But, other sources of carbon include the vial, the water, the swab itself (for swab sampling), and the air in the atmosphere where I prepare the sample. What I am really interested in measuring is the carbon removed from the surface. In a test sample analyzed by TOC, there are multiple sources of carbon. Now if I have a double beam spectrophotometer, the blank sample is measured at the same time as the test sample, and the instrument subtracts out the blank value.Ī second way a blank is used can be illustrated by the use of TOC (Total Organic Carbon) as the analytical technique.
This technique deals with impurities (for example) in the solvent I use for extraction of a swab. Once the zero is set, I then place my test sample in the spectrophotometer and measure the absorbance, which I can then attribute to the residue I want to measure. In one case (for example, in a spectrophotometric analysis) the blank is used to set a “zero” point for instrument output. As I generally use the term, a blank is a sample for which the measured value is subtracted from a test sample to determine the analyte in the test sample due to the residue removed from the sampled surface.
It should be recognized that as long as a company clearly defines its terms in an appropriate document, and uses them consistently, then different uses may be acceptable.Īs used for analytical measurements for cleaning validation studies, the two terms “blanks” and “controls” are sometimes used interchangeably. This month we’ll cover the use of terms as used in the cleaning validation.
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