ISSN:0003-2654    

DOI:10.1039/AN95075FX029

出版商:RSC    

年代:1950

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95075BX031

出版商:RSC    

年代:1950

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95075FP055

出版商:RSC    

年代:1950

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95075BP059

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

AUGUST, 1950 Vol. 75, No. 893 THE ANALYST PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS AND OTHER ANALYTICAL CHEMISTS Fluorescence Microscopy as an Aid to Food and Drug Analysis BY J. KING AND R. E. WESTON SYNOPSIS-A simple method has been devised for using fluorescence microscopy in food and drug analysis, the wavelength of 3650 A. being selected from the light given by a 250-watt compact-source high-pressure mercury-vapour lamp. The advantages over normal microscopy are discussed, and illustrations are given from the authors’ experiences of the application of the method, with special reference to the detection of minute quantities of aneurine added in the form of a solution in fine droplets sprayed on to wheat flour for the purpose of “enrichment.” THE principle of fluorescence microscopy has been widely used in biology, and an excellent summary of the subject up to 1940 has been given by E1linger.l A more recent review by White2 and a new edition of Pringsheim’s book on fluorescence3 give useful references up to -1949.Unfortunately the apparatus used is expensive, difficult to procure and requires a skilled technique. It has been found, however, that fluorescence is frequently generated when light in the near ultra-violet region impinges on materials of plant or animal origin. The recent introduction of compact-source high-pressure mercury-vapour lamps induced us to investigate their potentialities in fluorescence microscopy as applied to food and drug analysis. The radiant power output per unit area of source in this type of lamp is extemely high; this enables an intense beam of radiation to be focussed on to the object to be examined whether by incident or transmitted light.The wavelength of 3650 A. has been selected for the following reasons. Extremely intense emission occurs in the near ultra-violet at this wavelength and this radiation can readily be isolated by filtering through Wood’s glass which transmits about 65 per cent. of the light, or through a Wratten filter No. 18A. Light of this wavelength is transmitted freely by most optical glass and an ordinary microscope can be used without quartz condensers, slides, etc. It has the further advantage of being innocuous to the eyes, and so obviates the special precautions necessary with lower wavelengths. When examining the specimens by transmitted light it is an advantage, although not essential, to replace the normal silvered mirror by one made of “super-purity” aluminium, polished and anodised. Such a mirror reflects about 80 per cent.of the incident light of 3650 A. wavelength. When dark-ground illumination is required, an Abb6 condenser can be used and at high magnifications (using objectives of shorter working distance than 4 mm.) this is necessary, as the angle of incidence is of necessity so small under these con- ditions that severe distortion of the image occurs. It is an advantage when using objectives of the order of 4 mm. to have the highest numerical aperture possible. If it is desired to use the shorter wavelengths of the mercury-vapour lamp, the condenser system described by 397398 KING AND WESTON : FLUORESCENCE MICROSCOPY -4s [Vol.75 Smiles4 and used with success by Barnard and Welch5 is recommended; it is then necessary to use transmitted light. Recently, a type of glass that transmits light of shorter wavelength has become commercially available and from this lenses and prisms can be made. This should enable the optical system formerly made from quartz to be made much more cheaply, and greatly extend the use of fluorescence microscopy at the shorter wavelengths. The essential details of the system adopted by us are shown in Fig. 1, in which A is a choke made for use with this type of lamp, furnished with tappings to match accurately the voltage of the A.C. supply when under load (the lamp is unsuitable for D.C.). The lamp housing should be well ventilated, in view of the heat to be dissipated, and constructed so as to prevent stray beams of ultra-violet light of’ various wavelengths escaping and affecting the eyes of the operator.The lenses at B are of any type of optical glass that will readily transmit light of wavelength 3650 A., and are spaced to enable the light to be focussed readily on to the stage of the microscope. It is an advantage to have these mounted on an optical bench, as this enables them to be adjusted so that when transmitted light is used a parallel beam may be reflected through the substage condenser. If light of shorter wavelength is required, these lenses must be of quartz or the special glass referred to above, as must also be the slip covering the preparation to be examined; C is a sheet of Wood’s glass approximately 3 mm.in thickness, or a Wratten filter No. 18A. For some purposes it is essential to utilise the maximum intensity of ultra-violet light, and this is made possible by careful focussing on to a small sheet of paper impregnated with a dilute solution of acidified quinine sulphate and mounted on a glass slide in the usual position on the microscope stage. Unfortunately, the image is in the form of an elongated ellipse, which makes even illumination of the field impossible at the highest light intensities when using low-power objectives. Even- ness of illumination is improved greatly by adopting an “out-of-focus” position, but at the expense of intensity. A compromise may be obtained by presenting the stage of the microscope at an appropriate angle to the incident light or by interposing a lens having a cylindrical face.The microscope slides and cover-slips rnay be of ordinary glass, but they should be examined for mechanical inclusions by observing them under ultra-violet light and rejecting any showing fluorescent patches or spots. These spots as well as any extraneous matter that may have settled on the top of the slide may be troublesome when working with objectives of greater power than 16 mm., and on all occasions when a hazy fluorescence is encountered it is essential to focus accurately on to the material responsible, so that its nature may be identified. The appearance of objects seen under ;t powerful beam of ultra-violet light differs markedly from that under normal lighting and the microscopist will need to build up his own experience with this medium.Objects such as leaves, powders, hairs, textiles, etc., should first be examined in the dry state by incident light under a low power objective, about 16 mm., with a x 10 eyepiece. Specimens should be reduced t o a suitable size and form for examination in a water or dilute alkali mount with superimposed cover-slip. The usual clearing agents may be employed, but this is seldom necessary except when using transmitted light. A brief study has been made of the appearance under ultra-violet light of leaves, whole and powdered, seeds, fibres, animal and vegetable hairs, powdered roots, cereals, flour and insects. Chase and Pratt6 have described the colour of the general fluorescence observed under comparatively low intensities of ultra-violet light of wavelength approximately 3650 A.of 151 powdered drugs, and of their alcoholic extracts ; but our investigation relates to the fluorescence, under intense ultra-violet light, exhibited by individual structures. Stanfill‘ has also given some account of the detection of contamination by rodents. Certain constituents of vegetable and ardmal matter exhibit marked fluorescence, e.g., aesculin, fisetin, lignin, xylin, riboflavine, lyochromes, porphyrins, vitamin A. Differential staining with fluorescent dyes such as fluorescein or acriflavine may be used when the sub- stance under examination does not exhibit a natural fluorescence, but this subject has not been pursued by us, our attention having been given entirely to naturally fluorescent substances.A fluorescent paste has also been describeda to render interstices in surfaces fluorescent. As a rule no special treatment of objects to be examined by ultra-violet light is necessary. They may be examined in the dry state or mounted in fluids such as water, dilute glycerol, 1 per cent. sodium hydroxide, or 2 N hydrocliloric acid, without clearing. The translucency of starch gelatinised by the alkaline ferricyanide mounting fluid referred to later enables ultra-violet light to penetrate readily to cellu1a.r structure in starchy powders ; if this fluoresces,August, 19501 AN AID TO FOOD AND DRUG ANALYSIS 399 its fine structure is seen much more clearly than when submitted to normal microscopy with transmitted light.The jelly holds the fragments of fibre in positions that enable the structure to be seen in perspective if a binocular microscope is used with the direct