesy of Union Carbide Co., Bhopal, A 0.5 N solution in methanol. Dissolve 0.6 g of vanillin in 100 ml of analytical-reagent grade glacial acetic acid. Preparation of Standard Solution Dissolve 100 mg of carbaryl in acetone and make the volume up to 100 ml with acetone in a calibrated flask. Transfer 2 ml of the solution into a 100-ml calibrated flask and make the volume up to the mark with acetone, thus obtaining a solution containing 20 pgml-l of carbaryl.Preparation of Standard Graph test-tubes. the solvent under a current of dry air. methanolic potassium hydroxide solution. Transfer 0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 ml portions of standard solution into clean, dry Dilute the volume to 3.0 ml with acetone in all of the test-tubes, then evaporate Into each of the tubes pipette 0.2 ml of 0.5 N Rotate the test-tubes in order to wet the sides1186 SHORT PAPERS Analyst, Vol. 104 with solution for 5 min and evaporate the methanol from each test-tube. Next pipette 1 ml of vanillin solution and 4.0 ml of orthopho'sphoric acid into each tube.Place the test- tubes in a water-bath at 60 "C for 20 min; remove them from the bath and cool in a beaker of cold water and then read the absorbance of each solution in the spectrophotometer at 575 nm. Extraction of Water Samples After collection of the water samples (minirnum volume 11) adjust them to pH values below 5 with 20y0 sulphuric acid. Dissolve l o g of sodium sulphate in each 1-1 sample. Next extract each sample in a 2-1 separating funnel with 150ml of methylene chloride, shaking the funnel for 2-3 min. Transfer the methylene chloride extract into a 1-1 funnel and re-extract the aqueous phase (2-3 min) with a further 100 ml of methylene chloride. Add the second methylenq chloride extract to the first and wash the combined extract with 0.1 M potassium carbonate solution, then dry the methlylene chloride by passing it through 15-20 g of sodium sulphate in a filter funnel and collect the extract in a 500-ml flask fitted with a ground-glass stopper.Concentrate the methylene chloride extract to 100 ml. Determination of carbaryl) and place it in a test-tube. exactly as described under Preparation of Standard Graph. Take a suitable portion of the methylene chloride extract (expected to contain 10-60 pg Evaporate the solution in the test-tube and proceed Results Standard Graph for Carbaryl described under Experimental. The results shown in Table I were obtained by using standard solutions for carbaryl as TABL~E I ABSORBANCE VALUES OF STANDARD SOLUTIONS OF CARBARYL Carbaryl added/ tG Absorbancc 10 0.065 20 0.125 30 0.195 Carbaryl added/ r*g Absorbance 40 0.255 5 0 0.320 GO 0.390 Recovery of Carbaryl Added to Field Water Samples To obtain an indication of the efficiency of the proposed procedure, field water samples to which known amounts of carbaryl had been added were analysed. Water samples (1 1 each) were fortified with concentrations of 0.10, 0.15 and 0.20 p.p.m.of carbaryl. Samples of water were extracted with methylene chloride and determined by means of the procedure described. The results given in Table I1 indicate that acceptable recoveries ( 92-96y0) of carbaryl were obtained with the proposed procedure. TABLE I1 RECOVERY OF CARBARYL ADDED TO FIELD WATER SAMPLES Sample 1 2 3 4 5 Averagelpg ml-' . . . . Average, yo . . . . Carbaryl added/pg ml-1 0.10 0.15 0.20 0.090 0.145 0.190 0.095 0.140 0.195 0.D90 0.142 0.190 0.096 0.145 0.195 0.090 0.140 0.192 0.8092 0.142 0.192 A 7 -7 92 94 90December, 1979 SHORT PAPERS 1187 Discussion Under acidic conditions protons attack the aldehyde group of vanillin to give an electro- philic radical, which condenses with the phenol to form an intermediate.This intermediate undergoes dehydration to give a coloured compound.ll These reactions were carried out between vanillin and cc-naphthol (from carbaryl) in acetic acid medium to form the coloured compound. Characteristics of the colour reaction The absorption spectrum of the coloured compound was determined in the wavelength range from 450 to 600 nm (see Fig. l), the absorption maximum occurring at 575 nm. StabiZity of the coloured compound.The stability of the coloured product developed with 20 pg of carbaryl was studied by recording absorbances at 575 nm a t intervals of 6 h for a period of 36 h. The colour was found to be stable for 24 h, beyond which there was a gradual deterioration (Fig. 2). 