Blank value

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Blank value is a technical term from the field of analytical chemistry and measurement technology . The blank value corresponds to the measured value ( measurement signal ) of a measuring device (a measuring device) if the measured variable being examined has the value zero or is not available.

The blank value should actually also result in a measured value of zero. The measured value (signal value) of a blank sample deviates from zero due to random and / or systematic errors (due to influences from the sample, the device or the process). The blank value must therefore be determined and subtracted from the measured values ​​of the actual samples (or taken into account when calculating the results).

The standard deviation of the blank value is often used to calculate the detection limit and the quantification limit of measurement procedures and analytical methods.

For determinations in analytical chemistry , the blank value is made up of several components:

  • Blank value of the device: in many cases the measuring device delivers a (mostly low) signal even if there is no sample
  • Reagent blank value: the measured value of a blank sample that has gone through the entire analytical process and contains all the reagents described in the test specification , but no portion of the analyte being examined .
  • Sample blank value: Measurement value of a blank sample that not only contains the reagents according to the test method, but also the matrix of the sample without the component (s) to be determined ( analysis sample without analyte). The sample blank can also contain internal standards .

Blank values ​​are mostly based on systematic analysis errors and can e.g. B. have the following causes:

  • Contaminated reagents contain small amounts of the component to be determined
  • Poor selectivity : Components of the sample matrix interfere with the measurement by behaving similarly to the component to be determined (similar reactions of analyte and matrix with the intended reagents)
  • Contamination of the test equipment, thereby z. B. increased absorption in photometry .
  • Decomposition of reagents due to poor or too long storage (aging)

Individual evidence

  1. S. Ebel and HJ Roth (editors): Lexikon der Pharmazie , Georg Thieme Verlag, 1987, p. 99, ISBN 3-13-672201-9 .
  2. S. Ebel and HJ Roth (editors): Lexikon der Pharmazie , Georg Thieme Verlag, 1987, pp. 35–36, ISBN 3-13-672201-9 .