摘要:

Dec., 19501 FOR THE ANALYSIS OF FINE CHEMICALS 679 Attempts at the Potentiometric Determination of Chloride in Biological Fluids with the Silver - Silver Chloride Electrode BY McD. DUXBURY SYNoPsIs-Unsuccessful attempts to use the silver - silver chloride electrode for the potentiometric determination of chloride in biological fluids are described. It is shown that this electrode can be used for the rapid and accurate determination of chloride in simple non-biological fluids. The construction of a simple calomel half-cell suitable for this purpose is described. The poisoning effect on the silver - silver chloride electrode of various substances has been investigated. The effect of glycine on the electrode has also been investigated. THE method of using the silver - silver chloride electrode for the determination of chloride in biological fluids was suggested in 1947 by Dr.W. R. Domingo, of Kampen (Netherlands), who had been using the method for the determination of chlorides in soil. The writer was asked by Prof. E. J. King to see whether the method could be used for the determination of chloride in routine biochemical analysis. In the past, nearly all the work done on the silver - silver chloride electrode has been by physical chemists studying ionic activities. The electrode has also been widely used for potentiometric titration. In the present work the electrode has been placed in a chloride solution of unknown concentration and the potential measured. From this potential the concentration of chloride ion that controls the electrode potential has been determined from680 DUXBURY : ATTEMPTS AT THE POTISNTIOMETRIC DETERMINATION [Vol.75 a potential - concentration graph prepared by calibration of the electrode with standard sodium chloride solutions. METHOD PREPARATION OF THE SILVER - SILVER CHLORIDE ELECTRODES- The electrodes were prepared by two methods, (a) after Dr. Domingo, and (b) after In method (a) free cyanide is present during the deposition of silver, and in method (b) all traces of free cyanide are excluded. The platinum electrodes used were of the plate type with a total surface area of about 0.5 sq. cm. (a) After Dr. Domingo-The electrodes consisted of squares of platinum of surface area 0.5 sq. cm. These were silver-plated in a solution containing 1.6 g. of silver nitrate and 1.9 g.of potassium cyanide per 100 ml. (C.D. 5 mA. per sq. cm. for 1 hour) and then “chloridised” in a 2 per cent. potassium chloride solution (C.D. 1 mA. per sq. cm. for 30 minutes). (b) After A . S. BYOZE.‘IZ (modified)-The electrodes consisted of circular plates of platinum of surface area 0.5 sq. cm., the surface being highly polished and the edges smooth so as not t o produce focal points during electrolysis. The silver-plating solution was prepared by adding a solution of silver nitrate (2 g. in 50 ml. of water) to a solution of potassium cyanide (2 g. in 50 ml. of water) until there was a small amount of undissolved silver cyanide to ensure that there was no free cyanide present. The electrodes were silver-plated in this solution by using a platinum foil anode, and to prevent the liberated hydrocyanic acid from contaminating the cathode, the electrodes were in separate containers joined by an inverted U-tube acting as a liquid.junction. The electrodes were silver-plated for 6 hours at a C.D. of 0.5 mA. per sq. cm. and then, after having been washed in running water for 2 days, they were “chloridised” in a 1 per cent. sodium chloride solution for 1 hour at a C.D. of 0-5mA. per sq. cm. The author found that the characteristics of both tvpes of electrodes were approximately the same. S. Br0wn.l PREPARATION OF SATURATED CALOMEL ELECTRODE- This was prepared as described by Britton2 with the following modifications. A4 potassium nitrate - sodium nitrate - agar gel bridge was used in place of the usual saturated potassium chloride bridge so as not to contaminate with chloride the solution under test.In order to reduce errors due to liquid-junction potentials to a minimum, a solution was used in which the mobilities of the ions were balanced. This solution consisted of the two salts in the ratio KNO, : NaNO, = 6.3 : 1, the solutions being saturated in respect of potassium nitrate. The apparatus, which is shown in Fig. 1, has proved to be satisfactory in the deter- mination of chloride in non-biological fluids, and is simpler than the lead sulphate electrode described by Scott.3 POTENTIOMETER- A simple slide wire type potentiometer was used-Unicam H.1 Portable Potentiometer. Since polarisation took place when the electrodes were made to supply a current, the following null method was used in taking potentiometer readings.The potentiometer was set to give a reading below the expected reading. The potentiometer key was momentarily depressed and the deflection of the galvanometer needle observed. The potentiometer readings were then increased by successively smaller increments (5 to 1 mV.) and after each increment the key was again momentarily depressed and the deflection observed. This process was carried out until there was no movement of the galvanometer needle upon depressing the key. To obtain an accurate reading, the potentiometer was set to 1 mV. below the last reading obtained and then the setting was increased by 0.25 mV. at a time until there was just no movement on momentarily depressing the potentiometer key. The observation of small movements of the needle was facilitated by means of a black hair line and a small hand lens fixed over the null-point.By this means, readings within 0-25 mV. could be taken. Using this type of potentiometer, which caused the silver - silver chloride electrode to give a current while a reading was being taken, it was found that the usual wire type electrode, owing to its small surface area, tended to polarise more