Simple Methods for Sampling Process Tank Residues (LabX)

Mary Stellmack
Lab X – March 10, 2015

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Processing tanks may display residues on the tank surfaces after routine cleaning, typically appearing as faint whitish or dark stains that cannot be easily wiped off. In order to remove the residue without damaging the tank surface, it is necessary to identify the residue so that the correct solvent or cleaning method can be used. However, it can be challenging to obtain a large enough sample for analysis, due to the small amount of residue. For unambiguous identification of the residue, the sampling method should allow for complete removal of the residue from the sampling tool prior to analysis, without any attached material from the sampling tool.

Traditionally, white cotton or polyester swabs have been used as sampling tools, but they are not ideal because only a small amount of residue is transferred to the swab, the sample is difficult to remove from the swab for analysis, and light-colored residues cannot be seen on the white swabs. The purpose of this study was to investigate alternative sampling methods that would fulfill three objectives: 1) obtain a larger volume of residue than the swab method; 2) the residue should be easily removable from the sampling tool for micro-analysis; and 3) the sampling tool should not damage the tank surface.