ANALYTICAL CHEMISTRY
538 Table 111. Determination of 2,5-Pyridinedicarboxylic Acid in Synthetic Mixtures Composition of Mixture Added, M g . HNOa 3-PCAa 5-E-2MPb 2,5-PDA 2.50 2.50 2.50 2.50 2.50 2.50 2.50 5.00 5.00 5.00 7.50 2.50 5.00 5.00 7.50 5 00
2,5-Pyridinedicarboxvlic Acid Found, M g . Replicates Mean 2.52,2.48 2 50 5.00,5.08 5.04 2.50,2.50 2 50 5.09,s 09 5.09
3-PC.4 = 3-pyridinecarboxylic acid. 5 5-E-2hIP = 5-ethyl-2-methylpyridine. C 2.5-PDA = 2,5-pyridinedicarboxylic acid
a
hours at 25' C., any unnecessary delay in measuring the color Ehould be avoided. Irm(I1) is always present in excess in the solutions and will be oxidized gradually to iron(II1) if allowed to remain standing for a long period of time exposed to air. Reproducibility. A sample of crude 2,5-pyridinedicarboxylic acid was assayed eight times by the method described. Good
reproducibility was obtained with a maximum deviation of 0.16% from the mean (Table 11). Accuracy. The results obtained for the analysis of known mixtures of nitric acid, 3-pyridinecarboxylic acid, 5-ethyl-2niethylpyridine, and 2,b-pyridinedicarboxylic acid are shown in Table 111. These results indicate that the maximum deviation obtained was zk1.87,. CONCLUSION
A rapid colorimetric method for the determination of 2,5pyridinedicarboxylic acid based on the formation of complex between iron( 11) and 2,5-p~.ridinedicarboxylic acid in slightly acid medium has been developed. Less than 10 minutes are required for a single determination; the accuracy is &1.8%. LITERATURE CITED
(1) Skraup, Z. H., Monatsh., 7,210 (1886) R E C E I Y Efor O review August 11, 1953. Accepted November 18. 1953.
Semimicro System of Qualitative and Quantitative Elementary Analysis ERNEST H. SWIFT and CARL NIEMANN Ca/ifornia h s t i t u t e o f Technology, Pasadena 4, Calif.
A semimicro system of qualitative and quantitative elementary analysis including some 32 elements is described and the chemistry involved is shown by tabular outlines. A 20- to 40-mg. sample is fused with sodium peroxide in a Parr bomb. Treatment of the fusion mass with water results in a residue consisting of those basic elements forming insoluble oxides and carbonates; this residue is separated and analyzed. A portion of the resulting fusion solution is analyzed for the predominantly amphoteric elements and another portion is analyzed for the acidic elements. Numerous qnalitative tests are made on smaller portions of the fusion solution in order to expedite the systematic analysis. Any element of the system which constitutes 1% of the sample should be detected and, with certain exceptions, the accuracy Table I. of the estimation should be within h 0 . 3 mg.
D
Representative analyses are shown.
URING 1942 there was established a t the
California Institute of Technology under the direction of the authors a project, sponsored by the National Defense Research Committee and carried out in cooperation with the Chemical Warfare Service, now designated as the Chemical Corps, which had for its objective the development of systematic procedures and instructions that could be applied to the rapid identification of new and unknown chemical warfare agents. Consideration of the over-all problem indicated the need for systematic procedures which would sequentially provide for (1) the procurement of suitable samples and, in the case of organic materials. their seoaration into their pure components; (2) the qualitative and I
quantitative determination of the elementary composition of each component or of the original sample; (3) the recognition of known and most unknown inorganic compounds on the basis of the above knowledge; (4) the determination of the functional groups present in components which are pure organic compounds; ( 5 ) the identification of known organic compounds on the basis of the above information and that in respect to their physical properties and those of their derivatives; and (6) the final characterization of previously undescribed organic compounds from a consideration of their elementary composition, their physical properties, their behavior in the functional group tests, and their degradation to and synthesis from known compounds b>-unambiguous reaction$.
