Rapid analysis of total mercury in waste waters and process waters with elevated mercury content using direct pyrolysis technique - Water and Wastewater - Water Monitoring and Testing

Introduction

A conventional standard method of total mercury det ermination in water using atomic absorption spectrometry (AAS) involves preliminary sample digestion that ta kes from 30 minutes to 8 hours depending on the digestion conditions.

The use of a mercury analyzer RA-915M/RA-915+ with Zeeman background correction in combination with PYRO-915+ pyrolysis attachment provides direct dete rmination of mercury in process and waste waters contaminated with mercury without digesti on or any other sample preparation stages.

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 water sample is placed into the sample boat with a charcoal bed, which is inserted into the first chamber of the atomizer, where the sample is heated at a temperature of 200–800°C (depending 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-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.

RA-915+/915M is compliant with US EPA 7473 and ASTM D7622 methods.