rays, III I and this greatly facilitates the examination of starchy powders such as wheat flour. The interior structure of leaves can only be seen by drying and powdering or by suitable dis- section. Many oils, the dry endosperm of cereals, etc., fluoresce so brilliantly that the visible light emitted greatly impairs the definition of the fine structure of cellular matter. It is therefore an advantage to mount in a fluid, and sometimes to remove the oil by extraction400 KING AND WESTON: FLUOR.ESCENCE MICROSCOPY AS [Vol. 75 with a suitable solvent. Hairs of either plants or animals almost invariably fluoresce under ultra-violet light.The cell walls of most plants exhibit a green fluorescence in 1 per cent, caustic soda solution and blueviolet in an acid or neutral aqueous medium. In some cases, e.g., powdered rue, the aqueous mounting mediuim, particularly if alkaline, becomes fluorescent. On the whole, as stated by Helmhol~,~ the image is better differentiated, and the detail of structure is more readily discernable, when fluorescent substances are associated with the objects under examination, and it is our experience that for many substances differentiation and recognition is easier by the ultra-violet technique than by ordinary microscopy, and certainly with far less preliminary preparation. The following is a short account of the fluorescence microscopy of some well-known foods and drugs, with their characteristic features.Hairs-Most vegetable hairs fluoresce in the dry state, but it is better to examine them in an aqueous medium which may be neutral, acid or alkaline. Wheat hairs fluoresce with a blue colour when mounted in 1 per cent. sodium hydroxide, and the structure is well defined. Rat and mouse hairs also fluoresce with a blue colour in an aqueous medium, and the structure is thrown into sharp relief. This structure can readily be seen in contaminated flour in 1 per cent. sodium hydroxide solution, but unless contamination is gross, the method cannot replace that described for hairs and insect fragments by Kent- Jones, Amos, Elias, Bradrjhaw and Thackray.lo Vegetable strmture-Many naturally occurring oils fluoresce both in the oil cells of plants and as oils. Thus the germ oils of cereals fluoresce with a violet colour, and the oil-containing cells also appear to be violet, the cell walls being green in an alkaline mounting fluid.The bast fibres of roots, stems, etc., fluoresce with a blue or blue-green colour when mounted in water or in an alkaline medium. Imects-Mounted dry, the outer surface of insects exhibits a variety of brown and red colours, the hairs standing out in sharp relief. The compound eyes fluoresce with a blue colour. Insect fragments can be recognised in powdered cereals mounted in sodium hydroxide solution, but a slight contamination could only be established after a most exhaustive examination by this method.Detection of aneurine hydrochloride added to wheat flour in the form of a solution as a f i n e spray-In view of the possibility of flours being sprayed with a solution of aneurine hydrochlo- ride for enrichment purposes, a special study of the method as applied to the detection of such flours was undertaken. Experience has shown that, while the method of Hintonll for the detection of added powdered aneurine hydrochloride is adequately diagnostic, sufficient light to be visible to the unaided eye is not obtainable when the vitamin is added as a solution of aneurine hydrochloride. If, however, the specjimens are examined by fluorescence microscopy using our technique, the violet fluorescent spots due to thiochrome formed by the action of the oxidising medium are readily apparent, even when the addition has been made in the form of extremely fine drops produced by an atomiser.The technique is as follows: the mounting fluid consists of an aqueous solution containing 0.1 per cent. of K,Fe(CN), and 1 per cent. of sodium hydroxide, with the addition of a wetting agent such as “Teepol.” The latter enables the microscope slide to be wetted easil.y, and makes the preparation of a bubble-free slide much easier. The mounting fluid is spread with a glass rod on to a microscope slide 3 inches x 19 inches (as free as possible from flaws that fluoresce). The flour is sprinkled as evenly as possible over the wetted surface by means of a small sieve (mesh about 0.7 mm. square). Only sufficient flour is used to cover amply but to avoid thick patches, which are not completely wetted by the oxidising fluid and in the dry state fluoresce brilliantly. It is essential to avoid fluorescence due to this dry flour.A slide of similar dimensions is wetted with the same fluid and carefully placed wetted side down on to the prepared sample engaging one edge first and making complete contact slowly so as to avoid the formation of air bubbles. The slides are then inverted and examined systematically, on a travelling stage, with a 2-inch objective in combination with a x 10 eyepiece. The presence of diffused round spots of violet fluorescence which cannot be sharply focussed and are not associated with recognisable cell structure are indicative of a sprayed solution of the vitamin. Care should be taken not to mistake for thiochrome, fluorescence derived from other sources such as wheat germ oil, flaws in the glass slidle, or dry material in the preparation or on the surface of the slide.A little experience is necessary before such spots can be recognised with certainty and it may be necessary to examine a number of slides, depending on the quantity added and the size of the drops, as even with flours known to have been enriched A few hairs exhibit a pale pink colour. Mites exhibit a very pale violet fluorescence.August, 19501 AN AID TO FOOD AND DRUG ANALYSIS 401 by fluid aneurine sprays, a proportion of slides exhibiting no typical spots may be encountered. Comparison with flours of known authenticity is necessary in the event of doubt. In the sam- ples of flour examined by us as little as 0.1 pg.of aneurine per g. of flour, added in the form of finely atomised droplets, has been detected. We prefer to use a binocular microscope and mechanical stage for the examination of these specimens, the slides being made from old photographic quarter-plates from which the gelatin has been removed. For rapid scanning, the slides may be manipulated by hand, resort being had to the screw mechanism only when a systematic survey of the whole of the material on such large slides is necessary. A moderate contamination by insect fragments or rodent hairs may be detected by this arrangement. The various parts of the wheat grain appear as follows when mounted in water or alkaline solutions. Wheat hairs-In water mounting the fluorescence is blue-green ; the fluorescence is much stronger in 1 per cent.sodium hydroxide. Germ-In water the fluorescence is pale blue-violet; in 1 per cent. sodium hydroxide the contents of the cell fluoresce with a stronger violet colour and the cell walls brilliant green, After de-fatting, which removes the oil, the violet colour no longer appears. CeZZuZar tissue-In water the fluorescence is pale blue; in 1 per cent. sodium hydroxide the aleurone cells walls are a brillibt green. Parts of the surface of the outer bran may be a pale brown in colour and show little distinctive green fluorescence. WhoZemeaZ-Mounted in 1 per cent. sodium hydroxide the starchy matter is invisible, but the structures enumerated above can be seen quite clearly. Occasionally a single field contains specimens of hairs (blue), internal cellular structure (cell walls brilliant green) and germ (cell walls green with violet contents), the whole exhibiting a very striking effect and giving a much clearer delineation than is possible by using ordinary microscopy.Much time is saved as no previous preparation of the specimen is necessary, the structure being as a rule more clearly defined. The authors wish to express their thanks for gifts of samples of “enriched” flour prepared by Dr. D. FV. Kent-Jones, Dr. L. George, and Dr. T. Moran and his staff of the Research Association of British Flour Millers, and also to the Government Chemist for permission to publish this paper. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Ellinger, P., Biol. Rev., 1940, 15, 323. White, C. E., Anal. Chem., 1950, 22, 69. Pringsheim, P., “Fluorescence and Phosphorescence, ’’ Interscience Publishers, Inc. , New York, Smiles, J., J . R. Micro. Soc., 1933, 53, Ser. 111, 207. Barnard, J. E., and Welch, F. K., Ibid., 1936, 56, Ser. 111, 361; 1937, 57, Ser. 111, 256. Chase, C . R., and Pratt, R., J . Amer. Pharm. Ass., 1949, 28, 324. Stanfill, R. C., Quart. Bull. Assn. Food and Drug Ojicial U S . , 1946, 10, 141. Deribere, M., Rev. gen. Mecan, 1949, 33, 251. Helmholtz, H., Ann. Phys., LJ~z., Jubelband, p. 557. Kent-Jones, D. W., Amos, ,4. J., Elias, P. S., Bradshaw, R.C.A., and Thackray, G. B., Analyst, Hinton, J. J . C., Chem. and Ind., 1946, 65, 94. 1949. 1948, 73, 128. GOVERNMENT LABORATORY STRAND, LONDON, W.C.2 February, 1950