rapidly than the plate type of electrode. The plate type electrodes were more sensitive to small changes in potentiometer settings than the wire type electrodes.Dec., 19503 OF CHLORIDE IN BIOLOGICAL FLUIDS 681 VARIABLE POTENTIOMETER READINGS- The plate electrode was tested in standard sodium chloride solutions from 100 mg. of sodium chloride per 100 ml.to 1 mg. of sodium chloride per 100 ml. It was found that the potential readings of successive series gradually increased. As an example, readings for a 10 mg. of sodium chloride per 100 ml. solution in successive series were 122-7, 123.2, 124.5, 125.0, 126.8, 128.2, 129.2 and 131.8mV. Various possible causes for these variable readings were considered and investigated. They were: (1) contamination by diffusion of chloride through the agar gel bridge, (2) temperature changes, (3) irregular concentration of silver chloride attained when the silver - silver chloride electrode was placed in the solution under test, (4) potentiometer inaccuracies containing NaN0,-KNO, g-AgCI electrode Hg CI,- Platinum wire -- Mercury ____ Fig. 1. Apparatus and (5) “ageing effect” caused by concentration polarisation as described by Smith and T a y l ~ r .~ All causes except the last were eliminated. After a period the gradual increase in the readings ceased but the readings did pot remain constant-there were still small fluctuations of about 0-5 to 1.0 mV. It was considered that the fluctuating readings were due to variations in the characteristics of the silver - silver chloride electrode itself. A possible explanation for this might have been due to the un- covering of “hot spots” in the silver chloride layer, as has been suggested by Hornibrook.6 The electrode was tested, after it had aged, against a series of standard sodium chloride solutions ranging from 100 to 1.0 mg. of sodium chloride per 100 ml. and the resulting figures (Table I) were plotted logarithmically.Comparison of the figures in columns 2 and 3 shows that the observed values for the e.m.f. of the cell (E) fall very close to those calculated from the straight line drawn through the experimental points for 50 mg. per 100 ml. and 1 mg. per 100 ml. on the graph of E against the logarithm of the chloride ion concentration (log C ) E (calc.) = 179-2 - 51.4 log C where 179.2 (mv.) is the point at which the straight line intercepts the X axis, and where 51.4 = (179.2 - E)/log C = cot (180 - +), 4 being the angle which the straight line makes with the X axis.682 DUXBURY ATTEMPTS AT THE POTENTIOMETRIC DETERMINATION [Vol. 75 RESULTS ATTEMPTS AT THE POTENTIOMETRIC DETERMINATION OF PLASMA AND CEREBRO-SPINAL FLUID CHLORIDE- An attempt was then made to determine the chloride in plasma after initially calibrating the electrode against four standard NaCl solutions.The potentiometric determinations of chloride were carried out on 1 in 100 dilutions of plasma, the chloride content of which had previously been determined by the iodometric method of Haslewood and King.61' The potentiometric determinations were carried out with (a) proteins present, and (b) proteins precipitated by the zinc method of Somogyi.8 TABLE I POTENTIOMETER NaCl concn.. 100 90 8 0 70 60 50 40 30 20 10 9 8 7 6 5 4 3 2 1 READINGS FOR STANDARD SODIUM CHLORIDE SOLUTIONS Potential difference Potential difference Diff erencc observed (mv.) calculated (mv.) (mv. 1 76.8 76.4 + 0.4 79.0 78.8 + 0.2 81.0 81.4 - 0.4 84.0 84.4 - 0.4 87.5 87.8 - 0.3 91.8 91.8 0.0 96.5 96-9 - 0.4 102.2 103.4 - 1.2 112.8 112.3 + 0.5 127-2 127.8 - 0.6 130.2 130.2 0.0 133.2 132.8 + 0-4 136.2 135.8 + 0-4 139.5 139.2 + 0.3 143.2 143.3 - 0.1 147.8 148.3 - 0.5 154.8 154-7 + 0.1 163.5 163.7 - 0.2 179.2 179.2 0.0 E 1: (calc.) E--E (calc.) The calculated values in the third column are obtained from the equation for the straight line drawn through the experimental points on the graph of E against log C.E (calc.) = 179.2 - 51.5 log C. The potentiometric determinations were erroneous, the results with proteins present were too high, and with proteins precipitated too low (Table 11). While taking the readings, it was noticed that the potential tended to drift. It was thought that this was due to poisoning effect.9 The filtrate after the precipitation of proteins by Somogyi's method was found to contain zinc ions.TABLE I1 DETERMINATION OF PLASMA CHLORIDE BY CHEMICAL AND POTENTIOMETRIC METHODS Chloride determined by iodometric method Specimen of Haslewood and King, NaCl mg./100 ml. A 632 R 563 C 573 D 563 E 56 1 Potentiometric method 7--- A I Proteins present Proteins precipitated 7--, Ir mV., NaC1, mV., NaCl, 1 in 100 diln. mg./100 ml. 1 in 100 diln. mg./100 ml. 135*0* 620 139*2* 620 130.2 760 142.8 440 129.5 790 142.2 450 125.0 960 141.8 460 132.2 700 141.2 475 * During the taking of the potentiometer readings it was noticed that the potential tended to drift, becoming lower in the presence of proteins, and higher after proteins had been precipitated by the zinc method of Somogpi.This potential drift was of the order of 0.25 mV. per minute. An attempt was then made to determine chloride in cerebro-spinal fluid (C.S.F.), but even with the small amounts of protein present in C.S.F. potential drift was observed.Dec., 19501 OF CHLORIDE I N BIOLOGICAL FLUIDS 683 POISONING EFFECT- Potential readings were taken in chloride solutions containing increasing concentrations of (a) zinc sulphate, (b) potassium hydroxide, (c) sodium sulphate and (d) sulphuric acid. Each of these substances had a poisoning effect on the electrode and potential drift was observed. The observed changes in potential were not proportional to the concentration of the foreign substance. No poisoning effect was observed in the presence of the crystalloids normally found in the blood, i.e., glucose, urea, sodium carbonate, potassium and phosphorus as dihydrogen potassium phosphate, and