4.50 500 550 600 650 700 Wave length/nm 0.3 B Q 0.2 0 6 12 18 24 30 Ti me/h Fig. 2. Stability of coloured compound. Fig. 1. Absorption spec- trum of coloured compound. Rate of colour formation. The colour reaction was carried out for 5, 10, 15, 20, 25 and 30 min. The relationship between the temperature of the reaction and absorbance is shown in Fig. 3. Different concentrations of vanillin solution, ranging from 2 to 10 mg ml-1, were used for the formation of the coloured compound. At a vanillin concentration of 4 mg ml-1, the absorbance reached a maximum and remained constant in the range 4-10 ml-l (Fig.4). The minimum time required for full colour development was 20 min (Fig. 3). Eflect of vanilZin concentration. 0 5 10 15 20 25 30 Heating time/min Fig. 3. Rate of colour development. I 1 0 2 4 6 8 1 0 Va ni i i i n coixentra tion/mg I-' Fig. 4. Effect of concentration of vanillin on coloured compound. Conclusions A sensitive and precise method for the determination of carbaryl in field water samples is presented. I t is based on the reaction of or-naphthol, resulting from the hydrolysis of carbaryl and vanillin in an acetic acid medium. The method can be used for the determination of carbaryl in lake, stream and pond water samples. The authors express sincere gratitude to Dr.S. K. Mukerjee, Head of the Division of Agricultural Chemicals, for his sustained interest in the work.1188 SHORT PAPERS Analyst, Vol. 10.1 References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Stansbury, H. A.. Jr., and Miskus, R., “Analytical Methods for Pesticides, Plant Growth Regulators and Food Additives,” Volume 2, Academic Press, New York, 1964, p. 438. Miskus, R., Gordon, H. T., and George, D. A., J . Agric. Fd Chem., 1959, 7, 613. Vonesch, E. E., and Riveros, M. H. C. K., J . Ass. Off. Analyt. Chem., 1971, 54, 128. Rangaswamy, J . R., and Majumder, S. K., J . A s s . Off. Analyt. Chem., 1974, 57, 592. Zweig, G., and Archer, T. E., J . Agric. Fd Chem., 1958, 6, 910. Rolls, J . M7., and Cortes, A., J . Gas Chromat., 1964, 2, 132. Holden, E. R., Jones, W. M., and Beroza, M., J . Agric. Fd Chem., 1969, 17, 56. Cohen, I. C., Norcup, J., Ruzicka, J . H. A., and Wheals, B. B., J . Chromat., 1970, 49, 215. Gutenmann, W. H., and Lisk, D. J . , J . Agric. Fa‘ Chem., 1965, 3, 48. Coburn, J . A., Riplay, B. D., and Chau, A. S. Y., J . A s s . Off. Analyt. Chem., 1976, 59, 188. Ribereau-Gayon, P., “Plant Phenolics,” Oliver and Boyd, Edinburgh, 1972, p. 449. Received July loth, 1978 Amended October llth, 1978 Accepted July 9th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401185

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

1188 SHORT PAPERS Analyst, Vol. 10.1 Selective Spectrophotometric Determination of Zinc with 2,2’-Dipyridyl- 2-q uinolyl hydrazone R. B. Singh, P. Jain, B. S. Garg and R. P. Singh Department of Chemistry, University of Delhi, Delhi-110007, India Keywords : 2,2‘-Dipyridyl-2-quinolyllzydrazone reagent ; spectrophotometry ; zinc determination ; alloy analysis In our studies on hydra~ones,l-~ the synthesis of 2,2’-dipyridyl-2-quinolylhydrazone (DPQH, I) (2 [di-(2-pyridyl)methylidenehydrazino]quinoline} and its application in the micro- determination of cobalt8 has been reported earlier. In this work, DPQH has been examined for use as a reagent for the selective spectrophotometric determination of zinc. DPQH ( I ) The proposed method is based on a differential demasking technique proposed by Platte and M a r ~ y , ~ in which the zinc was determined with Zincon in the presence of Zincon- interfering metals, such as iron and copper. The cyanide complexes of the metals present in the solution were formed and the zinc compound was then preferentially destroyed with chloral hydrate.The zinc - Zincon complex formed by the liberated zinc was measured spectrophotometrically, before other metals were liberated from their cyanide complexes (i.e., before other cyanide complexes were decomposed by chloral hydrate) and interfered in the determination. I t was reported laterl09l1 that the cyanide complexes of copper(I1) and iron(II1) are not stable enough to prevent interference by copper and iron in the determination of zinc using the above procedure, and the reduction of copper(I1) and iron(II1) with ascorbic acid was proposed.12 The copper(1) and iron (11) complexes are more stable towards chloral hydrate.December, 1979 SHORT PAPERS Experimental Apparatus 1189 A Unicam SP 600 spectrophotometer with 1-cm silica cells was used for measuring absor- bance and a Reckman Expandometic SS-2 pH meter for pH measurements.Reagents All other solutions were .prepared with analytical-reagent grade chemicals in doubly distilled water unless indicated otherwise. DPQH reagent. DPQH was synthesised by refluxing an ethanolic solution of equimolar amounts of 2,2’-dipyridyl ketone and 2-hydrazinoquinoline