Ultratrace determination of mercury in water following EN and EPA standards using atomic fluorescence spectrometry

Abstract

Chemical vapour generation has been used in combination with atomic fluorescence spectrometry to determine mercury at ultratrace concentrations down to 0.1 ng L⁻¹. A time-based injection of 1 mL of solution for measurement was sufficient to generate a steady-state detector response in the direct mode of measurement. The detection limit calculated from a ten-point calibration curve according to DIN 32645 was 0.26 ng L⁻¹. Instrument noise is limited by reflected radiation from the light source rather than by the dark current of the photomultiplier. The detection limit is directly influenced by the reagent blank which was 2 ng L⁻¹ in the experiments described. Focusing by amalgamation and subsequent thermal desorption generates a detector response which is about eight times higher in peak intensity and about twice as large in integrated intensity. The detection limit under these conditions is 0.09 ng L⁻¹ which can be further improved by preconcentration of larger volumes of solution for measurement. The cycle time for one individual reading is about 40 s without amalgamation and 125 s with amalgamation. The linear dynamic range of the system is five orders of magnitude with a single photomultiplier gain setting. The carry-over is less than 0.3% in direct measurement mode. Reference water samples and a surface water containing approximately 5 ng L⁻¹ were used to prove the validity of the method for real samples. Good accuracy and recoveries of 103% were calculated using the fast direct determination technique.