Arsenic bound proteins confirmatory test 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/
You may wish to give this suggestion a try, courtesy of the literature on constructing nano-particles. 

First, dissolve the protein samples in say ethanol or other flammable solvents.

Next, place it into an alcohol lamp with a wick composed preferably from glass fiber, but one may be able to employ woven cotton or a cotton string.

Lastly, light the lamp and place a bowl over the lamp to capture/condense escaping particles.

My recollection is that the target metal of interest, is slowly draw through the wick and thermally broken down. Still looking for the source, but here is a related article.

This is clearly relates to the final step in the Marsh Test, where the arsenic presence is distinctive.

Note, this proposed procedure, if successful, avoids the conversion of a sample of a compound into deadly AsH3 gas per a nascent hydrogen pathway, which is perhaps not required here, as you already have constructed (via an alcohol lamp), a path to 'burn' the As(III).