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US EPA Method 325 defines a procedure for sampling and analysis of benzene and other VOCs at refinery fencelines, and requires two-week passive monitoring.

What’s involved in US EPA Method 325?

US EPA Method 325 was developed to enable refineries to comply with the updated US federal regulation CFR 40, and requires monitoring stations to be set up at defined points around the perimeter of petrochemical refineries.

Each monitoring station contains a set of sorbent tubes, onto which volatile airborne pollutants adsorb over a sampling period of two weeks. Analysis is by TD–GC analysis, in conjunction with detection by MS or another technique, with adsorbed masses being used to calculate airborne concentrations by reference to published uptake rates.

Compounds monitored under US EPA Method 325

While benzene is the primary target compound of Method 325, the sampling and analysis methodology can also be used to determine other hazardous air pollutants, enabling analysts to obtain a fuller picture of overall emissions.

Complying with US EPA Method 325

The simplicity of the Method 325 procedure makes it a robust approach to monitoring pollutants at refinery fencelines. However, a challenge can be posed by the number of sorbent tubes required (duplicates and field blanks at each of up to 24 monitoring stations).

To streamline the process of adhering to Method 325, Markes therefore offers a package of instrumentation and supplies that includes TubeTAG technology. This allows easy, reliable sample tracking through the entire process of sampling and analysis, and complements the multi-tube capability of the TD100-xr thermal desorber and TC-20 TAG tube conditioner, also included in the package.

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