摘要:

Analyst, December, 1968, Vol. 93, $$. 821-826 821 A Simple Field Test for the Determination of Hydrogen Fluoride in Air BY B. S. MARSHALL AND R. WOOD (Ministry of Technology, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, S.E. 1) A field method is described for determining hydrogen fluoride vapour in air at concentrations up to 20pg of hydrogen fluoride per litre. The gas is collected in an acidic solution of zirconium - Solochrome cyanine R reagent and the observed bleaching of the colour compared with standards. The apparatus used is simple to operate and the time required for a determination is less than 5 minutes. h dynamic method for the generation of standard atmospheres of hydrogen fluoride is also described. HYDROGEN fluoride is widely used in the chemical industry and in the petroleum industry in the synthesis of high octane spirit.It is also used in the manufacture of aluminium fluoride and synthetic cryolite for the production of aluminium. Considerable amounts of hydrogen fluoride are also used in the manufacture of refrigerants and fluorine-containing plastics. As hydrogen fluoride gas is highly toxic, with a threshold limit value of 3 p.p.m. v/v (2.5 pg per litre) in air,l there is a need for a simple, rapid field test for its detection in industrial atmospheres at this level. Any such test should preferably be capable of being used by non-scientific staff. Several methods for the determination of hydrogen fluoride in air have been reviewed by Farrah.2 Most of them involve the preliminary trapping and concentration of the gas in water or sodium hydroxide solution, or on filter-papers impregnated with calcium hydroxide, followed by a fluoride distillation and a final colorimetric determination of the fluoride ion.This general method, although normally precise and specific, is time consuming, requires considerable expertise with the necessary distillation apparatus and thus cannot be used to give a rapid check on the hydrogen fluoride concentration present in a factory atmosphere. The main requirements of a field test are ease of manipulation, rapid colour development and a good visual colour discrimination between neighbouring standards. When possible, a positive increase in colour, rather than a bleaching effect, with increasing concentration of air-borne contamination is desirable.With these points in mind we selected for examination two of the methods in general use in fluoride determinations for possible development of a field test for hydrogen fluoride. These were the lanthanum - alizarin - fluorine blue method3 and the zirconium - Solochrome cyanine R method: as modified by Dixoa6 A preliminary assessment of these two methods was carried out with aqueous solutions containing a range of total fluoride from 0 to 2.5 pg. This would be equivalent to the range of hydrogen fluoride concentrations collected from 500-ml samples of industrial atmospheres containing up to twice the present threshold limit value of the gas. Although the zirconium - Solochrome cyanine R method involves bleaching of the colour, it was found to give better visual colour differentiation for this range of fluoride concentrations than the positive colours of the lanthanum - alizarin - fluorine blue method and, consequently, was chosen for further examination as a possible basis for a field test.0 SAC; Crown Copyright Reserved822 MARSHALL AND WOOD: A SIMPLE FIELD TEST FOR THE EXPERIMENTAL [ktna@st, vol. 93 PREPARATION AND CALIBRATION OF STANDARD ATMOSPHERES OF HYDROGEN FLUORIDE- As hydrogen fluoride gas attacks glass, the apparatus for the generation of standard atmospheres of it was constructed so that all of the surfaces in contact with the gas were made of non-reactive materials, e.g., polythene. Prefiaration-Hydrogen fluoride gas from a low-pressure cylinder (supplied by the Matheson Company Inc.) maintained at 22°C in a thermostatically controlled bath was passed through a polythene restrictor and then into a polythene mixing chamber, into which 10 litres of diluting air per minute were flowing.By using a second restrictor, a short length of PTFE tubing with an adjustable screw-clip, 10ml of the dilute atmosphere per minute were passed into a second polythene mixing chamber, in which it was diluted with a further 10 litres of air per minute to give a working atmosphere of about 2.5 pg of hydrogen fluoride per litre. The 10-ml per minute flow-rate was achieved beforehand by connecting the output of the second restrictor to a flow meter and adjusting to the required flow by using hydrogen fluoride free air. Hydrogen fluoride atmospheres of other concentrations were prepared by suitably adjusting the flow-rate of the second diluting stream of air.The polythene restrictor was made by removing the central wire, outer sheath and screening from a piece of co-axial cable, 70 mm long, closing down the bore of the remaining 5-mm 0.d. polythene tubing, by heating, on to a piece of 42 s.w.g. wire and then removing this wire when cold. Adiabatic cooling and consequent liquefaction of the hydrogen fluoride vapour issuing from the polythene restrictor were overcome by inserting, between the cylinder and the restrictor, a 65-mm length of stainless-steel tubing of 6-mm i d . wound with a low-output wire heater. Polythene screw-top bottles of 250 and 1000-ml capacity were easily adapted to serve as the first and second mixing chambers, respectively, and all of the pipework in contact with the hydrogen fluoride was made of polythene.No conditioning problems were experienced with this apparatus when used for the generation of hydrogen fiuoride atmospheres. Calibration-The output of the cylinder was checked by passing the gas issuing from the first restrictor into 0.1 N sodium hydroxide solution for a known length of time, and back- titrating the excess of alkali with standard acid. Under the above conditions, 31 ml of hydrogen fluoride gas were delivered per minute. The working atmospheres were calibrated by passing samples at the rate of 1 litre per minute for 5 minutes through 15 ml of water contained in an absorber fitted with a polythene inlet tube. It had previously been found that virtually 100 per cent. of the hydrogen fluoride at the atmosphere concentrations used was collected in one absorber.Other workers6 had shown that water was as efficient as an alkaline solution as a trapping agent for hydrogen fluoride from air samples. The fluoride collected was determined spectrophotometrically3 with the lanthanum - alizarin - fluorine blue reagent at 625 nm and the concentration of the atmosphere was calculated by reference to a previously prepared standard graph. DEVELOPMENT OF FIELD TEST- With the zirconium - Solochrome cyanine R reagent, Dixon6 has devised an improved spectrophotometric method for the determination of fluoride in water in the range 0 to 2.5 pg. This procedure, and the range of fluoride it covered, appeared to suit our requirements.The development of a test involving the use of visual colour standards equivalent to 0, 1-25, 2.5 and 5 pg of hydrogen fluoride per