as described previously.8 An approximately 10-2~r solution in 95% ethanol was prepared and was stored in an amber- glass bottle. This solution was prepared freshly on alternate days and stored in amber-glass bottles.Borax (4 g) and potassium cyanide (0.2 g) were dissolved in 4 M sodium hydroxide solution (about 40 ml) and diluted to 50 ml with distilled water. When 1 ml of the buffer is mixed with 5 ml of working standard or blank solution, the resulting pH should usually fall between 11.8 and 12.2. If it does not, the amount of alkali added should be adjusted and the pH re-checked. Once the correct conditions have been established for this solution, it is easy to prepare a new buffer when it is needed. A standard zinc solution was prepared by dissolving analytical- reagent grade zinc sulphate heptahydrate in doubly distilled water. Chloral hydrate solution was prepared by dissolving 1.5 g of chloral hydrate in 100 ml of water.This solution was stable for several weeks. Ascorbic acid solution, 10% m/V. B u f e r solution. Standard x i n c ( l 1 ) solutioqz. Chloral hydrate solution, 1.5%. Procedure To a suitable aliquot containing 3.75-22 pg of zinc(I1) is added 1 ml of ascorbic acid, followed by 5 ml of buffer solution, then 1 ml of The mixture is diluted to 25 ml with 1 + 1 ethanol - water. The absorbance of the solution is measured, within 25 min after the addition of DPQH, at 480nm against a reagent blank prepared under the identical conditions. M DPQH solution. Absorption Spectra, Effect of pH and Reagent Concentration A pH study of the complexation of DPQH with zinc(I1) showed that the orange complex (Amax. = 480 nm) gives a constant absorbance in the pH range 11.5-12.7.On carrying out the proposed procedure, it has been found that pH adjustment in the desired range was achieved more effectively when the buffer solution and the masking agent, i.e., the cyanide, are added simultaneously. I t was observed that separate addition of cyanide and buffer, irrespective of their order of addition, made pH adjustments difficult. For complete complexation a 10-fold molar excess of DPQH is sufficient. The absorbance of the reagent at the wavelength of maximum absorbance of its zinc complex (480 nm) is negligible. This is advantageous because a large excess of reagent can be employed. Presence of Chloral Hydrate It was found that the presence of chloral hydrate (2 ml of 1.5y0 solution), added after the addition of UPQH, is not necessary for the clestruction of the zinc - cyanide complex or for full colour development.The zinc - cyanide complex is conipletely destroyed and the zinc - DI’QH complex is completely formed despite tlie absence of chloral hydrate. This must be related to the stability constants of the zinc - cyanide and zinc - DPQH complexes. The latter complex probably has a higher apparent stability. Stability of the Complex In the absence of chloral hydrate the time necessary for full colour development, i.e., for complete formation of the zinc - DPQH compkx, is about 5 min after the addition of DPQH. The absorbance remains stable for about 25 min, then diminishes slowly. If chloral hydrate is added after DPQH to facilitate the liberation of zinc from the zinc - cyanide complex,1190 SHORT PAPERS Analyst, Vol.104 the maximum absorbance is achieved immediately. It remains stable for 4-5 min, but then diminishes. Hence the absorbance of the test solution should be measured within 5-25 min after the addition of DPQH in the first instance and within 5 min if chloral hydrate solution has been added. Characteristics of the Complex Beer’s law is obeyed for up to 1.17 p.p.m. of .zinc(II) in the presence or absence of chloral hydrate. The optimum concentration range, evaluated by Ringborn’s method,13 is 0.15- 0.88 p.p.m., the Sandell sensitivity1* is 0.0010 pg cm-2 and the molar absorptivity is 6.3 x lo4 1 mol-l cm-1 at 480 nm. Composition of the Complex Job’s method of continuous variations15 showed that the metal to ligand ratio is 1 : 2.Effect of Other Ions Synthetic solutions containing a known amount of zinc (0.26 p.p.m.) and various amounts of other ions were prepared and the proposed procedure for the determination of zinc (without addition of chloral hydrate) was followed. An error of *2% in the absorbance reading was considered tolerable. There was no interference from the following ions : chloride, bromide, iodide, fluoride, citrate, tartrate, thiourea, acetate, sulphate, sulphite, nitrate, nitrite (2000 p.p.m.) ; thio- cyanate (800 p.p.m.) ; thiosulphate, oxalate (400 p.p.m.) ; phosphate (100 p.p.m.) ; Ca(II), Sr(II), Ba(II), Mg(II), Pb(II), Mo(VI), W(V1) (600 p.p.m.) ; Al(III), Sn(II), Sb(II1) (500 p.p.m.) ; Ru(III), Rh(III), Ir(III), Au(III), Os(VIII), Ti(IV), Mn(II), Ag(1) (200 p.p.m.); Pd(II), Ni(II), Co(II), Hg(II), V(V) (100 p.p.m.); and Cu(I1) and Fe(I1) (80 p.p.m.). How- ever, EDTA and Cd(I1) interfered seriously.Practical Applications The solutions of the alloys were prepared as described by Singh et a1.16 given in Table I. Zinc was determined in some alloys by using I>PQH (without addition of chloral hydrate). The results are TABLE: I DETERMINATION OF ZINC IN ALLOYS Zinc co-ntent, yo Number of Relative standard Alloy Reported Found determinations deviation, yo Brass (BCS No. 5g) . . . . . . . . 