Masking Agents for pCI Measurements SIR: A new technique in pC1 measurements] masking of cationic interferences] was successful for the measurement of chloride in the presence of iron and uranium. The determination of chloride in clinical samples by a pC1 measurement with a Ag/AgCl//S.C.E. electrode system was reported by Stern et uZ. (4). However, the presence of cations that form complex ions or weakly dissociated compounds with chloride ions causes an error in the pC1 measurement. The theoretical requirements of masking agents for analytical determinations were described recently by Cheng (3). EDTA should be a suitable masking agent for iron since the complex ion, iron(lI1)-chloride, is dissociated by the addition of EDTA (I) and the silver chloride on the electrode is not dissociated by the EDTA (I, 9). Table I shows the effectiveness of EDTA as a masking agent for iron(II1) in pC1 measurements. Except for the addition of masking agents the procedure of Stern (4) was follonecl. KOkinetic study was made because the reaction seemed to be almost instantaneous. Chloride in LO,was determined when U02 was dissolved in nitric acid and the pC1 measured in the presence of sodium citrate. Table I1 shows the effectiveness of citrate as a masking agent for uranium. The addition of the masking agents did not change the pC1 of the standard
Table 1.
EDTA as Masking Agent for Iron in pCI Measurements
KCl solutions of 0.02M Fe(III), 0.5M “Os C1- Measured in 0.12M C1- Measured, KO EDTA EDTA C1- Added, P.P.M. PC1 P.p.m. PC1 P.p.m. 1.70 X 104(0.5MC1-) 0.59 7.5 x 103 0.32 1 . 5 x 104 1.70 x 103 1.67 4.8 X lo2 1.25 1.5 x 103 1.70 X lo2 2.79 2.9 X IO1 2.22 1.5 x i o 3 1.70 X lo1 4.40 0.50 3.16 1 . 5 X 10’ 1.70 4.40 0.50 3.89 1.8 Table 11.
Citrate as Masking Agent for Uranium in pCI Measurements
C1- Added, F.P.M.
8.70 X lo2 8.70 X 10’ 8.70 0.870
KCl solutions of 0.5M U(VI), 0.5M “ 0 8 C1- Measured, S o Citrate C1- Measured in 1.OM Citrate pC1 P.p.m. PC1 P.p.m. 1.69 3.7 x 102 1.53 7.6 X 10’ 2.70 3.7 x 101 2.54 5.7 X io1 3.65 3.5 5.45 5.0 4 38 0.4 5.92 0.71
solutions of chloride; therefore, the use of standard solutions that contain cations in concentrations close to those expected in the unknowns should eliminate the bias indicated by the foregoing tables. LITERATURE CITED
(1) Bjerrum,
J., Schwarxenbach, G., SillBn, L. G., “Stability ConstantsPart I-Organic Ligands,’] p. 77, Chemical Society, London, 1957. (2) Ibid., “Part 11-Inorganic Ligands,” p. 97.
(3) Cheng, K. L., ANAL.CHEM.33, 783 (1961). (4) Stern, M., Schwachman, H., Licht, T. S., deBethune, A. J., Ibid., 30, 1506 (1958). MYRON 0. FULDA Savannah River Laboratory E. I. du Pont de Nemours & Co. Aiken, S. C. RECEIVED for review July 7, 1961. Accepted August 29, 1961. The information contained in this article was developed during the course of work under contract AT(07-2)-1 with the U. S. Atomic Energy Commission.
Color Reaction of Epoxy and Furanoid Carotenoids with Mercuric Chloride SIR: When ether solutions of certain epoxy and furanoid carotenoids are shaken with concentrated hydrochloric acid, the acid layer is colored blue. The epoxy carotenoids are isomerized to the furanoid oxide (2). This reaction, until now, has been the only distinguishing color reaction characteristic of these pigments. A color reaction of the epoxy and furanoid carotenoids with mercuric chloride is described here. The reaction takes place in the solid state. EXPERIMENTAL
Synthetic 8-carotene was obtained from Hoffmann-La Roche. Crystalline lutein, violaxanthin, and neoxanthin were prepared from spinach (6). 1792
0
ANALYTICAL CHEMISTRY
The crystalline pigments were mixed with dry powdered HgC12 in a 1 to 5 (weight) ratio. The mixture was sealed in a 7-mm. tube in air or in vacuo (10-5 mm.). The tubes were then heated in a steam bath for 1 minute. After heating, the tubes were broken and the pigments dissolved in acetone. The absorption spectra were recorded with a Beckman DK-2 spectrophotometer. RESULTS AND DISCUSSION
Violaxanthin, a diepoxide, and neoxanthin, a monoepoxide ( I ) , when heated in the solid state with mercuric chloride rapidly form intense blue and blue-green complexes with absorption maxima in the 600- to 700-mp region. Figure 1 illustrates the absorption spec-
tra of the complex of violaxanthin. The peak of the broad absorption is 635 mp. The absorption in the 400- to 450-mp area probably represents unreacted xanthophyll. Neoxanthin shows a similar absorption curve with the peak of the broad absorption a t 655 mp. While neoxanthin has its absorption a t a lower wave length than violaxanthin (4, the situation is reversed in the case of the mercury complex. The corresponding furanoid derivatives of these epoxy pigments also form HgClz complexes with absorption spectra similar to the mercury complexes of the parent epoxy xanthophyll. When. @-carotene and lutein (two pigmenits containing no epoxy groups) were reacted with mercuric chloride, no