Behavior of Elements after Sodium Peroxide Fusion" and Treatment with Water
P. I. Fuse the sample with NazOz and sucrose in a P a r r micro or semimicrobomb; dissolve t h e melt. boil until peroxide is decomposed, a d d KzHa.Hz0. boil (108- and 101reduced t o I-$; add HzOz; boil until peroxide is'decomposed; (Lxcess SzHa is oxidized to Nz); centrifuge; dilute the centrifugate t o a n exact volume Fusion Residue (SonFusion Solution amphoteric Basic Elements) Amphoteric basic elementsb Acidic elementsc FetOa, TiOr, M n O (iron SeOd--, HaTeO8-- (selenium I-, Br-, C1- (halogen group) group) Ki(OH)r, C d ( 0 H ) z (cadmium Cu(OH)r--, Pb(OH'r--. CrO4- , HaTeOa--, group) [Cd(OH)z], Zn(OH)a--. AsOa---, Pod--- (arAsOa---, Pb(0H)e-. Snsenic group) (OH)a-- ihvdroeen sulfide group)
'
SeOa--. Sod-(sulfur Mg(OH)z, BaC03, SrCOa, CaCOa (alkaline earth group) group) [SnOl, N a ~ H ~ T e O s NaSb, HzBOaF-, Nos-, s i o s (OHIO,CuO, PbO;]d a Nitrogen and carbon a n d hydrogen estimated on separate portions of original sample. b Bmphoteric basic elements determined on a single 10-ml. portion of fusion solution. Sonamphoteric basic elements determined on fusion residue. C Acidic elements determined on several portions of fusion solution. A 10-ml. portion is analyzed for I Br C1 C r T e 4 s P Se, S,and B. A 2-ml. portion is analyzed for F and a 1-ml. porkon'is &alfzed io; Si. Furthermore, specific qualitative tests for I , Br, Te. Se, As, P. and N are made on separate uortions of the solution. d Elements which m a y be present where shown only when occurring in large amounts or under unusual conditions are enclosed in brackets.
V O L U M E 2 6 , N O . 3, M A R C H 1 9 5 4 Table 11.
539
Separation of Elements of Fusion Residue into Groups"
P. X I .
Treat the fusion residue (see Table I ) with 9 b HCI; centrifuge; dilute the centrifugate to a n exact volume. Soln.: HeTeOe, FeCld-, Ticla--, M n + + , CdCIa--, S i + + , l ' l g + + , Ba ++, Residue: [SnOz], [BaCln] (treat S r + + ,C a + + . [SbCle-, CuClr--.PbCla--] P. X I I . Take an aliquot porb y Kote 4,P. XI) tion of the HC1 solution; add 1;zHa.HzO; make 3 F i n HC1; heat Ppt.: Te (to P. XIX) Soln.: FeCla- Ticla-- h l n + - CdClc-- X i + + , h I g - T , B i t + + ,S r + - , C a + + , SbCla-. C THE
significance of catalytic action in submicroanalysis has been only recently recognized, though the underlying principle was known long ago. A comprehensive r e v i m b y West (11) refers to 145 publications. Continuing earlier investigations on the kinetics of the reaction of potassium ferrocyanide and nitrosobenzene in aqueous solution (1-3) the catalytic influence of mercuric ions was particularly studied. The reaction proceeds according to Equations 1, 2, and “
CS-
+ €120
HCS
+ OH-
(3)
The concentration of the violet complex a t a fived time depends on the concentration of mercuric ions in the solution; it is therefore possible to determine the concentration of mercuric ions by meawring the extinction of the violet complex Using a calibration curve very small amount;: of mercuric ions could be determined in distilled nater, doKn to concentrations of the order of 10-7 mole per liter. The catalytic action of mercuric ions can be influenced by various foreign substances Disturbanceq, arising from a negative salt effect, occur a t higher ionic strengths. The negative salt effect agrees with Bronsted’s theory, since the charges of ferrocyanide and mercuric ions have opposite signs. In performing determinations of mercuric vapor- in the atniosphere all theqe difficulties could be overcome by using a method for trapping mercury vapor first developed by lloldawskij (8)and checked by Stock and Cucuel (10). According to the latter authors, this method coniists in mixing the atmosphere containing mercury with bromine vapor and absorbing the mixture in bromine water. I n this lvay mercury i- converted into mercuric bromide and its solution, after evaporation of excess bromine, contains practically no foreign ions, which is not the case with the usual absorbent.. Stock an 1 Cucuel found Moldawskij’s method convenient. Stock and Cucuel further d e w i b e another method of trapping mercury vapor by condensation in traps immersed in freezing mixtures such as liquid air or liquid nitrogen. This method is considered as one of the best, but it is not so widely practicable. The condensate in the traps is subsequently dissolved in chlorine water and, after removal of excess chlorine on a water bath, here again are obtained aqueous solutions of mercuric ion9 free of foreign electrolytes. The catalytic action of mercuric ions in such solutions can be measured without disturbance. Thus the determination of mercury in the atmosphere is reduced to the determination of mercuric ions in bromine or chlorine