30.0 29.8 6 1.40 Gun metal (BCS No. 6g) . , . . . . 1.5 1.43 6 2.96 6% zinc - aluminium alloy (BCS No. 300) . . 5.98 5.76 6 1.49 Conclusion A highly selective and sensitive method for the determination of zinc is proposed.minations can be carried out in aqueous solution and there is no need for extraction. can be determined in alloys without its separation from other metals. Deter- Zinc Two of us (R.B.S. and P. J.) are grateful to the C.A.S. in Chemistry, University of Delhi, and C.S.I.R., New Delhi, for the award of a teac:her and a senior research fellowship, respec- tively. References 1. 2. 3. Katyal, M., Kundra, S. K., Goel, D. P., and Singh, K. P., J . Indian Chem. SOC., 1974, 51, 576. Rastogi, I>. K., Dua, S. K., Prakash, S., and Singh, R. P., Analusis, 1973-74, 2, 661. Kay, H. L., Garg, €3. S., and Singh, R. P., Curr. Sci., 1973, 42, 852.December, 1979 SHORT PAPERS 1191 4. 6 . 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Singh, R. B., Jain, P., Garg, B. S., and Singh, R. P., Analytica Chim. Acta, 1979, 104, 191. Singh, R. B., Kulshreshtha, H., Garg, B. S., and Singh, R. P., Curr. Sci., 1979, 48, 109. Ray, H. L., Garg, B. S., and Singh, R. P., Curr. Sci., 1979, 48, 346. Kulshreshtha, H., Singh, R. B., and Singh, R. P., Analyst, 1979, 104, 572. Singh, R. B., Ray, H. L., Garg, B. S . , and Singh, R. P., Talanta, in the press. Platte, J . A., and Marcy, V. M., Analyt. Chem., 1959, 31, 1226. Williams, L. A., Cohen, J. S., and Zak, B., Clin. Chem., 1962, 8, 502. Zak, B., Nalbandian, R. M., Williams, L. A., and Cohen, J . S., Clinica Chim. Acta, 1962, 7, 634. Watkins, R., Weiner, L. M., and Zak, B., Microchem. J., 1971, 16, 14. Ringbom, A,, 2. Analyt. Chern., 1939, 115, 332. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Third Edition, Interscience, Job, P., Annls Chirn., 1928, 9, 113. Singh, R. B., Kulshreshtha, H., Garg, B. S., and Singh, K. P., Bull. Chem. SOC. Japan, in the press. New York, 1959, p. 83. Received May 22nd, 1979 Accepted July 9th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401188

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

December, 1979 SHORT PAPERS 1191 Determination of Oxycarboxin Residues in Medicinal Plants W. Debska, 6. Gnusowski and 6. Zygmunt Department of Phytochemical Analysis, Institute of Medicinal Plants, Libelta 27, 61-707 Poznah, Poland Keywords : Oxycarboxin determination ; fungicide residue analysis ; spectro- photometry ; medicinal plants Oxycarboxin is a systemic fungicide used in the control of Puccinia (mould) parasitic fungus on different plants, e.g., cereals, pod-bearing plants and ornamental plants. I t can be applied during the plant disease or prophylactically during the different stages of the plant evolution. The properties of oxycarboxin have been reported.lS2 As the effects of applying oxycarboxin for plant protection were positive, analytical methods for its determination in medicinal plants have been developed.According to the literature, the determination of oxycarboxin residues has developed in two directions, direct oxycarboxin determination and determination of free aniline formed on alkaline hydrolysis of oxycarboxin. In the former instance, thin-layer chromatography has been employed, with the use as detection reagents of 0.05y0 fluorescein in methanol ~ o l u t i o n , ~ detecting the spots under ultraviolet light at 254 nm,394 and silver nitrate with potassium permanganate in an acidic medium.5 Radi~autography~ and high-performance liquid chromatography6 have also been used. The latter method consists in the determination of free aniline, which is formed as a result of alkaline hydrolysis of oxycarboxin.Aniline has been determined spectrophotometrically at 440490 nm,’v8 after reaction with dimethylaminobenzaldehyde, and by gas chromato- g r a p h ~ . ~ *lo Raw plant material has many chemical constituents, which interfere in analytical pro- cedures, and the results using Lane’s7 test have been