摘要:

596 TRINDER: A RAPID ME.THOD FOR THE [Vol. 76 A Rapid Method for the Determination of Sodium in Serum BY P. TRINDER A rapid method for the determination of sodium in serum has been developed. The sodium and the protein in the serum are simultaneously precipitated by means of a magnesium uranyl acetate reagent containing 80 per cent. v/v of alcohol. After separation by centrifugation, the sodium is calculated from the loss in concentration of the reagent solution. The recovery of sodium added to dialysed serum varied from 98 to 99 per cent. in the range 400 to 200 mg of sodium per 100 ml. A single determination can be completed within fifteen minutes of receipt of the sample. CHEMICAL methods for the determination of sodium in serum usually depend on the precipita- tion of a triple acetate of sodium, uranium and a divalent metal, after removal of the protein either by acid digestion or by precipitation with trichloro-acetic acid.The triple acetate is then washed and the sodium determined by gravimetric, titrimetric or colorimetric measure- ment of the precipitate. The divalent metal may be zinc, magnesium, copper, nickel, cobalt or manganese. As the triple acetate is easily soluble in water, but insoluble in excess of the reagent or in alcohol, a large excess of the reagent must be used; washing, especially in micro determinations, must be thorough. Such procedures, though accurate, are not very rapid, and great care must be taken during the washing process to avoid mechanical loss of the precipitate. Recently, modifications have been made in an effort to devise a quicker and simpler method.In the method of Fowweather and Anderson,l only a slight excess of a zinc uranyl acetate reagent is added to a trichloro-acetic acid filtrate of serum; the solubility of the triple acetate is reduced by adding alcohol, so that the final solution contains 37.5 per cent. v/v of alcohol. The precipitated triple acetate is removed by filtration and the sodium determined by colorimetric measurement of the loss in concentration of the reagent solution. Although the number of manipulations is reduced in this method, the sodium is completely precipitated only after standing for 2 hours in an ice chest. As chemical methods are not rapid, determination by flame photometry, in which the yellow light emitted by excited sodium ions is measured, is becoming increasingly popular.Until recently it is doubtful if the flame photometer could give results comparable in accuracy with those given by chemical methods, as standardisation of conditions is very important but difficult to achieve in practice. However, the introduction of an internal standard into the solution to be analysed, has, it is ~ l a i m e d , ~ ? ~ solved many of these problems. A direct analysis of diluted serum can be achieved by flame photometry and a result can be obtained within 15 minutes of receipt of the sample. As the flame photometer is an expensive instrument, a rapid chemical method for serum sodium determination should be useful. The experiments described below were conducted with the object of devising such a method. EXPERIMENTAL A reagent that would simultaneously precipitate the sodium and the protein in serum was prepared by diluting, with alcohol, a magnesium uranyl acetate solution containing 4 g of uranyl acetate, 15 g of magnesium acetate and 15 ml of glacial acetic acid per 100 ml.At an alcohol concentration of 80 per cent. v/v, 5 ml of this reagent completely precipitated 0.5 mg of sodium contained in 0-1 ml of solution. The presence of 0.1 mg of potassium caused no interference. At higher concentrations of alcohol, potassium ions interfered, whilst at lower concentrations the sodium was not completely precipitated. This reagent, which contained sufficient alcohol to precipitate the proteins in serum, was used in further investigations. As it was desired to estimate the loss of strength of the uranium in the reagent solution after precipitation of the triple acetate, the colour reactions of uranium with salicylates, salicylsulphonates, 8-hydroxyquinoline, 7-iodo-8-hydroxyquinoline-5- sulphonic acid, catechol and ferrocyanides were examined.Of these, only the brown colourOct., 19511 DETERMINATION OF SODIUM IS SERUM 597 given with potassium ferrocyanide obeyed Beer’s law when filters giving a high transmission were used. This colour has been stated to increase in intensity with time1; but, as only differences in colour intensity were measured and not the absolute value of the colours, this increase is not apparent in the method described below. (See Note 2.) PROPOSED METHOD REAGENTS- All the reagents used conformed to recognised analytical standards.Sodium reagent-With the aid of heat dissolve 8 g of uranyl acetate, U02(C,H,0,),.2H,0, 30 g of magnesium acetate, Mg(C2H,0,),.4Hi0, and 30ml of glacial acetic acid in about 150 ml of water. Boil the solution for 2 minutes, cool, dilute to 200 ml with water and add sufficient absolute ethyl alcohol to bring the volume to 1 litre. Pour the solution into a brown bottle, add 1 ml of 1 per cent. sodium chloride, mix and allow to stand for several days until the precipitated triple acetate has settled. The clear upper solution is then ready for use. Potassium ferrocyanide, 10 per cent.-Dissolve 50 g of K4Fe(CN),.3H,O in sufficient water to make 500ml of solution. Acetic acid, 1 per cent.-Add 50 ml of glacial acetic acid to 5 litres of water.Store in an aspirator bottle. Standard sodium solution (500 mg of sodium per 100 m1)-Dissolve 1.271 g of dry sodium chloride in sufficient water to make 100 ml of solution. For the data required in plotting the calibration graph, prepare a series of standards containing 100, 200, 300, 350, 400 mg of sodium per 100 ml by diluting this standard solution with water. GLASSWARE- Most of the ordinary laboratory glassware is satisfactory for use in this method. A11 pipettes used should be plugged with cotton wool, to prevent contamination by saliva. Glass stoppered tubes, 4; x g inches-Clean new tubes by boiling them in N hydrochloric acid and then rinsing in distilled water. Clean used tubes with distilled water, with the aid of a small test tube brush kept solely for this purpose.These tubes should be used only for sodium determinations. Pipettes, 0.1 ml-Clean the pipettes after use by rinsing well with 0.1 N potassium hydroxide, followed by distilled water and finally by acetone. Remove the acetone by suction. PROCEDURE- By means of a pipette, transfer 5ml of sodium reagent into each of two 4; x *-inch glass-stoppered tubes. To one tube (the blank) add 0.1 ml of water; to the other tube (the test) add 0.1 ml of serum by means of a pipette calibrated “to contain,” agitating the reagent solution vigorously by blowing through the pipette. Stopper the tubes and let Store in a brown bottle. Dry in a hot-air oven. Confine the use of these pipettes to sodium determinations. TABLE I DATA FOR CALIBRATION GRAPH Filter: Ilford Blue 303.Cells: 10-mm light path Sodium, mg per 100ml 0 100 200 300 350 400 500 Optical density . . 0.000 0.150 0.293 0.440 0-510 0.590 0.730 them stand for 5 minutes to allow the triple acetate precipitate to form. Then shake the tubes vigorously for 30 seconds and centrifuge at moderate speed (3000 r.p.m. ; radius 6 inches) for 1 minute. Transfer by pipette 2-ml quantities of the supernatant fluid into 100-ml volumetric flasks and add about 80 ml of 1 per cent. acetic acid followed by 4 ml of 10 per cent. potassium ferrocyanide. Finally, dilute to the mark with 1 per cent. acetic acid and mix. Within the next 10 minutes set a direct-reading photo-electric colorimeter to full scale deflection (optical density 0) with the test solution and read the optical density of the blank through a Chance OB2 or Ilford Blue 303 filter; use 10-mm cells (see Notes 1 and 2).Read the sodium content of the serum from a calibration graph prepared by treating O-l-ml quantities of solutions containing 100, 200, 300, 350, 400 and 500 mg of sodium per 100 ml in the same way as the serum and plotting the results. If the galvanometer scale is calibrated598 TRINDER: A RAPID METHOD FOR THE [Vol. 76 in optical densities this graph should be a straight line passing through the point of origin. Check the calibration graph at intervals by analysing a solution containing 350 mg of sodium per 100ml as if it were a test solution. The instrument used in these experiments was a Unicam G.P. photo-electric colorimeter, in which the source of light was a 6-volt; 6-watt lamp in place of the 6-~0lt, 2-7-watt lamp supplied with the instrument.The weaker light source does not allow full-scale deflection with small amounts of sodium. Any instrument that will give a full-scale deflection with the Chance OBlO filter is suitable for the determination. All the instruments in use in hospitals in this area were found to be suitable. These were the Spekker photo-electric absorptiometer, the Gallenkamp photo-electric colorimeter and the Evans Electroselenium portable photo-electric colorimeter, in addition to the Unicam instrument. By this method the optical densities read on analysing solutions containing 250 to 400 mg of sodium per 100 ml lie between 0.35 and 0-60. This places the readings for normal or abnormal serum in the range in which the relative error is least.4 RESULTS To test the accuracy of the new method, recovery experiments were performed. Pooled serum was dialysed under pressure through a collodion membrane against water.The dialysis was continued through four changes of water for 48 hours and the sodium content of the dialysed serum was determined by a gravimetric m e t h ~ d . ~ Known amounts of sodium were added to the dialysed serum and the samples were analysed by the new method. The results are shown in Table I1 (see Note 3). The simultaneous addition of the following ions and substances in the amounts shown (in mg per 100 ml), was found to have no effect on the results: calcium, 70; potassium, 100; ammonium, 65; bicarbonate, 150; sulphate, 25; urea, 600; glucose, 600.If phosphate is also present there is a slight increase in the results. Addition of 105 mg of phosphate ion per 100 ml increases the results by 10 mg of sodium per 100 ml. As the normal inorganic phosphate content of serum is only 12mg of phosphate ion per 100m1, the error is negligible. In severe kidney disease, the inorganic phosphate content may rise to 60mg of phosphate ion per 100ml of serum, but even so, the error will only be 6 mg of sodium per 100 ml. TABLE I1 RECOVERY O F SODIUM ADDED TO DIALYSED SERUM Sodium present, mg per 100 ml . . . . 18 18 18 18 Sodium added, mg per 100 ml . . .. 100 200 300 400 Sodium found, mg per 100 ml. . .. . . 122 216 312 412 Recovery, per cent. . . .. .. .. 104 99 98 98.5 Ten successive serum samples analysed by the new method and by a gravimetric method5 gave the results shown in Table 111.TABLE I11 ANALYSIS FOR SODIUM BY THE PROPOSED METHOD AND A GRAVIMETRIC METHOD Gravimetricmethod, mgper 100ml 313 329 331 316 327 343 338 328 332 330 Proposedmethod, mgper 100ml .. 317 325 336 307 334 341 336 326 331 335 NOTES- 1. Although the brown uranium ferrocyanide is in colloidal solution, the colour has been found t o be accurately reproducible under the conditions of the test. The solution remains crystal-clear for a t least 12 hours after the addition of the ferrocyanide. The reading made immediately (within 2 minutes) after addition of the ferrocyanide and the reading made 10 minutes later differ by less than 1 per cent. The colour intensity increases slightly during the next 50 minutes, but the increase is so small that it cannot be accurately measured.The readings made on developing the colours at 18" C and at 37" C are identical. 2. The method is so arranged that half of the uranium in the reagent solution is used in precipitating the sodium present in normal serum. Therefore an error of 0.5 per cent. in measuring the colour of the blank will lead to a n error of 1 per cent. in the result. As it is possible to measure 2 ml of fluid with an accuracy of 0-5 per cent. or better, the error from this source will be less than 1 per cent.Oct., 19511 DETERMINATION OF SODIUM IN SEERM 599 3. The recovery experiments show that any co-precipitation of uranium with protein is small; otherwise the recovery figures would have been high. The comparison figures between the gravimetric and colorimetric methods show that there is but little co-precipitation. REFERENCE s 1. 2. 3. 4. Archibald, R. M., Anal. Chem., 1950, 22, 639. 5. Fowweather, F. S., and Anderson, W. N., J. Clin. Path., 1948, 1, 177. Gilbert, P. T., Hawes, R. C., and Beckman, A. O., Anal. Chenz., 1950, 22, 772. Spencer, A. G., Lancet, 1950, ii, 623. Harrison, G. A., “Chemical Methods in Clinical Medicine,” J. & -4. Churchill, Ltd., London, 1947, p. 390. BIOCHEMISTRY DEPARTMENT ROYAL INFIRMARY SUNDERLAND, Co. DURHAM March, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600596

