Sampling and Analysis for Vapor and Particle Phase Mercury in Ambient Air Utilizing Cold Vapor Atomic Fluorescence Spectrometry (CVAFS)
This method is from EPA's Inorganic Compendium of methods and is for the determination of vapor and particle phase mercury form gold-coated bead or sand traps and glass fiber filters using cold vapor atomic fluorescence spectrometry (CVAFS). This method is an improvement for mercury and is recommended over IO-2 and IO-3 series methods.
A key element to the performance of this method is the use of clean sampling procedures. These procedures include acid cleaning all supplies that come in contant with the samples, using particle-free gloved hands at all times when handling sample containers, plastic bagging all containers before and after sample collection, and staying downwind of the sample during all phases of sample installation and removal.
A trap containing either gold-coated glass beads or sand is used for the collection of vapor phase mercury. A 47mm, specially prepared glass fiber filter is needed for collection of particle phase mercury. A Class 100 Clean room is required for the preparation of the glass fiber filter. A 47mm Teflon filter is used in the sampling train for the vapor phase mercury to remove particulates before they reach the
The sample is collected by using a sampler containing pump, box to shelter the filters and traps from the atomosphere and rotameter as outlined in IO-5. A separate collection system is needed for each type of mercury as different flow rates are needed. The amalgamation for vapor phase mercury requires a flow rate low enough to allow the adsorption onto the gold surface in the trap. The specified flow rate is 0.3L/min. for a 24 hour collection period. The lower levels of particle phase mercury require a higher flow rate in order to collect enough particulate to detect the mercury. The specified flow rate is 30L/min. and typical collection periods are 12-24 hours. The sampler box containing the traps and filters must be at least 3 meters above ground level.
Two gold traps are used for sample collecion of vapor phase mercury. The traps are connected by Teflon tubing. The typical collection period is 24 hours. A Teflon filter is placed in front of the traps to collect particulates but this filter is discarded after sampling. The glass fiber filter used for collection of particle phase mercury is put in an open-faced Teflon filter pack for sampling.
After sample collection, the glass fiber filter is removed and placed in a glass petri dish for shipment to the laboratory. The filter is microwave digested with nitric acid and analyzed using CVAFS.
The gold traps are removed from the sampling train, the ends are capped and it is sent to the laboratory for analysis. The traps are thermally desorbed and analyzed separately to check for sampling breakthrough by CVAFS. Results of both traps are summed to give the total vapor phase mercury in the sample.