A computerized automatic apparatus for determination of mercury in biological samples

The determination of trace amounts of mercury in biological material is of considerable interest for the control of occupational exposure, as well as for the study of environmental pollution generally. Atomic absorption analysis, which was introduced in about 1965, has become the most popular method for determination of trace metals. However, the standard technique for mercury is unfavourable because the sensitivity is not very high. Instead, a modification called ’flameless’ (or cold vapour) atomic absorption has become the method ofchoice for determination oftrace amounts ofmercury. After the fundamental paper by Poluektov, Vitkun and Zelyukova [1] in 1964, hundreds of publications have described small variations of the same technique. Hg ions in solution are reduced by Sn + or some other reducing agent to metallic mercury, which is driven out of the solution by an air or gas stream. The mercury-containing gas passes through a gas cell in a spectrophotometer, where its light absorption at 253"7 nm is measured. In this laboratory, a rapid, flameless atomic absorption method for mercury in urine was worked out in 1970 by Lindstedt [2]. This principle is very well suited to automation and an instrument was later constructed by Lindstedt and Skare [3], which was able to analyse 60 digested urine or blood samples in about 2 h without supervision. The detection limit was about ng ofmercury per sample. This instrument worked well in the laboratory for more than 10 years; when it began to fail due to excessive wear, it was evident that a succeeding automatic mercury analyser ought to be computerized. Since the worn-out mercury analyser had functioned quite well, it was decided that the purgation-tower principle should be retained. Three separate pumps were introduced for transferring sample solution and tin solution to the tower and emptying the tower after the mercury had been blown out. The mechanical relays and switches were replaced with electronic tools. Other automatic instruments for mercury analysis have been constructed by Agemian and Chau [4], Koirtyohann and Khalil [5], Matthes et al. [6], Coyle and Hartley [7] and others. Most of these instruments are based upon Technicon Auto-Analyzer equipment and different arrangements have been invented for the separation ofthe purging gas from the sample solution.