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

Oct., 19511 DETERMINATION OF SODIUM IN SEERM 599 The Determination of Nitrites BY H. BARNES AND A. R. FOLKARD A number of modifications of the well known Griess - Ilosvay reaction for the estimation of nitrites has been examined. The method recommended by Rider and Mellon gives optimum absorption with the Ilford green filters (604) and rapid colour development. The causes of reported discrepancies are examined. A modification of the Shinn method is slightly more sensitive and colour development is extremely rapid. If the solutions, after colour development, are kept in the dark the colour does not fade. A COMPARISON OF EXISTING TECHNIQUES- The determination of nitrites by diazotising sulphanilic acid and coupling with a- naphthylamine to produce a red azo dye has long been a standard procedure.The details of the technique used by different workers vary somewhat, and there are a number of dis- crepant statements concerning the relative efficiency of the several modifications.2,3,4 These differences relate to the composition of the reagents, particularly with respect to their acid content, to the rate of colour development and to the intensity and stability of the coloured dye. In order that a rapid, sensitive and reliable method may be recommended, a comparison has been made of a number of well known variations of the method. 1. WATTENBERG’S METHOD5- This recommended procedure for sea-water analysis is similar to many others given in The reagents are made up in acetic acid solution and are used together, as the literature. a mixed reagent. .2. RAKESTRAW’S METHOD^- coupling reagent. given regarding the time interval between the two additions. This is similar to method 1, but a small quantity of hydrochloric acid is used in the The reagents are added in successive portions, but no instructions are 3. THE AMERICAN METHOD’- This is very little different from method 2, but no hydrochloric acid is used in the coupling reagent. 4. RIDER AND MELLON’S METHOD*- After addition of the first reagent a t a fairly low pH and a time allowance for diazotisation, the second reagent is added and the solution buffered at a higher pH value. A summary of these four methods is given in Table I, the pH values recorded being those determined during the present investigation of the reaction. Both reagents are made up in hydrochloric acid solution.600 Technique Wattenbergs .. BARNES AND FOLKARD: THE DETERMINATION OF TABLE I SUMMARY OF METHODS Rakestraw6 .. U.S.A.' . . Rider and Mellon8 Sulphanilic acid 0.3% in 5% v/v acetic acid O*B"/g in 30% v/v acetic acid 0.8% in 28.5% V/V acetic acid 0.6% in 20% v/v hydro- chloric acid a-Naphthylamine O*OSO/d in 4.4'3, v/v acetic acid 0.8% in 30% v/v acetic acid + 1 yo v/v hydro- chloric acid 0.5% in 28.5% V/V acetic acid 0.480,/, in 1.3% v/v hydrochloric acid NITRITES [Vol. 76 Remarks Reagents mixed (1 + 1) and 2ml added per 100ml solution 2 ml of each reagent added in successive portions per 100 ml solution: pH after first addition = 3.02 and 2.88 after second addition. No time given for addi- tions 2ml of each reagent in successive portions to 100 ml of solution: pH after first addition = 2.98 and 2.94 after second addition. No time given for addi- tions 1 ml of reagent per 50 ml of solution, pH = 1.73; after standing 3 t o 10 minutes add 1 ml oi the second reagent, pH now equals 2-02 and buffer with 1 ml of 2 M sodium acetate soIution pH = 3.27 THE REAGENTS AND METHODS- The reagent solutions were made up in acetic or hydrochloric acids as prescribed for the foregoing methods.A stock solution of sodium nitrite, 3-00 g per litre, was made up in boiled distilled water, preserved by the addition of a little chloroform and standardised against potassium permanganate. A stock nitrite solution so prepared showed no detectable change in concentration over several weeks. This stock solution was diluted just before use as required.The reaction mixture was kept in light-proof vessels, stirred gently and maintained at a temperature of 25" 0.1" C in a thermostatically controlled bath, or in an ice-water bath at 0" C. The reaction was followed by withdrawing samples at intervals and determining the absorption by means of the Spekker absorptiometer, using 4-cm cells and green filters (Ilford 604), with an instrument setting of 0.500 against distilled water. A blank was run under identical conditions with each series of determinations. The pH values were determined by means of a Marconi pH meter, a glass electrode and standard buffer solutions. RE s ULTS- The results, which are shown graphically in Figs. 1 and 2, in which the corrected drum reading is plotted against time, may be summarised as follows- There is little to choose between methods 2, 3 and 4 as regards rate of colour develop- ment; a t 25" C all require about 15 minutes for full colour development.In Wattenberg's method the colour development is slow, the maximum intensity being reached only after at least 90 minutes at 25" C. In methods 2 and 3 maximum absorption is obtained when from 5 to 10 minutes is allowed for the diazotisation. Rider and Mellon's method is the most sensitive; the maximum absorption is 18 per cent. greater than that given by the Wattenberg method and 15 per cent. greater than that of methods 2 and 3. The maximum absorption in any of the methods was not affected by a change in tempera- ture from 0 to 25" C. Lowering the temperature of the reaction reduced the rate of colour development in all the methods; the effect was least in methods 2, 3 and 4 and greatest in method 1, in which at 0" C the maximum colour development was riot reached until after 9& hours.With Rider If the reagents are added together this maximum is not reached.OCt., 19511 BARNES AND FOLKARD: THE DETERMINATION OF NITRITES 601 and Mellon's procedure the full colour development should take place with a coupling time of about 25 minutes at normal working temperatures, say 18" to 25" C. DISCUSSION- In assessing the efficiency of the various techniques examined, three criteria must be considered, namely, the time taken to reach a stable maximum, the value of this maximum, i.e., the sensitivity, and its reproducibility.The third criterion need not be discussed, since it is well known that, under standard conditions, values can be adequately reproduced. 0 3M) 0 350 M V u E 20400 T) " 0 U Tjme. howr 04501 G 5oOo I S Time. hours 4 5 60 Fig. 1. Colour development a t 25" C Fig. 2. Colour development at 0" C Figs. 1 and 2. Rate of colour development at 25' C and 0" C. nitrite nitrogen per litre, measured with Ilford No. 604 green filters. follows- Solutions containing 15.2 pg of Curves for different methods as 0- Rider and Mellon n- A- - 0- 0- - X- Wattenberg Rakestraw, 5 and 10 minutes diazotising Rakestraw, reagents added together U.S.A., 5 and 10 minutes diazotising U.S.A., reagents added together It is clear that the Rider and Mellon method is superior in all respects to the other methods examined, and it is recommended that it should be generally adopted.It would seem to be a better method than those in which a mixed reagent is used, and further, it avoids the necessity for working at an elevated temperature in order to accelerate colour development, as is recommended by Rao9 and Morpeth.lo Other methods given in the literature are minor variants of those tested. The A.O.A.C.ll method specifies reagents prepared in aqueous solution without the addition of acid: the sample is made acid to litmus prior to addition of the reagents in successive portions. Such a procedure seems