unsatisfactory. We have developed an alternative method for the determination of pesticide contaminants in medicinal plants, involving the release of free aniline by alkaline hydrolysis and its diazotisation and coupling with N-1-naphthylethylenediammonium chloride to form a coloured complex, which is determined spectrophotometrically at 558 nm. The medicinal plants examined include peppermint leaves (fresh and dry) and marsh- mallow leaves (fresh). Method Reagents All reagents were of analytical-reagent grade.Methanol. A cetoii e .1192 SHORT PAPERS Analyst, Vol. 104 Ammonia, sp. gr. 0.907. Benzene. Orthophosphoric acid, sp. gr. 1.71. Hydrochloric acid, sp. gr. 1.18 and 0.25 N. N-1-nafihthylethylenediammonium dichloride solution, 2% ml V . Sodium hydroxide solution, 30% m/V. Ammonium amidoszclphonate solution, 10% ml 17. Sodium nitrite solution, 2% m/V. Titaniztm(III) chloride solution, 15%. Iron(II) chloride dihydrate. Silicone an.tti-foam emulsion. Schuchard, Munich. Aniline standard solution, 5 pg ml-l. Mikrotechna N.P. Dissolve 1.0 g of aniline in 1 N hydrochloric acid - methanol (1 4-1) and make up to 100 ml with the hydrochloric acid - methanol. Dilute 5 ml of this solution to 100 ml with 0.25 N hydrochloric acid and then 1 ml of the resulting solution to 100 ml with methanol.Dissolve 0.0050 g of oxycarboxin in methanol and make up to 100 ml with methanol. Dilute 10 ml of the resulting solution to 100 ml with methanol. Oxycarboxin standard solution, 5 pg ml-l. Apparatus All glassware must be scrupulously clean and have ground-glass joints. Blender. Spectrophotometer. Rotary evaporator. Waring-type blender with 1-1 jar. Specol spectrophotometer, Type EK 1. Buchi rotary evaporator, Type Rotavapor-R. General Procedure Oxycarboxin is extracted from the plant material with acetone, and the extract is con- centrated and hydrolysed in an alkaline medium. The resulting aniline is steam distilled into the receiver, which contains concentrated hydrochloric acid. The distillate is adjusted to pH 7.2 and shaken with benzene, then the benzene layer is shaken with 0.25 N hydrochloric acid.The acid layer containing the aniline is sepaxated and the aniline diazotised and coupled with N-1-naphthylethylenediammonium chloride to form a coloured complex. The absorb- ance of the complex is measured, using 1-cm glass cells at 558 nm, against 0.25 N hydrochloric acid. Preparation of Plant Extracts Cut a representative sample into small pieces, mix thordughly, weigh l o g of the sample and place it in the blender. Add 100ml of acetone to the sample and mince the mixture for 2 min at high speed. Filter the homogenate through a Filtrak 3 m (or equivalent) 18.5-cm fluted filter-paper into a 500-ml flask. Add a further 50ml of acetone to any residue remaining in the blender and mince for Z min at high speed and filter.Combine the extracts and evaporate to dry- ness under reduced pressure. Add 50 ml of 30% sodium hydroxide solution, 1 g of iron(I1) chloride and 5 ml of titanium(II1) chloride solution to the dry residue and heat the reaction mixture under reflux for 2 h. Cool the hydrolysate, add a few drops of anti-foam emulsion and steam distil the aniline into a receiver containing 1 ml of concentrated hydrochloric acid, placed in an ice-bath. Adjust the pH of the distillate (which will be about 80 ml in volume) to 7.2 with concentrated ammonia solution or concentrated orthophosphoric acid. Add 2 g of sodium chloride and shake the solution with 50 ml of benzene in a 250-ml separating funnel for 2 min. Run off and discard the aqueous layer and wash the benzene layer three times with 20-1-111 portions of water adjusted to pH 7.2, discarding each aqueous extract.Shake the benzene layer with 10- and then 6-ml portions of 0.25 N hydrochloric acid. Collect the acid layers in a 20-ml calibrated test-tube and carry out the diazotisation and coupling reaction.December, 1979 SHORT PAPERS 1193 Determination of Aniline Add 0.4 ml of 2% sodium nitrite solution to the 20-ml calibrated test-tube containing the acid layers and, after shaking briefly, leave for 15 min. Add 0.4ml of 10% ammonium amidosulphonate solution, shake for a short time and leave for 10 min. Next, add 0.8 ml of 2y0 N-1-naphthylethylenediammonium dichloride solution and 2.0 ml of acetone, make up to the 20-ml mark with 0.25 N hydrochloric acid and shake well. After 15 min measure the absorbance of the red - violet complex that forms, in 1-cm glass cells at 558 nm, against 0.25 N hydrochloric acid.Preparation of Calibration Graph To each of nine 20-ml calibrated test-tubes add 0.02, 0.04, 0.1, 0.2, 0.4, 0.7, 1.0, 1.5 and 2.0 