litre of air was envisaged. A 500-ml sample would normally be taken in the field by using a hand aspirator of 125-ml capacity. However, by reducing the number of aspirations and using the same set of colour standards, the range of hydrogen fluoride concentrations in air capable of being determined could be extended. Standard hydrogen fluoride atmospheres (500ml), containing 1.25, 2.5 and 5.0p.g of the gas per litre, were sampled at the rate of 125 ml per minute through 5 ml of water; 1 ml of each of the Solochrome cyanine R and zirconium solutions6 was added to the absorbing solutions after sampling.The respective colours obtained were compared with those of a similar set of solutions prepared from an aqueous fluoride solution and containing 0.6, 1.2 and 2.4 pg of fluoride. The visual colour matches obtained showed that the hydrogen fluoride was being quantitatively trapped and determined. Later, to minimise the number of opera- tions required, it was found that 5 ml of diluted, mixed reagent containing 1 ml of eachDecember, 19681 DETERMINATION OF HYDROGEN FLUORIDE IN AIR 823 of the chromogenic reagents could be used directly as trapping agent, and also gave colour matches with similarly prepared fluoride solutions over the range 0 to 2-4 pg of fluoride. The visual colour differentiation between the four fluoride levels, 0, 0.6, 1.2 and 2.4 pg, was considered to be entirely satisfactory for field test purposes.PREPARATION OF COLOUR STANDARDS- A set of colour standards for use with the proposed test was conveniently prepared by using a standard sodium fluoride solution and solutions of the chromogenic agents. Details of the preparation are given later. With these standards it was found possible to determine the fluoride content of a sample at least to the nearest f0.625 pg per litre ( i e . , a quarter of the present threshold limit value) between 0 and 2-5pg of hydrogen fluoride per litre and at least to the nearest 1.25 pg per litre between 2.5 and 5Opg of hydrogen fluoride per litre. INTERFERENCES- Aluminium, phosphate and sulphate are well known interferences in the zirconium - Solochrome cyanine R method for fluoride,4 the first being a negative interference and the others positive interferences.The effects of these interferences on the proposed test were individually assessed by adding increasing amounts of each species in solution to a series of fluoride solutions equivalent to 0, 1.25, 2.5 and 5.0 pg of hydrogen fluoride per litre of air, and finally adding the mixed chromogenic reagent. The level of interference of each of the species was taken as the lowest concentration that would just produce a significant visual colour difference between the solution and an equivalent fluoride standard. The concentra- tions for aluminium, phosphate and sulphate were 1, 1.6 and 100, respectively, expressed as micrograms per litre of air. Besides the above study, the effects on the proposed test of several substances, which might occur together with hydrogen fluoride in industrial atmospheres, were examined.When the threshold limit value of any gas known to interfere with the proposed field test is present in an industrial atmosphere, then such a concentration constitutes a hazard in its own right, irrespective of the hydrogen fluoride concentration. In view of this, experiments were conducted to ascertain the effects on the proposed test of possible interfering gases and vapours up to an arbitrarily chosen equivalent of twice their present threshold limit value. Atmospheres were prepared containing 1.25, 2.5 and 5*0pg of hydrogen fluoride per litre by using, in the second dilution stage, air containing amounts of the interfering substances up to a concentration of twice their threshold limit value.These atmospheres were then sampled by the proposed test method. It was found that nitrogen dioxide and sulphur dioxide did not interfere at concentrations up to twice their present threshold limit values. i.e., 18 and 26 pg per litre, respectively. Also, sulphur trioxide did not interfere at concen- trations up to 1.6 pg per litre of air, ie., equivalent to twice the present threshold limit value for sulphuric acid. Experiments were also performed to assess the effect on the test of various amounts of water vapour present in atmospheres containing hydrogen fluoride by setting up, as above, standard atmospheres of gas and using air containing known amounts of water vapour for the second dilution stage.Water vapour did not interfere at concentrations up to 18mg per litre of air at 22" C. In view of the interfering effects of aluminium and phosphate, this field test is not recommended for the testing of industrial atmospheres polluted with fluoride-containing dusts. Several such materials used in industry, e.g., cryolite, apatite and various other phos- phate rocks, contain sufficient aluminium or phosphate to interfere with the proposed test. Although water vapour does not appear to interfere with the test, provided that con- densation does not occur in the sampling apparatus, it is recommended in certain instances that the inlet tube be washed with the mixed reagent after sampling. This is especially important when samples are taken of a damp atmosphere or one in which a dilute aqueous hydrogen fluoride spray has been used.In the sampling of such atmospheres, hydrogen fluoride may be trapped in water droplets on the inside of the inlet tube. The washing of this tube can be carried out by blowing carefully down the side-arm of the glass test-tube and thereby raising the level of liquid in the inlet tube to within 10 mm of its top. (This is equivalent to a relative humidity of 92.5 per cent.)824 APPARATUS- Absorbers-Several are required, each comprised of a glass test-tube with a polythene inlet tube (see Fig. 1). For ease of dispensing reagents, make a mark at the 5-ml leveI. Each test-tube should be fitted with its own inlet tube. MARSHALL AND WOOD: A SIMPLE FIELD TEST FOR THE FIELD TEST FOR THE DETERMINATION OF HYDROGEN FLUORIDE IN AIR [Analyst, Vol.93 A= Rubber bung B=Glass tube, 13mm i.d., C= Polythene inlet tube, 5mm i.d., 18-5-cm over-all I5.5-cm over-all length length Fig. 1. Absorber Asj5irator-A rubber-bulb hand aspirator (obtainable from Siebe Gorman and Co. Ltd,, Davis Road, Chessington, Surrey) adjusted to deliver 125ml of sample per minute. REAGENTS- All reagents should be of analytical-reagent quality unless otherwise stated. Zircoaizlm soZzctiort-l>issolve 36 mg of zirconium oxychloride octahydrate, ZrOC1,.8H20, in water, add 1201111 of concentrated hydrochloric acid and dilute to 500ml. Solochrome cyanivze R (C.I. 43820) soZzctio.n--Dissolve 60 mg of the purified reagent in water, add 24ml of N hydrochloric acid and dilute to 250ml. This reagent, as normally supplied, contains variable amounts of sodium sulphate.The dye can be separated from it by extraction with methanol. The extract is evaporated to dryness under reduced pressure, and the resulting purified material used to prepare the reagent solution. Mixed reageat-Combine 10ml of each of the zirconium and Solochrome