Evaluation of different digestion methods for organic and inorganic samples for the analysis of mercury by cold vapor atomic absorption spectrophotometry

Date

10-2006

Degree

Bachelor of Science in Chemistry

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Veronica P. Migo

Abstract

Two methods of digestion were compared for Hg determination, namely, wet digestion and microwave digestion using samples of organic and inorganic matrices. The levels of mercury in corn leaves, soil and janitor fish (both in the edible and inedible portions) were determined. Mercury was not detected in all the three samples prepared by wet digestion. However, mercury was detected in samples prepared by microwave digestion. The values are 31.01μg/kg for corn leaves, 8.26 μg/kg for soil and 14.64 μg/kg for the inedible portion of janitor fish.

Accuracy was evaluated using recovery runs in spiked blanks and using three concentrations of mercury, namely 10, 50, 100 μg/kg. The percent recoveries ranged from 60.14 — 94.25% for corn leaves, 44.87 — 94.39% for soil, 64.22 — 87.29 for edible portion and 60.74 — 87.61% for inedible portion of janitor fish. All spiked blanks, regardless of method of digestion and Hg concentration, have higher percentage recoveries than the spiked samples. For the spiked samples, results showed that there is no significant difference between mean percentage recoveries in corn leaves and janitor fish samples. Hence, it can be said that no digestion method can be considered as better in terms of accuracy for analyzing mercury using samples of similar matrices as corn leaves and fish. In soil sample, however, microwave digestion gave better accuracy than wet digestion.

Relative standard deviation (RSD) for test of repeatability (with-in rim) ranged from 9.5 — 43.9%; reproducibility (between run) ranged from 11.0 — 40.3%. Comparing the two methods, the microwave digestion gave lower %RSD than the wet method. Wet digestion is prone to losses and contamination.

This study showed that sample preparation is very crucial in trace metals analysis, specifically mercury in this study. Wet digestion is prone to losses due to volatilization, spattering and charring, as well as contamination. The type of sample matrix also affects the analysis in terms of accuracy; microwave digestion showed better results in soil than in samples of organic matrices (corn leaves and fish). In terms of precision, microwave digestion gave lower relative standard deviation.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 993.5 2006 C4 P39

Document Type

Thesis

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