Bi, Sb, Fe, Cr, Zr, Co, Sn, Cd, and Ga. Cyanide forms complexes with most of the transition elements and is especially useful for complexing Fe as the ferrocyanide complex after it has been reduced by TGA. Hydrogen peroxide forms complexes with Ti, V, Cr, and their congeners. Hexametaphosphate prevents precipitation of Sc, Y,and the rare earth elements by ammonium carbonate and also prevents precipitation of thorium peroxide after addition of H202. Ammonium carbonate serves as a complexing agent for uranium, for other actinide elements, and for some transition metals. The order of addition of masking agents is important and must be followed because some masking agents are added to prevent precipitation of elements by other masking agents-e.g., U is precipitated by hexametaphosphate in the absence of carbonate. Up to 100 mg of formate, acetate, oxalate, borate, phosphate, perchlorate, nitrate, sulfate, cyanide, bromide, iodide, and triethanolamine, and 50 mg of tartrate, gave no interference with the method. Fifteen milligrams of HzOz did not interfere but quantities greater than 20 mg gave negative interference. Because H202in a basic medium oxidizes some of the BPHA and prevents formation of the Al-BPHA complex, the specified amount of BPHA (20 mg) must be added to each sample. Fluoride, EDTA, and citrate interfered by masking the aluminum. Five milligrams of fluoride gave about 10% negative interference when polyethylene separatory funnels were used in the procedure. The presence of fluoride in samples contained in borosilicate glass gave high results because of the aluminum leached from the glass walls. Color Development. The AI-8-quinolinol complex forms rapidly at pH 9 in the ammonium carbonate solution and is extracted into CHCI, within a 1-min shaking time. The stability of the colored complex is 1 hr when the CHCl, is drained directly into a 1-cm cell, 2 hr when drained through clean surgical cotton, and 3.5 hr when the CHC13 is first centrifuged and then transferred to a 1-cm cell. The A1-8quinolinol color was measured at 390 nm, the peak wavelength of the absorption spectrum determined under the conditions of the procedure. Sensitivity. The absorptivity of the Al-8-quinolinol complex measured under the conditions of the procedure at 390 nm was calculated from a Beer’s law plot to be 262 liters/g-cm. The corresponding molar absorptivity (ionic molar absorptivity) is 6800, and Sandell‘s sensitivity index is 0.004 y/cm2. The colored species obeys Beer’s law over the range 0-50 fig A1 in 10 ml of CHC1,. The optimum concentration range is 5-30 pg A1 as taken from a Ringbom plot. AI-BPHA Complex, The composition of the AI-BPHA complex was determined from both a continuous variations plot and a mole ratio plot to have an AI-to-BPHA ratio of
1422
e
ANALYTICAL CHEMISTRY
1 :3, in agreement with Shome (9),who determined the composition of the dried Al(BPHA)3 precipitate. Precision. The relative precision of the method at the 15-pg level for a standard aluminum solutlon was Zk2x at the 2a level. For the determination of aluminum at the 0.01 % level in uranium alloy and the 0.05 Z level in stainless steel, the relative precision of the method at the 20 level was Zk2Z. In the analysis of stainless steel for AI at levels less than 0.01 Z, the quantity of Fe in the sample limits the precision of the method because of incomplete masking with TGA-KCN. Discussion. The method described is suited for the determination of microgram quantities of aluminum in uranium alloys, stainless steel, and various other materiaIs. The unique feature of the described method is the highly selective separation of aluminum with BPHA, while the selection of 8-quinolinol as a chromogenic reagent was merely due to its suitability. The determination of aluminum after it has been separated into the 0.20M HCl may be completed by addition of more sensitive or less sensitive chromogenic reagents. Fluorescence methods might easily follow the BPHA separation for the determination of submicrogram quantities of aluminum. The highly selective separation achieved by this method should make it widely applicable for the determination of aluminum. ACKNOWLEDGMENT
The authors thank Ronald DiFelici for preliminary work on the procedure and Earl Ebersole for his technical assistance and help in preparing the report. RECENED for review May 5 , 1969. Accepted June 26, 1969. Work performed under auspices of U. S. Atomic Energy Commission.
Correction Preparative Thin-Layer Chromatography a.nd High Resolution Mass Spectrometry of Crude Oil Carboxylic Acids In this article by Wolfgang K. Seifert and Richard M. Teeter [ANAL.CHEM.,41, 786 (1969)l on page 786, column 2, the final sentence should begin “Zone 2 (Table I and. . . . . . .” On page 794, Table VII-A, footnote 6 should read “To skeletal structures found in petroleum.” The final sentence of the manuscript, page 795, should read “Presented in part at the Gordon Research Conference on Geochemistry, New Hampshire, August 1968.”
