142
A N A L Y T I C A L CHEMISTRY
Since fluoride ion does not interfere a t pH 4.1 (I), it was necessary to adjust to this acidity by buffering the hydroxylamine
hydrochloride solution. Of the elements commonly present in brass, zinc, which may be present up to 40%, causes the most serious interference by reducing the intensity of the iron color (1). This can be diminished almost entirely by adding an excess of o-phenanthroline (Table 11). Aluminum and manganese may be present in 250 times the amount of iron without interfering ( I ) . Nickel produces a change in hue but its interference is negligible below 1%. Most brasses and bronzes contain less than this amount. Tin does not interfere (4). Known amounts of iron were added to N.B.S. samples 124A and 6311 containing 4.8% and 9.7% of tin, respectively. The amounts of iron recovered were identical with the amoutlts added.
The proposed procedure is especially useful when applied to silicon bronze. If the sample is dissolved in the presence of hydrofluoric acid, a clear solution is obtained and an accurate value for copper, lead, and iron can be obtained. LITERATURE CITED
(1) Fortune, W. B., and Mellon, M. G., IND. ENQ.CHEM.,ANAL. ED., 10, 60 (1938). (2) McCay, L. W., J. Am. Chem. Soc., 31, 378-81 (1909). (3) Ravner, H., IND.ENQ.CHEM.,ANAL. ED., 17,41 (1945). (4) Yoe, J. H.,and Hall, R. T., J. Am. Chem. Soc., 59,872 (1937). (5) Y o e , J. H., and Jones, A. L., IND.ENG.CHEM.,ANAL. ED., 16,
115 (1944). THEopinions contained in this article are those of the author and are not t o be construed as official or reflecting the views of the Navy Department.
Adaptation of the Beckman Quartz Spectrophotometer for Measurement of Vitamin A by the Carr-Price Reaction G. IVOR JONES, F. BRUCE SANFORD, LYNNE G. McKEE, AND DAVID T. MIYAUCHI Fishery Technological Laboratory, U . S . Fish and Wildlife Service, Seattle, Wash.
HE quantitative determination of vitamin A by measurement the blue color developed when the vitamin is treated with antimony trichloride (Carr-Price reaction, 2 ) is difficult because of the corrosive nature of the reagent and the rapidity with which the color fades. Because of these undesirable features, ultraviolet absorption measurements for the determination of vitamin A have usually been favored. However, a recent paper by Oser et al. (3) presents data to show that the colorimetric assay for vitamin A gives results in essential agreement with the biological assay, even with materials for which the ultraviolet absorption method is unsatisfactory. While most vitamin A testing laboratories possess the Beckman quartz spectrophotometer for ultraviolet absorption measurements, this instrument has apparently not been widely used for the colorimetric assay. One reason for this might be that the absorption cells customarily used are small and their arrangement does not facilitate the rapid manipulations required in the antimony trichloride technique. Since many vitamin A laboratories ~
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do not have a separate instrument for measuring color, an adaptation of the Beckman spectrophotometer for this purpose would appear to be of value. This nrticle presents constructional details of a cuvet holder, by means of which the Beckman spectrophotometer more readily can be employed in vitamin A assays using the Carr-Price reaction. The cuvet holder was designed to accommodate square glass cuvets 0.5 inch in inside dimensions (more exactly 13 X 13 mm.) and 4.125 inches in length (procured from the Wilkens-Anderson Co., Chicago, Ill.). The outside dimensions of the cuvets were 20/32 X 21/32 inch. The cuvet chamber (Figure 1, E ) was constructed slightly larger than this to allow for small variations in the external dimensions of the cuvets. The entire adapter was constructed of semihard sheet brass. The sides of the cuvet chamber were cut from sheet brass 8/04 inch thick and then soldered together on the corners to form a tube 21/32 inch square inside and 4.625 inches in length. The cover plate, C, cuvet chamber cover, A , and casing, B , were made from 0.125-inch sheet brass and designed to fit cell compartment aswere 412/32 X 419/31 sembly No. 2510 ( I ) . The cover gibs, 19,
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V O L U M E 19, NO. 2, F E B R U A R Y 1 9 4 7 inches outside. This part should be made to fit exactly in Beckman cell compartment housing 2510 in order to position properly the cuvet chamber and to make the compartment light-tight. The over-all measurements of the cover plate, C, were 49/1~X 416/,8 inches. The lieht ooenines. F. must be accuratelv centered and a t the proper d k a n c e fro& the cover plate to allow the light beam from the monochromator to pass unobstructedly through the solution to the phototube. The light openings were X 13/16 inch and the distance from the cover plate to the top of the opening was 1.375 inches. The openings were made larger than the light beam from the monochromator to eliminate any possible obstruction to the beam. The outside edges of the openings were beveled at approximately 45 degrees to reduce reflection of stray light from the edges of the opening into the cuvet chamber. The cuvet chamber, E, passes through a square hole in the cover plate, C, and the portion above the cover plate was enclosed by a small casing, B , made of 0.125-inch sheet brass fitted with a hinged cover, A , made of the same material. In the bottom of the cuvet chamber was placed a hard rubber plug, G , 0.375 inch thick t o act as a cuvet arrest. The plug has a 0.125-inch hole, H , in the center to serve as a drain in case of accidental spillage. In order to minimize reflection of stray light by the adapter it wa8 blackened by immersion, first in a dilute solution of copper nitrate and second in a dilute solution of potassium sulfide. The black precipitate formed by this treatment was then baked on the adapter surfaces by moderate heating with a small Bunsen flame. I n making a vitamin B determination using the cuvet holder, the fogowing technique was employed: Five milliliters of a saturated solution of antimony trichloride were measured into a cuvet. With the cuvet in place, the spectrophotometer was adjusted for dark current and zero optical den.sity, using a slit width of 0.04 mm. and a wave length of 620