ISSN:0003-2654    

DOI:10.1039/AN9507500397

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

402 FRASER AND WESTON: GASOMETRIC METHOD FOR THE ESTIMATION OF [VOl. 75 Gasometric Method for the Estimation of Creta Praeparata in National Flour BY J. R. FRASER AND R. E. WESTON SYNOPSIS-A method for the routine estimation of Creta praeparata in National flour has been developed on similar lines to the Chittick gasometric method for baking powder. Apparatus for multiple determinations is described, and a mathematical formula has been evolved from which the amount of Creta praeparata in a sack of flour may be calculated directly from the volume of gas evolved and from factors which can be tabulated. These factors take account of the temperature, barometric pressure and vapour pressure of the liquid under which the estimation has been carried out. THE following method has been adopted at the Goverpment Laboratory as rather more convenient for the routine examination of a large number of samples than other methods1p2 previously published for this purpose.The procedure has been developed on similar lines to the Chittick gasometric method for baking p ~ w d e r . ~ It has proved applicable to multiple simultaneous determinations, is reasonably easy to manipulate and free from hidden sources of error, whilst the operator has the advantage of a progressive visual change to observe. EXPERIMENTAL APPARATUS- An approximately 400-ml. flask with ground glass fitted head is connected with a manometer burette by means of well secured pressure tubing, as shown in the diagram (Fig. 1). The reaction flasks are mounted on a shaking machine. PROCEDURE- Introduce 2Og.of flour into a flask, add 50ml. of saturated brine, insert the stopper and shake the flask gently to mix the contents thoroughly. Wash the rubber stopper and neck of flask with a further 20ml. of brine. Then place the flask on the platform of the shaker and clip it into position. Cautiously lower the special phial containing 20 ml. of hydrochloric acid (1 + 1) so that i t stands upright in the middle of the flask. Fit the head connecting the flask with the measuring limb of the burette, and allow the apparatus to stand for a few minutes until it has reached temperature equilibrium with the surrounding atmosphere. Adjust the brine in the burette by running sufficient out of the tap provided at the U-bend so that the levels are the same in both limbs (the air within the flask is then at atmospheric pressure) and note the level (see Fig.l), and record the temperature and barometric pressure. Start the shaking device; this causes the acid phial to fall over and allows the acid to mix with the other contents of the flask. The carbon dioxide evolved from the reaction of the acid with any chalk present in the flour will cause a displacement of air in the head into the burette limb, the pressure in which will be apparent by the alteration of the levels in the two limbs. Periodic adjustment must be made during the course of the reaction so that it may proceed at atmospheric pressure all the time. Twenty minutes is sufficient to reach a final equilibrium. Stop the shaker, allow the contents of the apparatus to settle for 2 or 3 minutes, make the final adjustment of the levels, and record the increase in volume of gas in the system.Vigorous shaking is necessary to ensure rapid and efficient evolution of gas, as is demonstrated in Fig. 2. This volume, adjusted for vapoa pressure, temperature and barometric pressure to N.T.P., is directly proportional to the amount of chaik originally present. The temperature of the surroundings milst be kept as steady as possible throughout the determinations. There is a slight rise of about 0.5" C. between the initial and final temperatures of the liquor in the reaction flask. This difference is always checked as well as any differences between the air temperatures. All flasks and fittings are of standard pattern and interchangeable.August , 1950 J CRETA PRAEPARATA I N NATIONAL FLOUR 403 As all standards will experience the same minor fluctuations, the effect of these will have been taken into account and therefore may be ignored in the final calculation.n i ;I Fig. 1. Apparatus Standards can be included in a batch of determinations so that direct comparison can be made and much calculation avoided. Alternatively, it is sufficient to make one calibration from a series of standards, and this will be within the accuracy required, provided that the necessary corrections for pressure and temperature are first applied to all data. CALCULATION OF RESULTS Let V = volume increase observed, T = temperature in degrees absolute, B = barometric pressure, Aq = vapour tension of liquid at temperature T, 1-976 g.= weight of 1 litre of carbon dioxide at N.T.P.404 FRASER AND WESTON: GASOMETRIC MLETHOD FOR THE ESTIMATION OF [VOl. 75 It can be demonstrated that: Ounces of Creta praeparata per - 273 B-Aq 1.!376 100 280 453.6 -o,Fi x -- x - x - sack of 280 1b- -[ (T 760 1000 44 28.35 -%-) ] x 1406 x F -0.5 > I 273 B-Aq The factor within brackets ( r K ) can be ta.bulated for values of B, T and Aq (Fig. 4). The vapour tension of brine is approximately 0.75 of that of water at the same temperature. c - . 2 4 6 8 I0 12 I4 16 I8 M 21 24 26 ZE 30 TIME Of SHAKING, MIN Fig. 2. Effect of Shaking Fig. 3 FACTOR, K Fig. 4. Factors for values of B, T and Aq.August, 19501 CRETA PRAEPARATA IN NATIONAL FLOUR 405 It has been determined experimentally for the brine - acid mixture used and found to be 0.70 of that of water.A correction for the “blank” in Creta-free flour is necessary. This varies only slightly from an average of 1 mg. of carbon dioxide per 20 g. of flour, which may be taken as the standard deduction to be made, and this deduction is represented by the figure of 0.5 appearing as the final term in the expression above. The factor F is dependent upon the solubility of carbon dioxide and the nature of the apparatus used and must be determined experimentally. The actual value obtained was 1.14 which was found to be fairly constant throughout the working range (17” rt 5” C.). Factors found from standard runs containing known additions of Creta praeparata (0, 25, 50 and 75 g.) are as follows- Barometric Experimental Temperature pressure factor F 14 763 1-160 18 760 1.136 20 755 1.140 21 755 1-145 22 749 1.140 TST An approximate relation F = 1 + - 273H These results are shown graphically (Fig.3). may be deduced, where : ST = solubility of the gas in liquor at temperature T, and H = headspace of flask, i.e., total volume less volume of liquor. Some calculated factors obtained from this expression and recorded solubilities of carbon dioxide,4s6 taking H as 300 ml. and volume of liquor as 100 ml. are: Calculated factor F at temperatures of r 16” C. 20” c. 25” C.’ Water . . .. .. .. .. 1-36 1-31 1.28 Brine, 16 per cent. w/v of NaCl . . 1.18 1.16 (1.14) 0.5 N hydrochloric acid . . .. 1-37 - 1.30 Brine, 30 per cent. w/v of NaCl . . 1.12 1.10 (1.09) Hence, routine examination comprises the recording of volume of gas evolved, temperature and pressure and then making the calculation- where values of K and F are defined as above. Ounces per sack = (V x K x F)-0-5, We wish to thank the Government Chemist for permission to publish this work. REFERENCES 1. 2. 3. 4. 6. Greer, E. N., Mounfield, J . D., and Pringle, W. J . S., AnaZyst, 1942, 67, 352. Hartley, A. W., and Green, A., Ibid., 1943, 68, 142. Chittick apparatus, “A.O.A.C., 1945,” p. 208. Seidell, A., “Solubilities of Inorganic and Metal Organic Compounds,” van Nostrand Co., Inc., Comey, A. M., and Hahn, D. A., “Dictionary of Chemical Solubilities,” Macmillan & Co., New New York, 1940. York, 1921. GOVERNMENT LABORATORY LONDON. W.C.2 December, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500402

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

August, 19501 CRETA PRAEPARATA IN NATIONAL FLOUR ERRATUM: April (1950) issue, p. 206. Below Fig. 3,for “g.” read ‘‘pg.” 405