calcium as calcium gluconate, in concentrations normal in plasma.PLASMA ULTRA-FILTRATES- A 1 in 10 dilution of plasma was filtered through cellophane in a Seitz pressure filter. The plasma ultra-filtrate was shown to be free from protein by means of the biuret reaction. A 1 in 100 dilution of plasma was prepared from this filtrate and the potentiometric determination of chloride attempted. Again potential drift was observed. This potential drift could not be put down to the presence of protein. It therefore seems that the substance having the poisoning effect on the electrode is neither a protein nor any of the usual blood crystalloids.It might possibly be due to amino-acids, although these are present in small quantities only. EFFECT OF GLYCINE- As it was thought that the potential drift observed might be caused by the presence of amino-acids, it was decided to repeat the experiments of KatsulO on the effect of glycine on the silver - silver chloride electrode. It was found that with glycine in a concentration of 1 M (7500 mg. per 100 ml.) there was an immediate rise in potential of approximately 3mV. but no potential drift, which thus confirms Katsu’s results. In the presence of glycine in a concentration of 5 mg. and 10 mg. per 100 ml. there was no significant effect upon the potential readings. Katsu did not examine the effect of glycine in low concentrations. Katsu suggested that in the presence of glycine the chloride ion activity of chloride solutions was reduced and considered that this reduction was caused by the adsorption of the chloride ions by glycine because his measurements could be made to fit Freundlich’s adsorption isotherm. But since the idea of adsorption on a small molecule like glycine has no physical meaning, all that can safely be claimed is that in the presence of a large excess of glycine, the chloride ion activity of chloride solutions is diminished. ATTEMPT AT THE DETERMINATION OF PLASMA CHLORIDE BY CALIBRATING AFTER EACH Since it had been impossible to determine plasma chloride potentiometrically in an ultra- filtrate, it was decided to attempt the determination in the presence of protein and to allow for drift by taking a reading with a standard sodium chloride solution after each plasma reading and to apply the necessary correction to the initial calibration curve of the electrode.Readings were taken after the electrode had been immersed in the test fluid for a period of 5 minutes. By this method results varying by 1 to 5 per cent. from chloride determinations by the iodometric method of Haslewood and King6 were attained. READING- DISCUSSION OF RESULTS Neuhausen and Marshallll stated that their potentiometric determinations of chloride in serum and blood were in agreement with those found by chemical methods. In view of the findings of the present author, those of Neuhausen and Marshall are surprising. They obtained their chloride ion concentration by direct calculation from the Nernst equation on the assumption that their electrodes were perfect, i.e., gave a change of 59 mV.for a tenfold change in chloride ion concentration. In their paper they gave no experimental proof that their electrodes were perfect. The electrodes prepared by the writer, using a modified Brown1 technique, gave a difference of only 52 mV. between concentrations of sodium chloride of 50 mg. and 5 mg. per 100 ml., and 50 mV. between concentrations of sodium chloride of 10 mg. and 1 mg. per 100 ml. The earlier electrodes prepared gave similar figures. The author therefore believes that the results of Neuhausen and Marshall should be treated with reserve.684 PURUSHOTTAM AND RAGHAVA RAO: PHTHALIC ACID AS A CONCLUSIONS While it is possible to determine the chloride concentration within 1 per cent.in pure chloride solutions by means of the silver - silver chloride electrode, the determination in biological fluids is unsatisfactory owing to the poisoning effect causing potential drift. If correction is made for this potential drift, a determination correct to about 5 per cent. can be carried out in biological material. It would be possible to determine the chloride in very small amounts of material, e g . , on 0.1 ml. or even 0.01 ml., with one hundredfold dilution; but in view of the simple and more accurate microchemical methods available, the potentio- metric determination of chloride in biological iluids cannot be considered satisfactory. The silver - silver chloride electrode can however be used for the rapid detection and accurate determination of chloride in tap water or other simple chloride solutions (cf. Scotts). A full account of this work is deposited in the Department of Chemical Pathology, Post-graduate Medical School, London, W. 12. [Vol. 75 ACKNOWLE:DGMENTS The author is indebted to Professor E. J. King for the opportunity of carrying out the investigation in his department, and to Dr. W. Klyne for helpful criticism. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Brown, A. S., J . Amev. Chem. SOC., 1934, 56, 646. Britton, H. T. S., “Hydrogen Ions,” Chapman & Hall, London, 1942. Scott, B. A., J . SOC. Chem. Ind., 1948, 67, 1. Smith, E. R., and Taylor, J. K., J . Res. Nut. Bur. Std., 1938, 20, 837; .I. Anzer. Chem. SOC., 1942, Hornibrook, W. J., Jaiiz, G. J., and Gordon, A. R., J . Amer. Chem. Soc., 1924, 64, 613. Haslewood, G. A. D., and King, E. J., Biochem. J . , 1939, 31, 920. King, E. J., “Micro-Analysis in Medical Biochemistry,” J. & A. Churchill, Ltd., London, 1946, Somogyi, M., J . Bid. Chem., 1930, 86, 655. Clark, W. 11.. “The Determination of Hydrogen Ions,” Bailliere, Tindall & Cox, London, 192s. Katsu, Y., J , Biophys. Japax, 1927, 2, 95. Neuhausen, B. S., and Marshall, E. K., J . H i d . Chean., 1922, 53, 365. 64, 3053. p. 44. DEPARTMENT OF CHEMICAL PATHOLOGY POSTGRADUATE MEDICAL SCHOOL LONDON, W.12 May, 1950

