Measurement of arsenic in water and soil based on gas-phase chemiluminescence

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Title: Measurement of arsenic in water and soil based on gas-phase chemiluminescence
Author: Idowu, Ademola David
Abstract: Arsenic occurs widely in nature and is a known human carcinogen . Developmental , immunological , and neurological defects are linked with chronic exposure to arsenic in drinking water . The United States Environmental Protection Agency (US EPA ) prescribed safe limit is 10 & #956 ;g /L . Standard atomic spectrometry based methods are expensive . Field wet techniques require large amounts of acid , other reagents and paper strips impregnated with toxic mercury and lead compounds . This dissertation presents a new , fast , safe , affordable automated system configurable for laboratory or field use . Arsenic in the sample is chemically or electrochemically reduced to arsine that reacts with ozone atop a photomultiplier tube , producing chemiluminescence . Direct chemical , electrochemical , and liquid chromatography methods are described . The first method uses sodium borohydride for the reduction of arsenic . Differential determination of arsenate and arsenite is based on the different pH dependence on their conversion to arsine . At pH & #8804 ;1 , both arsenate and arsenite are quantitatively converted . At pH 4 -5 , only arsenite is converted . Under these conditions , limit of detection (LOD ) is 0 .05 and 0 .09 & #956 ;g /L for total arsenic and arsenite , respectively , with a 3 -mL water sample . The relative standard deviation for 3 determinations was 1 .2 and 2 .1 % for 1 & #956 ;g /L total arsenic and arsenite respectively . The arsenic concentrations in this dissertation are all based on that of elemental arsenic . The Electrochemical method uses a Platinum screen anode and stainless steel cathode in two compartments , separated by a Nafion & #61666 ; membrane . Arsenite is selectively reduced on a stainless steel cathode while a cadmium -coated cathode reduces both forms . The limit of detection is 1 .5 and 4 & #956 ;g /L for arsenite and total arsenic respectively with a 2 -mL water sample . The relative standard deviation for 3 determinations was 2 .6 and 4 .5 % for 10 & #956 ;g /L arsenite and total arsenic respectively . This environment -friendly method uses only re -usable sulfuric acid electrolyte , air , water and electricity but requires further development . Arsenite , arsenate , dimethylarsinic acid (DMA ) and monomethylarsonic acid (MMA ) are separated on anion -exchange column using carbonate and hydroxide eluents . Separated species are photolytically oxidized by UV -light , converting organic species to their respective inorganic forms . Subsequent online reaction with acid and borohydride produces arsine , detected by CL . For arsenite , arsenate , MMA and DMA the LOD is 0 .4 , 0 .2 , 0 .5 and 0 .3 & #956 ;g /L respectively for a 100 - & #956 ;L injected sample . The relative standard deviation for 3 determinations was 3 .5 , 2 .8 , 2 .2 , and 4 .1 % for 10 & #956 ;g /L of each of arsenite , arsenate , MMA , and DMA respectively . The system has been tested successfully on water and soil samples , and can be adapted for matrices such as biological samples and body fluids . There are no significant practical interferences
URI: http : / /hdl .handle .net /2346 /9431
Date: 2007-05

Citation

Idowu, Ademola David Measurement of arsenic in water and soil based on gas-phase chemiluminescence. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /9431 .

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