ml of the aniline standard solution, which correspond to 0.1,0.2, 0.5, 1.0,2.0,3.5, 5.0, 7.5 and 10.0 pg of aniline, respectively, make up to 18.4 ml with 0.25 N hydrochloric acid and carry out the diazotisation and coupling reaction as described above. If a calibration graph is constructed it gives a straight line that passes through the origin and obeys the Beer - Lambert law up to a level of 10 pg of aniline in 20 ml of reagent. The calibration graph is reproducible, and the coefficient of variation is 6.68%.Use the 5 pg ml-l aniline standard solution. Galculation Use the calibration graph to determine the concentration of aniline in unknown samples. The amount of oxycarboxin residue, r , in parts per million of oxycarboxin, is given by the equation Y = 2.87 p/m, where p is the concentration of aniline determined in micrograms per 20 ml, m is the mass of sample taken in grams and 2.87 is the relative molecular mass conver- sion factor for aniline into oxycarboxin. Results and Discussion Blanks and Recoveries Blank determinations on untreated samples of peppermint leaves gave mean results of 0.56 and 0.11 mg kg-l of oxycarboxin residue for 1977 and 1978 crops, respectively, whereas the corresponding results for untreated marsh-mallow leaves were 0.23 and 0.20 mg k g l , respectively .These high blank values are caused by the numerous chemical constituents of the plant materials, These data are, however, lower than the blank values obtained by Lane,' which ranged from 0.4 to 4.0 mg kg-l for determinations in coffee and tea using colorimetry following a colour reaction with dimethylaminobenzaldehyde. The recovery of oxycarboxin from crop samples was checked by adding known volumes of oxycarboxin standard solution to the sample before extraction. Oxycarboxin was then determined in the samples as described under General Procedure using the 5 pg ml-l oxy- carboxin standard solution. The results are given in Table I. TABLE I RECOVERY OF OXYCARBOXIN FROM CROP SAMPLES The recoveries are results from four samples a t each determination and are corrected for blank determinations.Oxycarboxin content/mg kg-l I A \ Mean recovery, yo Crop (10 €9 Added Found, Peppermint leaves . . . . 0.2 0.124-0.138 65 Peppermint leaves . . . . 0.5 0.3 11-0.328 64 Marsh-mallow leaves . . . . 0.2 0.124-0.134 64 Marsh-mallow leaves . . . . 0.5 0.320-0.330 65 The low recoveries are probably caused by incomplete hydrolysis of oxycarboxin and the yield of aniline from the steam distillation.1194 SHORT PAPERS Analyst, Vol. 104 Application The method has been applied to the determination of oxycarboxin residues in treated medicinal plants. Table I1 shows results for oxycarboxin residues in peppermint and marsh-mallow leaves after treatment with 0.3%) Plantvax 20 and 0.1% Plantvax 75 formula- tions.The data obtained are within the permitted tolerance limits for carboxandide compounds (0.2-0.5 mg kg-l) and show that these formulations can be employed in the protection of medicinal plants. The samples were collected 25 d after treatment. TABLE I1 RESIDUES OF OXYCARBOXIN FOUND IN TREATED MEDICINAL PLANTS The results are mean values of three determinations and were obtained on crops grown du;ng 1978. Amount of oxycarboxin found/mg kg-1 A 7 7 Crop Pla.ntvax 20 Plantvax 75 Peppermint leaves . . . . 0.17 0.00 Marsh-mallow leaves . . . . 0.00 0.44 Interferences Any contamination of a crop sample by chemicals containing an aniline group, such as other carboxanilide fungicides and the substituted phenylurea herbicides, and carbamates interfere in this method and give positive results (due to the relative molecular mass con- version factor) for oxycarboxin residues.Conclusion The analytical method described can detect (3.1 pg of aniline, and the limit of detection is 0.03 mg k g l of oxycarboxin, after correction for blank determinations. Mean recoveries of oxycarboxin added to peppermint and rnarsh-mallow leaf samples are 64.5%. The relationship between the absorbance and concentration obeys the Beer - Lambert law in the range 0.1-10.0 pg of aniline. The method has been applied to the determination of residues of oxycarboxin in medicinal plants of different: chemical constitution and morphology, and will be useful for determining oxycarboxin contamination in medicinal plants. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Martin, H., “Pesticide Manual,” Third Edition, British Crop Protection Council, London, 1972. Perkow, W., “Wirksubstanzen der Pflanzenschutz- und Schadlingsbekampfungsmittel,” Verlag Chin, W. P., Stone, G. M., and Smith, A. E., J . Agr. Fd Chem., 1970, 18, 709. Allan, A. J.. and Sinclair, J. B., Phytupathology, 1969, 59, 1548. Tripathi, R. K., and Bhatkavatsalam, B., J . Chromat., 1973, 87, 283. Walkoff, A. W., Onuska, F. I., Comba, M. E., and Larose, R. H., Analyt. Chem., 1975, 47, 754. Lane, J . R., “Microdetermination of Plantvax Residues,” Uniroyal Chemical, Naugatuck, Conn., Lane, J. R., J . Agr. Fd Chem., 1970, 18, 409. Sisken, H. R., and Newell, J . E., J . Agr. Fd Chem., 1971, 19, 738. Verz2r-Petri, G. and Haggag, Y. M., Herba HuTzg., 1976, 15, 87. Paul Parey, Berlin and Hamburg, 1971. September, 1972. Received December 29th. 1978 Accepted M a y l l t h , 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401191

