Speciation of five arsenic compounds in urine by HPLC/ICP-MS


Courtesy of PerkinElmer, Inc.

High-performance liquid chromatography (HPLC) coupled to an ICP-MS has become an invaluable analytical tool for the determinations of trace levels of individual arsenic compounds (speciation). Speciation of arsenic is used to improve our knowledge of arsenic’s biochemical interactions and to evaluate toxicity risks. The toxicity and bioavailability of arsenic is highly dependent on form or species. Five of the most commonly found arsenic compounds are listed in Table 1 with their LD50 values determined in mice.1

The World Health Organization has established that the total daily intake of inorganic As should not exceed 2 μg/kg body weight. Human exposure to the inorganic forms of arsenic has been linked to increased rates of cancer. Seafood can contain up to 25 μg As/g, but the major species is AsB which has a low toxicity; therefore the quantification of individual arsenic species is vital to accurate risk assessment. Analysis with speciation of urine can indicate the source of recent arsenic intake.2

In addition to arsenic’s diverse toxicity, its chemical form determines arsenic’s mobility in the environment. Therefore, new environmental regulations are being developed to specifically monitor for individual species of arsenic.3

While many different analytical techniques have been applied to analyses of arsenic species, highperformance liquid chromatography (HPLC) coupled to an ICP-MS has several significant advantages. These include the excellent separating power of HPLC, coupled with the high degree of elemental specificity and very low detection limits of the ICP-MS. ICP-MS can detect the inorganic and organic arsenic species without on-line digestion of organic forms.4 Additionally, the system is totally integrated and easily automated giving excellent precision with ease of analysis.

Samples with a high chlorine component, such as urine, can potentially cause a polyatomic isobaric spectral overlap interference at the ICP-MS from the formation of 40Ar35Cl+, which has the same m/z as 75As. Some investigators have resolved the ArCl+ peak from the arsenic species by optimizing chromatographic parameters.5-6 In this work we will use dynamic reaction cell (DRC) technology to “move” the arsenic ions away from the ArCl+ by reacting the arsenic ions with oxygen to form the 75As16O+ ion, measurable at m/z 91.

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