ISSN:0003-2654    

DOI:10.1039/AN9507500679

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

684 PURUSHOTTAM AND RAGHAVA RAO: PHTHALIC ACID AS A [Vol. 75 Ph thalic Acid as a Selective Reagent for Zirconium BY A. PURUSHOTTAM AND BH. S. V. RAGHAVA RAO SyNopsIs-Phthalic acid precipitates zirconium quantitatively from solutions 0.35 N with respect to free hydrochloric acid. From solutions 0.3 N in hydrochloric acid, most elements, such as thorium, iron, aluminium, beryllium, uranium, manganese, nickel and ceria earths can be separated in a single precipitation, but tin, titanium, vanadium and chromium require a second precipitation. The reagent is thus selective for zirconium. SCHOELLER~ recommended tannic acid as a selective reagent for zirconium. This reagent gives an easy separation from most other elements, although two stages are required, but does not prove so satisfactory in separations from thorium.This paper describes the use of phthalic acid, which reacts more advantageously than tannic acid to thorium, titanium and tin. EXPERIMENTAL ESTIMATION OF ZIRCONIUM- A stock solution of pure zirconyl chloride in 0.1 hT hydrochloric acid was standardised by precipitation with m-nitrobenzoic acid2 and mandelic acid.3 Two 20-ml. portions were found to contain 0.0550 and 0.0551 g. of ZrO,. The precipitation with phthalic acid was carried out by diluting 20-ml. portions to 100 ml., boiling, and adding 100 ml. of a boilingDec., 19501 SELECTIVE REAGENT FOR ZIRCONIUM 685 4 per cent. solution of phthalic acid. The boiling was continued for 2 minutes after the addition of the reagent. The white gelatinous precipitate was collected, after an hour, on an ll-cm.Whatman No. 42 filter-paper, washed with hot 0.1 per cent. solution of the reagent and ignited to ZrO,. The ZrO, found was 0-0550 g., which was in excellent agreement with values obtained by the m-nitrobenzoic acid and mandelic acid precipitations. SEPARATIONS- As the separation of other elements that give precipitates with phthalic acid depends on the acid concentration, the solubility of the zirconium precipitate was investigated by carrying out the precipitation under various conditions of acidity. The results are shown in Table I. With in'crease in acid concentration the nature of the precipitate alters, becoming more gelatinous and taking longer to settle. When ammonium nitrate is added in sufficient quantity, the flocculence returns and the precipitate settles more readily.Hydrochloric acid concentration 0.01 N 0.01 N 0.1 N 0.1 N 0.1 N 0.2 N 0.3 N 0.3 hi 0.3 N 0.3 N 0.3 N 0.35 N 0.4 LY 0.4 N TABLE I EFFECT OF FREE ACID ZrO, taken, g. 0.0275 0.0550 0.0275 0-0550 0-0275 0.0550 0.0028 0.0275 0.0275 0.0550 0.0550 0.0550 0.0560 0-0275 21-0, found, g . 0-0275 0.0560 0.0275 0.0551 0.0274 0.0550 0.0029 0.0274 0.0276 0.0560 0.0551 0.0549 0.0535 0.0265 Difference, g. o*oooo 0~0000 0~0000 + 0~0001 - 0*0001 0~0000 + 0~0001 - 0~0001 -+- 0~0001 0~0000 + 0~0001 - 0~0001 - 0.0015 - 0~0010 The precipitation of zirconium is thus quantitative in solutions containing free hydro- chloric acid up to a concentration of 0-35 N , but for the best results an acid concentration of 0.3 N is recommended. PROCEDURE- Add sufficient 2 N hydrochloric acid to give a solution that will be 0.3 N in acid when the solution is diluted to 200 ml.by the subsequent operations. Add, with continuous stirring, 100 ml. of a boiling 4 per cent. solution of phthalic acid and gently boil for 2 minutes. Keep hot over a boiling water-bath for 2 hours and then set aside to cool for an hour. Collect the precipitate on an ll-cm. Whatman No. 42 filter-paper, wash once with a hot 0.1 per cent. solution of phthalic acid in 0.3 N hydrochloric acid and then with To the chloride solution, add 30ml. of saturated ammonium nitrate solution. Dilute to 100 ml., and boil. 0.1 per cent. of-phthalic acid in 2 per cent. ammonium nitrate solution. as ZrO,. Ignite and weigh TEST SEPARATIONS- Results obtained with the above procedure are given in Table 11; the weight of the metallic chloride or nitrate added has been calculated to the oxide.The concentration of hydrochloric acid was adjusted to 0.3 N in the final solution. OBSERVATIONS ON THE TEST SEPARATIONS- hydrochloric acid no precipitation occurs. solution of thorium chloride or nitrate. precipitate forms, but dissolves on the addition of a few drops of hydrochloric acid. 0.3 N hydrochloric acid solution thorium is not precipitated under any conditions. Irun-Iron is incompletely precipitated by phthalic acid in neutral solution. In 0.3 IV Thorium-No precipitation takes place on the addition of phthalic acid to a cold neutral On long and continuous boiling, however, a white From686 PURUSHOTTAM AND RAGHAVA R.40 [Vol.75 Nickel-Nickel is not precipitated by phthalic acid even from neutral solutions. This is very convenient in the determination of zirconium in ores that have been subjected to peroxide fusion in a nickel crucible. Tin and titanium-Tin h the form of stannous chloride is not precipitated by the reagent from 0.3 N hydrochloric acid solutions, but in the presence of zirconium small quantities are carried down. Titanium (as titanium tetrachloride) behaves similarly. For both metals, the first precipitate is dissolved in hydrochloric acid (1 + l), diluted and neutralised with ammonia (Congo red indicator), and the calculated quantity of 2 N hydrochloric acid is TABLE I1 RESULTS OF TEST SEPARATIONS BY THE RECOMMENDED PROCEDURE Added ZrO, taken, ----7 ZrO, found, Difference, g.substance g. 6- g. 0.0550 Tho, 0.0870 0.0550 0~0000 0*05:50 Tho, o.oaao 0.0551 + 0~0001 0.0550 Tho, 0-1740 0,0551 + 0~0001 0.0550 ThO, 0.1740 0.0549 - 0~0001 0.0550 Fez03 0.2014 0.0548 - 0.0002 0.0275 Tho, 0.0870 0.0275 0~0000 0.0550 x120, 0.4 102 0.0548 - 0.0002 0.0550 MnO 0.1804 0.0550 0~0000 0.1732 0.0548 - 0*0002 0.1648 0.0549 - 0*0001 0.0550 GO," 0.0550 Be0 0.0550 U308 0.1920 0.0550 o*oooo 0.0550 NiO 0.521 6 0.0548 - 0.0002 0.0550 v204 0.2648 0.0549 (a) - O * O O O l ~ 0.2648 0.0548 (b) - 0.0002 0.0550 v204 0.0550 xo, 0.1 14 3 0-0577(~) + 0.0027 0.0550 TiO, 0.1143 0-0546(b) - 0.0004 0.0550 SnO, 0-1840 0*0563(a) + 0.0013 0.0550 SnO, 0.1840 0.0547 ( b ) - 0.0003 0.0550 Cr203 0.3050 0*0550(a) o*oooo~ 0-0550 cr203 0.3050 0.0549 ( b ) - 0*0001 * Ceria earths; composition not determined. t Slightly coloured.(a) Single precipitation. ( b ) Double precipitation. added to give a 0-3 N solution at a dilution of 200 ml. A slight precipitate that appears during neutralisation will dissolve at this stage. Precipitation with phthalic acid is now repeated. Other elements-Aluminium, beryllium, uranium, manganese, ceria earths, vanadium (V,O,) and chromium are not precipitated even in neutral solution,.but the precipitate of zirconium in admixture with vanadium or chromium is slightly coloured although the weight of 21-0, does not show an excess. It is possible that the vanadium and chromium ions are adsorbed and that traces resist washing; even these traces are removed in a second precipitation. Thus in the absence of iron, thorium, tin and titanium, most other separations can be affected in neutral solution. Tantalum, niobium and tungsten are not usually present in chloride solution; other elements have not been investigated, but they rarely occur in association with zirconium. REFERENCES After a double precipitation, the 21-0, is pure white. 1. Schoeller, W. R., Analyst, 1944, 69, 259. 2. Osborn, G. H., Ibid., 1948, 73, 381. 3. Kumins, C. A., Anal. Chem., 1947, 19, 376. ANDHRA UNIVERSITY WALTAIR, INDIA April, 1950