cyanine R solutions and dilute to 200ml with water. This solution appears to be stable for a con- siderable time, but to obviate any possible contamination problems, it is recommended that fresh mixed reagent be prepared for each series of tests. Stavzdard j h r i d e solutioa-Dissolve 2.121 g of sodium fluoride in water, add 1 ml of 0.1 N sodium hydroxide solution and dilute to 1 litre with water. Dilute 2-5 ml of this solution to 1 litre to give a solution containing 2.4pg of fluoride per ml, i.e., equivalent to 2-5pg of hydrogen fluoride per ml. PROCEDURE- In an uncontaminated atmosphere, well away from the suspected source of hydrogen fluoride, place 5 ml of the mixed reagent in the absorbing tube, insert the inlet tube and connect the aspirator to the side-arm.Transfer the assembled apparatus to the sampling site, and draw a 500-ml sample (i.e., four aspirations) of the atmosphere through the reagent. Remove the apparatus to an uncontaminated atmosphere. Disconnect the aspirator fromDecember, 19681 DETERMINATION OF HYDROGEN FLUORIDE IN AIR 825 the side-arm of the glass test-tube. If the sample has been taken in a humid atmosphere, wash the inlet tube by gently blowing down the side-arm, and raise the level of the mixed reagent to within about 1Omm of the top of the inlet tube.Place a finger on the end of the inlet tube to hold the mixed reagent in that position for a few seconds. Allow the liquid to flow back into the glass test-tube and remove the inlet tube. Compare the colour of the sample solution, preferably in daylight, in turn with 5ml of each of the fluoride colour standards contained in tubes of similar diameter to the sample test-tube. View through the depths of the respective liquids against a white (paper) background. Should the level of hydrogen fluoride with a 500-ml sample of atmosphere be above 5 p g per litre, a more accurate determination of the true concentration can be made by using a 125-ml sample. The standard that gives a colour match with the sample solution is then multiplied by four to give the amount of hydrogen fluoride in micrograms per litre present in the atmosphere.When a test is required on an atmosphere that is either not readily accessible or possibly contains high concentrations of hydrogen fluoride, the sampling should be carried out as follows. Connect the site to be tested to the sampling apparatus with a length of polythene tubing. Start aspirating and continue until a colour change is obtained in the mixed reagent. Dis- connect the absorber and rapidly replace it with another containing fresh mixed reagent. Carry out the test as described above. It is recommended that an operator sampling high concentrations of hydrogen fluoride in an atmosphere should have suitable respiratory pro- tection.NOTE- should be rinsed with a few millilitres of fresh reagent and the inlet tube dried before re-use. To avoid cross-contamination between samples, each absorber, i.e., test-tube and inlet tube, PREPARATION OF FLUORIDE COLOUR STANDARDS- To a set of four 100-ml graduated flasks add 0, 5, 10 and 20 ml of the dilute standard fluoride solution. Add 5 ml each of the zirconium and Solochrome cyanine R solutions to each flask and dilute to volume with water. These standards represent 0, 1-25, 2.5 and 6 pg of hydrogen fluoride per litre of air, respectively. The standards, if stoppered, are stable for at least 1 week. APPLICATION OF METHOD- The proposed test was assessed and checked under field conditions at various sites where hydrogen fluoride was being used.The check testing was normally carried out by taking three concurrent samples for each atmosphere analysed and using a 3-way manifold and a common sampling inlet. The three samples taken were as follows. (i) A 500-ml sample by the proposed test over a period of 5 minutes. (G) A 5-litre sample taken at 1 litre per minute, with 50 ml of mixed reagent as absorbing solution. This was a ten times scaling-up of the field test, and the fluoride collected was determined visually as in (i) by using colour standards. (iii) A 5-litre sample taken at 1 litre per minute, with 15ml of water as absorbing solution to which lanthanum - alizarin - fluorine blue reagent was added after sampling. The fluoride was determined spectrophotometrically, with reference to a previously prepared calibration graph.Table I gives the results obtained in one check-testing series carried out in and around a fume cupboard in a laboratory in which hydrogen fluoride was being used. Some of the samples were deliberately taken inside the fume cupboard to enable an assessment of the field test to be made at high levels of hydrogen fluoride contamination. The results shown in Table I, and those obtained at other sites, appeared to confirm the validity of the proposed field test for the determination of hydrogen fluoride in air. It should, however, be mentioned that in some of the early check tests performed, high and erratic results were obtained when using the field method compared with the other two concurrently taken samples.This was traced to the contamination of the sampling absorber, the polythene inlet tube in particular, between the taking of successive samples. It appeared826 MARSHALL AND WOOD TABLE I COMPARISON OF THE RESULTS OF THE ANALYSIS OF HYDROGEN FLUORIDE CONTAMINATED ATMOSPHERES BY THE PROPOSED FIELD TEST AND TWO OTHER METHODS Hydrogen fluoride concentration found, pg per litre, by- r A -l Lanthanum - alizarin - fluorine blue reagent, Sample Field test Field test x 10 spectrophotometrically 1 0 0 0.26 2 0.625 0.625 1.0 3 0.625 0.625 0.625 4 0-625 0-625 0-86 5 1-25 1-25 1.76 6 1.25 1-25 1-12 7 2-5 2 4 2.6 8 3.75 3.76 2.5 9 1@0* 1o.ot 9.3 10 20.0* 20.0f. 24-52 * A 125-ml sample taken at the mid-point of time during which the sample for spectrophotometric determination was taken. t A 2.5-litre sample. $ A 1-25-litre sample. that as the volume of absorbing solution used in the field test was small compared with those used in the other two concurrent tests, it was relatively more susceptible to contamina- tion from the inlet tube used. This effect was obviated either by using fresh absorbers for each test or washing the absorber components with mixed reagent between tests and drying the inlet tube. The test apparatus should always be assembled in an uncontaminated atmosphere. This work was carried out on behalf of the Department of Employment and Productivity Committee on Tests for Toxic Substances in Air. We thank the Government Chemist for permission to publish this paper. REFERENCES 1. 2. 3. 4. 5. 6. “Ministry of Labour, Safety, Health and Welfare, New Series No. 8, Dusts and Fumes in Factory Farrah, G. H., J. Air Pollut. Control Ass., 1967, 17, 738. Greenhalgh, R., and Riley, J. P., Analytica Chim. Ada, 1961, 25, 179. Megregian, S., Analyt. Chenz., 1964, 26, 1161. Dixon, E. J., in preparation. Pack, M. R., Hill, A. C., Thomas, M. D., and Transtrum, L. G., A.S.T.M. Special Technical Received June 27th, 1968 Atmospheres, Third Edition, H.M. Stationery Office, London, 1966. Publication No. 281, 1958, p. 27.

