Direct atomic absorption mercury determination in tissues and biological samples

INTRODUCTION

Mercury and its compounds are highly toxic substances fo r humans. It occurs naturally and exists in various forms: elemental (or metallic); inorganic (e.g. mercuric chloride); and organic (e.g., methyl- and ethylmercury). These forms all have different toxicities and implications for health. Among naturally occurring mercury compounds, methylme rcury exerts a significant influence (neurotoxic action) on human health.

The toxic properties of methyl mercury are caused by the ability of its ions to bond with sulfhydryl groups of proteins. This changes protei ns’ structure and properties, re sulting in disfunction of the protein metabolism and the course of enzymatic processes. Mercury exposure level is determined by analysis of blood, hair, nails and other biosamples.

For an acute type of poisoning, the diagnosis is confirmed both by clinical presentation and by results of analysis of body flui ds (urine, blood, saliva). In case of chronic poisoning the situation is complicated.

Mercury concentration in urine may rapidly decrease after the termination of exposure to mercury, whereas it may be high in internal organs for a long time because mercury is prone to accumulate in liver, kidneys, spleen, brain, and hair. In this case, the analysis of hair provides more information about mercury concentration in the body because they hold the trapped mercury for much longer time.

The use of atomic absorption mercury analyzer RA-915M/RA-915+ with Zeeman background correction equipped with PYRO-915 + pyrolytic attachment provides direct mercury determination in biological samples at a ppb level.

MEASURING METHOD

The measuring method is based on thermal atomization of mercury from a sample using a PYRO-915+ attachment and its consequent determination by flameless AAS with Zeeman background correction using a RA-915M/RA-915+ mercury analyzer. A sample is placed into the sample boat, which is inserted into the first chamber of the atomizer, where the sample is heated at a temperature of 200–800°C (depen ding on the selected operation mode). The mercury compounds are evaporated and partially dissociated, forming elemental mercury.

All the gaseous products formed are transported into the second chamber of the atomizer by a carrier gas (ambient air). Mercury compounds are totally dissociated and the organic matrix of the sample is burnt out. Downstream from the atomizer the air flow enters the analytical cell heated up to 700°C, and the mercury atoms are detected by RA-915M/RA-915+ analyzer. This approach does not involve preconcentration on a gold trap and “cooling step”, thereby eliminating ensuing problems.

The use of ZAAS combined with a “dry” converter provides the highest sensitivity with no interferences from the sample matrix. Purified ambient air is used for combustion, so that no cylinders with oxidizer or compressed gases and “clean room” environment are required.

The total time needed for determination of mercury is not longer than 2 minutes.