to have little to recommend it, since the acidity, which affects the rate of colour development, may vary from one estima- tion to mother and at the same time the pH may be too high for rapid colour development; moreover no definite time is given for diazotisation.The reagents recommended by Snell and Snelll2 are made up in acetic acid solution and are similar to those in methods 2 and 3. Moreover, large quantities of reagents are used, with a consequent decrease in sensitivity. The method given by Allport13 is also similar to methods 2 and 3, but again no instructions are given regarding diazotisation time. The theoretical background to the above results is readily seen, particularly in the light of Rider and Mellon's investigation. The development of the red colour takes place according to the following reaction. First diazotisation, C6H4 (SO,H) NH, + 2H+ + NO, + C6H4 (SO,H) N+-N + 2H,O C6H4 (S0,H) N+=N + ClOH,NH, +- C6H4 (SO,H) N=N.C,,H,NH, + H+ .. * * (1) (2) followed by coupling,602 BARNES AND FOLKARD: THE DETERMINATION OF NITRITES [Vol. 76 It would therefore be expected that an increase in hydrogen ion concentration would lead to an increase in the rate of diazotisation, equation (l), but to a decrease in coupling rate, equation (2) ; as a result of their investigations Rider and Mellon were able to choose optimum conditions for colour development. In the Wattenberg method the pH is too high for rapid diazotisation and moreover the addition of the two reagents together, Le., without allowing time for complete diazotisation of the sulphanilic acid before the coupling reagent is added, tends to a loss of nitrite, since any unreacted nitrite present when the second reagent is added may be lost in side reactions.THE EFFECT OF pH ON THE COLOUR QUALITY- spectrum green filters (604) with a maximum transmission at about 520 mp. the sensitivity (as distinct from the rate of reaction) this must be borne in mind. All the foregoing remarks concern the results obtained in conjunction with the Ilford In assessing The azo Tlme. hours Fig. 3. Rate of colour development at 0" C and 25OC by the method of Shinn. Solutions con- taining 15.2 pg of nitrite nitrogen per litre, measured with Ilford No. 604 green filters. Curves as follows- -0- 0 ° C - 0 - 25OC Fig. 4. Calibration curves for nitrite deter- mination by modified Shinn method dye is itself an indicator, red in acid and yellow - orange in alkaline s01ution.l~~~~ The more alkaline condition in Wattenberg's method tends to shift the colour of the azo dye towards the yellow and this effect, with the spectrum green filters, may result in decreased sensitivity as compared with that of the redder acid solution at pH 2-02 given by Rider and Mellon's method.It is possible that, by using more appropriate filters, Wattenberg's method might be made as sensitive as that of Rider and Mellon, although the disadvantage of slow colour development would remain. It is hoped to carry out a spectrophotometric investigation on the effect of pH value on the colour at a later date. A MODIFICATION OF SHINN'S METHOD Shinn's method16 for the determination of nitrites follows the technique of Bratton and his co-workers17 in using sulphanilamide as the diazotising reagent and N-( 1-naphthy1)- ethylenediamine hydrochloride as the coupling reagent. It is claimed that the method gives a colour that is more rapidly developed and more stable, Certain modifications of the original technique have been suggested by Kershaw and Chamberlain.ls It seems that the considerations already brought forward with regard to the older reagents would apply also to this method and that a similar technique, with the conditions adjusted to those of Rider and Mellon, should give the optimum results.Oct., 19511 BARNES AND FOLKARD: THE DETERMINATION OF NITRITES 603 THE MATERIALS AND METHOD- In addition the following reagents were used- (i) a 0.5 per cent.solution of sulphanilamide in 20 per cent. v/v hydrochloric acid; (ii) a 0-3 per cent.solution of N-(l-naphthy1)-ethylene diamine hydrochloride in 1 per cent. v/v hydrochloric acid. To 100ml of the solution under test, 2ml of the first reagent were added and after allowing to stand for 5 minutes to complete diazotisation, 2 ml of the coupling reagent were added. Absorptions were again measured with the Spekker absorptiometer with green filters (Ilford 604). The pH after the first addition i s 1‘64 (compared with pH 1.73 in the Rider and Mellon method) and 1.53 (compared with I 0.2). after the second addition. RESULTS- The rate of colour development is extremely rapid, full colour being obtained in 10 minutes at 25” C, that is, somewhat more rapidly than in Rider and Mellon’s method. At 0” C half an hour is required, but again, as with the other reagents, the maximum absorption is not affected.The maximum absorption is greater than for Rider and Mellon’s method by about 5 per cent. and greater by 23 per cent. than in Wattenberg’s technique. Under these conditions there is no difficulty in obtaining a satisfactory calibration curve over a wide range of nitrite concentration. Fig. 4 shows calibration curves for the ranges 0.0 to 6.1, 0.0 to 30.5 and 0.0 to 121 pg of nitrite nitrogen per litre with the 20, 4 and l-cm Spekker cells. The methods were as in the previous section (p. 600). L The results are shown in Fig. 3. GENERAL DISCUSSION The older reagents are adequate for most purposes if Rider and Mellon’s technique is adopted. If desirable the sodium acetate may be omitted and the test solution allowed to stand 30 minutes for full colour development.If the greatest sensitivity is required with the Ilford 604 filters, Sh‘inn’s method should be adopted. It should be noted that Shinn’s method has the disadvantage that the coupling reagent discolours even if kept in the dark, and as a result the blank becomes large. A point of minor interest is that the reagents are more easily prepared in hydrochloric than in acetic acid solution. In none of the methods tested was fading encountered even after several hours standing. The reaction vessels used were light-proof and therefore the fading so often reported would seem to be caused by exposure of the azo dye to light. REFERENCES 1. Griess, J. P., Ber., 1879, 12, 426. 2. Ilosvay, L., Bull. SOC. Chim. Fr., 1889, [3], 2, 388. 3. Warrington, J., .J. Chem. SOC., 1881, 231. 4. Weston, R. S., J . Amer. Chem. SOC., 1905, 27, 281. 5. Wattenberg, H., Cons. I n t . Explor. Mer. Rapp. et Proc.-Verb., 1937, 103, 1. 6. Rakestraw, N., Biol. Bull. Wood’s Hole, 1936, 71, 133. 7. American Public Health Association, “Standard Methods for the Examination of Water and 8. 9. ’10. 11. 12. 13. 14. 15. 16. 17. 18. Sewage,” 8th Ed., New York, 1942. Rider, B. F., and Mellon, M. G., Ind. Eng. Chem., Anal. Ed., 1946, 18, 96. Rao, W. V. B. S., J . Indian Chem. SOL, 1944, 21, 51. Morpeth, J. C., Chem. and Ind., 1946, No. 41, 370. A.O.A.C., “Official and Tentative Methods of Analysis,” 6th Ed., Washington, 1945. Snell, F. D., and Snell, C. T., “Colorimetric Methods of Analysis,” Vol. I, 2nd Ed., New York, Allport, N. L., “Colorimetric Analysis,” London, 1945. Sorensen, S. P. L., Prozessen Ergeb. Physiol., 1912, 12, 393. Thiel, A., and Wiilfkin, F., 2. anorg. Chem., 1924, 136, 393. Shinn, M. B., Ind. Eng. Chem., Anal. Ed., 1941, 13, 33. Bratton, A. C., Marshall, E. K., Babbitt, D., and Hendrickson, A. R., J . Biol. Chem., 1939, 128, Kershaw, N. F., and Chamberlain, N. S., Ind. Eng. Chem., Anal. Ed., 1942, 14, 312. 1944. 537. THE MARINE STATION MILLPORT, SCOTLAND April, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600599