ISSN:0003-2654    

DOI:10.1039/AN9507500405

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

406 MIDDLETON AND STUCKEY THE DETERMINATION [Vol. 75 The Determination of the Purity of Propylene Glycol BY G. MIDDLETON AND R. E. STUCKEY SYNOPSIS-A description is given of a test using the critical solution temperature of propylene glycol and ether. With this test the presence of 0.1 per cent. of ethylene glycol, 0.1 per cent. of di-propylene glycol or similar amounts of water and ethyl alcohol in propylene glycol can be deter- mined. IN spite of the large number of organic solvents that are at present available, only a few can be administered in ternally, while the number available for parenteral administration is extremely restricted. The addition of propylene glycol to the last group is therefore of special interest, and a high standard of purity is necessary for material required for injection purposes.A number of specifications1 p2 p3 have been published for propylene glycol for pharmaceutical purposes. These specifications include upper and lower limits for physical constants, together with tests for general impurities such as sulphates, arsenic and lead; the American National Formulary VIII has an assay using periodic acid. An examination of these specifications shows them to be, in general, deficient with regard to tests for impurities of a glycol character. Ethylene glycol is an impurity that is not likely to be found to any great extent in commercial propylene glycol, more likely impurities being di- and tri-propylene glycols; at the same time, in view of possible confusion between various glycols, a test that would limit the presence of glycols other than propylene glycol appears to be desirable. The refractive indices of propylene glycol and ethylene glycol are practically the same, and although there is an appreciable difference in density between the two compounds, this can hardly be relied upon to show the presence of small amounts, say a few per cent., of ethylene glycol in propylene glycol.The method given by Warskowsky and Elvig4 for the determina- tion of ethylene glycol and propylene glycol in admixture, being based on periodate oxidation followed by estimation of the relative proportions of acetaldehyde and formaldehyde produced, is equally unsuitable for this purpose. It is, similarly, difficult to determine the presence in propylene glycol of condensed compounds, such as di-propylene glycol, which can be formed from propylene glycol by the elimination of water and the formation of an ether linkage.A search for a chemical test does not appear to be a very promising line of attack. Direct physical measurements, such as refractive index and density, are also, as has been indicated, of little value in solving the problem. Attempts were therefore made, in experiments on mixtures of known amounts of ethylene glycol with propylene glycol, to concentrate the ethylene glycol by extraction with ether. Propylene glycol is about eight times more soluble in ether than is ethylene glycol, but preliminary trial of this method showed considerable difficulties. It did, however, indicate that a more sensitive test could probably be based on the critical solution temperature with a solvent, and ethyl ether was found to be suitable. In using such a test it is necessary to obtain a sample of pure propylene glycol, a matter of some difficulty owing to the ease with which the substance absorbs water.As a suitable criterion of purity, the constancy of the critical. solution temperature of a series of successive fractions obtained by distillation in an efficient fractionating apparatus was used. For the determination of the critical solution temperature, a method based on that of the Institute of Petroleum5 for the determination of the aniline point was used. Owing to the necessity of guarding against er:rors due to the volatility of the ether and to the hygroscopic nature of the components, the test was carried out in a closed vessel and, to avoid the need for stirring, with a falling temperature.A clear mixture of propylene glycol and ether, when cooled slowly, shows at first a faint turbidity, which gradually increases as the temperature falls, so that it is not possible to state a definite point at which turbidity commences. On continuing the cooling there is, at a particular temperature, a sudden increase in turbidity, followed immediately by a “streakiness” due to convection currents and separation into two phases. This point, at which there is a marked increase in the turbidity, was found to be the most easi1.y reproducible, and it was taken as the critical solution temperature, or what we have termeld the “ether-point.”August, 19501 OF THE PURITY OF PROPYLENE GLYCOL 407 TECHNIQUE OF THE TEST- The ether used must be anhydrous and free from alcohol; it can be prepared by distilling pure Analytical Reagent grade ether over sodium; the distillate may, if required, be kept for a short time over sodium.The ether and propylene glycol were mixed in a 10-ml. stoppered measuring cylinder, the stopper of which was specially ground with fine corundum. Propylene 10 PERCENTAGE OF GLYCOL IN THE PROPYLENE GLYCOL-ETHER MIXTURE Fig. 1. Temperatures of separation of propylene glycol -ether mixtures. Curve A, pure propylene glycol and ether; curve B, propylene glycol containing 1 per cent. of water and ether. glycol was first added quickly from a wide-bore bulb tube (an inverted pipette is satisfactory), care being taken to see that none of the glycol was allowed to come into contact with the ground portion of the neck of the cylinder. When the propylene glycol had run down in the cylinder, the volume was noted and the requisite quantity of ether was added.The ether - propylene glycol mixture was then stoppered, warrned and shaken to obtain a clear solution. The cylinder, suitably weighted, was placed in a rectangular glass trough forming a water-bath and containing a stirrer, and cold water was allowed to drip in from a tap- funnel to give the desired rate of fall of temperature. The test was carried out with top lighting, and a dead black background with a horizontal white line 0-5cm. in width was placed so that the cylinder cut across the line. The "ether-point" was taken as that point at which the white line was indistinguishable through the cylinder.This point can be repro- duced very accurately in successive experiments. The results of experiments with pure propylene glycol and ether in different proportions are shown in Fig. 1 (curve A). It will be seen that the two liquids are completely miscible above 21.6" C., but that at lower temperatures two solutions of different concentrations are in equilibrium with each other. The summit of the curve is flattened, so that at concentra- tions of propylene glycol between 30 and 35 per cent. the temperature of separation is only slightly altered by variation in concentration. For this reason a concentration of propylene glycol of 33-3 per cent. (one volume of propylene glycol plus two volumes of ether), practically a t the peak of the curve, was selected as a convenient standard concentration.408 MIDDLETON AND STUCKEY : THE DETERMINATION [Vol.75 Pzcri$cation of the propylene &cod-After preliminary work had shown the value of the ether-point in classifying samples of the glycol, a quantity of 1 litre of purified glycol was fractionated through an electrically heated column, 4 feet long, containing glass helices, with a reflux ratio head. Fractions 1D to 9, showing no significant difference in ether-point, were mixed together, the resulting product being taken as pure propylene glycol of ether-point 21-62" C. TABLE I Details of the fractionation are given in Table I. Fraction 1A 1B 1c 1D 2 3 4 5 6 7 8 9 10 Residue FRACTIONATION OF PF.OPYLENE GLYCOL Boiling-point, O c.23-26 90-95 to 96 to 97 97 97 97-8 97 97 97 97 97 97 - Pressure of distillation, mm. of Hg. 24 24 22 24 24 24 24 23 23 23 23 23 23 - Approx. vol. of fraction, ml. 2 25 25 40 80 100 140 100 100 100 140 100 40 20 "Ether-point" of fraction, O c. - 30 21.95 21-60 21.60 21-67 21-62 21.65 21.60 2 1-60 21-63 21-60 21-76 I The physical constants of pure propylene glycol were determined on the sample prepared as described above and the following values were obtained- Weight per ml. at 20" C, = 1.0374 g. Refractive index at 20" (3. = 1.4330 The effect of 1 per cent. of water added to the carefully purified propylene glycol is shown Fig. 2 shows the alteration in the ether-point resulting from the' addition of water and Within the range of concent.rations examined, the graphs are practically The alteration in ether-point produced by the presence of 0.1 per cent.of in Fig, 1, curve B, and it will be noted that this curve remains parallel to the original one. other substances. straight lines. various impurities is shown in Table 11. TABLE: Ir EFFECT OF 1 MPURITIES Impurity Alteration of "ether-point" per 0.1 per cent., Water . . .. .. .. .. + 0-35 Ethylene glycol . . .. .. .. + 0.15 Di-propylene glycol . . .. .. - 0.055 Ethanol .. . . .. .. .. - 0.25 APPLICATION OF THE TEST-DEHYDRATION OF THE SAMPLE- The ether-point cannot be used directly a s a measure of purity as it is greatly affected by the moisture that is usually present in samples of propylene glycol. In passing, however, it may be mentioned that, if the absence of other substances can be assumed, the ether-point can be used accurately to determine the percentage of moisture present provided that the amount is small.When 3 per cent. of water is present, the critical solution temperature approaches the boiling-point of the ether. A method was, therefore, required for the dehydration of samples of propylene glycol. This was first attempted by the direct addition of suitable substances to the propylene glycol and to the propylene glycol - ether mixture. None of the agents tried, viz., calcium oxide, barium oxide, anhydrone, silica gel, sodium sulphate, magnesium sulphate, sodium sulphite, copper sulphate and sodium metal, was of any value; either they were ineffective or they dissolved in the liquid and altered the equilibrium.August, 19501 OF THE PURITY OF PROPYLENE GLYCOL 409 Both ethylene glycol and di-propylene glycol have a boiling-point higher than that of propylene glycol, and although the difference in boiling-point between ethylene and propylene glycols is only about 10” C., this should be sufficient to ensure that the concentration of the forrner would increase as part of the mixture is removed by distillation.This was confirmed in experiments in which samples of propylene glycol, to which were added small quantities 0-5 1-5 2.0 PERCENTAGE OF IMPURITIES IN THE PROPYLENE GLYCOL Fig. 2. The effect of impurities on the temperature of separation of propylene glycol -ether mixtures. of the other glycols and of water, were distilled in a simple distillation apparatus.The results given in Table I showed that the water present in an ordinary commercial sample was removed in the first 5 per cent. of distillate. The results shown in Table I1 were obtained by distillation at atmospheric pressure in an ordinary distillation apparatus with a splash head. TABLE I11 DETECTION OF IMPURITIES IN PROPYLENE GLYCOL Impurity in residue, Residual “Ether-point” calculated from Added impurity Added water, quantity, of residue, “ether-point,” YO O c. % nil . . .. .. 1.0 90 21.6 0 Y O Ethylene glycol 1.0 per cent. . . .. 1.0 0.2 99 . . .. 1.0 0.1 9 ) . . .. 1.0 Di-propylene glycol 0-5 per cent. . . .. 1.0 0.1 w . . .. 1.0 90 90 10 23.3 21.9 22.05 1.2 0.22 0.32 90 21.2 0.66 10 21-15 0.75 The results given in Table 111 show that it is possible by this method to detect less than The percentage 0.1 per cent.of ethylene glycol or of di-propylene glycol in propylene glycol.410 MITCHELL: THE DETERMINATION OF THE MARC CONTENT [Vol. 75 of the latter was found gradually to increase in the residue during distillation, although the increase was slight. The sensitivity of the test can be increased by taking the ether-point of the residual 10 per cent. rather than of the residual 90 per cent. (Le., with only 10 per cent. removed by distillation) in which only slight concentration of the impurity had been achieved. In view of the ease with which propylene glycol polymerises in the presence of a trace of acid or alkali,B it was thought advisable to check the possibility of such a reaction occurring on prolonged boiling. Pure propylene glycol was boiled under reflux for 4 hours, 10 per cent. was distilled off in order to remove any water, and the ether-point was determined on the residue.It was found to be 21.58”, which indicates at the most such a slight degree of polymerisation as to be negligible. In order to apply the method to a sample of propylene glycol about which little is known, the glycol should be distilled and the ether-points of fractions of the distillate determined. Water will be removed in the first fractions and the trend of the ether-point of subsequent fractions and of the residue will give an indication of the purity of the glycol under test. Although the only impurities studied were ethylene glycol, di-propylene glycol, ethyl alcohol and water, the test can obviously be extended to other miscible impurities. It is possible that suitable amounts of impurities, e.g., ethyl alcohol and ethylene glycol, would mutually compensate each other and would produce an ether-point of pure propylene glycol; distillation, however, followed by a determination of the ether-point of the fractions, would reveal such impurities. The authors wish to thank the Directors of the British Drug Houses Ltd., for permission to publish this paper. REFERENCES 1. 2. 3. 4. 5. 6. THE BRITISH DRUG HOUSES LTD. GRAHAM STREET, CITY ROAD “National Formulary VIII,” 1947, p. 420. “New and Non-Official Remedies,” 1945, p. 488. “British Pharmaceutical Codex 1949,” p. 375. Warskowsky, B., and Elving, P. T., Ind. Eng. Chem., Anal. Ed., 1946, 18, 253. Institute of Petroleum, “Standard Methods for Testing Petroleum and its Products,” Aniline Levene, P. A., and Walti, A., J . Biol. Chem., 1927, 75, 325. Point (1.P.-2/47), Method C. LONDON, N.l March, 1950

