Flow-injection on-line sorbent extraction preconcentration and separation for flame and graphite furnace atomic absorption spectrometry

Abstract

Significant progress has been made recently in on-line preconcentration of trace elements for flame (F AAS) and graphite furnace atomic absorption spectrometry (GF AAS) by the use of solid sorbents. The use of microcolumns which were eluted in a direction opposite to the direction of sample loading, and an overall optimization of the system made it possible to increase efficiency and sampling rate substantially. Enrichment factors of 20–25 could be achieved with only 20 s loading time so that the sampling frequency could be increased to 120/h, a value which is compatible with routine F AAS operation. On-line coupling of sortent extraction preconcentration with GF AAS was found to provide a number of important advantages. A 20- to 25-fold increase in sensitivity was typically obtained with 1 min preconcentration, using eluate zone sampling for the most efficient analyte transfer into the graphite tube. An effective separation of the analyte element from interfering matrix components could be achieved using carefully designed wash steps between sample loading and elution. This resulted in detection limits for a number of trace elements which were essentially identical for pure solutions and samples with a high total salt content such as seawater. Finally, sorbent extraction could be used to preconcentrate selectively one oxidation state of elements occurring in more than one valency, providing a means of speciation which is particularly attractive because of its speed of operation. Total analyte element concentrations could be determined after on-line or off-line reduction or oxidation of the other valency states.