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

604 DESHMUKH : ESTIMATION OF PHOSPHORUS BY CERIC SULPHATE [Vol. 76 Estimation of Phosphorus by Ceric Sulphate BY G. S. DESHMUKH Ceric sulphate oxidises phosphorus quantitatively to phosphoric acid. description is given of a new titrimetric method for the estimation of red phosphorus that is based on this oxidation. The adaptation of this procedure to the determination of the solubility of phosphorus in various solvents has been suggested. THE quantitative estimation of phosphorus is usually carried out by precipitating it as magnesium ammonium phosphate or phosphomolybdate. These methods are, however, time consuming and depend for their accuracy on numerous experimental precautions, especially the complete oxidation of phosphorus to orthophosphoric acid, H,PO,, by nitric acid.Rosensteinl suggested the use of red phosphorus as a reductant for ceric sulphate, but the quantitative aspect of this oxidation - reduction procedure was not investigated in detail. Preliminary experiments in these laboratories showed that the addition of red phosphorus to hot acidic ceric sulphate solution discharged its characteristic yellow colour, so indicating reduction to the cerous condition. The added ,phosphorus dissolved gradually, presumably owing to its oxidation to phosphoric acid. Since it is known that, unlike potassium dichromate, potassium permanganate and other familiar oxidants used in quantitative analysis, ceric sulphate is remarkably stable even on boiling under reflux,2 and that the presence of phosphoric acid does not interfere with its titrimetric estimation by ferrous ammonium ~ulphate,~ the above observations suggested the possibility of using standard ceric sulphate solution for a direct volumetric determination of phosphorus.In the data presented in this paper only red phosphorus was used for estimation because it could be handled and weighed accurately in a dry form. Extension of these results to white (or yellow) phosphorus has not yet been successful owing to certain experimental dficulties referred to below. EXPERIMENTAL Red phosphorus of reagent grade quality was purified initially by Chapman’s method.4 I t was then added to an excess of saturated solution of extra-pure copper sulphate and boiled for about 15 minutes. The precipitated copper phosphide was filtered, washed thoroughly with hot water and then treated with hot concentrated nitric acid.The liberated red phosphorus was filtered and washed with hot water until free from any adsorbed copper nitrate. This sample was dried in a vacuum desiccator and used for estimation. Ceric sulphate was prepared by digesting ceric oxide with concentrated sulphuric acid as suggested by Willard and Young.5 ,4n accurately weighed quantity of red phosphorus was taken in a kjeldahl-type round-bottomed flask fitted to a Leibig’s condenser with a ground-glass seal. A known volume of ceric sulphate was placed in the flask and the solution was heated under reflux until the red phosphorus dissolved completely, as indicated by the disappearance of the red particles. During this procedure ceric sulphate was reduced gradually to the cerous condition.The quantity of ceric sulphate solution added to the flask was such that its yellow colour persisted even after the complete oxidation of phosphorus. The solution was cooled to room temperature and the unreacted excess of ceric sulphate was estimated by tiiration against standard ferrous ammonium sulphate, with o-phenanthroline ferrous complex as indicator. The oxidation of red phosphorus by ceric sulphate can be represented by the equations- The total acidity of the solution was kept above 4 N . .. * - (1) 2Ce(SO,), + H,O + Ce,(SO,), + H,SO, + 0 . . .. .. lOCe(SO,), + 2P + 5H20 -+ 5Ce,(S04), + 5H,S04 + P,05 . . .. - * (2) .. ’ - (3) P205 + 3H20 +2H3P04 . . . . . . . . . . . . 10Ce(SO,), + 2P + 8H,O -+ 5Ce,(S04), + 5H2S0, + 2H3P0, .. * * (4) Adding equations (2) and (3) we get- I t follows from (4) that 30.9 g of phosphorus reacts with 5 x 332.25 g of ceric sulphate. The difference between the initial quantity of ceric sulphate added to red phosphorus andOct., 19511 DESHMUKH : ESTIMATION OF PHOSPHORUS BY CERIC SULPHATE 605 that left after the completion of the reaction gives the amount used in the oxidation of phosphorus, and hence the phosphorus is quantitatively estimated. A typical set of results is shown in Table I. TABLE I Weight of phosphorus taken, g 0.0102 0-0133 0.0094 0.0118 0.0096 0.06 12 0.0410 TYPICAL RESULTS Weight of phosphorus found, g 0.0103 0.0133 0.00926 0.0119 0.009512 0.0609 0.04109 Difference, g + 0.0001 nil - 0*00014 + 0*0001 - 0~00009 - 0.0003 + 0~00009 I t will be seen that the agreement between the actual weight of phosphorus taken and that found by the procedure described is within the limits of experimental error.It has not been possible to apply this method to the determination of white (or yellow) phosphorus, chiefly owing to the difficulty of weighing it accurately in the dry form. Further, it was observed that while being heated under reflux the yellow phosphorus tended to float on the surface of the ceric sulphate solution and gave out white fumes, presumably owing to its aerial oxidation. A quantitative reduction of ceric sulphate by yellow phosphorus was not therefore to be anticipated. Further work on the application of this method to the determination of the solubility of phosphorus in various solvents is in progress. The thanks of the author are given to Professor S. S. Joshi for facilities and kind interest in the work, and to the National Institute of Sciences of India for an award of a research fellowship. REFERENCES 1. 2. 3. 4. 5. Rosenstein, L., J . Amer. Chem. SOL, 1920, 42, 883. Willard, H. H., and Young, P., Ibid., 1929, 51, 149; 1933, 55, 3260. -,- , Ibid., L928, 50, 1334. Burgess, C. H., and Chapman, D. L., J . Chem. S O ~ . , 1901, 1 2 4 3 ~ ; cf. also Traxler, R. N., and Willard, H. H., and Young, P., J . Amer. Chern. Soc., 1928, 50, 1322. Germann, F. E. E., J . Phys. Ckem., 1925, 29, 1119. CHEMICAL LABORATORY BENARES HINDU UNIVERSITY BENARES, INDIA March, 1951

