I would like to test for arsine, arsenic, phosphine, and phosphorus compounds in an exhaust stream. the concentrations are going to be very low. I have a Zellweger CM4 monitor calibrated for arsine continuously monitoring hydrides on an outlet of carbon abatement. I detect between 2 and 3 ppb hydrides in about 1000 cfm stream. Exhaust from three of these carbon units (roughly 1000 cfm and 2-3 ppb hydrides each) are routed to a common exhaust with further air dilution. I am looking for an EPA test method that would be able to selectively measure low concentrations of arsine, phosphine, arsenic, and phosphorus compounds.