Abstract:
Arsenic in groundwater used for drinking is now regarded as one of the
most serious health hazards of this decade. Long term exposure to low
concentrations of arsenic has been reported to cause cancer of the skin, bladder
and other internal organs. Also, various ionic forms of arsenic are known to be
very toxic to most microorganisms. Measurement of trace arsenic at parts per
billion (ppb) levels in environmental and biological samples is a key component
for the mitigation and understanding of this crisis. This M.S. Thesis Project deals
with the development of an analytical technique for the measurement of arsenic
based on a gas-phase chemiluminescence reaction between ozone (O3) and
arsine (AsH3) as the detection principle. The approach is capable of analyzing
arsenic concentration in a 1.0 mL sample in one minute. The determination of
As(III) and As(V) was achieved based on the different pH dependence and the
reducibility of these species to arsine gas by sodium borohydride (NaBH4). The
intense chemiluminescence formed in a reflective glass reaction cell from the
reaction of AsH3 – O3 is detected by a sensitive photomultiplier tube (PMT). The
signal is further amplified, digitalized and recorded with a complete data
acquisition computer controlled system. The limit of detection (LOD) is 0.146
μg/L (ppb or 146 ppt) for total arsenic concentration in 10 determinations.
To validate the performance of the gas-phase chemiluminescence based
arsenic analyzer, results were compared with Hydride Generation Atomic
Absorption Spectroscopy (HG-AAS) and Atomic Fluorescence Spectroscopy
(AFS) techniques. The chemiluminescence detection system was also coupled
with a flow injection system to enhance its efficiency. Sequential procedures
including direct chemical and data analysis methods and step by step
development of the analyzer are described in depth. The system has been
effectively tested using standard and unique field water samples from several
regions of Ethiopia.