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DOI:10.1039/AN9517600604

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年代:1951

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[Vol. 76 606 WADE POTENTIOMETRIC TITRATION OF Pot en tiometric Titration of Small Amounts of Bromides BY PETER WADE The construction and use of an electrode assembly for the titration of quantities of bromide of the order of 0.1 mg and less in a minimum volume of 1 ml are described. The reference half-cell is in the form of a dipping electrode, based on the “bottled end-point’’ principle, the electrodes being silver - silver bromide. THE electrode assembly to be described was designed for the potentiometric titration of quantities of bromide of the order of 0-1 mg and less in a minimum volume of 1 ml of solution. The reference half-cell is in the form of a dipping electrode and is based on the “bottled end-point” principle first described by Pinkh0f.l The indicator and reference electrodes are silver - silver bromide, prepared by “anodising” silver wire.APPARATUS CONSTRUCTION- The method of construction is shown in Fig. 1. A rubber bung is drilled to take the two silver electrodes and to hold them firmly in place. One of the holes is widened, from the narrow end of the bung, to a depth qf about 1 cm to take the tube of the “bottled end- point.” I t is essential that the bung makes an air-tight seal with the glass. The upper A B C D E F G H I 1 KEY Rubber-covered flex sealed to bung with rubber solution Air vent Soldered joint between silver wire and flex Glass tube held in bung Rubber bung Waterproof- sheathi ng Silver wire elec- trodes, I rnm in diameter Rubber band Reference electrode Grade 4 sintered plate Fig. 1. Electrode assembly ends of the holes are slightly widened to facilitate anchorage of the flexible leads.A third hole is drilled through the bung, away from the first two, to serve as an air vent when the assembly is plugged into a closed tube; a piece of polythene sheathing is pushed through this hole to prevent the rubber closing when under slight pressure. The electrodes are made from two pieces of stiff silver wire about 1 mm in diameter, the indicator electrode being 8 cm long and the reference electrode 7.5 cm long. To one end of each electrode is soldered a length of flexible conductor, covered with rubber insulation. The wires are pushed through the bung so that the soldered joints are well inside the rubber, and the ends of the insulation of the flex are fastened into the cavities in the top of the bungOct., 1951) SMALL AMOUNTS OF BROMIDES 607 with rubber solution.A length of waterproof sheathing about 5 cm long is placed over the indicator electrode and fastened in place with a drop of “Durofix.” This acts as a spacer to prevent the indicator electrode touching the glass cell containing the reference electrode. The reference cell is made from a micro-filter-stick of 5 to 6 mm external diameter and 7.5 cm long, carrying a grade 4 sintered plate. It can readily be made by any well equipped glass-blower; alternatively, a standard filter-stick of 1 cm diameter can be used, when the over-all diameter of the assembly must be increased and the minimum volume of liquid required in the titration cell will be proportionately larger.COATING THE ELECTRODES- The ends of the wires, cleaned with emery cloth for a length of 1.5 cm, are made the anodes in an electrolytic cell containing 0.1 N potassium bromide. The cathode is a platinum wire and the current is drawn from a 2-volt accumulator, the circuit including a milliammeter and a 5000-ohm variable resistance. A current of 2 mA is passed for 30 seconds (cf. Brown,2 and Yeck and Kissin3). The coating of silver bromide must not be allowed to dry and the electrodes are best kept in the reference solution (see below). If looked after carefully the electrodes will retain their sensitivity for several months. The coating of silver bromide is formed on the ends of the wires by anodising. FILLING THE CELL- The solution with which the reference electrode is filled is prepared as follows (cf.Haslam and Soppet,* and Russell.5) Reference solution-To 250 ml of a saturated solution of sodium sulphate add 10 ml of 0.1 N silver nitrate and 10 ml of 0.1 N potassium bromide. Then add one drop of bromide solution in excess and 1 in1 of N sulphuric acid. Dilute the mixture to 500 ml and allow the precipitate to settle. Sufficient of the liquid is placed in the filter-stick to cover the anodised portion of the shorter wire and the top of the tube is pushed well into the bung. The air-lock formed in the tube prevents loss of liquid through the sintered plate. The assembly is stored in a test tube or specimen tube containing sufficient of the reference solution to cover the anodised part of the indicator electrode.This solution will keep indefinitely in a brown glass bottle. MOUNTING- A convenient mount for the assembly is made by bolting a “Terry,’ clip, of suitable size to hold the bung firmly, to the end of a short length of 2 B.A. brass rod, which is clamped to a retort stand by means of a small boss. The complete unit should be stored in the dark to avoid the formation of a deposit of metallic silver in the sintered disc. METHOD OF TITRATION Titrations of 1 to 2 ml are performed in a cup cut from the end of a 6-inch by :-inch test tube and mounted in a cork. Stirring is effected by rotating the titration cell about the eccentrically placed electrodes (Russell5). Addition of silver nitrate solution is conveniently made from a micro-burette or a calibrated micrometer syringe.The depth to which the electrodes are immersed is immaterial provided that contact is established. After each titration the part of the assembly that has been in contact with the solution is rinsed with distilled water and the indicator electrode is wiped with a piece of damp filter- paper to remove any adhering precipitate. Larger volumes are titrated in a small beaker. RE-ANODISING- If the electrodes lose their sensitivity and re-anodising becomes necessary, the rubber band and the filter-stick are removed and the latter immersed in nitric - chromic cleaning acid for half an hour to 1 hour. The old coatings of silver bromide are removed from the ends of the wires by gently scraping with a knife or with fine emery cloth, and the wires are then re-anodised as already described.The filter-stick is washed free from traces of cleaning acid with distilled water, filled with fresh reference solution and the electrode re-assembled.608 WADE : POTENTIOMETRIC TITRATIOK OF [Vol. 76 MEASUREMENT OF POTENTIAL- To prevent undue drainage of current from the cell, the changes in potential during titration are followed by means of an electronic titrimeter. A suitable circuit, given by Anderson and Hindman,, consists of a pentagrid bridge, balanced by external potentiometers. The electrodes are connected across the bridge, which is balanced a t the beginning of the titration. As the titration proceeds the bridge is thrown out of balance, the change being measured by means of a micro-ammeter in the circuit of a triode cathode follower.Slight modifications in the construction of the instrument have been made. The valves recommended in the original paper are not readily available in this country, and Lubatti’ has replaced the 1A7GT by a DK32 and the IE4G by a XY1.5 (midget pentode strapped to operate as a triode) with satisfactory results. The author prefers to use a PM2HL in place of the 1E4G as this avoids the use of voltage-dropping resistors where the filament current is drawn from a 2-volt accumulator, and gives equally good results. The high tension supplies found most suitable for both these replacements are 50 volts. Easier operation has been found to result by introducing 5 to 1 reduction drives on the biassing potentiometer (R,) and one side of the bridge (RJ. The logarithmic potentiometer (R,) in the D-battery circuit has been replaced by a linear control, and fitted with a 10 to 1 reduction drive.(Symbols in brackets refer to the circuit diagram in the original paper.6) Where the titrimeter is to be used only with low-resistance electrode systems, the use of ceramic switches is not necessary, Yaxley-type switches being adequate. The meter used is a Cambridge “Unipivot” with a full-scale deflection of 240 micro-amps. RE s u LTS Electrodes of this type have now been in use for several months for the determination of brominated hydrocarbon fumigants. The gas samples containing fumigant are catalytically oxidised and the products absorbed in a solution of sodium hydroxide containing hydrogen TABLE I TITRATION OF BROMIDE UNDER VARIOUS CONDITIONS Volume of liquid Concentration of Concentration of in titration cell, sodium sulphate silver nitrate Bromide present, ml n1g Titration from a micro-burette reading to nearest 0.01 w&- 10 0.025 N 0.01 N 1-50 1-50 1.50 10 0.025 N 0.002 N 0.500 0.500 0.500 5 0.05 N 0.002 N 0.100 0.100 0.100 Titration from a micrometer syringe reading to nearest 0.001 d- 2 0.025 N 0.1 N 1 -00 1.00 1.00 1 0.05 N 0.01 N 0*100 0.100 0.100 Bromide found, mg 1-51 1-51 1.51 0.502 0.504 0.504 0.101 0.102 0.101 1.02 1-02 1.02 0.102 0.102 0.101 peroxide.5~s To eliminate the hydrogen peroxide, which de-sensitises the electrode^,^ the solutions are evaporated to dryness, the residue dissolved in water and made just acid to neutral red indicator with N sulphuric acid.The bromide present is then determined by titration with a silver nitrate solution of suitable strength.The concentration of sodium sulphate in the solution for titration has not been found to affect the position of the end-point of the titration over the range 0-0125 N to 0-5 N of sodium sulphate. When titrating solutions of pure bromides, 2 to 5 ml of 0-05 N sodium sulphate solution, acidified with sulphuric acid, are added to increase the conductivity of the solution. Table I shows the recoveries attained when solutions containing known amounts of bromide were titrated under various conditions. The silver nitrate solutions used were obtained by accurately diluting a 0.1 N stock solution, which had been carefully standardisedOct., 19511 SMALL AMOUXTS OF BROMIDES 609 by titration against a standard solution of sodium chloride with potassium chromate solution as internal indicator, an allowance being made for the amount of reagent required to change the colour of the indicator.Recoveries are seen to be consistently slightly high when this method of standardisation is used. In practice the silver nitrate solutions used are standardised by potentiometric titration against known amounts of bromide. Very little trouble has been caused by passage of liquid through the sintered plate in either direction, except when a coarse grade of disc was used. Large changes in temperature should be avoided, as these cause the liquid to pass through the sintered plate by affecting the volume of air in the reference cell. Any seepage of liquid from the reference cell into the titration cell will, of course, make no difference to the value of the titration. This work has been carried out with the aid of a grant from the Agricultural Research Council, whose assistance and interest are hereby acknowledged. REFERENCES 1. Pinkhof, Dissertation, Amsterdam, 1919; Callan, T., and Horrabin, S., J . Soc. Chem. Ind., 2. 3. 4. 5. 6. 7. Lubatti, 0. F., unpublished. 8. 1928, 47, 3 2 9 ~ . Brown, A. S., J . Amer. Chem. SOC., 1934, 56, 646. Yeck, R. P., and Kissin, G. H., Ind. Eng. Chem., Anal. Ed., 1945, 17, 692. Haslam, J., and Soppet, W. W., J . SOC. Chem. Ind., 1947, 67, 33. Russell, J., Ibid., 1947, 66, 22. Anderson, L. J., and Hindman, J. C., Ind. Eng. Chem., AnaZ. Ed., 1943, 15, 42. Lubatti, 0. I?., and Harrison, -4., J . SOC. Chem. Ind., 1944, 63, 140. IMPERIAL COLLEGE FIELD STATION SUNNINGHILL, BERKS. May, 1951