ISSN:0003-2654    

DOI:10.1039/AN9507500684

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

686 PURUSHOTTAM ANID RAGHAVA R.40 [Vol. 75 ERRATA: September (1950) issue, p. 459. November (1950) issue, p. 569. Third line of “Procedure,” for “30 ml.” read Line 20, for “is more efficient” read “is no more “300 ml.” efficient.”

ISSN:0003-2654    

DOI:10.1039/AN9507500686

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

Dec., 19501 NOTES 687 Notes PAPER TEST FOR CITRUS JUICES WHEN lemon, orange and grapefruit juices are titrated with dilute caustic soda for the determination of acidity, the solution develops a yellow colour when the pH exceeds 7.0. It has now been found that if the reaction is carried out on filter-paper under standard conditions, the colour appears to be characteristic of citrus juices. The reaction is not given by mixtures which might reasonably be termed “citrus substitutes” and it can be used to estimate approximately the proportion of citrus juice present in a liquid. The test conditions adopted are as follows-cut filter-paper (Ford’s white blotting 408 mill, or Postlip 633DL have been found suitable) into strips 2.5 cm. wide and 20 to 22 cm. long. Support the strips above a sheet of plate glass so that they are vertical, with the lower end just touching the glass.Run 0.1 ml. of juice on to the plate glass by the end of the filter-paper strip so that it is absorbed by the paper. As soon as absorption is complete, run 0.1 ml. of distilled water on to the plate, and when this in turn has been absorbed, run on 0.1 ml. of 0.1 N sodium hydroxide. When absorption of the sodium hydroxide is complete, a yellow band is visible, the top edge of which is about half-way between the lower end of the paper strip and the upper edge of advance of the solutions (RF approximately 0.5). It has been our practice to dry the test strips as soon as possible at a temperature of 55” C. and to inspect them closely when dry. When this is done soon after preparation, the coloured band becomes more intense and is seen to consist of two bands diffusing into one another; the forward edge is of a deeper, orange, colour.The following juices have all given strong positive reactions to this test- Lemon juice . . . . South African var. Eureka (two samples) Orange juice . . . . South African var. Valencia (three samples) Italian 9) Messina 9 ) 9, )) Navel Grapefruit juice . . * . 9, $9 2) Marsh >2 ’3 9 ) Triumph Lime juice also gave a strong yellow band, but it was distinguishable from the citrus reaction by its much greater width. The upper edge of penetration of the juice into the filter-paper was marked by a translucent line. It affords a very delicate test for the presence of oil, 5 x ml. of oil giving a definite line, and 2 x 10-6 ml.a line readily detected. Davis1 has described a similar colour reaction in diethylene glycol solution and has used it to determine naringin and hesperidin in citrus fruits. As the colour reaction now described might be expected to occur with extracts from a wide variety of fruits, etc., extracts were prepared from various materials by boiling under reflux with dilute sulphuric acid and chloro- form. The two layers were finally separated, the chloroform layer being evaporated and the residue taken up in dilute sulphuric acid. The two fractions were then tested for colour production by the method described. It was first ascertained that lemon juice when extracted still gave a strong positive reaction. Extracts were prepared from rose hips (Rosa canina), privet berries (Ligustrum vulgare), dandelion (Taraxacurn dens Zeonzs) leaves and flowers, onion (AZZium cefia) skins, and walnut (Juglans regia(?)) twigs and leaves.None of these in acidified aqueous extract gave a positive reaction and hence it appears that the paper test is more characteristic of citrus juices than is that described by Davis. A wide range of citrus squashes known to be genuine and of various ages has been tested and all have given a positive result. Boiling such a solution, or boiling with hydrogen peroxide before testing, did not impair the development of the yellow colour. The presence of much oil, as in orange squash, interfered with the reaction on Postlip paper and a less clearly defined band was obtained, but with a very wide oil band.Thus, this paper provides a very delicate test for oil, but is correspondingly less sensitive for citrus juice in the presence of much oil (about 0.03 per cent .) . The presence of tartrazine in amounts such as are sometimes used for the colouring of lemon or grapefruit squashes did not interfere with the test, nor did the artificial colouring matters added to orange squashes. When tartrazine was present, the quantity of colour was too small to be detectable, and the orange colours formed one or more separate bands, according to the colours This has always been found in tests on citrus juices and is caused by citrus oil.688 NOTES [Vol. 75 present. These bands, however, were faint, separate from the reaction band and usually of a different colour.Juices of granadilla, rhubarb and golden plums gave faintly discoloured zones extending about half-way up the zone of penetration; cherry and apple juices gave two fairly distinct bands, the upper being the most marked and of a purple-brown colou.r, followed closely by a yellow band; gooseberry and plum syrups gave dark