ISSN:0003-2654    

DOI:10.1039/AN9507500406

出版商:RSC    

年代:1950

数据来源: RSC

摘要:

410 The MITCHELL: THE DETERMINATION OF THE MARC CONTENT Determination of the Marc Content of [Vol. 75 Fresh and Dried Sugar Beets BY THOMAS J. MITCHELL SuNoPsrs-The marc content of the sugar beet is important on account of the volume error it introduces in the determination of the sugar in the beet. After a short reference to earlier work, some experiments on the estimation and effects of the marc in fresh and in dried cossettes produced from beets grown in Oxfordshire and Buckinghamshire are described. The volume correction for the normal saccharimetric weight (26 g.) of fresh beets was found to be close to 1.2 ml., with a specific gravity of 1-19 for the dry marc. In a series of 100-ml. mixtures of different weights of dried marc ( 1 to 8 g.) with a pure sucrose solution that itself polarised 36-9, the polarisations of the filtered mixtures showed increases that averaged 0.34 per gram of marc taken.The marc content of dried beet cossettes appears to be higher than might be expected from calculations from the marc in the fresh beets. CLAASSEN~ defined beet marc as the residue remaining after complete extraction of the sugar and the readily soluble non-sugars from the beet under conditions similar to those in the factory, the extraction being effected as rapidly as possible in order to avoid the formation of soluble substances from hemicelluloses, pectin, and the like.August, 19501 OF FRESH AND DRIED SUGAR BEETS 41 1 This marc, or insoluble cellular matter, is sometimes assumed to be present in a constant amount, 5.0 or 4.75 per cent., but this cannot be true, because the proportion of cellular matter varies considerably with climatic conditions, the age of the plant and the soil fertility.Claassen’s definition must therefore be regarded as empirical, and the marc cannot be regarded as the water-insoluble portion of the beet without further definition of how it is determined. The particle size of the beet pulp, the length and mode of treatment and in particular the quantity and temperature of the water used for extraction influence the result considerably. The temperature must be at least 60” C. to destroy protoplasm. The proportion of marc present in the sugar beet is important on account of the volume error caused by the presence of this insoluble matter in determinations of sugar in the beet by digestion methods.The corrections generally accepted are those of Rapp and Degener2 who assumed 4.8 per cent. as the average dry marc content of the beet, and 2.0 as the density of the marc, which gives a correction of 0-6 ml. per normal weight (26 g.). HeintzS found that dried sugar beet marc would absorb water from sugar solutions, and ScheibleI.4 later showed the presence of colloidal water in beet marc. He found an average of 2 4 ml. for the hydrated marc per normal weight of beet, this is much higher than the volume occupied by the dry marc. The principal corrections that have been proposed for the marc volume per normal weight of beet are shown in Table I. TABLE I Authority Stammer, K. .. .. Rapp, G., and Degener, P. . . Pellet, H. . ... .. Fribourg, C. . . .. .. Claassen, H. . . .. .. Sidersky, D. . . .. .. Spengler, O., and Brendel, C. Stan&k, V., and VondrAk, J . Muller, E., and Pucherna, J. Kopeckfr, 0. .. .. Spengler, O., and Paar, W. Bachler, F. R. . . .. Osborn, S. J. . . .. Spengler, O., Paar, W., and StanGk, V., and Pavlas, P. . . Muck, E. Carolan. R. J. . . .. Reference 2. ver. deut. Zucker-Ind., 1882,32, 634 Ibid., 1882, 32, 786 . . .. .. Ibid., 1906, 56, 903 . . . . .. “Analyse chimique,” Paris, 1907 . . 2. ver. deut. Zucker-Ind., 1916, 66, 359 “Manuel du chimiste de Sucrerie,” 2. vey. deut. Zucker-Ind., 1926,76, 880 Paris, 1909, p. 241 2. Zuckerind. Cechoslov., 1926-27, 51, Ibid., 1929-30, 54, 99 . . .. 2. ver. deut. Zucker-Ind., 1931, 81, 447 Ibid., 1933, 83, 342 . . . . ..101, 115 Facts about Sugar, 1934, 29, 191 . . Ind. Eng. Chem., Anal. Ed., 1934,6, 37 2. ver. deut. Zucker-Ind., 1937, 87, 594 2. Zuckerind. Cechoslov., 1937-38, 62, 357, 365 Int. Sugav J., 1944, 46, 179 . . .. Correction per normal weight, 0.6 0.80 0-75 - - 1.35 2.42 1.54 1.7 1.30 0-83 2.31 1.00 2.1 1.06 - Remarks Original method 4.8% of dry marc; density 2.0 Improved method of estimation 3.0 to 4.5% of dry marc, Av. 3.5 yo ; density 1.13 In presence of lead acetate In presence of lead acetate In presence of lead acetate Confirms work of Spengler, Paar and Muck (1937) METHODS OF ESTIMATING MARC IN SUGAR BEET- Stammer’s method-The finely divided sample (20 g.) is digested in a beaker with 300 to 400 ml. of cold water for 30 minutes. The liquid is sucked off and digestion and filtration continued until the filtrate is free from sucrose (by a-naphthol test).The residue is treated with boiling distilled water, collected on a dry weighed filter-paper; and washed with alcohol and ether. I t is dried first at low temperature and then at 100” to 110” C. to constant weight. The final residue is ignited and the ash weight deducted from the first weight. The difference, multiplied by five, gives the percentage of dry marc. CZaassen’s method-The ground pulp (25 g.) is placed in a beaker marked at 400 ml. and boiling water poured in up to the mark. After 2 minutes digestion the pulp is rapidly filtered on a Buchner funnel and returned to the beaker. The extraction is repeated three times, and the marc collected on a tared filter-paper, washed with a few ml.of alcohol and dried for 6 to 8 hours at 105” to 110” C. The calculation to percentage of dry marc is made as in Stammer’s method, but by multiplying by 4 instead of 5 .412 MITCHELL: THE DETERMINATION OF THE MARC CONTENT [Vol. 74 The amount of marc found by these methods depends primarily upon the temperature of digestion. During exhaustive hot water extraction certain normally insoluble pectins are known to undergo hydrolysis and pass into solution; other constituents may behave similarly. EXPERIMENTAL The data following were obtained in a study of sugar beets grown in Oxfordshire and Buckinghamshire and of fresh and