ISSN:0003-2654    

DOI:10.1039/AN9689300821

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

AlzaZyst, December, 1968, Vol. 93, $$. 827-831 827 A Simple Apparatus for Separating Fluorine from Aluminosilicates by Pyrohydrolysis BY A. C. D. NEWMAN (Rothamsled Experinzental Station, Harpenden, Herts.) Fluorine-bearing minerals are hydrolysed a t 700" to 800°C in a gas- heated fused-silica tube. The hydrogen fluoride evolved is absorbed in alkali and determined by titration with thorium nitrate or absorptiometrically with cerium - alizarin complexone. Recoveries from sodium fluoride averaged 98-6 per cent,, with a coefficient of variation of 3.2 per cent., and the deter- mined fluorine contents of the silicate rock standards GSP-I and G2 were 0.381 and 0.134 per cent. The method is simple and rapid, and is suitable for determining fluorine in micas and related aluminosilicates. FLUORINE is still most often separated from interfering elements by steam-distillation as fluorosilicic acid from sulphuric, phosphoric or perchloric acids (Willard - Winter distillationl) ; in silicate analysis, a preliminary fusion and precipitation of alumina and silica from the leached melt is usual.The procedure is long and its success depends on close attention being paid to detail.2 Special stills have been designed to improve control of the distillation condi- tions, for recovery of fluorine is slow and often incomplete, so that a correction factor is sometimes a~plied.~ High-temperature hydrolysis ("pyrohydrolysis") quickly releases fluorine its hydrogen fluoride without preliminary fusion, and this reaction is the basis of an attractive alternative to Willard - Winter distillation,4,6 yet recent literature suggests that pyrohydrolytic separation is still not widely known or applied, perhaps because the original workers used expensive, specially designed platinum apparatuss The purpose of this paper is to show that alumino- silicates can be readily pyrohydrolysed in simple apparatus and that good results are obtained in a fraction of the time required for the Willard - Winter distillation.The method is based on the following thermodynamic principle. The position of equili- brium in the general reaction MF,, + nH,O + MO, + 2nHF depends on temperature and, because the standard entropy of two moles of hydrogen Auoride is about twice that of one mole of water, lies increasingly to the right as temperature increases. The rate of reaction is accelerated in the presence of some oxides, for instance, those of uranium, vanadium, aluminium and tungsten; vanadium pentoxide melts at about 670" C, so it also acts as a flux, and is preferred in this laboratory to tungsten trioxide.Warm carrier gas, saturated with water vapour, is passed over a heated mixture of sample and accelerator, and the hydrogen fluoride evolved is collected in dilute alkali. Fluoride in the condensate can be determined by many methods; a titrimetric and an absorptiometric finish have been used in this laboratory. 0 SAC and the author.828 NEWMAN: A SIMPLE APPARATUS FOR SEPARATING [Analyst, Vol. 93 EXPERIMENTAL APPARATUS- As shown in Fig. 1, compressed air is filtered through cotton-wool, A, and bubbled through distilled water heated to 90" C in a Pyrex flask, B, on an electric hot-plate. The warm, moist air passes through a water-trap, C, and immediately into the transparent fused- silica reaction tube, D, which is 45 cm long, with an outside diameter of 20 mm narrowing to 6-mm diameter, and bent at right angles a little beyond the constriction." A small, detachable condenser, J, made from two Quickfit SQ13 screw-thread joints joined end-to-end with two side-tubes for water inlet and outlet, is fitted to the vertical section of the tube.The reaction tube is heated by two batswing burners, E and F, and a bunsen burner, G. The condensate is collected in a polythene bottle, H, containing sodium hydroxide solution. n Fig. 1. Apparatus for separating fluorine by pyrohydrolysis (lettered parts of the apparatus are referred to in the text) REAGENTS- Except where specified, analytical-grade reagents are used throughout.Vanadium pentoxide-Heat ammonium vanadate in a silica basin to between 500" and 550" C for 4 hours; should any black lumps remain, stir the powder and heat for a further period until the residue is uniformly dark red. Thorium nitrate, 0.005 M-Dissolve 2.94 g of thorium nitrate, Th(NO,),.6H,O, in 1 litre of distilled water containing 0.4 ml of nitric acid. StandardJEuoride solfition-Dissolve 1-105 g of sodium fluoride in 1 litre of distilled water; this solution contains 500pg of fluorine per ml. Acidimetric i~zdicator-Dissolve 0.2 g of $-nitrophenol in 100 ml of distilled water containing a little sodium hydroxide to assist dissolution. Alizarin red S indicator-Dissolve 100 mg of purified' Alizarin red S in 100 ml of distilled water.The normal-grade reagent can be used but the end-point is less clear. Bufer solution, pH 2.9-Dissolve 22.7 g of monochloroacetic acid in 100 ml of distilled water. Titrate 50 ml with 25 per cent. sodium hydroxide solution, with phenolphthalein as indicator, mix with the remaining 50 ml of monochloroacetic acid solution and dilute to 500 ml. Colloid stabilisefl-Mix 1 g of starch into a thin paste with a little water and pour it, with stirring, into 100ml of boiling distilled water; boil for 1 minute, then cool. Absorbent solution (0.1 M sodium hydroxide)-Dissolve 4 g of sodium hydroxide in 1 litre of distilled water. Neutralising acid (0.1 M hydrochloric acid)-Dilute 8.6 ml of concentrated hydrochloric acid to 1 litre.* A suitable tube was inexpensively made to order by T. W. Wingent, Ltd., Cambridge.December, 19681 PYROHYDROLYSIS- FLUORINE FROM ALUMINOSILICATES BY PYROHYDROLYSIS METHOD 829 Weigh 10 to 100 mg of sample (<300 mesh) containing 0.1 to 4 mg of fluorine, and about 250 mg of vanadium pentoxide accelerator. Grind the sample and one third of the vanadium pentoxide in an agate mortar and transfer the mixture to a silica boat (50 x 15 mm). Transfer the remainder of the mixture from the mortar by grinding with the remainder of the accelerator in two portions. Heat the water to 90" C, light the burners and pass moist air through the silica tube for 10 minutes. Separate the connection between the water-trap and the silica tube and turn off the burners.When cool, dry the mouth of the tube with absorbent tissue and push the boat into position above burner F. Place a polythene collecting vessel, containing 5ml of alkaline absorbent solution and a few drops of p-nitrophenol indicator, under the exit of the reaction tube; the end of the tube should dip below the level of the liquid. Re-connect the water-trap to the reaction tube, light burners E and G, and pass air through the apparatus. When the vertical part of the silica tube below the condenser is slightly warm to the touch, light burner F, increasing the heat slowly until the vanadium pentoxide melts. Maintain this heat and collect the condensate for 30 minutes. Disconnect the air inlet from the silica tube, and turn off the burners. Remove the polythene collector, wash down the end of the silica tube with a little distilled water and add 0.1 M hydrochloric acid until the yellow colour of $-nitrophenol is just discharged.Dry the