Effect of contact time and contact pressure on the transfer of oil to surface sample media

Wipe sampling is common practice for the assessment of surface contamination; however, several different wipe sampling methods are currently being used. When the results of one study are compared with those of other studies, it is important to understand the effect of sampling parameters on the collection of contaminants from surfaces. A review of the literature addressing the subject of wipe sampling revealed that while several authors were concerned with parameters such as the contact time and contact pressure, no information was provided on the effect of these parameters on the collection of wipe samples. This study examines the effect of contact time, contact pressure, and surface concentration on the transfer (collection) of oil from contaminated surfaces to wipe sample media. An exposure jig was designed and built that allowed contact time, contact pressure, and surface concentration to be varied individually. This jig was used to test the effect of these parameters on the mass of oil transferred to Whatman #3 and Whatman #50 filter papers. A factorial study was designed in which the effect of three contact times, three contact pressures, and three surface concentrations could be investigated. The results of this study demonstrated that increasing either the contact time or contact pressure increased the transfer of oil to the filter papers. The difference in the mass of oil transferred was not statistically significant when contact time was increased from 10 to 20 minutes or when contact pressure was increased from 0.18 to 0.36 kg/cm2. Under identical test conditions a greater mass of oil was transferred to the Whatman #50 paper than to the Whatman #3 paper. These results indicate that although contact time and pressure have an effect on the transfer of oil to filter paper, the composition of the filter paper is equally important. Therefore, in the development of a standard wipe sampling method and in the field application of the method, a maximum contact time and contact pressure, as well as the type of sample collection medium to be used, should be specified. McArthur, B.R.; Lees, P.S.J.: Effect of Contact Time and Contact Pressure on the Transfer of Oil to Surface Sample Media.