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DOI:10.1039/AN9517600606

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年代:1951

数据来源: RSC

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Oct., 19511 SMALL AMOUXTS OF BROMIDES 609 OCCURRENCE OF fl-~-HYDROX17PHENTL-PROPIONIC ACID IN VISCERA IN 1935, G. Roche Lynch and R. H. Slater presented a paper to the Society on the occurrence of 8-p-hydroxyphenyl-propionic acid in viscera. This important communication was never pub- lished in The Analyst, but Dr. Roche Lynch has contributed a Note, which follows on p. 610. I have recently met with another specimen of this substance, the properties of which warrant its description, with a warning to workers in toxicology that it can be expected in conditions that make anaerobic decomposition of protein possible. According to Julius Schmidt1 “ &%hydroxyphenyl-propionic acid results from the putre- faction of tyrosine, and occurs in old cheese and in the pancreas.” Recently we examined some toxicological material for the presence of a suspected barbiturate.The material consisted of the viscera and muscle tissue of a body that had been exhumed after burial for a number of months under wet conditions. An extraction of the viscera for the purpose of isolating the barbiturate fraction yielded a yellowish gum that slowly solidified to a mass of crystals. The melting-point of these crystals was raised by successive crystallisations to 128’ C (uncorr.). The crystalline compound gave the following reactions, which may be compared with the normal group reactions of barbiturates. Unknown compound Barbiturates Soluble in ether. Soluble in water. Slightly soluble in chloroform. Insoluble in light petroleum. Slightly extracted from ether solution by Completely extracted from ether solution by Strong pinkish colouration with the cobalt White gelatinous precipitate with Millon’s aqueous sodium bicarbonate. aqueous sodium hydroxide.acetate - isopropylamine test. reagent . Soluble in ether. Moderately soluble in water. Slightly soluble in chloroform. Insoluble in light petroleum. Some barbiturates slightly extracted from ether solution by aqueous sodium bicar- bonate. Completely extracted from ether solution by aqueous sodium hydroxide. Strong pinkish colouration with the cobalt acetate - isopropylamine test. White gelatinous precipitate with Millon’s reagent.610 NOTES [Vol. 76 This strongly suggested that the unknown compound was a barbiturate. In addition, a sodium fusion on an impure specimen of the material gave a positive test for nitrogen.A further test on the purified recrystallised material gave a negative test for nitrogen, but the original sodium fusion proved very misleading in view of the conformity of the other tests with the general properties of barbiturates. On the assumption that the material isolated from the viscera was a barbiturate, mixed melting- point determinations were made with all the common barbiturates having melting-points within the range of 120" to 150" C, but in every experiment a very considerable lowering of the melting- point occurred. Through the courtesy of Messrs. Boots Ltd., Nottingham, micro-analyses were performed ; these showed that the purified material contained no nitrogen and the carbon - hydrogen figures were consistent with the formula C,H,,O,.An authentic sample of p-p-hydroxyphenyl-propionic acid was prepared from phloridzin by acid hydrolysis to the aglycone phloretin, then alkaline hydrolysis to phloroglucinol and the required acid. The crude acid was decolourised in chloroform solution with animal charcoal and recrystallised from hot chloroform. The authentic acid, the material from the viscera and a mixture of both all had melting-points of 128" C. The authentic specimen gave all the reactions described above for the unknown material, including the strong pink cobalt colour. I found, however, one diagnostic characteristic of /3-P-hydroxyphenyl-propionic acid ; this is that the precipitate with Millon's reagent is soluble in excess of reagent and that a further excess produces a fine blood-red colour in the solution.This colour is not given by barbiturates under similar conditions. Nevertheless, in practice, a positive cobalt test is usually accepted as prima facie evidence of the presence of a barbiturate, as substances known to give cobalt colours, such as theophylline and various imides, are eliminated during the purifying stages or can be readily identified by other means. The behaviour of the material isolated from the viscera under examination resembled that of a barbiturate so closely that it emphasises the necessity in all instances of the possible isolation of barbiturates from viscera that the suspected barbiturate should be identified by a mixed melting- point and not by a series of tests relying upon colour, crystal formation or solubility. It is generally recognised that the cobalt test is not specific for barbiturates.REFERENCE 1. Schmidt, Julius, "Textbook of Organic Chemistry," Second English Edition, Gurney & Jackson Ltd., London, 1932, p. 448. FORENSIC SCIENCE LABORATORY WAKEFIELD, YORKSHIRE L. C. NICKOLLS April, 1951 IDENTIFICATION OF /3-~-HYDROXYPHENYL-PROPIONIC ACID IN VISCERAL EXTRACTS THE compound that forms the subject of this Note was isolated from human viscera taken from a body that had been exhumed after nine months' burial under very wet conditions. The isolate was acidic in character and was contaminated with fatty substances; the quantity of the crude material extracted amounted to 129 mg. It was ground with light petroleum (boiling range 40" to 45" C) to remove fatty substances and the residue (45 mg) was recrystallised from benzene to yield a first crop of crystals (29 mg) melting a t 126.5" to 127.5" C with slight preliminary shrinkage at 120" C (uncorr.).Micro-analysis of this purified material gave the following results- Carbon, 65.00 per cent.; hydrogen, 6-08 per cent.; nitrogen (micro-Dumas), nil; oxygen (by difference), 28-92 per cent. ; molecular weight (micro-Rast), 170. C,HIoO, requires C, 65.00 per cent.; H, 6.07 per cent.; 0, 28.93 per cent. The white crystalline substance was soluble in water and in benzene but insoluble in light It was thought a t first that it might be optically active tropic acid, which is of identical This supposition was disproved M.W. 166. petroleum. composition and molecular weight and has similar characteristics.by a mixed melting-point determination with authentic tropic acid.Oct., 19511 NOTES 61 1 Further reference to the literature suggested that it might be /3-$-hydroxyphenyl-propionic acid produced by the anaerobic decomposition of protein matter. This proved to be correct, identity being established by a mixed melting-point determination with an authentic specimen of this compound prepared from cinnamic acid by reduction of the double bond with sodium amalgam followed by nitration in the para-position, reduction of the nitro-group with ferrous sulphate and ammonia and replacement of the amino-group by hydroxyl via diazotisation to yield /l-p-hydroxyphenyl-propionic acid. It may be of further interest to note that this substance, when treated with bromine in acetic acid, yields a crystalline bromo-derivative, m.p.112.5” to 11 3.5” C ex water, whose composition was not determined. Also that it gives a very strong brownish-red coloration on coupling with diazotised sulphanilic acid in alkaline solution, a reaction that serves to distinguish it from many of the non-phenolic substances with which it may be confused in the course of forensic work. Porges and Pribram (Autenrieth, “Detection of Poisons,” 1928, p. 23) record that /3-p-hydroxy- phenyl-propionic acid is present in the urine in cases of acute phosphorus poisoning. Acknowledgments are due to the Department of the Government Chemist, where the micro- analyses and preparation of the authentic substance were carried out by Mr.H. C. Gull. - DEPARTMENT OF CHEMICAL PATHOLOGY ST. MARY’S HOSPITAL PADDINGTON, LONDON, w.2 G. ROCHE LYNCH May, 1951 THE COMPOSITION OF CONCENTRATED TOMATO PURGES OF NON-AMERICAN ORIGIN SINCE the publication of the paper “The Composition of Concentrated Tomato Pur6e and the Estimation of the Tomato Content of Tomato Ketchup, ”l abnormal conditions have considerably diminished the importation of American and Canadian purees into this country. Purees mainly of non-American origin are at present being used for the manufacture of tomato ketchup. Between 1947 and 1950 seventeen samples of such pur6es from France, Hungary, Italy and Palestine have been analysed in order to provide information for calculating the tomato solids contents of tomato ketchups.The results are presented in Table I, the sample numbers being continued from the earlier publication for ease of reference. The analytical characteristics now presented fall mainly in the ranges of those previously reported, the exceptions being (a) free acid (as citric), per cent. on total solids: 1 sample is higher than the previous maximum, (b) total acid, per cent. on total solids: 1 sample is higher than the previous maximum and (c) potash, per cent. on total solids: 5 samples are higher than the previous maximum. The averages for the latest characteristics are all distinctly higher than those of the earlier samples, which were mainly of American origin. More accurate estimations of the tomato solids contents of ketchups can be made by the use of the latest analytical characteristics while ketchups are being made from purees of pre- dominantly European origin.When normal conditions return, and both American and European pur6es are freely available, it will be necessary to use the average figures from all the 48 samples when the origin of the puree used is not known. The averages for the 48 samples are- Free acid (as citric) on total solids . . .. .. . . 7.14% Combined acid 9) 3 ) . . .. .. . . 6.66% Total acid 9 ) 1 ) .. .. .. . . 13-80’7(0 Potash 9 ) 7 ) . . * . .. . . 5.41% Acetone lead number per 1 g of total solids . . . . .. 17.7 Aqueous lead number per 1 g of total solids . . .. . . 13.5 It is interesting that the previous surmise that there are two distinct types of tomato (as shown by the free acid percentage on the total solids) used in pur6e manufacture is borne out.The non- American purbes examined are all of the higher acid type, whereas both high and low acid forms were present in the first group of 31 samples. Another point is that the average natural sodium chloride percentage on the total solids (without added salt) for the European and Palestinian pur6es is higher than that of the previously analysed samples, 1.72 against 0.98. The commonly accepted value for the natural salt content is 1 per cent. on the dry solids. This difference should be borne in mind when calculating the added salt content of tomato purees.No. 32 33 34 36 36 37 38 39 40 41 42 43 44 45 46 47 48 Origin Palestine Y > Y Y 9 ) Italy .. 99 . . 3) . . )) . . )Y . . Palestine Italy .. France 79 Italy ( ?) Hungary Italy . . )) . . Averages . . Total solids*, % . . 28.30 . . 26-60 . . 28.00 . . 27-20 . . 28.26; . . 31.16 . . 25-30: . . 32-19: . . 34.70: . . 25.80 . . 28.43 . . 29.00 . . 30.35 . . 29.99: . . 29.52 . . 31.44: . . 31.75 .. .. TABLE I COMPOSITION OF CONCENTKATED TOMATO PUREES OF NON-AMERICAN ORIGIN Insoluble solids, % on total solids 9.86 7.82 8.28 7.02 16-18 12-36 14-32 14.64 12-67 10.58 14.35 12.34 9-26 10.69 10.09 12.80 - 11-45 Combined acid (as citric), % on total solids 7.59 6.3 1 6.47 7.14 8.54 7-35 8.07 7.93 6.99 7.17 7.95 8.3 1 7.22 7-02 6-13 9-30 8-25 7.5 1 Free acid (as citric), % on total solids 9.22 8-08 7-68 9.24 8.17 8.09 7.10 7-63 7.32 9.92 7-81 7-48 7.58 7.67 8-27 11-05 9.51 8.34 Total acid (as citric), on total solids 16.81 14.39 14-15 16.38 16-71 15.44 15.17 15-56 14.31 17.09 15-76 15.79 14-80 14.69 14.40 20.35 17.76 15-85 Aqueous lead number -- Per 1 g of total solids 17-1 13.8 13.3 16-0 16.4 15.3 15.3 15.2 14.1 18.5 14.9 14.1 14-4 14.6 15.3 - - 1.5.2 Per 1%’ of total acid 10.2 9.6 9.4 9-8 9-8 9-9 10.1 9.8 9.9 10.8 9.4 9.0 9.8 9.9 10.6 - - 9.9 Acetone lead number - Per 1 g of total solids 22.1 18.6 17.8 20.0 21.0 20.2 19.3 19.7 18.9 22.9 19.2 18.6 19.2 20.2 16-3 - - 19.6 Per 1% of total acid 13.1 12.9 12.6 12-2 12.6 13-1 12.7 12.6 13.2 13-4 12.2 11.8 12-9 13.8 11.3 - - 12-7 sugars (as invert), % on total solids 51.00 57.53 57.31 56-39 42.89 53.21 - 45.67 51.70 55.62 49.17 53-44 59.68 57.49 59- 17 66-13 - 54-43 * Other than in column 13 (sodium chloride, yo on total solids), total solids are corrected for t Total solids as determined, including any added salt. $ Average for samples without added salt.$ Sample contained added salt. Sodium chloride, % on total solidst 2.40 1.80 1.61 1.77 4-49 1.32 7.04 7.36 3.69 2.06 1-86 1.31 1.42 4.50 1.67 6.58 - 1-725 Potash, % on total solids 6.68 5.45 5.36 5.74 7.22 5.81 6-18 6.07 5.12 6-98 6.51 5.90 5.64 5-43 4.50 6.06 6.78 6.55 Ash, total solids % on 11.99 10-39 10.19 8.98 11.90 9.85 10.67 10.55 9-32 9.57 11.79 10.59 8-21 9-40 7.22 10.98 10.99 10.15 added salt, where necessary. Potash in ash, % 55-7 52.5 52.6 63.9 48.1 58.9 36.4 34.9 40.7 72.9 55.2 55.7 68.7 41.5 62.3 35.8 60-6 59.95 PH 4.13 4.23 4.23 4.18 4.37 4.27 4.34 4.26 ‘L: 4.30 8 4.11 E 3-94 3.64 4.03 4.16 - 4.12 - 4.15 m 2 4 03Oct., 19511 APPARATUS 613 This Note is published with the permission of the Council and Director of the British Food Manufacturing Industries Research Association, and the Department of Scientific and Industrial Research. REFERENCE 1. Morpeth, 3. C . , Analyst, 1948, 73, 449. BRITISH FOOD MANUFACTURING INDUSTRIES RESEARCH ASSOCIATIOX RANDALLS ROAD, LEATHERHEAD, SURREY J. C. MORPETH Febvuavy, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600609