dried cossettes prepared from them. Estimation of the specific gravity of dried beet cossettes and of the marc from them-A composite sample of dried cossettes taken over a 3 months' drying campaign was found to contain 7.5 per cent.of water and 64.4 per cent. of sugar by polarisation. The specific gravity was determined by weighing 5 g. of the fine cossette "flour" in light petroleum of sp.gr. 0.79216 at 20" C. The average of six tests gave 1.4300 at 20" C. Dried marc-A similar method applied to dried marc gave specific gravity 1.19012 as the average of six determinations. The specific gravity of sucrose at 20" C. is 1.5877. Check on specific gravity from the composition of dried beets-Assuming 64.4 per cent. of sucrose at sp.gr. 16877 and 7.5 per cent. of water in the dried cossettes, there would remain 28.1 per cent. of marc and soluble non-sugars which can be assumed to have a specific gravity of 1.19.On this basis- 64.4 at 1-5877/100 = 1.022 28.1 at 1-19/100 7.5 at 1.00/100 Total Weight 9er cubic foot of dried beet cossettes widely in weight per cubic foot according to Dried cossettes : 0.334 0.075 .. . . 1.431 - - - and of fresh beets-Loose dried cossettes vary how the slices are packed. Lb. per cu. ft. Cu. ft. per ton Composite sample over 7 days . . 14.9 150.8 Average from storage bins (3-months Stan6k and Sanderas .. .. 25.0 Fresh beet cossettes . . .. .. 26-2 composite sample). . .. .. 19.0 Fresh beets : 120.0 89.6 85.5 Washed beets (Claassen) . . .. 34-37 60-66 Direct estimation of marc in dried beet cossettes-The sample of dried cossettes was ground in an impact mill to a fine flour passing an 80-mesh sieve. A weighed amount was treated in a beaker with water at 50" C.using 100 ml. of water per 5 g. of sample. Digestion was continued for 5 minutes, and the pulp rapidly filtered off on a Buchner funnel. The pulp was returned to the beaker and the process repeated thrice. After the fourth digestion the marc was collected on a tared filter-paper and washed with water at 50" C. until there was no reaction with the a-naphthol test. - A final washing was given with The residue was dried at 105" C. for 6 hours and weighed; it was then No. 1 2 3 4 5 6 7 Cossettes weighed, g. 3 3 4 4 4 2 20 Average . . TABLE Marc, % 20.83 21.20 21.30 21.48 21-73 19.60 20.61 20.96 - I1 Ash, 2-07 2.43 2.43 2.40 2.60 2.60 2.50 2.43 % - a few ml. of alcohol. ashed and re-weighed. Ash-free marc, % 18.76 18.77 18.87 19.08 19.13 17-00 18.11 18.53 These beets were selected from a week's average delivery in early October at the beginning of a crop.August, 19501 OF FRESH AND DRIED SUGAR BEETS 413 TABLE I11 Method as for Table 11, but using proportions of a Cossettes No.weighed, g. 1 6.6 2 6.5 3 13.0 4 13.0 5 26.0 6 26.0 Marc, % 23.37 24-54 24.80 24-75 23-38 24-30 Ash, 2.59 2.7 1 2-46 2-63 2-55 2.42 % Ash-free marc, % 20.78 21.83 22-34 22.12 20.83 2 1-88 normal weight Correction per Volume normal weight occupied, of fresh beets, ml. ml. 1.16 1.16 2-43 1-22 4.67 1.17 In Table I11 the volume occupied by the dry ash-free marc was obtained by dividing the weight of marc found with each proportion taken originally by the specific gravity of the marc (taken as 1-19>. The correction per normal weight of fresh beets assumes a drying factor of 4.0 for dried cossettes, Le., 1 part of dried cossettes is equivalent to 4 parts of fresh beets.The beets used in this test were an average sample from a week's delivery in mid- December. Indirect estimation of marc volume error-About 50 g. of dried cossettes were continuously extracted with cold water for 9 hours until free from sugar (as shown by a-naphthol test). The resultant pulp was dried for 6 hours at 105" C. Various amounts of this dry marc were weighed into dry 100-ml. flasks which were then filled to the mark with a sucrose solution containing 96 g. per litre. Air was removed from the solutions before completing to volume. The solutions were filtered and read in a saccharimeter.The results are shown in Table IV. TABLE IV NO. 1 2 3 4 6 6 7 8 9 10 Dry pulp taken, g. 0 0.5 1.0 2.0 3.0 4.0 5-0 6.0 7.0 8.0 Polarisation reading, % 36.9 37.2 37.3 37-5 37.8 38.6 38.8 39.3 39.9 38.2 Polarisation reading calculated, 36.9 37.1 37.2 37.6 37-8 38.2 38.6 38.9 39.2 39.6 % Difference per g. of marc - 0.60 0.40 0.30 0-30 0.33 0.34 0.32 0.34 0.38 Their precision is limited by the accuracy possible in reading the saccharimeter. The calculated figures were obtained by using the specific gravity of 1.19 for the dried marc. The average difference per gram of marc, omitting No. 2, is 0.34. Average figures for the marc content of fresh beets and dried cossettes derived from them are given in Table V. The fresh beets were treated by Claassen's method, and the dried cossettes by the method used for Tables I1 and 111.An extraction temperature of 50" C. is permissible with dried cossettes because the protoplasm is no longer active. TABLE V AVERAGE MARC CONTENT OF BEETS Fresh beets Dried cossettes Number of samples . . .. .. 15 Minimum 99 99 .. . . 4.00 Maximum 99 99 .. . . 5.40 Average water content, % . . . . 78.00 Average percentage of marc . . .. 4434 20 22.45 19.60 26-70 7-50 The average percentage of marc in the fresh beets, calculated to a dry basis, becomes The latter value Owing to the difficulty of comparing 22-00, and calculated to 7.5 per cent. of water, becomes 20.35 per cent. is 2.1 per cent. below the percentage of marc found.414 JACKSON: A NEW METHOD FOR THE DETERMINATXON OF SODIUM [Vd. 75 fresh and dried samples, and to the limited accuracy of the method it is not possible to attach much importance to this difference; it may point to coagulation rendering insoluble certain constituents of the beet during t.he drying process. REFERENCES 1. 2. 3. 4. 5. Claassen, H., 2. ver. deut. Zucker-Ind., 1916, 66, 359. Rapp, G., and Degener, P., Ibid., 1882, 32, 786. Heintz, A., 2. anal. Chem., 1874, 13, 262. Schiebler, C., Ibid., 1879, 18, 176, 256. Stanek, V., and Sandera, K., Z . Zuckerind. Cechoslov., 1929, 525; Int. Sugar J., 1929, 31, 501. DEPARTMENT OF TECHNICAL CHEMISTRY THE ROYAL TECHNICAL COLLEGE GLASGOW September, 1949

