Use of Flow Injection and Sequential Injection Analysis Schemes for the Determination of Trace-Level Concentrations of Metals in Complex Matrices by ETAAS and ICPMS

Despite their excellent analytical chemical capacities for determination of low levels of metal species, electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry often require suitable pretreatment (separation and preconcentration) of the sample material to facilitate the desired sensitivity and selectivity of measurement. Such pretreatment schemes are advantageously performed in flow injection (FI) or sequential injection (SI) manifolds, where all unit operations can be effected on-line and under enclosed and strictly controlled conditions. Various separation/preconcentration procedures are feasible, such as liquid–liquid extraction (possibly including back extraction), (co)precipitation with collection in knotted coils, adsorption on hydrophilic or hydrophobic reactors, hydride generation, or the use of ion-exchange/chelating packed columns. After describing the particulars and characteristics of FI and SI, we present, via selected examples, various separation/preconcentration FI/SI schemes for the determination of trace levels of metals, with particular emphasis on the use of the novel extension of FI/SI, that is, the so-called lab-on-valve concept.

*Presented as an invited plenary lecture at “The 2nd Asian International Conference on Ecotoxicology and Environmental Safety” (SECOTOX 2004), Songkla, Thailand, 26–29 September 2004.

Keywords:

• ETAAS
• Flow injection
• ICPMS
• Lab-on-valve
• Preconcentration
• Separation
• Sequential injection
• Trace-level metal concentrations.

ACKNOWLEDGMENT

Thanks are due to the organizers of SECOTOX 2004 for inviting me to present the contents of this communication as an invited plenary lecture and to the persons in my group who have been involved in the research activities described herein, that is, Drs. Steffen Nielsen, Jianhua Wang, and Manuel Miró and Ph.D. students Xiangbao Long, Roongrat Chomchoei, and Piotr Gata. Constructive comments on the manuscript from Dr. Manuel Miró are most appreciated.

Notes

*Presented as an invited plenary lecture at “The 2nd Asian International Conference on Ecotoxicology and Environmental Safety” (SECOTOX 2004), Songkla, Thailand, 26–29 September 2004.

aReference value.

aForm of the cation exchanger.

bThe enrichment factor was obtained by comparing with direct introduction of a 20-μL sample solution into the graphite tube.

cC_Ni = 0.30 μ g L^{− 1}, n = 7 (replicates). IA, integrated absorbance; relative standard deviation.

aIndicated value.

aCertified value.

bFrom Ref. 36. Soil sample, 300 mg; extraction flow rate, 10 μ L s⁻¹(except step III, 5 μ L s^{− 1}); subfraction volume, 175 μ L; total extractant used, 12 and 18 ml for CH₃COOH and EDTA (single extraction) and 12, 24, and 12 mL for step I, II, and III (sequential extraction), respectively.

cTotal aqua regia digestion value (Ref. 36).