‘Control’ samplers are necessary for accurate results
A ‘Control’ sampler is a sampler that is loaded with a pre-coated pad from the same batch as the field samplers, and put in its brown airtight vial to be used as a ‘control’. This ‘control’ sampler should accompany the field samplers that are to be exposed, so that it is subject to the same temperatures and conditions as the others, but the control sampler should be kept in the brown vial (not exposed).
A batch of samplers consists of: (1) a ‘control sampler’ (never exposed) and (2) one or more field samplers (that are to be exposed), which share the same coating date, the same preparation date, the same handling, and preferably, the same analysis date.
Since the pre-coated filter pads are stored refrigerated before being loaded into samplers, all pads used for a designated batch must be removed from the refrigerated vial at the same time. Pads should be removed from the refrigerator about 12 hours before exposure for the purpose of equilibrating to the room temperatures. This is done to prevent condensation from forming on the pad. Moisture is the enemy of the coated pad, as it can remove some of the collecting material.
Samplers from the same batch are assembled, exposed, and disassembled over some period of time defined by the field study, but for the best results, the time period should not exceed four weeks. The ‘control’ sampler should be kept in the brown vial (not exposed). As much as is possible, keep the control and field samplers at the same approximate locations and temperature. When the sampling is completed, place the exposed samplers in the brown vial and keep at room temperature in a cool place until they are ready for analysis. This will minimize variation in the differences due to temperature effects within the batch. In a clean environment, remove the exposed field pads and ‘control’ unexposed pads from the samplers. It is best to do the analysis as soon as possible but can be done within 2 -3 weeks after exposure.
When the exposed pads and ‘control’ unexposed pads are sent to a lab to be analyzed, the ‘control’ pad is analyzed the same way as the field pads and clients will be billed for analysis of ‘control’ pad.
Further Instructions for filling out COC (Chain of Custody) Form that is to be sent to the lab with the exposed pads can be found on the Ogawa website, www.ogawausa.com, under the tab ‘Analysis Instructions/Form’.