出版商:RSC    

年代:1951

数据来源: RSC

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Oct., 19511 APPARATUS 613 Apparatus AN EFFUSIOMETER FOR MEASURING GAS DENSITIES IN CONTINUOUS FLOW SYSTEMS OR IN CLOSED SYSTEMS THE passage of a gas through a small orifice in a thin wall is known as effusion. It follows from kinetic theory (see Glasstonel) that if the diameter of the hole is small compared with the mean free path of the gas molecules, then the rate of effusion at constant pressure is inversely proportional G* In Fig. 1. The effusiometer to the square root of the gas density. Discovered empirically by Graham,2 this principle was first used for determining gas densities by B~nsen,~ although the experimental conditions for true effusion were probably not realised. However, it is shown (see Taylor4) that the amount of gas flowing per unit time through a relatively large orifice is also inversely proportional to the square root of the density for a constant pressure difference, and departures from this relationship occur only when the length of the hole, compared with its diameter, is large enough for viscosity effects to become appreciable.With a glass orifice of about 0.1 sq. mm cross-sectional area, the effusion manometer614 APPARATUS [Vol. 76 method has been used successfully by Eyring5 in determining the molecular weights of saturated vapours. In preparing iron nitrides by passing ammonia - hydrogen mixtures over heated iron, the degree of ammonia dissociation was calculated from the inlet and outlet gas densities determined with an effusiometer incorporated in the nitriding apparatus.6 The effusiometer is of a new design and is suitable for use in any system where the sample is returned to the gas stream, e.g., in con- tinuous flow systems, in circulating systems or in the manipulation of toxic gases.To carry out a density determination while gas is passing through the apparatus, mercury levels in the two limbs are adjusted to the orifice a and the The effusiometer is shown in Fig. 1. 750 - ZI $ 700- i! 650- 600- 6 5 550- v) ck 5 0 0 - 1 1 1 1 ' 1 1 1 " ' 0.98 1.00 1.02 1.04 1.06 1.08 i10 1.12 1'14 1.16 1.18 Pressure correction factor. C Fig. 2. Pressure correction factor curve Gas density (oxygcn=16) Fig. 3. Calibration curve showing density plotted against tC2 graduation b respectively by manipulation of taps c, d and e and the levelling bulb; taps f and g remain open. With e closed and c open, d is opened so that a sample from the gas stream is drawn through the orifice because of the difference in pressure, which initially is equal to the vertical height between a and b.The time taken for the mercury level in the orifice limb to fall from the graduation mark x to the marky is noted, after which the mercury levels are returned to a and b and the gas is returned to the system for a further determination. The size of the orifice (approximately 0.25 mm diameter; 0.05 sq. mm cross-sectional area) was such that effusion times for pure ammonia were of the order of three minutes. It was found (see below and also Fig. 3) that the gas density was not exactly proportional to the square of the effusion time. This slight departure from theory was probably due to viscosity effects and necessitated an empirical calibration of the apparatus.For this purpose, hydrogen, ammonia, nitrogen and known mixtures of these gases, all purified according to standard methods,' were used. From the effusion time t observed at a temperature To abs. and a pressure p mm, a value t,, corrected to 293" abs. and 760 mm, was calculated from the expression- t,' = t' x (T/293) x C Values of C, the pressure correction-factor, were obtained experimentally and, as shown in Fig. 2, they lie on a smooth curve for the range of pressures examined (500 to 775 mm) and are independent of the nature of the gas. The apparatus was used only within the room-temperature range 291" & 4" abs., over which any effects due to changes in the density of the mercury are, of course, negligible.Values of tC2 for standard gas mixtures are plotted against their known densities (oxygen = 16) in Fig. 3. The graph, from which the density of an unknown mixture is read directly, shows a slight curvature for densities below 6, b u t is linear for values above this. The observed effusion times, t, were 186.6, 187.0 and 186.8 seconds at 294" abs. and 776 mm. From Fig. 2, C = 0.9945. The following is an example of the method employed for partly dissociated ammonia. Hence, taking a mean value for t- tca = (186.8)' X (294/293) x 0.9945 = 3.48 x 104Oct., 19511 OFFICIAL APPOINTMENTS 615 From Fig. 3 the density was read as 6.60. Simple calculation shows that the degree of ammonia dissociation equals- and density of ammania - 1 density of “cracked” gas , in the above example was therefore 29 per cent.Observed effusion times were reproducible to within f 0.2 per cent. of the mean value. The effusiometer was constructed by Mr. J. H. Smith, to whom the author is greatly indebted. REFERENCES 1. 2. 3. 4. 5. 6. 7. Glasstone, S., “Textbook of Physical Chemistry,” Macmillan & Co. Ltd., London, 1940, p. 271. Graham, T., Quart. J . S C ~ . , 1829, 2, 74. Bunsen, R., translated by Roscoe, H. E., “Gasometry, Comprising the Leading Physical and Taylor, H. S., “A Treatise on Physical Chemistry,” Second Edition, Macmillan & Co. Ltd., London, Eyring, H., J . Amer. Chem. SOG., 1928, 50, 2398. Jack, K. H., Proc. Rqy. SOG. A , 1948, 195, 36. Farkas, A., and Melville, H. W., “Experimental Methods in Gas Reactions,” Macmillan & Co. Chemical Properties of Gases,” Walton & Maberly, London, 1857. 1931, Volume I, p. 168. Ltd., London, 1939. CHEMISTRY DEPARTMENT KING’S COLLEGE NEWCASTLE-UPON-TYNE, 1 K. H. JACK First submitted, October, 1950 Amended, April, 1951

ISSN:0003-2654    

DOI:10.1039/AN9517600613

出版商:RSC    

年代:1951

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Oct., 19511 OFFICIAL APPOINTMENTS 615 Official Appointments PUBLIC ANALYST APPOINTMENTS NOTIFICATION of the following appointments has been received from the Ministry of Food since the last record in The Analyst (1951, 76, 433). - tblic Analyst Appointments Borough of Colchester. [vor (Joint) . . .. .. . . County of Gloucestershire. LICKORISH, Adrian Joseph Clifford (Deputy) . . RYMER, Thomas Edward (Deputy) . . . . Borough of Guildford. TURNER, Mervyn Edward Dennant . . , . County Borough of Gloucester. WHITTLE, Ernest George (Joint) . . . . County of Gloucestershire. WOODHEAD, John Ezra . . .. . . . . Borough of Colchester. OFFICIAL AGRICULTURAL APPOINTMENTS NOTIFICATION of ,the following appointments has been received from the Ministry of Agriculture and Fisheries since the last record in The Analyst (1951, 76, 433). Agricultural Analyst Appointments LICKORISH, Adrian Joseph Clifford (Deputy) . . REYNOLDS, Cedric Victor (Deputy) . . . . County of Devon. TURNER, Mervyn Edward Dennant (Deputy) WOODHEAD, John Ezra . . .. .. . . County of the Parts of Kesteven, Lincolnshire. County of the Parts of Holland, Lincolnsfiire. County Borough of Gloucester.