brown bands. Grape juice gave hardly any colour, but a distinct oil line. It thus appears that the double reaction-the orange-yellow band (RF 0-5) and the translucent oil band-may be characteristic of citrus juices. The quantitative application of the test to the estimation of the proportion of citrus juice present in a liquid has not been fully explored. Colour “standards” have, however, been prepared by dilution of fresh juice, and “unknowns” have been compared with these “standards,” Solutions containing 30 per cent.by volume of citrus juice have on all occasions given a definite reaction. With but 10 or 15 per cent. of juice present, however, the reaction is uncertain and even with the help of “standards” it is difficult to distinguish between 10 and 20 per cent. by volume of juice. REFERENCE Of other fruit juices tested by this method, none gave a distinct yellow band. 1. Davis, W. B., Anal. Chem., 1947, 19, 476, abstracted in Analyst, 1948, 73, 283. RESEARCH DEPARTMENT SAML. HANSON & SON LTD. TODDINGTON, GLOS. D. DICKINSON F. J. T. HARRIS May, 1950 THE SEPARATION OF MIXTURES OF ADIPIC AND SEBACIC ACIDS WISE’ in a Note on the Separation of Mixtures of Adipic and Sebacic Acids has reached certain conclusions about the operations involved in obtaining fairly pure specimens of adipic and sebacic acids from a mixture of the two acids by the method of Clasper and Haslam,2 in which an aqueous solution of the two acids containing alkali equivalent to the adipic acid is extracted with ether in a continuous extractor.Fresh ether is supplied continuously to the system and it is very doubtful whether ?Vise’s simple treatment is applicable to this procedure. Careful experiments on purified samples of adipic and sebacic acid have been carried out in the following way. Known amounts of adipic and sebacic acids were weighed into a ground-glass stoppered flask and a volume of 0.1 N sodium hydroxide equivalent to the adipic acid was added. This volume was made up to 50 ml.with water and 35 ml. of ether were added. The whole was shaken thoroughly before placing it in a thermostat for half an hour a t 20” C. The contents of the flask were then transferred to a continuous liquid - liquid extractor and extracted for 4 hours. The ether extract was then removed, evaporated to dryness and finally dried to constant weight a t 120” C. The aqueous solution was acidified with 10 ml. of 20 per cent. v/v hydrochloric acid and re-extracted with ether €or 4 hours. The ether extract was again evaporated to dryness and dried to constant weight at 120” C. The weights of the recovered acids together with the determined equivalents are shown in Table I. TABLE I Mixture I Mixture I1 Weight taken, g . .. .. .. .. 0.2503 0.2508 acid Weight found, g.. . .. . . .. 0.2597 0.2604 Weight taken, g . .. .. .. .. 0-25 11 0.2515 .. . . .. .. 101.6 101.6 . . .. .. .. 0.2401 0.2389 acid Weight found, g. Adipic Equivalent .. .. .. .. 72.8 72.8 Equivalent .. .. .. .. 74.3 74.2 c { Equivalent . . . . .. .. 101.7 101.2 Sebacic Equivalent It is unlikely that these results can be explained on the basis of solvent extraction alone as I t does seem probable, however, that so-called stoicheiometric has been suggested by Wise. extraction plays some part in the separation. REFERENCES 1. 2. Wise, W. S., Analyst, 1950, 75, 219. Clasper, M., and Haslam, J., Ibid., 1949, 74, 224. IMPERIAL CHEMICAL INDUSTRIES LIMITED WELWYN GARDEN CITY, HERTS. PLASTICS DIVISION J. HASLAM XI. CLASPER July, 1950Dec., 19501 NOTES 689 APPLICATION OF RADIO-FREQUENCIES TO CONDUCTIMETRIC ANALYSIS IN a recent paper1 the author showed that by the application of a “negative set-back” a zero-shunt circuit could be employed to increase sensitivity when titrating by rectified radio-frequency c ~ r r e n t .~ , ~ Fig. 1 illustrates how, by a series of adjustments of the coupling between the R.-F. oscillator and the conductimetric tube, a solution concentration - conductivity graph was plotted over a range of concentrations from 37/10 to N/81920. The microammeter used had a range extending only to 60 p-amp. By this technique the actual current passed through the solution did not at any time exceed 50 p-amp., so that no appreciable temperature rise was observable. The procedure was to fill the conductimetric tube with 37/10 hydrochloric acid and then adjust the coupling to give a deflection of 50 p-amp. After noting the reduction of the meter reading that occurred when the solution was diluted by addition of an equal volume of distilled water, the coupling was further increased to restore the deflection to 50 p-amp. before repeating the process. The curves, Fig. 1, show the relationship between solution concentration and the sum of the SUM OF SUCCESSIVE METER DEFLECTIONS rr 320 I +- T I I Fig. 1 1 I20 I successive reductions of current from 50 p-amp. Curve A is parabolic and shows the relationship as far as N/1280. For curve B the ordinates are the logarithms of the concentrations shown on the right-hand side of the figure, and this curve goes to the extreme limit where the solution is no longer distinguishable from pure distilled water. The electrodes on the conductimetric cell were 1 mm. apart. REFERENCES 1. 2. 3. - , Ibzd., 1945, 22, 174. UNIVERSITY OF SYDNEY AUSTRALIA Blake, G. G., Analyst, 1950, 75, 32. -, J . .Sci. Inst., 1947, 24, 101. DEPARTMENT OF PHYSICS G. G. BLAKE July, 1950

