Determination of textra-alkyl lead vapour and inorganic lead dust in air

Abstract

Methods are described for the determination of particulate lead and of tetra-alkyl lead vapour in air, by passing the atmosphere under test through a glass-fibre filter and then through a hydrochloric acid solution of iodine monochloride. Tetraethyl lead and tetramethyl lead are collected in this solution by means of their reaction with iodine monochloride to give the corresponding dialkyl lead ions. The lead collected on the filter is extracted with a nitric acid-hydrogen peroxide reagent, and the amount present is determined colorimetrically as lead dithizonate. This may be done automatically with the Technicon Auto-Analyzer, or manually with a comparator and a standard disc.

Manual and automatic procedures are also given for the determination of the amount of tetra-alkyl lead collected. The manual method involves reaction of the dialkyl lead ions with dithizone at high pH and matching the colour of the dialkyl lead dithizonate with a standard disc. In the automatic procedure, the dialkyl lead is converted to the inorganic state before reaction with dithizone and colorimetric measurement as lead dithizonate.

The methods are designed for the measurement of lead-in-air concentrations down to 0·1 mg of lead per 10 cubic metres of air, with sampling periods of at least 8 hours. A modified method based on a sampling period of half an hour, and having a sensitivity of 0·3 mg of lead per 10 cubic metres, is also described.