Have you ever had a telephone call that starts out like this: "Hi, I have an unknown odor in my building and I would like you to tell me what it is?" Or: "Hi, I have a mixture of about 20 different Volatile Organic Compounds (VOCs), ranging from alcohols to xylenes. I have a limited budget, so can you collect them all at the same time on one sample?" If you did, what was your initial reaction? If you are like many Heath and Safety Professionals, it was probably to cringe. You knew you were going to have a hard time explaining to your potential client, either external or internal, that there is no magic black box that can tell you what is causing that odor or that will allow you to collect all those VOCs at once. Although there is still no magic black box, in recent years, two methods have been developed and refined that can make those types of phone calls much more enjoyable for everyone involved.
These 2 methods are very different from one another and have been developed in direct response to the type of telephone calls mentioned above. Both methods are suitable for known or unknown VOCs. One is a modification of a traditional OSHA method, OSHA Method 7. The other method has been modified from an EPA ambient air method and is now called OSHA PV2120.
Sample collection follows the traditional OSHA 7 method. Samples are collected using personal sampling pumps calibrated at 0.2 liters per minute on a standard charcoal tube. The modification takes place in the laboratory, during the desorption of the charcoal tube. In place of the traditional carbon disulfide extraction solvent, co-solvents, sometimes called universal solvents, are used to amplify the carbon disulfide extract prior to GC/FID analysis. The make up of the universal extraction fluid varies from laboratory to laboratory and is usually not made public. They are made of various polar and non-polar solvents of differing concentrations. The laboratory must have all of the required method QC in place before this modification is used. This includes desorption efficiencies, curve linearity, and detection limits. In addition to active sample collection with pumps and tubes, universal solvent extraction can also be applied to passive organic monitors. Once the samples have been desorped, the rest of the analysis follows the standard OSHA 7 procedures. The extracts are injected into a GC equipped with a FID detector.
Not all laboratories have developed universal solvents. Those that have will have different lists of reported VOC's.