ISSN:0003-2654    

DOI:10.1039/AN9507500687

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年代:1950

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690 BRITISH STANDARDS INSTITUTIOS [Vol. 75 British Standards Ins ti tution NEW SPECIFICATIONS* B.S. 1683 : 1950. One-mark bulb pipettes. Price 2s. B.S. 1669 : 1950. Industrial Perforated Plates. Price 2s. The British Standards Institution inform us that they have opened a branch office a t 12, Hilton Street, Manchester, 1, Telephone: Central 4856, where a complete set of British Standards may be consulted and copies may be purchased. * Obtainable from the British Standards s.w.l. Institut:ion, Sales Department, 24, Victoria Street, London, DRAFT SPIICIFICATIOS A FEW copies of the following draft specification, issued for comment only, are available to interested members of the Society, and may be obtained on application to the Secretary, Miss D. V. Wilson, 7-8, Idol Lane, London, E.C.3. Draft Specification preparcd by Technical Comnnittee LBC./6-Standard Distillation Apparatus. CM(LBC) 61 19-Draft Revision of B.S. 658, Distillation Apparatus.

ISSN:0003-2654    

DOI:10.1039/AN950750690b

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年代:1950

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Dec., 19501 REVIEWS 691 Reviews I’HYSICO-CHEMICAL CONSTANTS O F P U K E ORGANIC COMPOUNDS. By J. TIMMERMANS. Pp. viii + 693. Hume Press, Ltd. 1950. Price 95s. New York and Amsterdam : Elsevier Publishing Company, Inc. London : Cleaver- Chemical handbooks contain tables of physical properties that serve a purpose, but it is not generally realised until comparisons are drawn from the original literature how true is the author’s remark that most of the numerical data accumulated during the last hundred years must be excluded if “precision worthy of contemporary science” is desired. It is, for example, startling to read (p. 419) that there are no reliable data for n-amyl acetate. To separate the wheat from the chaff is no light undertaking where the bulk of the latter is so great.Chemists therefore owe Professor Timmermans a great debt for performing this operation, for which his association with the International Bureau of Physico-Chemical Standards renders him particularly well fitted. The properties quoted are critical constants, density of saturated vapour pressure, boiling- point, freezing- or melting-point, critical solution-point, density, surface tension, refractive index, viscosity, dielectric constant, specific rotatory power, specific heat and heats of vaporisation, fusion, transition and combustion. It must at once be stated that this whole range of properties is not available for each compound quoted; extensive lists of melting-points per se are not given. In addition t o the results, published or unpublished, of the Bureau a t Brussels, the literature has been covered to the beginning of this year. The appeal of this book to the analyst as such is limited; nevertheless, should the occasion arise, it is useful to know where thoroughly reliable data, if available, may readily be found.B. A. ELLIS PHYSICAL METHODS IN CHEMICAL ANALYSIS. Vol. I. Edited by WALTER G. BERLE. Pp. viii + This is the first of two volumes to be published under the general title “Physical Methods in Chemical Analysis,” It is stated that “the subject-matter has been divided in such a way that all methods dealing with the interaction of radiation with matter (in addition to mass spectrometry) appear together in Volume I. Electrical, magnetic and miscellaneous techniques and the methods of separation will appear in Volume 11.” These are: “Absorption Phenomenon of X-rays and y-rays,” by George L. Clark; “X-ray Diffraction Methods as Applied to Powders and Metals,” by William L.Davidson; “X-ray Diffraction as Applied to Fibres,” by John A. Howsmon; “Electron Diffraction,” by L. 0. Brockway; “Spectro- photometry and Colorimetry,” by W. K. Brode; “Emission Spectrography,” by J. Sherman; “Infra-red Spectroscopy,” by H. H. Nielsen and Robert A. Oetjen; “Raman Spectra,” by J. H. Hibben ; “Polariscopic and Polarimetric Examination of Materials by Transmitted Light,” by C. D. West; “Refractive Index Measurement,” by L. W. Tilton and J. K. Taylor; “Electron Microscopy,” by R. D. Heidenreich; “Mass Spectrometry,” by H. W. Washburn. The declared aim of the book is to describe those physical methods that have either proved themselves of considerable value in quantitative work or are destined to play an important role in the future.The plan has been to deal with each technique adequately enough “to minimise the need for consulting more specialised texts or the original literature.” It should perhaps be stated a t once that the main aim has been attained-the description of those physical methods that have proved of value. The more extravagant claim, which implies a knowledge of the future importance of this or that technique, can only be put to the test of time. Of the plan itself, this too may be said to come near succeeding. Each section does in fact present a very complete and clear account of all the important aspects of apparatus and techniques, including their limitations.The reader who is unfamiliar with these techniques will realise at once not only that most of them call for specialist operators, but that the reference concerning the minimising of literature searches and the like is somewhat superfluous. It will also be obvious that here is a composite picture not only of new techniques but of a new and wider conception of what is to be considered the analytical domain. There is a breadth and grandeur about this newly adopted picture that transcends conventional views of chemical analysis and also, for that matter, micro-chemical analysis. The first four sections have a common link in that they are all concerned with the information that may be deduced from techniques involving the absorption or diffraction of X- or y-rays.The lead content of petrol, for example, has been determined with a precision of 1 per cent. by 664. New York, Academic Press Inc. 1950. Price $12.00. Volume I comprises 12 sections, each written by a specialist in his particular field.692 REVIEWS [Vol. 75 absorption methods using an X-ray photometer and by means of micro-radiography it has been possible to analyse multi-component alloy systems in terms of phase structures, micro-defects and porosity, and strain. In the space of 100 pages there is an excellent account of the application of X-ray diffraction methods to powders and metals, including a section on the elements of crystal structure. Besides an account of the powder method of identification and analysis the author gives useful and clear explanations of the other possibilities of the X-ray method, including the measurement of crystallite size and alloy compositions, and the study of structure, precipitation hardening and magnetic properties.The section ends with clear illustrations of the special value of the methods in studying metal working processes-deformation, preferred orientation and annealing. An equally fascinating account is given in the next section of the use of diffraction methods in the study of fibres. The difficulties of examining systems in which theke is a gradual blending of all possible degrees of perfection from perfect crystalline forms to totally random arrangement of molecules in space are well brought out. Here at last we have a tool for analysis of surface films; the composition and structure of oxide films on metals have been deter- mined and variations of composition within the film for film thicknesses of 100 to 3 0 0 ~ .have been demonstrated. The ground covered in the section on “Spectr-ophotometry and Colorimetry,” by Wallace K. Brode of the Bureau of Standards, is best illustra-ted by the headings: Nomenclature, Theory of light absorption, Instrumentation, Experimental procedure, Application and interpretation of data, Colour description. In the sections on emission and absorption spectroscopy and on Raman spectra there are again very full accounts of the theoretical background to the techniques. Indeed, this is throughout a characteristic feature of the book. It is particularly true of the section on polariscopic and polarimetric examination and refractive index measurement, but sufficient examples of practical application are given to show the importance and value of these methods in analysis. The final section on mass spectrometry maintains the high standard and in the face of the results that are quoted, for example, of light hydrocarbon mixtures, it will be admitted that this technique has come to stay.The promise of simpler and more compact instruments, even at the expense of some versatility, is good news. I t will be realised that this book has much more to offer the reader than earlier and more superficial books setting out to cover similar ground. It will serve to emphasise the revolution that has taken place, is taking place and, with some, has yet to take place in analytical thinking.Nobody should be deceived into believing that one has only to read about one of these specialised techniques to become a competent practitioner. No specialist will expect his reading to be confined to one of these sections. Few, if any, of the special techniques can be really valuable until their practitioner has acquired sufficient skill and experience to merit the name of specialist. They are not likely to become dilettante side lines of the average analyst. While analytical practi- tioners are at present undoubtedly scarce, there is perhaps an even greater scarcity of those who can clearly formulate the “analytical problem.’’ The present renaissance of analysis springs largely from the needs of industrial research; for the problems that arise, simple arithmetical statements of composition seldom suffice, too narrow a conception of what constitutes analysis fails to give answers and the use of any or all of these newer tools and techniques is fully justified and is comprehended in the word “analysis.” Electron diffraction technique is equally well described. This indeed is micro-analysis. The treatment of this important subject reaches a high standard. The book makes no such promises. For the analyst, such a book is educative and probably revealing. I t remains only to add that the covers and binding are worthy of the book. R. C. CHIKNSIIZE

