Brief Introduction of  EPA Method 18 

Use for volatile organics such as vinyl chloride, benzene, methylene chloride, PCE, etc.

Collection

Samples are collected using canisters or bags. Syringes and glass bulbs may also be used but are not recommended. Canisters may be filled by simply opening the valve (grab sampling), by leaking in over a period of time (integrated w. critical orifice sampling) or with a pump of a period of time (integrated w. pump). Canisters may be used for both high or low level samples. Clients should inform lab which type to expect as canisters dedicated to low level sampling may be damaged by high level samples. Bags are suitable only for high level samples but may be required for certain polar compound classes such as mercaptans. Bags should be filled only halfway to prevent popping if shipped by air. Cartridges may be substituted for many applications. If they are, however, the method would best be described by a different number. Ambient samples should not be collected if it is raining or snowing.

Analysis

Analyzed by transferring a measured volume of air from the canister or bag to a cryogenic trap and hence to the GC/MS analytical system (preferred for legal defensibility).

Equipment

Canisters or bags plus one for QC, compensating critical orifice or small pump for integrated samples, flow controller/flow meter, pressure/vacuum gauge. Projects may also require onsite measurement of temperature, relative humidity, barometric pressure (absolute), wind direction and speed. Clients may also need heavy walled Teflon tubing, tees, connectors, etc.

Detection Limits

Detection limits – 1.0 ppbv

Advantages

Convenience, easy to ship, low detection limits, applicable to broad range of target compounds. Can run duplicates and/or MS/MSD with certified reference standard rather than client sample. Sampler does not need to estimates how much air to sample.

Disadvantages

Canister supply may be taxed by very large projects. Some polar compounds may have an affinity for canister walls at low concentrations. Bags can contaminate the sample with chlorinated compounds.

Alternatives

TO-1 & TO-2 separately or combined, TO-3, some NIOSH methods

Ambient air surveys, fence line monitoring, impacted neighborhoods, some odor problems, indoor air, risk assessment, sulfur gases (bag sampling required), TPH in air, etc.

 
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