ISSN:0003-2654    

DOI:10.1039/AN9507500410

出版商:RSC    

年代:1950

数据来源: RSC

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414 JACKSON: A NEW METHOD FOR THE DETERMINATXON OF SODIUM [VOl. 75 A New Method for the Determination of Sodium in Calcined Alumina and Aluminium Hydrates BY H. JACKSON SYNOPSIS-A method is described for the determination of sodium in alumina and aluminium hydrates. It consists in heating the sample with hydrochloric acid in a sealed tube at 200" C. Only partial dissolution of alumina is necessary for complete solution of the sodium; complete dissolution of alumina can, however, be effected under suitable conditions. Aluminium hydrates are dissolved completely. Sodium is determined gravimetrically, after removal of excess acid, by precipitation as the triple acetate. Separation of aluminium salts is un- necessary. The method is simple and the blank low. THE standard method for the determination of small amounts of sodium in calcined alumina (a-alumina) by the J.Lawrence Smith method is tedious and needs a skilled analyst to carry it out. The method involves sintering with calcium carbonate and ammonium chloride, extraction of calcium and sodium chlorides with water, and separation of the calcium as oxalate before the final determination of sodium by one of the usual procedures. The main fault of the method apart from the time required, lies in the high blank obtained, which is a disadvantage when the sample has a low sodium content. Wichers, Schlecht and Gordon1 used a technique involving treatment with hydrochloric acid at high temperatures in sealed tubes for the dissolution of a number of refractory oxides, ceramic materials and minerals.The method described below, p. 417, is based on this technique. Complete solution of the sample is unnecessary because the sodium appears to be present entirely on the surface of the crystal. Complete solution of a-alumina in hydrochloric acid can be readily attained, however, under suitable conditions. In preliminary work it was observed that when a-alumina was shaken with water, an alkaline solution with a pH of about 10 was obtained. Extraction of sodium from alumina with water in a Soxhlet apparatus was incomplete, however, even after 24 hours. Extraction with diluted hydrochloric acid, 1 + 1, on the other hand, gave a solution containing all the sodium together with most of the iron and a small amount of aluminium after boiling for 24 hours, The treatment was carried out in an all-silica apparatus consisting of a flask fitted with a stirrer and reflux condenser.Sodium was determined in the filtrate, after removal of iron and aluminium with ammonia, by precipitating with zinc uranyl acetate reagent. As this method was rather lengthy, and required a considerable expenditure on apparatus t o carry it out as a batch process, experiments were carried out on the extraction at tempera- tures above 100" C. in sealed glass tubes. It was found that alumina calcined at 1200" C. (or-alumina) could be completely dissolved in a 25 per cent. excess of hydrochloric acid by heating at 250" C. for 5 hours. Hence aAugust, 19501 IN CALCINED ALUMINA AND ALUMINIUM HYDRATES 41 5 simple method is available whereby the minor impurities present in alumina, e.g., sodium, calcium, iron, sulphur and phosphorus may readily be determined without introducing a high blank from reagents.Aluminium mono- and tri-hydrates, which are only slowly dissolved by hydrochloric acid at normal boiling-point, are also readily dissolved under pressure by heating with excess of hydrochloric acid for 1 to 2 hours at 200" C. The time required to carry out the determination was shortened by precipitating the sodium directly with zinc uranyl acetate, without separation of aluminium, which did not interfere. Monax tubing of 4.5 mm. bore and 1.5 to 2-0 mm. wall thickness was used throughout the work since this glass was easy to seal by means of an air-gas flame and no contamination of the solution by soda from this glass was observed. Any other borosilicate glass with low soda contefit, such as W1* or Pyrex, is suitable, but Pyrex requires a gas-oxygen flame for sealing off.Taking the tensile strength of glass as approximately 10,000 lb. per sq. in. and the bursting pressure (A) in lb. per sq. in. as A = (2W/D) 10,000, where W is the wall thickness and D the internal diameter, the calculated bursting pressure of tubing of the above dimensions is over 6000 lb. per sq. in. If this is halved for safety the bursting pressure will still be over 3000 lb. per sq. in. The pressure developed by hydrochloric acid (32 weight per cent., sp.gr. 1.16) calculated from the formula given (Zoc. cit.) is 743 lb. per sq. in. and 1635 lb. per sq. in. at 200" and 250" C. respectively so that the safety margin is high, especially when working at the lower temperature.No accidents occurred from bursting tubes throughout this work, although well over 100 determinations have been carried out. As a precaution, however, each tube may be wrapped in asbestos paper and placed in a steel shell made from a piece of %-inch gas piping of suitable length with a loose-fitting screwed cap at each end. EXPERIMENTAL SECTION I-THE DETERMINATION OF SODIUM IN CALCINED ALUMINA- The method described on p. 417 was applied to several samples of alumina from normal to finely ground samples. The sodium was also determined by the J. Lawrence Smith method. Treatment of reaction ides-Surface impurities were removed from the tubes by heating in a chromic - sulphuric acid mixture for half an hour, followed by boiling in nitric acid for half an hour after an intermediate rinse in distilled water.The tubes were then washed in distilled water and dried. Tubes 14 inches long (35.5 cm.) with a bore of 4.5 mm. gave a total volume of 5.65 ml. Thus a sample weight of 0.4 g. alumina with a 10 per cent. excess of hydrochloric acid, sp.gr. 1.16, over the stoichiometric amount, could be taken without having the tube more than two-thirds full. Dissolution of alumina at 250" C.-Preliminary tests were carried out at 250" C. in a thermostatically controlled air-oven on 0.4 g. calcined alumina and 2.6 ml. hydrochloric acid (10 per cent. excess) for various times. Each tube was sealed off, after thickening the wall, with a well-rounded end and, after cooling, the contents of the tube were mixed by a vigorous shaking.The tube was then placed horizontally in the oven with the alumina distributed along its length. Even after 6 hours, complete dissolution of the alumina was not reached. Since the reaction is of the first order, increased acid should increase the rate. This was found to be so and by using a 25 per cent. excess of acid over the stoichiometric amount (total 3.0 ml.), 0-4 g. alumina was completely dissolved in 5 hours at 250" C. After treatment, the tubes were removed from the oven and placed vertically to cool after shaking the contents out of the top of the tube. As there is no pressure increase due to the reaction, the tubes were opened by making a scratch about half an inch from the end, which was then broken off.The contents of the tube were washed out by inversion over one limb of a U-tube of 2 to 3 mm. diameter drawn down to a jet and reaching to the end of the reaction tube. Any undissolved alumina was removed directly by filtration under reduced pressure through a pulp pad contained in a sintered glass funnel of porosity 1 (see Fig. 1). Aluminium was removed from the solution as chloride2 and sodium determined gravi- metrically in the filtrate by precipitation with zinc uranyl acetate in the usual manner. High blanks were obtained, amounting to as much as 16 rng. (weight of precipitate), compared to a weight of 120 mg. for the sample. The other wider limb of the U-tube was connected to a wash-bottle. * A tungsten-sealing glass manufactured by the General Electric Company, Wembley.416 JACKSON: A NEW METHOD FOR THE DETERMINATION OF SODIUM [VOl.75 Extraction of sodium at ZOO" C.-In an attempt to reduce the value of the blank, further experiments were carried out at a lower temperature (ZOO" C.) and sodium determinations made on the resulting solutions, although complete solution of alumina was not attained. The results are given in Table I and show that complete solution of the alumina is unnecessary for a perfect extraction of the sodium. Moreover the blank value is reduced to a much more reasonable level (2 to 4mg. weight of precipitate). This indicates that the attack on the glass at 200" C. and with a shorter time of extraction is much less than the attack at 250°C. Examination of the tubes after treatment failed to show any surface attack; several of the tubes were used for a number of determinations.Fig. 1. U-tube for washing reaction tubes As shown in Section 11, p. 419, aluminium was found to have no effect on the precipitation of the triple sodium salt. Consequently, no attempt was made to separate it in these tests. The time saved was considerable. Care had to be taken, however, during the final stages of evaporation. Loss by spirting was prevented by finishing the evaporation on a low temperature hot-plate, working at 120" to 130" C., controlled by a Sunvic Energy Regulator; with this low temperature there was no danger of hydrolysis of the aluminium chloride to hydroxide, and excess acid was readily removed. TABLE I EXTRACTION OF SODIUM (CALCULATED TO Na,O) FROM ALUMINA WITH HYDROCHLORIC ACID (25 PER CENT.EXCESS) (SAMPLE ~.406) 0.4 g. alumina, 3-0 ml. hydrochloric acid Time of Alumina Temperature treatment dissolved, Na,O found, Yo % 200" c. Y9 99 250" C. 1 hour 12.33 2 n 19-95 4 99 31.45 5 9) 100 0.506 0-507 0-602 0-504 As a result of these experiments the sample weight was increased to 1 g . using the same amount of hydrochloric acid, thereby increasing the precision of the analysis, especially where the sodium content of the sample was low. Experiments using the larger sample weight gave results in close agreement with those obtained for a 0.4g. sample.August, 19501 I N CALCINED ALUMINA AND ALUMINIUM HYDRATES 417 Variations in time and temperature of treatment-Further experiments were carried out t o determine the limits of the treatment, in which the time was reduced to 30 minutes and the temperature to 160" C.The results are summarised in Table 11. TABLE I1 EFFECT OF VARIATION