A rapid method for the micro-estimation of lead in urine.

In the literature on the estimation of urinary lead, it is usually recommended that not less than 100 ml. aliquots of the urine sample be taken for analysis. This has certain disadvantages, not the least of which is the time required to ash the organic content of the urine. In addition, spot samples of urine collected from groups of workmen are often less than the 200 ml. volume required for duplicate estimations. For these reasons, a rapid and accurate method was sought for the determination of total lead in small volumes of urine. The method finally devised is based on the dithizone mono-colour method described by Fischer and Leopoldi (1940). The organic matter in a 20 ml. sample of urine is destroyed by ashing with nitric acid and the residue is dissolved in water. Bismuth is detected and removed by washing at pH 3 0-3 4 with a solution of dithizone in chloroform which is then discarded. Cyanide solution, buffered topH 10, and an alkaline solution of dithizone are added and lead is extracted as the dithizonate into chloroform. Excess dithizone is washed out of the organic phase with potassium cyanide solution. The optical density of the washed chloroform extract is directly proportional to the quantity of lead present. The advantages claimed for the method are as follows: 1. The small volume of urine needed for an accurate determination considerably reduces the time required to ash the sample and hence the time taken for the determination. 2. The ashing and extraction of lead with dithizone are carried out in the same vessel, thus reducing contamination from external sources. Apparatus