ISSN:0003-2654    

DOI:10.1039/AN9507500691

出版商:RSC    

年代:1950

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Dec., 19501 PUBLICATIONS RECEIVED 693 MICROCHEMISTRY GROUP THE following meetings of the Group will be held during 1951- Annual General Meeting-This will be held on Friday, January 26th, at the Sir John Cass College, Jewry Street, Aldgate, London, E.C.; it will include an exhibition of micro- chemical apparatus and a symposium on “Radiochemical Techniques in Microchemistry.” Spring Meeting-This has been tentatively arranged for Edinburgh at the beginning of April. It is hoped that this will be a joint meeting with the Edinburgh and East of Scotland Section of the Royal Institute of Chemistry and that it will include a symposium on “Micro- biochemical Methods.” Azctumn Meeting-This has been tentatively arranged for Liverpool at the end of September, in conjunction with the Liverpool and North-Western Section of the Royal Institute of Chemistry. I t is intended that this meeting shall include a symposium on “Chemical Microscopy,’’ with special reference to Fluorescence Methods.

ISSN:0003-2654    

DOI:10.1039/AN950750693c

出版商:RSC    

年代:1950

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THE SOCIETY OF PUBLIC ANALYSTS AND OTHER ANALYTICAL CHEMISTS FOUNDED 1874. INCORPORATED 1907. THE objects of the Society are to encourage, assist and extend the knowledge and study of analytical chemistry by holding periodical meetings, by promoting lectures, discussions and conferences, and by the publication of a journal devoted to analytical chemistry; to study questions relating to the adulteration of food, drugs and commercial articles generally, and its detection; and to promote the efficiency and proper administration of the laws concerned with the repression of adulteration. Every candidate for membership of the Society must be not less than twenty-one years of age and be or have been engaged in analytical, consulting or professional chemistry. Each candidate for election must be proposed by three members of the Society, who must provide written testimony of their personal knowledge of his or her scientific and professional fitness.If the Council of the Society in their discretion think fit, such testimony may be dispensed with for a candidate not residing in the United Kingdom. Every application is placed before the Council and the Council have the power in their absolute discretion to suspend or reject any application, or to elect the candidate to membership. The Society’s official year runs from March to March, but the financial year begins on January 1st and subscriptions are due on that date. Ordinary Meetings of the Society are held in London, usually on the first Wednesday in October, November, December, February, April and May; the Annual General Meeting is usually held on the first Friday in March. Notices of all meetings are sent to members by post. The Analyst, the official organ of the Society, is issued monthly to members, and contains reports of the proceedings of the Society, original papers and notes, information about analytical methods, Government reports and reviews of books. All members receive in addition Abstracts C, the analytical section of British Abstracts, providing a reliable index to the analytical literature of the world. Forms of application for membership may be obtained from the Secretary, 7/8, Idol Lane, London, E.C.3. The Entrance Fee is it]l 1s. The Annual Subscription is E2 2s.

ISSN:0003-2654    

DOI:10.1039/AN950750694a

出版商:RSC    

年代:1950

数据来源: RSC