not contain appreciable amounts of monotungstate. However, the partial paratungstate A sorption with its concomitant p H increase during the chelate formation ( 1 ) again causes formation of monotungstate. The elution a t Kd = 1.05 with clearly less tailing which is observed from the fourth day on, points to the presence of paratungstate A mainly. This again is due to the rising elution of W ~ aggreZ gates, the sorption of which also causes an increase in p H and thus a stepwise decondensation. Decondensation processes of tungsten(V1) are slow so t h a t paratungstate A rather than monotungstate is formed during elution. The dependence of the sorption caused by chelate formation on the degree of condensation can thus be summarized as follows: +-Metatungstate ( W Z ~naturally ) exhibits the least sorption tendency. Because of molecular sieving (Kd = 0.14),it contacts only a small part of the total gel and the contact time is short. Chelate formation tendency of the WI2 condensation products increases with increasing hydroxyl group content of the isopolytungstate molecule. This explains the aforementioned absence of the W12 peak for the large column in the case of one- or two-day-old solutions as well as the trend of the total yield (Figure 3). Paratungstate B and species X are considerably more adsorbed (and also more easily decondensated by a p H increase) than the very slowly formed metatungstate. Because of the large bed volume of the large column, paratungstate B does not appear a t all in the elution profile of one- and two-dayold solutions. After two days, a maximum of paratungstate B (and species X) in the test solution leads to a yield mini-
mum. The decrease in the total yield of two-week-old solutions can be accounted for by a decrease in the +-metatungstate concentration in favor of metatungstate formation. Paratungstate A and monotungstate are eluted a t Kd = 1.0 t o 1.2, with W1 being more strongly adsorbed than We. Thus, the elution profiles obtained can be interpreted on the basis of modern concepts of degrees of condensation and conversion reactions of individual isopolytungstates as well as the chelate complex formation of tungstates on dextran gels. It is hoped t h a t the method of molecular sieve chromatography, especially on tightly cross-linked dextran gels, in combination with conventional methods such as dialysis, electrophoresis, sedimentation, diffusion, etc., may provide valuable new insights into the highly complex chemistry of iso- and heteropoly acids.
LITERATURE CITED (1) H.
M. Ortner.
H. Krainer, and H. Dalmonego, J. Chromatogr., 82, 249
(1973). (2)S.Karajannis, H. M. Ortner, and H. Spitzy, Manta, 19, 903 (1972p (3)H. M.Ortner and H. Dalmonego, J. Chromatogr., 89, 287 (1974). (4)J. C. Giddings, "Dynamics of Chromatography," Part I, Marcel Dekker, New York. N.Y.. 1965. (5)0. Glemser, W. Holznagel. W. Hoitje, and E. Schwarzmann, Z. Naturforsch., 206, 725 (1965). (6)P. Souchay, "Ions Mineraux Condenses," Masson, Paris, 1969. (7)Y. Ueno, N. Yoza, and S.Ohashi, J. Chromatogr., 52, 469 (1970). (8)Y. Ueno, N. Yoza, and S.Ohashi, J. Chromatogr., 52, 481 (1970).
RECEIVEDfor review February 4, 1974. Accepted September 17,1974.
Rapid Simultaneous Determination of Picogram Quantities of Aluminum and Chromium from Water by Gas Phase Chromatography Thomas A. Gosink Institute of Marine Science, University of Alaska, Fairbanks, Alaska 9970 7
The simultaneous analysis of aluminum and chromium has been reported by Genty and coworkers ( I ) , but the procedure is lengthy, requires repeated handling, and, as a consequence the accuracy and precision, though good, suffers some deterioration. In our efforts to adapt fluorinated metal chelate gas chromatography to natural water samples, we have developed the improved procedure described in detail in this report. There are a t least two advantages in the use of gas phase chromatography and of chelates for the analysis of aluminum and chromium. The first is that by taking advantage of the electron capture detectors sensitivity to perfluoroalkyl groups, several orders of magnitude greater sensitivity over most standard methods is achieved, and the second is that it appears that the chelation technique will enable investigators to differentiate between dissolved, particulate, and adsorbed forms of the element from the analysis differences for raw, filtered, and acid digested samples which can be prepared, and thus stabilized, a t the collection site rather than a t a later time after the sample has changed. This aspect will be discussed in an article to be submitted elsewhere.
EXPERIMENTAL Apparatus. A Varian Model 1520B gas chromatograph, equipped with a tritium source electron capture detector and thick walled (0.25-inch o.d., 0.12-inch i d . ) Teflon columns and crossover, was employed. The flow rate of the nitrogen carrier was 70 ml/min. The temperatures for the injector, column, and detector were, respectively: 150, 145 and 185 O C . Column 1. The principal column used was 60 inches in length, and filled with 60-80 mesh silanized glass beads lightly coated with D.C.-710. T h e coating was accomplished by boiling ethyl acetate in a beaker containing one-half the volume of glass beads as solvent, and 2% of the weight of the beads of D.C.-710. The beads were isolated from the hot solvent by suction filtration on a Buchner funnel. Columns 2 and 3. A 46-inch column prepared as above, but using only 0.3% D.C.-710, was similar in retention time to a 32-inch column packed with 5% by weight of SE-30 on silanized chromosorb P; both operated a t 120 O C . Glassware. All glassware was initially cleaned with NOCHROMIX and then silanized with a 25% solution of hexamethyldisilazane in benzene. T h e 15-ml screw cap culture tubes and the Teflon-lined caps thereafter were cleaned by soaking them for several hours in 3M HC1, followed by a thorough rinsing with deionizeddistilled water. In order to ensure uniform low blanks, the screw
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cap culture tubes were pretreated with 2 ml each of buffer and chelating solutions, heated, the solutions discarded, and the tubes rinsed with an additional 2 ml of buffer solution before they were loaded for analysis. Reagents. A stock solution of distillation purified trifluoroacetylacetone (Htfa), kept under refrigeration, was made by diluting 1.5 ml of the reagent in 100 ml benzene (Matheson, Coleman and Bell-pesticide quality; Mallinckrodt-nanograde quality). The metal chelates were prepared, isolated, and purified in quantity as adequately described in the literature. These pure solids were used to prepare the pure standard solutions by routine serial dilution using pesticide quality hydrocarbon solvents. The more concentrated stock solutions were stored in the refrigerator. The known solutions were prepared by dissolving the pure metals in concentrated HC1 in volumetric flasks followed by dilution with distilled water to the mark. Working dilute (