silica tube with absorbent tissue and remove the sample boat. The apparatus is now ready for the next determination. TITRIMETRIC FINISH- Transfer the whole condensate to a 150-ml conical flask, with a mark at 50-ml volume, and add 5ml of starch solution, 2ml of buffer and 3 drops of Alizarin red S indicator. Dilute nearly to the mark at 50m1, and titrate the solution to a pink colour with thorium nitrate, so that the volume at the end-point is 50 ml. Prepare a calibration graph by titrating 1, 2, 3 and 4-ml aliquots of sodium fluoride standard containing 0.5, 1.0, 1.5 and 2.0 mg of fluorine, respectively, with exactly the same conditions as in the titration of the condensate.ABSORPTIOMETRIC FINISH- The colour reaction of fluoride with cerium(II1) - alizarin complexone is a reliable spectro- photometric method; the preparation of the reagent solutions and the procedure have been described.s After neutralising the condensate, dilute to 100ml and use a suitable aliquot containing 10 to 40 pg of fluorine, which is the range of the method. BLANK DETERMINATION- insignificant. Occasionally repeat the determination without adding sample ; the blank should be NOTE- Water vapour in the air stream sometimes condenses to a fog and recovery of fluorine is then incomplete. Formation of fog can be prevented by decreasing the water flow in the condenser and increasing the air flow so that the air is still warm after passing through the condenser and thus does not become supersaturated; for additional control, the heat from burner G may be varied.An air flow of about 1 litre per minute was used, but accurate metering* seems unnecessary. If water collects near the constriction in the silica tube, it must be driven over into the condensate by gently heating, because it is likely to contain dissolved hydrofluoric acid. RESULTS AND DISCUSSION The procedure was evaluated by determining the recovery of fluorine added as sodium fluoride or as ground, clear, colourless fluorspar, which was assumed to contain the theoretical amount of fluorine (Table I), and by determining the fluorine contents of several standard samples. During the development of the method, the reaction tube was heated in an electric furnace but, later, gas heating was preferred, and Tables I and I1 include results obtained with both methods of heating.Recoveries were 98.6 per cent. from sodium fluoride (coefficient of variation 3.2 per cent.) and 98.9 per cent. from fluorspar (coefficient of variation 4.2 per cent.), both rather better than the 95 per cent. recovery often found after Willard- Winter830 NEWMAN: A SIMPLE APPARATUS FOR SEPARATING [AWdJ&, VOl. 93 distillation9; the determined fluorine contents of the standard samples agreed well with those reported elsewhere. Results obtained by titration did not differ from those obtained by the absorptiometric method, so that the variance of the results can be attributed to slight variations in the experimental conditions during pyrohydrolysis. RECOVERIES (PER CENT.) Method Sodium fluoride Biotite (B6) Muscovite (M8) Fluorspar Biotite (B6) Muscovite (45.3 per cent.of fluorine) + sodium fluoride + sodium fluoride (48-7 per cent. of fluorine) + fluorspar + fluorspar TABLE I OF FLUORINE FROM SODIUM FLUORIDE AND FLUORSPAR Electric heating r A 1 Titrimetric Absorptiometric 100.2, 98-3 99.3, 103.0 97-4, 101.7 99.5, 92.8 99.2, 97.7 101.5, 99.9 - 96.7, 97-6 97-2, 92.5 99.6 99.1, 98.3 96.2, 100.7 98-3, 97-0 96.9, 96.6 96.0, 99.8 - 91-8, 89.8 Gas heating Absorptiometric 101.8, 100.7 94.9, 99.7 98.2, 97.2 97.3 99.0, 104.6 90.0 107.1, 102-3 96.3, 100.0 105.1, 95.4 103.0 99.5, 97.3 FLUORINE CONTENTS Method Phosphate rock, N.B.S.No. 66 . . GSP-1 (69/19) .. .. .. G2 (76/10) .. .. .. .. Phlogopite (Pl) . . .. .. Phlogopite (P6) . . .. .. P6, not ground with accelerator . . Biotite (B6) . . .. .. .. Muscovite (M8) . . .. .. TABLE I1 OF ROCK STANDARDS AND SOME MICAS Electric heating Gas heating Reported absorp tiome tric absorptiometric values - 3.44, 3-63 3.491 3.54 3.6310 3-6W - 0.384, 0.380 0*3812 - 0.134, 0.129 0*1412 0.380 0.138 6-01 6.07, 6.05 - 5.99 6-01, 5.96 6-08, 5.87 - 5.94, 6.95 6.02, 6-19 4-6, 5-1 - - 3.9, 6.5 0.263, 0-270 - - 0.272 0.476, 0.465 - - 0-439 Experience with the method shows that successful pyrohydrolysis depends mainly on two factors. (i) Intimate mixing of the sample and vanadium pentoxide.(ii) Condensation of hydrogen fluoride without formation of fog. If the sample is not ground with an accelerator, erratic results may be obtained with refractory samples such as phlogopite (P6 in Table 11). An extreme example was a rnicaceous mineral that had previously been ignited at 1OOO" C; when mixed with the accelerator without grinding, only one fiftieth of the fluorine was released, whereas after grinding together the full amount was recovered. The reaction temperature is not critical, although below 600" C the reaction is slow,* and above 800" C vanadium pentoxide distils along the reaction tube, and small amounts may occasionally be detected in the distillate. Only when the temperature exceeds 850" * I am grateful to Dr. P. G. Jeffery of Warren Spring Laboratory, Stevenage, for details of a procedure in which a temperature in the range 665" to 665OC is used; the full method is to be published by G.R. E. C. Gregory and G. 0. Kerr.December, 19681 FLUORINE FROM ALUMINOSILICATES BY PYROHYDROLYSIS 831 to 900°C does sufficient vanadium pentoxide reach the condensate to cause slight inter- ference in the absorptiometric determination, but it is not enough to interfere in the thorium nitrate titration. As close temperature control is not necessary, gas heating is preferred to electric heating. The reaction tube cools rapidly after each pyrohydrolysis so that more determinations can be completed in 1 day. Also, because other parts of the reaction tube can be heated inde- pendently of the sample, it is much easier to prevent a fog forming when the sample is first heated and most of the fluorine has evolved.The method is much quicker than any requiring a preliminary alkaline fusion, and very reliable, provided the sample and accelerator are well mixed and the hydrofluoric acid does not condense to a fog. One person can complete eight analyses in 1 day when using the absorptiometric finish. I acknowledge with thanks the assistance of Mrs. Sylvia Shepherd, who carried out the analyses given in Tables I and 11. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. REFERENCES Willard, H. H., and Winter, 0. B., Ind. Engng Chem. Analyt. Edn, 1933, 5, 7 . Ingamells, C. O., Talanla, 1962, 9, 507. Evans, W. H., and Sergeant, G. A., Analyst, 1967, 92, 690. Nardozzi, M. J., and Lewis, L. L., Analyt. Chem., 1961, 33, 1261. Bennett, H., and Hawley, W. G., “Methods of Silicate Analysis,” Second Edition, Academic Warf, J. C., Cline, W. D., and Tevebaugh, R. D., Analyt. Chem., 1954, 26, 342. King, H. G. C., and Pruden, G., Analyst, 1968, 93, 601. Belcher, R., Leonard, M. A., and MTest, T. S., J. Chem. Soc., 1959, 3577. Peck, L. C., and Smith, V. C., Talanta, 1964, 11, 1343. Reynolds, D. S., J. Ass. Off. Agric. Chem., 1934, 17, 323. Newman, A. C. D., Analytica Chim. Acta, 1958, 19, 471. Flanagan, F. J., Geochim. Cosmochim. Acta, 1967, 31, 289. Press, London, 1965, p. 288. Received May 20th, 1968