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

December, 1979 SHORT PAPERS 1195 Determination of Nitrate and Nitrite in River Waters Mieko Okada, Haruo Miyata and Kyoji Toei Japan Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka 3-1-1, Okayanza-shi 700, Keywords : Nitrate determination ; nitrite determination ; water analysis ; spectrophotornetry For the determination of trace amounts of nitrite in river waters, nitrite in water diazotises 9-aminoacetophenone, which is then coupled with m-phenylenediamine at pH 1.5-3.0. The 2,4-diamino-4'-acetylazobenzene formed is extracted into toluene at pH 9 and the absorbance is measured at 450nm. By this method, the nitrite content in river waters can be determined successfully at the parts per lo9 1evel.l This paper reports a convenient method for the determination of nitrite based on the same principle.As the extraction procedure is time consuming and complicated and the toluene used causes problems, the 2,4-diamino-4'-acetylazobenzene formed is measured as such using 10-cm cells at 460 nm. The molar absorptivities in the extraction method and the proposed method were 2.3 x 104 and 4.7 x 104 1 mol-1 crn-l, respectively. For the determination of nitrate, river-water samples are passed through a cadmium - copper column, where nitrate is reduced to nitrite quantitatively and the nitrite thus formed plus that originally present is determined by the method mentioned above. Experimental and Results Apparatus A Hitachi 139 spectrophotometer was used with 1- or 10-cm glass cells. For the absorption spectrum, a Hitachi EPS-3T automatic recording spectrophotometer was employed.pH was determined with a Hitachi-Horiba M-5 pH meter. Reagents All reagents were of analytical-reagent grade. Standard nitrite solution. About 1 g of dried sodium nitrite was dissolved in 100 ml of re-distilled water. The titre was determined with standard potassium permanganate solution .2 Standard nitrate solution. Potassium nitrate (1.1 g) dried at 105-110 "C was weighed accurately and dissolved in 100 ml of distilled water. p-A minoacetophenone hydrochzotde solution. 9-Aminoacetophenone (0.5 g) was dissolved in 5ml of concentrated hydrochloric acid and diluted with distilled water to 50 ml in a calibrated flask. m-Phenylenediammonium chloride (1.34 g) was weighed and dissolved in 0.08 ml of concentrated hydrochloric acid, diluted with distilled water to 50ml in a calibrated flask and stored in a brown-glass bottle.This solution can be used for 10 days without deterioration. Bufer solution (pH 9.3). Ammonium chloride solution (0.1 M) and aqueous ammonia (0.1 M) are mixed, the pH being adjusted with a pH meter. Cadmium-copper column. Cadmium powder (Merk, 20-60 mesh) was used for the preparation of the cadmium - copper c01umn.~ The solution was stored in a brown-glass bottle. m-Phenylenediamine solution. Determination of Nitrite The procedure for the determination of nitrite was devised on the basis of previous wmkl as follows. A water sample (25 ml) is pipetted into a 50-ml calibrated flask and 10-20 ml of distilled water, 0.5 ml of $-aminoacetophenone hydrochloride solution are added and the solution is mixed well.The pH of the solution is 2.0-2.5. After 3-5min, m-phenylene- diamine solution (0.5 ml) is added, the solution is made up to the mark with distilled water and the solution is mixed. After 30 min, the absorbance at 460 nm is measured in 10-cm cells. The calibration graph is a straight line passing through the origin and the molar1196 SHORT PAPERS Analyst, Vol. 104 absorptivity is 4.7 x lo4 1 mol-l cm-l, whereas the molar absorptivity in toluene, in the previous work,l is 2.3 x lo4 1 mol-1 cm-l. The sensitivity is double that of the extraction method. Determination of Nitrate The reducing power is influenced by the grain size and amount of the reductant, the flow-rate and pH of the water used and other factors.Although it is difficult to select constant reducing con- ditions, after