collected in a fresh activated carbon scrubber. All of the organic lead present in the known air sample was collected in the activated carbon scrubber. No organic lead was adsorbed in the filter cake. When collecting organic lead in ambient air samples, automobiles should not be parked immediately adjacent t o and up-wind from the air sampling scrubber. Leaded gasoline if escaping from Leaking gasoline lines, carburetors, vented gasoline tanks or gasoline spills, will produce elevated results a t the parts-per-trillion level. Sampling points should be carefully selected to obtain representative samples free from immediate contamination sources. All connections in the air sampling train must be tight and the particulate lead filters must be properly seated t o avoid leaks around the filtering device. Freedom from interference from particulate lead is essential for accurately measuring organic lead-in-air. Adsorption of organic lead o n numergus surfaces is a problem frequently encountered in preparation of known samples. Laboratory tests have demonstrated that both tetraethyl or tetramethyllead will adsorb o n most organic surfaces such a s rubber stoppers, tubing, etc. Ultraviolet light
also decomposes organic lead compounds. Trace chemicals in air such as halogens, acids, o r oxidizing agents also decompose organic lead t o the particulate form. Therefore considerable precaution should be exercised in the preparation of known samples containing parts per trillion of organic leadin-air. For the same reasons it is quite understandable that only small concentrations of organic lead may be present in the ambient air over cites. h a d in air surveys recently conducted by the Air Pollution Control District County of Los Angeles (5) and the Three Cities Survey (6) demonstrated that the average organic lead-in-air level of ambient air is probably below 0.2 pg/m3. Analytical methods employed by these agencies are adequate for measuring peak levels of organic lead only. They are not of sufficient accuracy to measure changes in the average organic lead content cf ambient air. To measure such changes, a m r e accurate organic lead in air method such as described in this paper is recommended. RECEIVED for review August 25, 1966. Accepted February 20,1967. (6) U. S. Pubiic Health Sercice Publicdot? No. 999-AP-12, 1965.
Anion Exchange and a Selectivity Scale for Elements in Sulfuric Acid Media with a Strongly Basic Resin F. W. E. Strelow and C . J. C . Bothma National Clietriicai Research Laboratory, South African Council f o r Scientific and Industrial Research, Pretoria, South Africa
Anion exchange equilibrium distribution coefficients with Bio-Rad AG1-XI, 100- to 200-mesh, a quaternary ammonium resin in the sulfate form, are presented for 52 elements in sulfuric acid media. The acid concentration range from 0.01N to 4.ON i s covered. Coefficients for elements with strong hydrolytic tendencies iike Ta(V), Nb(V), and W(VI) a r e determined i n the presence of c;l,O,. The elements a r e arranged arbitrarily into a selectivity scale according to the distribution coefficients in 1.ON acid, or according to the coefficients at 0.1N or 0.01N acid when the coefficients are