IN TIME AND TEMPERATURE ON THE EXTRACTION 1 g. alumina, 3.0 ml. hydrochloric acid OF SODIUM FROM ALUMINA Na,O (mean of four results at r 1 200" C. for Sample No. Time 160"C., 17OoC., 180"C., 190°C., 200°C., 1 hour), Na,O found at a temperature of A % % % % % % o;* } 0.313 0y-o } 0.210 R103 1 hour 0.267 0.292 0.30'7 0.308 30 min. 0.306 R104 1 hour 0.181 0.190 0.202 0.210 30 min. 0-206 R391 1 hour 0.263 - R392 1 3) 0.326 R406 1 5) 0.242 - - 0.283 - 0.348 - 0-506 - - - - - - Table I1 shows that below 190" C. the sodium is incompletely extracted in 1 hour and that a time of 30 minutes is just sufficient at 200" C.It is however recommended that a temperature of 200" C. for 1 hour should be used to ensure complete extraction of all samples, At temperatures above 200" C., the blank increased with an increase of temperature. Since the pressure increasesrapidlyabove 200" C., it is not advisable to go much above this temperature in the interests of safety. Blank determinations varied from 0.7 to 4.9mg. with an average of just over 2 mg. (weights of precipitates), and are very small compared with the weight of precipitate from a sample. METHOD I. THE DETERMINATION OF SODIUM IN ALUMINA REAGENTS- Diluted acetic acid-(1 + 1). Et her-dry . Hydrochloric acid-sp.gr. 1.16 (32 per cent. by weight). Zinc uranyl acetate yeage&-- Solution A-77 g.of uranyl acetate, U0,(C2H302),.2H20, 13.3 ml. of glacial acetic acid and 410ml. of water. Solution B-231 g. of zinc acetate, Zn(C2H,0,),.3H,0, 6.6 ml. of glacial acetic acid and 262ml. of water. Heat solutions A and B to 70" C., mix, stir until clear an' allow to stand for 24 hours. Filter immediately before use. Alcoholic wash solution-Alcohol (95 per cent ., saturated with sodium zinc uranyl acetate, NaZn(U0,)3(C,H,0,)9.6H,0). Prepare by precipitating 0-1 g. of sodium chloride, dissolved in 5 ml. of water, with 50 ml. of zinc uranyl acetate reagent as described below under procedure. Filter the precipitate on a small sintered glass crucible (porosity 3) and wash thoroughly with 95 per cent. ethyl alcohol. Transfer the precipitate to a bottle containing 1 litre of ethyl alcohol, 95 per cent., shake, and allow to stand for 24 hours.Filter the solution immediately before use. Exposure to low temperatures during cold weather should be avoided. PROCEDURE- Introduce 1 g. of alumina into a dry glass tube 8 mm. external x 4 to 5 mm. internal diameter and 14 inches long of Monax, W1 or similar borosilicate, low soda, glass. (If a greater volum-e is required, the tube should be longer rather than wider. The contents should not occupy more than two-thirds of the volume.) Add 3.0 ml. of hydrochloric acid and seal off the tube as close to the end as possible, making sure that the end is thickened and Store the zinc uranyl acetate reagent and the alcoholic wash solution at 20" C.418 JACKSON: A NEW METHOD FOR THE DETERMINATION OF SODIUM [Vol.75 well-rounded and that no pinhole remains. Shake the tube vigorously to mix the contents and place it horizontally in an air-oven maintained at a temperature of 200" C. t 5" for 1 hour, with the alumina distributed along the length of the tube. Then remove the tube, stand it vertically and allow to cool to room temperature. Cut off the tip and wash it and the contents of the tube on to a medium-tight pulp pad contained in a sintered glass funnel of porosity 1. Draw the filtrate, under suction, into a 150-ml. silica beaker, using a Witt's apparatus, and wash the pad well with water. Evaporate the filtrate to dryness, carrying out the final stage on a hot-plate at 120" to 130" C. Stir until the residue has dissolved, add a further 1 ml. of water if the aluminium chloride does not dissolve com- pletely, and place the beaker in a thermostat at 20" C.f 1". Precipitate the sodium with 10ml. of zinc uranyl acetate reagent and allow to stand for 30 minutes with occasional stirring. Filter off the precipitate through a sintered glass crucible, porosity 3, and wash with five 2-ml. portions of zinc uranyl acetate reagent followed by five 1-ml. portions of alcoholic wash solution. Finally, wash with 5 ml. of ether, dry at 100" C. for 30 minutes, cool and weigh. Wash the crucible, under suction, with hot water followed by alcohol and ether, and again dry and weigh. The difference between the two weights is sodium zinc uranyl zcetate. Carry out a blank determination on 3-0 ml. of hydrochloric acid. The factor for conversion to Na,O is 0-02015.A selection of results obtained by the procedure described above, together with figures obtained by the Lawrence Smith method, are shown in Table 111. The standard deviation estimated from sixteen results on five samples of alumina with sodium contents from 0.2 to 0.5 per cent. as Na,O was *0.006 per cent. TABLE I11 DETERMINATION OF SODIUM IN ALUMINA BY EXTRACTING WITH Add 1.0 ml. of water and 5 drops of acetic acid (1 + 1). Sample No. R103 R104 R391 R392 R406* HYDROCHLORIC ACID FOR 1 HOUR AT 200°C. Na,O, % L f 7 Lawrence Smith Sample weight, Found Mean method g. 0-4 0.300 7 0.313 0.4 0.5 1.0 0.317 0.4 0.206 1 0.319 0.227 - 0.265 0.348 0.4 0-219 0.5 0-206 1.0 0.209 1.0 0-274 1-0 0-349 - 0.4 0.505 - 0.460 * See also Table I. SECTION II-THE DETERMINATION OF SODIUM IN ALUMINIUM MONO- AKD TRI-HYDRATES Similar experiments to those in Section I were carried out on samples of aluminium mono- and tri-hydrates, using sample weights of 0.5 g.and 0.6 g. respectively with 3.0 ml. of hydrochloric acid (25 per cent. excess), and heating at a temperature of 200" C. Complete solution was attained after 1 to 18 hours heating for the tri-hydrate, and 1+ to 2 hours for the mono-hydrate. It was necessary, however, to take the tubes out of the oven after half an hour and shake vigorously to disperse the cake that formed along the glass, and which otherwise was difficult to dissolve. THE DETERMINATION OF SODIUM IK THE: PRESENCE OF ALUMINIUM CHLORIDE A series of tests was carried out on synthetic solutions containing different amounts of standard sodium solution, together with aluminium chloride solution, prepared from super purity aluminium, equivalent to that obtained from 0.6 g.of aluminium tri-hydrate. The solutions were evaporated to dryness, the final stage being carried out on a low temperature hot-plate working at 120" to 130" C. as before.August, 1950 J I N CALCINED ALUMINA AND ALUMINIUM HYDRATES 419 The normal treatment of the residue prior to precipitation is to dissolve it in 1 ml. of water and a few drops of acetic acid. It was found that this was insufficient in the presence of so much aluminium chloride as a viscous solution was obtained and the salt was frequently co-precipitated with the sodium triple salt, which made the solution difficult to filter.The amount of water was increased to (a) 2 ml. and (b) 3 ml., and the sodium precipitated with 20ml. of reagent. This was wasteful of reagent, and so synthetic solutions with 2ml. of water and only 10 ml. of reagent were tested. The results are given in Table IV, and show that satisfactory recoveries are obtained by this latter method. Filtration and washing were carried out in the normal way and the determinations completed gravimetrically. TABLE IV DETERMINATION OF SODIUM IN SYNTHETIC SOLUTIONS CONTAINING ALUMINUM CHLORIDE Aluminium chloride added equivalent to 0.6 g. of Al(OH), Volume of solution before precipitation, ml . 2 2 2 2 3 3 Volume of reagent added, ml. 20 20 10 10 20 20 Na,O on 0.6 g. Found, Taken, 0-134 0.133 0.270 0.267 0.134 0.133 0-269 0.267 0.134 0-133 0-268 0.267 A I \ % % 11.THE DETERMINATION OF SODIUM IN ALUMIKIUM HYDRATES REAGENTS- PROCEDURE- Introduce 0.6 g. of tri-hydrate or 0-5 g. of mono-hydrate into a reaction tube, add 3.0 ml. of hydrochloric acid and seal off the end of the tube. Mix the contents of the tube by vigorous shaking and place horizontally in an air-oven at 200" C. f 5" with the hydrate spread along the length of the tube. Allow the reaction to proceed for 1 to 2 hours until the solid has dissolved completely. This is facilitated by removing the tube from the oven after Q to 2 hour, and shaking vigorously to re-distribute the solid which tends to cake on the walls of the tube. After solution of the sample, remove the tube from the oven and stand it vertically until cold. Cut off the end of the tube and wash it and the contents of the tube into a 150-ml. silica beaker.Evaporate the solution to dryness, carry out the last stages on a hot-plate at 120" to 130" C. to effect removal of excess hydrochloric acid without decomposition of the aluminium chloride or loss by spirting. Dissolve the residue in 2.0 ml. of water and 5 drops of acetic acid (1 + 1). Precipitate the sodium with 10 ml. of zinc uranyl acetate reagent and complete the determination as in I., p. 418. Carry out a blank determination on 3-Oml. of hydrochloric acid. A series of eighteen determinations was carried out on three samples of tri-hydrate, each containing approximately 0.3 per cent. of Na,O, by the recommended procedure. The standard deviation was 50.006 per cent. The results are shown in Table V. As for Method I. TABLE V DETERMINATIONS OF SODIUM IN ALUMINIUM TRI-HYDRATE Al(OH),, 0.6 g. Hydrochloric acid, 3.0 ml. 1 to 1Q hours at 200" C. Sample Na,O found, yo Mean Na,O, A No. f v Y O S4890 0.324 0.323 0.307 0.313 0.313 0.317 0-316 S6002 0-290 0.296 0.275 0-280 0.289 0.293 0.287 S6003 0.286 0.290 0.281 0.279 0.286 0.288 0.286420 SHORT: THE DETERMLNATION OF SMALL [Vol. 75 TREATMENT OF RESIDUES All solutions containing uranium salts should be collected and the uranium recovered The author wishes to thank the British Aluminium Company for permission to publish by one of the published method^.^^^!^ this work. 1. Wichers, E., Schlecht, W. G., and Gordon, G. L., J . Res. Nat. Bur. Stand., 1944, 33, 451470. 2. Hillebrand and Lundell, “Applied Inorganic Analysis,” Wiley & Sons, New York, 1929, p. 392. 3. Rodden, C. J., And. Chew., 1949, 21, 331. 4. Rune Hedin, “Colorimetric Methods for Rapid Analysis of Silicate Materials,’’ p. 84 (Swedish 5. Clark, F., Analyst, 1949, 74, 411. REFERENCES Cement and Concrete Res. Inst. at the Royal Inst. of Tech., Stockholm, 1947). RESEARCH LABORATORIES CHALFONT PARK BRITISH ALUMINIUM Co., LTD. GERRARDS CROSS, BUCKS. Jamavy, 1960

ISSN:0003-2654    

DOI:10.1039/AN9507500414

出版商:RSC    

年代:1950

数据来源: RSC