Evaluation of the different sample digestion methods for the analysis of lead (Pb) in aquatic species using flame atomic absorption spectrophotometry

Issue Date

12-2005

Abstract

Different sample digestion methods, such as the AOAC standard method 972.23, conventional dry ashing method, microwave digestion, and wet digestion using acid mixtures of HNO₃-H₂SO₄ and HNO₃-HCIO₄ for lead analysis by flame atomic absorption spectrophotometry, were compared. The two resonance lines of lead (217.0 nm and 283.3 nm) and the effect of using deuterium background correction (D₂-BGC) to minimize background signals were also investigated. The resonance line 283.3 nm with D₂-BGC provided better precision, stable signal and reduced signal suppression using the microwave and AOAC standard digestion methods. A comparison of precision and accuracy based on spiked blank, edible, and inedible carp bighead samples showed a % recovery range of 56.8% to 94.3%. Microwave digested sample gave the highest recovery while the wet digestion procedure using HNO₃-H₂SO₄ showed the lowest recovery. The precision of the methods showed greater variability with relative standard deviations of 17.4% (dry ashing method) to 39.3% (wet digestion, HNO₃-H₂SO₄) for repeatability and 19.3% (dry ashing method) to 45.0% (wet digestion, HNO₃-H₂SO₄) for repeatability. Results showed that microwave and AOAC method are both highly appropriate method of digestion for aquatic samples. Microwave and AOAC method have higher accuracy and showed minimal matrix interferences compared with other digestion procedures used in this study. The limit of detection (LOD) and limit of quantification (LOQ) were also determined. The lead content of some freshwater and marine fish and shrimp samples was determined using the optimized measurement condition. Results showed that the edible (fleshly) portions of the fish had lower lead levels than the inedible portions. Microwave digested samples yielded higher lead level for all aquatic species compared with the other digestion procedures. Among the samples studied, carp bighead, shrimp, and catfish showed significantly higher lead levels the the other fish samples and exceeded the limit set by WHO of 0.3 ug gˉ¹ wet weight. Regardless of the method used, the increase in the level of lead is alarming since lead was not detected in any aquatic species analyzed by Madamba and Pamulaklakin 10 years ago (1994).

Source or Periodical Title

Journal of Environmental Science and Management

ISSN

0119-1144

Volume

8

Issue

2

Page

33-43

Document Type

Article

Frequency

semi-annually

Physical Description

tables/graphs

Language

English

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