I want to confirm the presence of arsenic in some protein samples, apart from the marsh test can I use the following method?--
Arsenic is present as arsenic (III) ion in the samples. Hydrogen sulfide gas when passed in the sample of arsenic (III) ion gives precipitates which are yellow in color.
The yellow precipitates dissolve on adding concentrated nitric acid. This solution on reaction with ammonium molybdate in presence of concentrated nitric acid again gives yellow precipitate.
This confirms the presence of arsenic (III) ions in the sample.
If not, please suggest another method
P.S I have some info about arsenic bound proteins from- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3797521/