ISSN:0003-2654    

DOI:10.1039/AN9689300827

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

832 Analyst, December, 1968, Vol. 93, pp. 832-833 A Simple, Inexpensive, Pyrex to Aluminous Porcelain Vacuum Seal for Use in Thermal Analysis BY M. D. JUDD AND M. I. POPE (College of Technology, Portsmouth, Hants.) A simple and inexpensive method of making a vacuum-tight seal between a B34 Pyrex glass socket and an aluminous porcelain 525 tube is described. The need for a seal of this type is widely encountered in thennal analysis of compounds that evolve gases at temperatures within the range 1000° to 1350°C. TO carry out thermal analysis under vacuum at temperatures in the range 1OOO" to 1350" C, it is frequently necessary to connect an aluminous porcelain vessel to a Pyrex glass gas- handling system. This problem may be encountered in, for example, thermogravimetry, dilatometry, differential thermal and evolved gas analysis.Although it is possible to join Pyrex to aluminous porcelain directly, by means of a graded seal, joints of this type are both expensive and fragile. Furthermore, the life of aluminous porcelain tubes under vacuum at these temperatures is limited, so that the cost of seals becomes an important factor. Fig. 1. Details of the seal used (lettered parts of the apparatus are referred to in the text) The seal discussed here was used in conjunction with a McBain type, spiral silica spring- balance, details of the construction of which were recently described elsewhere.1 The appara- tus has been used to study the thermal decomposition of co-precipitated calcium, strontium and barium carbonates, at a minimum pressure of 2 x 10-4 ton-, with a rate of rise of temperature of 200" C per hour up to 1250" C.As the carbonate decomposed it was therefore necessary for the seal to withstand the passage of hot carbon dioxide gas. The results obtained in this work were presented2 at the Second International Conference on Thermal Analysis. 8 SAC and the authors.JUDD AND POPE 833 Details of the seal are illustrated in Fig. 1. The XAM Pyrex glass adaptor, A, was ground to fit into a thermal aluminous porcelain 625 tube, of nominal bore 28*5mm, D, with the aid of coarse valve grinding paste. After cleaning off the paste, the cone and tube were coated with Holts “Gun - Gum No. 1,” C, pressed together, and then dried for 12 hours at room temperature, followed by 6 hours at 80” C. Finally, the junction between the cone adaptor and the tube was externally coated, B, with Epophen EL6 mixed with an equal volume of hardener EHRl (marketed by the Borden Chemical Co.) and allowed to harden for 48 hours at room temperature. In use, the seal was protected externally by a water-cooling coil, and has successfully withstood, over a period of several months, the conditions described. REFERENCES 1. 2. Pope, M. I., Educ. Ckem., 1965.2, 246. Judd, M. D., and Pope, M. I., Paper presented at the Second International Conference on Thermal Analysis, Worcester, Mass., 1968. Received May 22nd, 1968