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DOI:10.1039/AN9517600615

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年代:1951

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616 BOOK REVIEWS [Vol. 76 Book Reviews THE POLAROGRAPHIC METHOD OF ANALYSIS. By OTTO H. MULLER. Second Edition. Pp. xii + 209. Easton, Pa. (U.S.A.) : Chemical Education Publishing Co. 1951. Price $3.50. The first edition of “The Polarographic Method of Analysis” was a reprint of five articles published in the Journal of Chemical Education in 1941 ; it was intended to give a simple account of polarography suitable for students of physical and analytical chemistry. The purpose of the present edition is essentially the same, but the text has been completely revised and the size of the volume increased from 114 to 209 pages. The newer techniques, such as derivative and oscillographic polarography, which have been developed in the 10-year interval between the two editions, are described, but practical applications of polarography are not discussed in detail.Hence anyone wishing to know whether polarography would be of value for a specific metallurgical or biochemical problem must refer to one of the reviews or bibliographies listed at the end of the book. Professor Muller believes that a student should be trained on simple equipment that he can assemble himself. He gives directions for twenty-six experiments that can be carried out with ordinary laboratory apparatus and serve to illustrate the points discussed. The experiments are suitable for a practical course in polarography. It is of interest that Professor Muller advocates the use of the term polarometry to describe amperometric titrations. This term, which was originally introduced by Majer and is widely used on the Continent, shows the relation of the technique to polarography and avoids confusion * Obtainable from H.M.Stationery Office. Italics indicate changed wording.Oct., 19511 PUELICATIONS RECEIVED 617 with other techniques in which current is measured, such as Foulk and Bawden’s “dead-stop end-point” method. Nevertheless, it is doubtful whether the name will be generally accepted in this country. It can be recommended to all students of polarography and can be read with profit by experienced polarographers. The volume has few misprints and is well bound. J. E. PAGE OFFICIAL METHODS OF ANALYSIS OF THE ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS. Edited by HENRY A. LEPPER. Seventh Edition. Pp. v + 910. Washington, D.C.: The Association of Official Agricultural Chemists.1950. Price $10.00 (in U.S.A.) ; $10.50 (elsewhere). The seventh quinquennial edition of this standard work shows changes from the sixth in title, arrangement of subject-matter and style. In the title and text the designation “Tentative Method” is no longer used ; methods previously described as tentative now appear under the heading “First Action.” The number of chapters has been reduced from 44 to 41 by including Insecticides and Fungicides under a new heading, Economic Poisons, and omitting the chapters on Naval Stores, Leathers and Tanning Materials. The whole of the new matter and amendments proposed by the Association from 1945 to March, 1949, has been included, yet the total number of pages has been reduced by 22.This reduction in spite of the volume of new matter has been achieved largely by using the abbreviation system of Chemical Abstracts and also, as is evident from a comparison of the two texts, by much careful and expert editing. Many chapters have been enlarged in consequence of recent legislation in America, notably those on cosmetics, colouring matters, metals and other elements and residues in food, preservatives, vitamins, extraneous matter in foods and drugs, and economic poisons. This book is by now too well known to English analysts to make any special mention of its contents necessary; but its importance as a manual of standard methods can hardly be over- stated. This aspect of the book’s importance received emphasis from Mr. C. A. Adams, of the Ministry of Food, in an address to the Division of the American Bar Association specialisingin food, drug and cosmetic law in September, 1950, when discussing the advisability of including analytical methods in food standards, he said: “In this connection one cannot fail to notice the wide acceptance given by chemists the world over to the methods of analysis published by the -4.O.A.C.The obvious corollary seems .to be that gA t*n adequate facilities for amendment, agreement to apply the same standard methods of analysis to the foods exchanged between our countries should be a reasonable target for our chemists to aim at. Were that goal attained, the inclusion of these methods in food standards legislation could quickly follow.” The severely condensed style and system of abbreviation made necessary by the limits set to the size and weight of a book designed as a laboratory manual will be somewhat disconcerting to a reader who takes pleasure in words and their ordered arrangement. It is to be hoped that authors of chemical papers and books, with a less worthy motive and without the same insistent pressure on their space, will not subconsciously take this text as a model for their own writings; for the style, alas, is all too easily acquired, and this concd ext. of analytical chemistry contg max. of information in min. of space is calcd to be widely used by all chemists interested in the analysis and testing of agricultural materials, foods, drugs and allied substances. F. L. OKELL

ISSN:0003-2654    

DOI:10.1039/AN951760616c

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年代:1951

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Oct., 19511 PUELICATIONS RECEIVED 617 Publications Received AIDS TO PHARMACEUTICAL CALCULATIONS. By MARY E. BOLTON, B.Pharm., Ph.C. Pp. viii + 96 London: Baillihe, Tindall & Cox. 1951. Price 6s. This is an extensive revision of" Aids to the Mathematics of Pharmacy " by A . W. Lupton; First Edition, 1930; Second Edition, 1942. SURFACE CH.EMISTRY. AN INTRODUCTION TO ITS PRINCIPLES AND APPLICATIONS. By A. E. ALEXANDER, M.A., Ph.D. Pp. vii + 70. London: Longmans, Green & Co. Ltd. 1951. Price 7s. 6d. ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY FOR 1950. Pp. 490. London: The Chemical Society. 1951. Price 25s. INVESTIGATIONS INTO THE COMPOSITION OF SOUTH AFRICAN MILK.. 11. THE COMPOSITION OF MILK SUPPLIED BY PRODUCERS TO THE CITY DISTRIBUTIVE TRADE. By S. BAKALOR, M.Sc. (Agric.).Bulletin No. 285. Pp. 54. Pretoria (South Africa): Department of Agriculture. 1948. Price 6d.618 PUBLICATIONS RECEIVED [Vol. 76 THE SURFACE CHEMISTRY OF SOLIDS. London: Chapman & Hall Ltd. 1951. Price 30s. THE ACETYLENE INDUSTRY AND ACETYLENE CHEMISTRY IN GERMANY DURING THE PERIOD 1939-45. BRITISH INTELLIGENCE OBJECTIVES SUB-COMMITTEE SURVEYS REPORT No. 30. By R. OWENS, Ph.D., and A. W. JOHNSON, Ph.D., A.R.C.S. London: H.M. Stationery Office. 1951. Price 3s. 6d.; 90 cents. BRITISH STANDARDS INSTITUTION YEARBOOK, 1951. Pp. 399. London: British Standards Institution. 1951. Price 7s. 6d. FIFTY YEARS OF BRITISH STANDARDS, 1901-1951. London : British Standards Institu- tion. 1951. Price 10s. 6d. HANDBUCH DER ANALYTISCHEN CHEMIE. I1 Teil. QUALITATIVE NACHWEISVERFAHREN. Band VIIIb /3 : ELEMENTE DER ACHTEN NEBEN- GRUPPE. Part 11: PLATINMETALLE. By G. BAUER and K. RUTHARDT. Pp. xiv + 251. Berlin : Springer-Verlag. 1951. Price DM 45. CHEMICAL INDICATORS. By 0. TOMI~EK, Ph.D., translated by A. R. JETEIR, R.Nat.Dr., B.Sc., A.R.I.C. Pp. x + 258. London: Butterworths Scientific Publications Ltd. 1951. Price 21s. Twenty- seventh Edition. Pp. xii + 526. Berlin: Walter de Gruyter & Co. 1951. Price DM 24. By S. J. GREGG, Ph.D., F.R.I.C. Pp. ix + 297. Pp. 157. Pp. 103. Edited by W. FRESENIUS and G. JANDER. LEHRBUCH DER ORGANISCHEN CHEMIE. By A. F. HOLLEMAN and FRIEDRICH RICHTER.

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DOI:10.1039/AN9517600617

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年代:1951

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618 PUBLICATIONS RECEIVED [Vol. 76 BIOLOGICAL METHODS GROUP A MEETING of the Group will be held a t the Medical Society of London, Chandos Street, Cavendish Square, London, W.l, on Friday, October 26th, and Saturday, October 27th, 1951. The meeting will be in the form of “A Symposium on the Evaluation of Chemo- therapeutic Substances,” and Dr. G. M. Findlay will occupy the chair. The first part of the meeting will be held in the afternoon and evening of Friday, October 26th, and will begin at 2.30 p.m., with a break for tea from 4.30 to 5 p.m. After the Chairman’s Introduction, the meeting will be devoted t o “Antibiotics, Antituberculous and Antiviral Substances,” and the following papers will be presented and discussed: “The Design of Antibiotic Assays,” by W. L. M. Perry; “Evaluation of the Biological Properties of Newly- Isolated Antibiotics,” by J.Ungar ; “Factors Determining the Character of Inhibition Zones,” by J. Humphrey; “Evaluation of Antituberculous Compounds in vivo,” by J. M. Robson ; “Practical Aspects of the Routine Testing of Antituberculous Compounds,” by A. R. Martin ; “Evaluation of Antiviral Compounds,” by L. Dickinson. The second part of the meeting will be held in the morning of October 27th, and will begin at 10 a.m. The meeting will be devoted to “Antiprotozoal Substances,” and the following papers will be presented and discussed : “The Evaluation of Amoebicidal Substances in vivo,” followed by a Film “The Chemotherapy of Experimental Amoebiasis,” by L. G. Goodwin; “Routine Testing of Arnoebicidal and Leishmanicidal Agents,” by J. D. Fulton ; “The Evaluation of Chemotherapeutic Agents directed against Trypanosome Infections,” by E. M. Lourie; “The Evaluation of Antimalarial Substances,” by D. G. Davey; “Problems of Drug Resistance, with Special Reference to Malaria,” by A. Bishop. The Chairman’s Summary will follow at 12.15 p.m:

ISSN:0003-2654    

DOI:10.1039/AN951760618b

出版商:RSC    

年代:1951

数据来源: RSC