how to prepare 100 PPM Arsenic (iAS) solution out of NaAsO2?

Hi
I had a quick question.
I used to prepare 100PPM chromium out of potassiumdichromate K2Cr2O7. I used to dissolve 282.69mg in 1000ml to get 100PPM chromium.
One of the other person is preparing 100PPM iAS (arsenic) solution out of NaASO2 [Sodium arsenite]. He dissolves 100mg NaASO2 in 1000ml to get 100PPM. Is that right?. Or he has to take 173.3965 mg in 1000ml h2o. kindly advise. thanks