along with a basic nitrogen atom, it is amphoteric and extremely pH sensitive. The distribution ratio, therefore, of 8-quinolinol between chloroform and water reaches a maximum value in the pH range of 4 to 9 (5). More importantly, the optimum pH range for extraction of titanium with 8-hydroxyquinoline in the presence of excess hydrogen peroxide is 3.8 to 5.0 (6). The nature of the titanium-H202 complex is another variable to be considered. Four different structures are proposed for the following conditions of pH value: (a) less than 2, (b) from 3 to 6, (c) from 7 to 9, and (d) greater than 10 (7). Only structure (a) was reported as temperature insensitive. Mole ratio studies have likewise verified that the ligand-metal stoichiometry of the titanium (IV)-H202 complex is 1 : 1 (8). In our studies, the peroxy-titanium 8-hydroxyquinolate complex formed instantaneously at room temperature and the absorption maximum (450 mp) was unaffected by subjection to water bath temperatures of 60-70” C. The complex exhibited a fairly stable color; the absorbance readings remained constant for several hours, although a noticeable decrease occurred overnight. The optimum pH range for extraction was determined by plotting the absorbance value of the complex at 450 mp L‘S. pH. The absorbance value reached a maximum at pH 4 and remained constant up to pH 5. The effect of pH above 5 was not investigated because of the instability of hydrogen peroxide in weakly acidic and alkaline media. The calibration curve was linear, adhering to Beer’s law over the concentration range investigated (0-6 pg/ml). The molar absorptivity at 450 mp is 3.06 X lo3, which corresponds to a sensitivity of 0.055 pg of H202/cm2/0.005 absorbance unit. This sensitivity is 3.4 times greater than that obtained with the titanous sulfate method (0.185 pg of HzOZ/ cm2/0.005 absorbance unit) (2). The selectivity of the titanium reagent was tested with (5) G. H. Morrison and H. Freiser, “Solvent Extraction in Analytical Chemistry,” p 10, Wiley, New York, 1957. (6) Ibid., p. 164.
.,
(7) M. Motohichi. M. Shibeta, E. Kyuno, and S . Ito, Bull. C/zem. SOC.Japan, 29,904 (1956). (8) A. Babko and A. Volkova, Zh. Obdzch. Khim., 21, 1949 (1951).
peracetic acid, ozone, ethyl hydroperoxide, n-butyl hydroperoxide, acetyl peroxide, and peroxyacetyl nitrate. A negative response was notable in each case. It should be stated, however, that a positive interference is to be expected from any compound that can liberate hydrogen peroxide via acid hydrolysis (2). Accordingly, t-butyl hydroperoxide does give rise to the titanium-HzOz complex when it is heatsoaked with TiOS04reagent. The possible application of this method to analysis of gaseous samples was investigated. Volume parts-per-million concentrations of hydrogen peroxide vapor were prepared by injecting microliter quantities of liquid 30% HzOz into a metered stream of air while filling a bag, fabricated from fluorinated ethylene-propylene copolymer (FEP Teflon, Du Pont) to a predetermined volume. The HzOz concentration in a particular sample bag was determined by the 1 % potassium iodide colorimetric method. Further analysis of the bag contents consisted of sampling a measured quantity from the bag through a fritted bubbler containing the titanium sulfate reagent. A sampling rate of 0.5 liter per minute is desirable since nearly 100% absorption efficiency is achieved with only one bubbler. After treatment of the Ti-H2O2 complex in the prescribed manner, the resulting absorbance of the chloroform layer at 450 mp was found to be an accurate measure of the hydrogen peroxide concentration in the bag. For very dilute vapor mixtures, larger samples were withdrawn from the bag, or 10-cm absorption cells were used to obtain the necessary increase in absorbance. ISRAEL R. COHEN THOMAS C. PURCELL Laboratory of Engineering and Physical Sciences Division of Air Pollution Robert A. Taft Sanitary Engineering Center Public Health Service U. S. Department of Health, Education, and Welfare Cincinnati, Ohio 45226 RECEIVED for review June 2, 1966. Accepted October 20, 1966. In no case does the mention of commercial materials and instruments constitute endorsement by the Public Health Service.
Mechanism of Color Fading in the Direct Spectrophotometric Method for Calcium Using Glyoxal Bis(2-Hydroxyanil) SIR: In the presence of calcium in alcoholic solution and at high pH, glyoxal bis(2-hydroxyanil) forms a bright red color which has become the basis for direct methods for calcium. A great advantage is that few metal ions interfere at the high pH necessary for color development. A serious drawback is that the red color slowly fades. In the course of working with GBHA and numerous related reagents ( I ) observations were made which have led to a realization of the fading mechanism. Fading was originally thought to be due to reagent decomposition, At the high pH necessary for color development with GBHA, the reagent and its analogs slowly undergo base catalyzed hydrolysis to yield glyoxal and the appropriate amine. This was the reverse of the reagent synthesis. However, in all of our color development tests with calcium, an excess of the reagent was used, and the color should not have faded until the excess reagent had decomposed and the reagent bound to the metal began to decompose.
To demonstrate the presence of sufficient excess reagent in a solution that had faded, more calcium was added. The color was immediately restored. This showed that the fading was due to removal of calcium and not due to loss of reagent by decomposition. The calcium was reacting with some agent that was removing it from the color reaction. This interfering agent must arise as one of the compounds resulting from the hydrolysis of GBHA. The base catalyzed rearrangement of glyoxal to glycolic acid as shown below is well known.
0
0 0
////
H-C-C-H
+ OH- + HO-CH2-C-0-
//
At an initial pH of 12, glyoxal rearranges into glycolic acid 100% in one minute; at an initial pH of 11, 2 in six minutes (2). It has been shown that the reaction takes place by ~
(1) F. Lindstrom and C. Milligan, ANAL.CHEM., 36, 1334 (1964).
