Application of the Parr Acid Digestion Bomb to Decomposition of Tetraethyllead R. E. Mansell and T. A. Hiller Dow Chemical Co., Analytical Laboratories 574 Bldg., Midland, Mich. 48640
For the analysis of gasoline, the ASTM Standard Methods, ASTM D526-56, recommends refluxing 50 ml of gasoline with 50 ml of HC1 for 30 minutes to decompose the tetraethyllead. This is followed by time consuming washes before appropriate measurement of the lead concentration. A simple modification of this general technique is the use of the Parr Acid Digestion Bomb (Parr Instrument Co., 211 Fifty Third St., Moline, Illinois 61265). This apparatus consists of a cup and fitted cover made of Teflon (Du Pont) plastic, contained in a stainless steel bomb which is capable of withstanding up to 1200 psi and 150 “ C . This method eliminates possible loss of volatile lead compounds, and possible solubility problems associated with HzS04 wet ashing are eliminated as well as some solvent effects and calibration difficulties found troublesome with direct aspiration of Pb-rich organic solvents into a flame for atomic absorption measurements.
RESULTS The results in Table I, in grams Pb/gal. isooctane, were obtained on the synthetic standard and on two samples labeled A and B. Comparative data from other methods indicate &5% accuracy and precision. Table I . Analytical Results Standard Technique (3.68 gms Pb/gal) Parr Bomb-A.A. 3.54,a3.67,a 3.78.63.7ab X-Ray fluorescence X-Ray standard Wet ash-A.A. 3.50 1 :50dilution with MI BKC-A.A. ..
Sample Sample A B 2.93,a3.15,b 2.06= 3.156
3.23 3.07
2.17 2.12
2.86
R u n by analytical chemist A (single determination). * R u n by analytical chemist B (single determination). C Spiked with tetraethyllead-isooctane standard solution.
EXPERIMENTAL Two or three ml of isooctane containing 2-4 grams of leadlgal. as tetraethyl lead (-500-1000 pg lead/ml), were placed in the Teflon cup and 2 ml of HC1 added. The closed bomb was heated on a steam bath for 15-30 minutes. After cooling, the bomb had no internal pressure and its contents were washed into a small beaker and evaporated. The chloride residue was treated with 1 ml of nitric acid which was evaporated. The nitrate residue was then warmed with water and a few drops of nitric acid to dissolve the salts before dilution to known volume. Atomic absorption measurements on the solutions were made us. aqueous standards of P b as nitrate using a Perkin-Elmer Model 303 Atomic Absorption Spectrophotometer The pg lead/ ml results thus obtained were multiplied by the dilution factor and 3785 to convert to grams lead/gal. isooctane. A synthetic standard solution containing 3.68 grams Pbigal. as tetraethyllead in isooctane was also analyzed for comparative purposes.
CONCLUSIONS The method as outlined provides a rapid, and convenient system for decomposing tetraethyllead in isooctane. Measuring the lead content by A.A. following the sample treatment has been demonstrated to yield reliable results. The conversion of the lead to an aqueous system is advantageous and also eliminates some difficulties encountered with dilution of the sample in MIBK and A.A. analysis. The sample treatment technique could well be extended to the analysis of other organic or inorganic materials in which losses by volatilization or retention on equipment could be serious. Received for review October 20, 1972. Accepted December 29, 1972.
CORRECT10 N Piezoelectric Detectors for Organophosphorus Compounds and Pesticides In this article by E. P. Scheide [Anal. Chem., 44, 1764 (1972)], in heading for column two “100 ppb” read “Frequency change (cps) due ference. ”
and G. G. Guilbault Table 11, p 1767, the is incorrect. It should to 100 ppm of inter-
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