A method was developed for pre-concentration, speciation and determination of arsenic species (As(III), As(V), MMA and DMA) in various water samples by solid phase extraction flow injection hydride generation atomic absorption spectrometry (SPE-FI-HG-AAS). The packing materials used for SPE included strong cation-exchange and strong anion-exchange silica beads. The devised method was successfully applied to the quantification of arsenic species in the University of Massachusetts campus pond water. A new method was developed for the determination of methylation and reduction of arsenic species (As(III), As(V) and DMA) in Mueller-Hinton growth media by E. coli based on anion-exchange chromatography with post column hydride generation and inductively coupled plasma optical emission spectrometry (HPLC-HG-ICP-OES). The method was successfully applied to the determination of metabolism of arsenic by E. coli by analyzing the growth media and the cell extracts. The investigations suggested that E. coli did not methylate any of the arsenic species but simply reduced As(V) to As(III). The media created a “split peak” effect for DMA, resulting in shorter retention time for the majority of the bulk and longer retention time for the rest of the species. This effect is most likely due to the reaction of DMA with the protein present in the media, generating a positive complex, which resulted in the shifts in retention times. Although the presence of hydride generation help enhances the arsenic signal by almost 30 times, it also affects the intensities of each arsenic species differently, some, such as As(III), benefit from the reaction than others, such as As(V). The studies revealed that when measuring different arsenic species in the absence of hydride generation, the ICP-OES sensitivity is not the same for all. Results from t- and F-tests suggested that AsB, DMA and As(V) are statistically the same, whereas As(III) and MMA, which are statistically indistinguishable, are from a different distribution.