ISSN:0003-2654    

DOI:10.1039/AN9689300832

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

834 Analyst, December, 1968, Vol. 93, p . 834 Book Reviews SCHWEIZERISCHES LEBENSMITTELBUCH. Volume I-Special Part. Loose leaf, Pp. x + 214. Fifth Edition. Bern: Eidg. Drucksachen-und Materialzentrale. 1967. Price (Part I) Sw.Fr. 60. These pages are the first to be issued in the new format of the official Swiss Food Examination Manual which, when complete, will consist of two loose-leaf ring-binder volumes. I n addition to introductory material, they comprise four of the chapters that ultimately form part of the second volume: pasta; diatetic foods; honey and honey substitutes; and wines. The complete volumes will contain 66 chapters in all, the majority of which will be based on individual food commodities. From the table of contents included with the introductory pages, the chapters on milk, cooking fats and margarine, coffee, tea and substitutes, and microbiological examination are due to appear in 1968.The whole is under the direction of the federal Schweizerische Lebens- mittelbuchkommission, under the chairmanship of the doyen of Swiss food chemistry Professor 0. Hogl, who in making the publication generally available welcomes comments and suggestions.BOOK REVIEWS 835 This is clearly a comprehensive manual of practical food analysis, including, in many instances, both routine and reference methods for individual determinations and guidance for the interpreta- tion of the analytical results obtained. The interpretations, though sometimes related to Swiss law in particular, add considerably to the value of the compilation. Like other commodity chapters, that on pasta (pp.18) opens with guidance to characteristic analytical data giving, for example, typical ether extract, total lipid, sterols, soluble protein and phosphate data for plain and “3-egg” pasta. While the analytical directions normally provide full working details, calculations and references to original publications are given, there are occasional references to other chapters of the “Lebensmittelbuch,” for example for fibre determina- tion or for the identification of added synthetic colouring matter. A separate index is provided for each chapter. Dietetic foods (pp. 81) are divided into separate sections on infants’ foods; malt extracts; energy foods and slimming diet beverages (diatetische Friihstucksgetranke) ; diabetic foods; and low-sodium and sodium-free foods and adjuncts.The chapter contains a wealth of interpretative detail complete with statistical comment, e.g., for the determination of dried-egg content of compound foods. Honey (with artificial honey, pp. 34) is a commodity to which the Swiss have devoted special attention: details are given for solids (three methods), ash, pH, hydroxy- methylfurfural, dextrin, albumen precipitable by phosphotungstic acid, individual sugars (paper chromatography), apparent sucrose, saccharase and amylase (two methods) determination, together with general directions (including directions for further reading) for the microscopic examination of sediment. -The predominant pollen grains contained may not be so characteristic of the origin of a honey as the particular combination of these with such other features as fungal spores, starch grains, yeast cells, root particles, insect hairs and plant fragments. This is indeed a subject for the expert as is also the interpretation of the various analytical criteria which attempt to distinguish honey predominantly of floral origin ( i e ., bee-honey) from substitutes and mixtures. The chapter on wines (pp. 57) is supplemented by a specially compiled version of Osborne’s tables (pp. 22) for the calculation of the alcohol content of alcohol - water mixtures from the relative density 2Oo/2O0 or the absolute density at 20” C. Various standards for wines are des- cribed, most of the basic analytical methods for arriving at which are generally similar to those used in Britain. It is refreshing to learn that wine tasting is best done in the morning, about 2 hours after breakfast; for the Swiss this puts the optimum time for the dkgustution at about 0900 hours.ADVANCES IN CHROMATOGRAPHY. Volume 5. Pp. xviii + 317. London: Edward Arnold (Publishers) Ltd.; New York: Marcel Dekker, Inc. 1968. Price 135s. This volume continues the series, several of which have been discussed by the reviewer. However, it must be said at the outset that, in the reviewer’s opinion, this volume does not sustain the same standard as the previous volumes. Perhaps this is inevitable because one is conscious of the fact that chromatography could not expand a t the explosive rate of, say, 10 years ago. The articles in the present volume appear to be more of the review article type, which in certain cases have been included to make up the volume.As before, the book is divided into two sections, one dealing with general chromatography, the other with gas chromatography, each section containing three contributions. The first section contains chapters on prediction and control of zone migration rates in ideal liquid - liquid chromatography ; chromatographic advances in toxicology ; and inorganic chromato- graphy on columns of natural or substituted celluloses. Chapter 1 is important as it contains a relatively high proportion of references to the studies of Polish scientists who have worked in this field, most of which are not readily accessible to the majority of chromatographers. The problem facing the use of such models as are proposed, is that one is very rarely dealing with ideal models, and