they have been decided upon a constant reducing power is maintained for a long period. The following conditions were used: grain size, 20-60 mesh; column cross- section, 0.8 cm2; column length, 14 cm; flow-rate, 0.048 ml s-l; pH, 9.0-10.5; reduction percentage, 97%. The sample solution (10 ml) is pipetted into a 50-ml beaker and 5 ml of a buffer solution (pH 9.3) are added and mixed. The solution is passed through the column, which is then washed several times with 5 ml of &fold diluted buffer solution and 3 4 ml of distilled water. The eluate is collected in a 50-ml calibrated flask and made up to the mark with distilled water. The solution is used for the determination of nitrite mentioned above using l-cm glass cells.By this procedure the calibration graph was straight and the molar absorptivity was 4.6 x lo4 1 mol-l cm-l, which was 97% of the absorptivity for pure nitrite (4.7 x lo4 1 mol-l cm-l). At the same time nitrite was determined by this procedure and the recovery was 95%. The cadmium - copper reduction column is prepared according to the l i t e r a t ~ r e . ~ Effect of Diverse Ions less than The ions normally present in river waters do not interfere. No interference is caused by M Ca2+, Mg2+, Na+, K+, HC03-, SO,2-, C1- or NH,+. TABLE I DETERMINATION OF NITRATE AND NITRITE IN RIVER WATERS IN OKAYAMA PREFECTURE Sample location River Takahashz*- Niimi . . . . .. Jkura . . . . .. Naruto . . . . .. Minochi-Bashi . ... Kasumi-Bashi . . . . Kiyone . . .. .. River A sahi 7- Yubara . . .. .. Katsuyama . . .. Ochiai . . . . .. Eyomi-Bashi . . . . Shinada-Bashi . . .. Kanagawa . . .. Ohara-Bashi . . .. Sakura-Bashi . . . . River Yosh.ii$- Tsuyama .. .. Nigaki . . . . . . Kumayama . . .. Saidaiji . . . . . . Yanahara . . . . Osafune . . .. Values in parentheses are recoveries (yo). Total/mg 1-l Nitrite-N**/pg 1-1 Nitrate-N/mg 1-' . . . . .. .. .. .. . . .. . . .. .. .. . . . . .. . . . . .. . . . . 0.105 (97)$ 2.0 (100) 0.103 0.212 (102)s 3.6 (99) 0.209 0.222 (101)s 3.5 (97) 0.219 0.362 (101)s 14.4 (102) 0.348 0.309 (lOO)l] 5.6 (94) 0.304 0.333 (100)s 6.5 (100) 0.327 0.275 (10214 0.245 (102)s 0.280 (101)q 0.726 (98)1/ 0.482 (99)'v 0.657 (103)T 0.642 (102)T 0.580 (lO0)T 2.7 (100) 2.1 (100) 2.8 (100) 8.8 (101) 13.6 (99) 3.1 (98) 4.6 (95) 9.4 (105) 0.272 0.243 0.280 0.713 0.479 0.649 0.638 0.570 0.418 (98)'\[ 3.4 (99) 0.416 0.531 (lOO)T[ 12.1 (100) 0.520 0.572 (93)'l 10.0 (102) 0.563 0.592 (98)'B 9.3 (101) 0.583 0.628 (95j$ 8.5 ( 0.576 (99)'Ij 7.8 ( * Samples taken on 13th December, 1977.t Samples taken on 29th November, 1977. $ Samples taken on 17th January, 1978. 9: 7.2 pg of nitrate-N were added in a 50-ml calibrated flask. 7 2.9 pg of nitrate-N were added in a 50-ml calibrated flask. I/ 5.8 pg of nitrate-N were added in a 50-ml calibrated flask. ** 0.29 pg of nitrite-N was added in a 50-ml calibrated flask ooj 0.620 01) 0.569 n all instances.December, 1979 SHORT PAPERS 1197 Nitrate and Nitrite in River Waters in Okayama Prefecture The sum of nitrate and nitrite is determined by the cadmium - copper column method.The nitrate content is calculated by deducting 95% of the amount of nitrite from the sum of nitrate and nitrite, because nitrite existing originally is reduced to 95% by the column method. The river water samples should be filtered through a membrane filter (0.45 pm) and used for the determ- ination of nitrate and nitrite as soon as possible afterwards. Each value is the average of three determinations. The amount of nitrite in river water is measured by the above-mentioned method. The results for river waters in Okayama Prefecture are shown in Table I. A recovery test was carried out in each instance. Conclusion The nitrite-nitrogen content in river waters in Okayama Prefecture is 2-14 pg 1-1 and the nitrate-nitrogen content is 0.1-0.7 mg 1-1 in winter. The nitrite and nitrate contents increase gradually towards the lower reaches of the river. Standing water contains high concentrations of nitrate and nitrite, for example, at Eyomi-Bashi on the River Asahi and Minochi-Bashi on the River Takahashi. This effect is caused by micro-organisms. References 1. 2. 3. American Public Health Association, American Water Works Association and Water Pollution Control Federation, “Standard Methods for the Examination of Water and Wastewater,” Fourteenth Edition, American Public Health Association, New York, 1975, p. 423. TGei, K., and Kiyose, T., Analytica Chim. Actn, 1977, 88, 125. JIS (Japanese Industrial Standard), K8019, 1961. Received April 20th, 1979 Accepted June 6th, 1979

ISSN:0003-2654    

DOI:10.1039/AN9790401195

出版商:RSC    

年代:1979

数据来源: RSC