Abstract
This study investigates the identity of two unexpected arsenic species found separately in a number of urine samples sent to the Health and Safety Executive’s Health and Safety Laboratory for arsenic speciation (arsenobetaine, AB; arsenite, As3+; arsenate, As5+; monomethylarsonic acid, MMA5+; and dimethylarsinic acid, DMA5+). Micro liquid chromatography coupled to inductively coupled plasma mass spectrometry (µLC-ICP-MS) and electrospray time of flight tandem mass spectrometry (ESI-QqTOF-MS/MS) were used to identify the two arsenic peaks by comparison to several characterized arsenicals: arsenocholine, AC; trimethyl arsine oxide, TMAO; dimethylarsenoacetate, DMAA; dimethylarsenoethanol, DMAE; thio-dimethylarsinate, thio-DMA; thio-dimethylarsenoacetate, thio-DMAA and thio-dimethylarsenoethanol, thio-DMAE. The results from both the ICP-MS and ESI-QqTOF-MS/MS investigations indicate that the unexpected arsenic species termed peak 1 was thio-DMA. While the unexpected arsenic species termed peak 2 has yet to be identified, this investigation shows that it was not AC, TMAO, DMAA, DMAE, thio-DMA, thio-DMAA or thio-DMAE. This study demonstrates the incidence of unexpected arsenic species in both routine and non-routine urine samples from both workers and hospital patients.
Highlights
Identifying arsenic species in urine samples presents both an analytical and biological challenge, as the metabolism and biotransformation of arsenic compounds in humans is complex [1]
The analytical quantities of DMAA, DMAE, thio-DMAA, thio-DMAE, thio-DMA at approximate concentrations of 20–100 μg·L−1, and 5 μg·L−1 standards of AC and trimethyl arsine oxide (TMAO) were injected onto the Dionex AG7 column
This study has established that peak 2 is not thio-DMA, DMAA, thio-DMAA, DMAE, thio-DMAE, AC or TMAO
Summary
Identifying arsenic species in urine samples presents both an analytical and biological challenge, as the metabolism and biotransformation of arsenic compounds in humans is complex [1]. In part this is due to the fact that there is no exact agreed process for this human metabolic pathway of arsenic in the literature, with Hayakawa [2], Naranmandura [3] and Wang [4] all proposing slightly different biomethylation pathways. In 1945, the Challenger pathway [5] was first proposed in humans suggesting an initial reduction of arsenate to arsenite followed by steps of oxidation methylation and reduction methylation as follows: arsenate > arsenite > monomethylarsonic acid >. It is suggested that the primary site of arsenic methylation in humans is the Toxics 2017, 5, 12; doi:10.3390/toxics5020012 www.mdpi.com/journal/toxics
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