eventually complications arise that can only be surmounted by trial and error.The second chapter is one in which the emphasis is placed on problems facing the toxicologist, and how chromatography can be used to alleviate some of these problems. Although great progress has obviously been made, and the many references given show how useful the technique is, the out- standing feature of the chapter is really dealt with in the last 2 pages, where future trends are discussed. This gives an admirable key to where our society may lead, or in fact, drive us. The third chapter in this section on inorganic chromatography is probably the field closest to the reviewer’s heart.However, it is felt that the author has re-discovered columns of cellulose and found them useful. Indeed, in his closing remarks to the chapter he has very strong words to Cellar-treatment agents will be considered in a separate chapter. H. EGAN Edited by J. CALVIN GIDDINGS and ROY A. KELLEK.836 BOOK REVIEWS [Analyst, Vol. 93 say on the subject of why this field is neglected. This is appreciated, but some of his remarks are open to doubt or speculation and, as science is no less fashionable than fashion, he may be successful in obtaining popularity of this topic-but others have tried a long time ago. Turning to the gas-chromatography section, the chapter on quantitative interpretation of gas-chromatographic data is a very good one. It puts clearly and succinctly the problems involved, and describes how various gadgets and devices are used to overcome these problems.The kernel of the problem is outlined on pages 222-225, where the required quality of the gas-chromatographic data required is listed. How many separations live up to all of these criteria-the concluding paragraph on page 226 possibly provides the clue. On one hand are the people who say that pollution is intensifying and on the other those who say that maybe the case is overstated. Whichever school one follows, it is the analytical chemist who has cut through the morass of specu- lation and developed methods of analysis to combat the problem. The second chapter of this section discusses atmospheric analysis by gas chromatography, dealing only with “the atmosphere a t or near ground level over urban and non-urban land masses.” Diesel and internal-combustion engine pollution, etc., will be covered in a later volume of the series.Thus in the present chapter there is a discussion of the pollutants found as a result of man’s activities. The most surprising comment that can be made is the lack of analyses that have been carried out, and the development work that will be necessary to rectify this situation, as the conclusions of the chapter are 2 pages of might-be, the need for, and have-not-yet-been applied. The final chapter describes non-ionisation detectors in gas chromatography, and is a detailed survey review of the advances in the topic since 1964. Obviously, these detectors have a future, but how good it will be seems to depend almost entirely, not on their merits as detectors but on their cost, availability and, least tangible of all, on the whims and fashions of gas chromato- graphers.The chapter really says very little that is not already readily available in the literature. In line with previous volumes of the series the book is well produced, both with regard to printing and binding, but is very expensive for the information it contains. It is a book for an organisation to buy. G. NICKLESS STANDARD METHODS FOR TESTING TAR AND ITS PRODUCTS. Sixth Edition. Pp. viii + 662. Gomersal, Cleckheaton and York: Standardization of Tar Products Tests Committee. 1967. Price 80s. The first edition of this work was published in 1929 and fresh editions now appear to come every 5 years. This sixth edition represents a thorough revision of the previous one, and includes a list of the changes that have taken place. Among these may be noted the acceptance of a single expression for the weight/volume relationship, density a t 20” C. This should be a great help, for the confusion in different parts of the world in respect of density is great, while even in a single country different industries have their own definitions. It is to be noted that five gas-chromatographic tests appear, and these are accompanied by a 17-page dissertation on the general principles of the method. The five methods include deter- minations of benzene in toluene, toluene in benzene, o-cresol in cresylic acid and pyridine and homologues in tar bases. It is interesting to find details of three standard methods of the U.S. Customs Laboratory-for creosote oil distillation, cresylic acid and other coal tar distillates, and for naphthalene. The problem of pollution is one where argument abounds. Edited by P. V. WATKINS. Wherever possible, British Standard apparatus has been specified. K. A. WILLIAMS

ISSN:0003-2654    

DOI:10.1039/AN968930834b

出版商:RSC    

年代:1968

数据来源: RSC

摘要:

836 BOOK REVIEWS [Analyst, Vol. 93 Errata OCTOBER (1968) ISSUE, p. 673. Replace diagram above legend 4 with diagram above legend 11 (p. 678). IBID., p. 676. Replace key to Fig. 8 by A = Stout G = Light ale B = hlilk stout H = Pale ale C = Milk stout J = Polish lager D = Strong ale K = Danish lager E = Bitter ale L = Danish lager F = Brown ale M = Continental beer IBID., p. 677. 2nd line from the foot of the page. For “Fig. 10” read “Fig. 11.” IBID., p. 678, 13th line. For “Fig. 11” read “Fig. 10.” IBID., p. 678. Replace diagram above legend 11 with diagram above legend 4.

ISSN:0003-2654    

DOI:10.1039/AN9689300836

出版商:RSC    

年代:1968

数据来源: RSC