An Experimental Research On Preservation Of Arsenic Species In Water Samples And Extraction Of The Speciation From Soils And Sediments

Arsenic has a century-long reputation of being poisonous. For example, the inorganic arsenic compounds, such as arsenite and arsenate, are toxic and carcinogenic. Ingestion of inorganic arsenic may cause cancer of skin, bladder, kidney, lungs and liver. However, the toxicity of arsenic is greatly dependent on its species and inorganic arsenic is much more toxic than the organic. The major forms of arsenic in most marine organisms, organic arsenic compounds such as arsenobetaine (AsB) and arsenosugars are considered to be nontoxic. For this reason, speciation analysis is more necessary than the determination of the total amount of arsenic samples.In present dissertation, experimental studies of arsenic speciation in soils and sediments were carried out. Contrast experiments with some different extractants like water, ammonium oxalate, hydrochloric acid, phosphate and phosphoric acid to extract the arsenic species from sediment indicate: (1) The main forms in soils and sediments are inorganic arsenics like arsenate or arsenite. The organic arsenics are not detected. (2) Phosphoric acid can extract the maximum amount of arsenic, then the ammonium oxalate, phosphate and hydrochloric acid in turn. It is hard to extract any arsenic with water. (3) Several extraction strategies were evaluated using phosphoric acid as extractant in combination with either ethylenediamine tetraacetic acid (EDTA), hydroxylamine hydrochloride (NH2OH·HCl), or ascorbic acid. Addition of ascorbic acid in phosphoric acid achieved good quantitative recovery. (4) Good results were achieved using 0.6mol/L phosphoric acid and 0.1mol/L ascorbic acid with 30min ultrasonic extraction.The second part of dissertation presents experimental studis of preservation of arsenic species in water samples. Synthetic laboratory experimental water samples were made by adding a certain concentration of four arsenic species (As(Ⅲ), As(Ⅴ), MMA and DMA) in the underground water then were treated with different preservation procedures. The main achievements obtained in this research are: (1)The organic arsenic in the water samples can be preserved above 15 days without any preservation procedure. (2)The most effective preservation method is: Filtration ofsamples before preservation. hydrochloric acid, phosphoric acid or EDTA is recommended as preservation agent, combined with keeping the samples cool (4℃) and dark. Through this preservation procedure, the samples can be stably preserved exceed 15 days. This period is enough for the water samples from sampling to analyzing.