143 millimicrons. To the reagent in the cuvet 1 ml. of a chloroform solution of vitamin A was added from a serological pipet. The solution in the pipet was not released until the tip was positioned near the bottom of the cuvet. Any liquid remaining in the pipet was then gently blown out. This operation served also to mix the two solutions rapidly. The pipet was quickly withdrawn and the cover closed. A reading of optical density was taken immediately. Optical density could be determined with moderate rapidity; the average time required for a single reading, estimated from 21 measurements, was 7.2 seconds. The readings were reproducible. When different cuvets and pipets were used for each measurement, nineteen determinations on a vitamin A solution having an optical density of 0.551 resulted in a coefficient of variation of 1.347,. Using the same cuvet and pipet for making the measurement, the precision was improved. Ten readings on the same vitamin A solution used in the previous test had a coefficient of variation of only 0.317‘. When optical density was plotted against relative vitamin A concentration a straight line was obtained which passed through the origin. This indicates that the photometric principles of the spectrophotometer were not altered by use of the cuvet adapter. LITERATURE CITED
(1) Beckman, Accessory Bull. 94-B,Natl. Technical Laboratories, South Pasadena, Calif. (Jan. I , 1946). (2) Carr, F. H., and Price, E. A., Biochem. J . , 31,497-501 (1926). (3) Oser, B . L., Melnick, D., Pader, M., Roth, R., and Oser, &I., IN^. ENG.CHEM., A N L LED., . 17, 559-62 (1945).
BOOK REVIEWS A Textbook of Qualitative Analysis. William B. M e l d r u m and Albert F. Daggett. xi + 431 pages. American Book Co., 88 Lexington Ave., NewYork 16, N. Y., 1946. Price, $3.50. Although similar in many respects t o t h e authors’ “Semimicro Qualitative Analysis” published in collaboration with Earl W. Flosdorf in 1939, this book is essentially a completely new treatment of the subject. Based upon the semimicro approach, it is a clearly and carefully written volume which should find much favor among both teachers and students of qualitative analysis a t either freshman or sophomore level. T h e treatment is modern and handles present-day concepts logically and effectively. In its order of presentation, the book follows t h e conventional pattern. T h e first portion (264 pages) is a dicsussion of principles necessary t o the understanding of analytical practice. I n addition t o t h e usual chapters on solutions, equilibria, and t h e quantitative treatment of equilibria, material on atomic structure, types of ionic reactions, electrochemistry, and colloids is offered. T h e viewpoint throughout is t h a t of t h e physical chemist, and in some instances discussions are perhaps more comprehensive than the general subject warrants. Excellent exercises and problems are included. T h e latter portion of the book deals with laboratory work. After a discussion of laboratory techniques, Some 26 of the common cations are considered in the five conventional groups of t h e hydrogen sulfide procedure. Actual analysis in each group is preceded by a series of preliminary experiments designed t o acquaint the student with fundamental reactions and t h e bases for systematic analysis. T h e groups are dealt with in order from Group I (silver group) through Group V (magnesium-alkali group). T h a t comparatively few organic reagents are employed will recommend this section t o the teacher of inorganic chemistry. Analysis for the cations is followed by preliminary experiments and analytical procedures for 16 of the coninion anions. These anions a1.e detected systematically in four groups by conventional procedures A chapter summarizing the characteristic reactions of 170th anions and catioiis completes the book. T H E R I L hf E C~El.I.I:R
Microcalorimetry. W . Swietoslawski. x
+
199 pages. Reinhold Publishing Corp., 330 West 42nd S t . , New York, N. Y., 1946. Price, $4.75.
A4microcalorimeter is interpreted as a calorimeter which is sensitive t o very small amounts of heat a n d is usually not a small calorimeter. T h e author is well qualified t o write on microcalorimetry, having published numerous reports in this field while a t the Institute of Technology, Warsaw, Poland. It is only natural t h a t he emphasizes i n this book the work and methods of his colleagues and himself. Since the author has long been a proponent of t h e advantages of the method of comparative measurements, a chapter is included on this subject which shows how this method m a y be used to eliminate certain errors in calorimetry. Although this reviewer does not agree with the author t h a t the “only way to avoid both systematic and accidental errors is t o use the method of comparative measurement”, this method is certainly very useful. I n the chapter on calorimeter jackets, thermostats, and thermometers, some of the general principles are discussed., with special application t o microcalorimetry. Measurements with radioactive materials are rather extensively covered, since much of the earlier microcalorimetry was of this type. I n view of the new artificially radioactive materials, this subject might prove of renewed interest. Many different types of calorimeters used in microcalorimetry are discussed. Included are adiabatic, twin, labyrinth flow, and ice microcalorimeters. There are described many specific applications of these calorimeters to such measurements as heats of solution and dilution, heat of aging of alloys, heat of setting of cements, heat of absorption and adsorption, heat produced h y nerve tissue, and heat produced by gamma-rays and heta-particles. I n the chapter on the ice calorimeter, this reviever does not agree with the discussion of the cause of some of the past anomalies with the ice calorimeter. To those \Tho are starting measurements in microcalorimetry, this hook is recommended as the only one in its field. T o those who are in other fields of calorimetry, this book should prove of only moderate interest. D. C. GINSISGS