132
ANALYTICAL CHEMISTRY
(2) P. Shaffer and T. Friedemann, J . Biol. Chem., 61, 604 (1924).
means of a hydride shift and is an internal Canizzaro reaction (3). The literature also revealed that calcium glycolate was very soluble in water but quite insoluble in organic solvents (4). Glycolic acid has been used as a reagent for precipitating calcium from aqueous alcoholic solutions (5). In addition, the glycolate ion forrns a calcium complex of moderate strength (6). In brief, as the reagent decomposed into the amine and glyoxal in the basic alcoholic solution, the glyoxal rearranged into the anion of glycolic acid and precipitated the calcium or bound it into a complex.
To test this chemistry, 2 grams of GBHA and 2 grams of sodium hydroxide were dksolved in 125 ml of ethanol and refluxed under nitrogen for 90 min. The solution was yellow at the start but became colorless. The mixture was cooled in an ice bath and neutralized with concentrated hydrochloric acid to precipitate a crystalline product easily identified as oaminophenol by its melting point and infrared spectrum. The filtrate was evaporated to dryness on a steam bath. The white residue was dissolved in a small amount of water and methanol was added to precipitate the sodium chloride. Then 0.79 grams of calcium acetate in 10 mlof water was added to the filtrate. After evaporation to 40 ml, 100 ml of methanol was added and the mixture was allowed to cool in an ice bath to yield white cr:jstals. Recrystallization from methanol-water gave 250 rrig of product. The calcium content was determined by EDTA titration; 21.16%. A sample of calcium glycolate was prepared by the nitrite oxidation of glycine to glycolic acid and neutralization with calcium oxide as outli:ned by Viscontini (7). The needles were extracted overnight with reagent grade methanol and dried at 110” C. A determination of the calcium content by EDTA titration gave 21.11 %. Theory for Ca(C2H30& is21.08z. Infrared spectra of calcium glycolate and the calcium containing white residue from the reagent decomposition were recorded by suspension in a potassium bromide pellet using a Perkin-Elmer model 221 spectrophotometer with NaCl interchange. Tht: spectra were identical. X-ray diffraction refllxtions of calcium glycolate and the white residue were compared using a Norelco Automatic Recording X-ray Diff ractometer. The calcium glycolate needles were powdered, dried at 110” C and scanned from “two theta” 1.5” to 40‘ using copper radiation and a nickel The white residue was diluted with filter for X = 1.5418 i. cellulose acetate and ,treated in the same manner. The plane spacings or “d” values and relative intensities are given in Table I. Calcium glycolate forins several hydrates, each of which on drying may form different amounts of possible anhydrous crystal orientations, so intensity ratios were not expected to be the same. Some of 1:he weak peaks of the diluted residue (3) H. Fredenhagen and IC. Bonhoeffer, Z . Physik. Clzern., 181 A, 384 (1938). (4) J. Birkinshaw and H. :Raistrick, Phil. Trans. Roy. SOC.London, Ser. B., 220, 24 (1931). (5) I. Mellan, “Organic Reagents in Inorganic Analysis,” Blakiston Co., Philadelphia, Pa., 1941. (6) C. Davis, J. Chern. Soc., 1938, p. 280. (7) M. Viscontini, Helo. Cbirn. Acra, 29, 1491 (1916).
Table I. X-Ray Diffraction Reflections White residue Calcium glycolate d 7.68 6.08 5.85 5.01 4.85 4.62 4.11 3.88 3.83 3.61 3.23 3.19 3.01 2.92 2.59 2.49 2.46 2.42 2.39 2.34
IlliOO 30 37 100 7 9 6 11 33 17 40 8 71 7 16 6 7 8 5 6 11
d
7.69 6.07 5.84 5.01 4.87 4.62 4.11 3.88 3.83 3.60
Illloo 21 100 89 20 35 11 43 36 10 93
...
..
3,20 3.02 2.93 2.60
99 17 13 13
...
... ...
... 2.43
15
...
...
2.34
11
were lost in the background. The close agreement of the atomic plane spacings identified the white residue as calcium glycolate with certainty. To find a solvent which might keep calcium glycolate in solution, 1 ml of an aqueous solution containing 10 pg of calcium glycolate was equilibrated at room temperature in bottles rotated end-for-end at 278 rpm for 1 hour with 25 ml of each of the following solvents: methanol, ethanol, nbutanol, t-butanol, isoamyl alcohol, hexanol, allyl alcohol, ethylene glycol, glycerol, ethyl butyrate, isoamyl acetate, 4-methyl-2-pentanone, 2-methoxy-ethanol, anisole, n-butyl ether, 1,4-dioxane, tetrahydrofuran, 2-aminoethanol, N,Ndimethylformamide, N,N-dimethylacetamide, triethylamine, ethylenediamine, butylamine, nitroethane, acetonitrile, stetrachloroethane, and 1,2-dichloroethane. After equilibration, some liquid mixtures had formed homogeneous solutions. In these mixtures, a white precipitate settled. If two liquid phases separated, the organic phase was found to be free of calcium by the GBHA test. For a stable color with calcium and a reagent of the GBHA type, the reagent must be very resistant to basic hydrolysis or the hydrolysis should not result in the formation of glycolate anion. FREDERICK LINDSTROM CARLW. MILLIGAN
Department of Chemistry and Geology Clemson University Clemson, S. C. 29631 RECEIVED for review August 17, 1966. Accepted October 20, 1966. Work supported by the National Science Foundation, Research Grant No. G19699. Presented in part at the Anachem Award Symposium for Prof. Harvey Diehl, 14th Anachem Conference, Detroit, Mich., October 1966.
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