Interference (analytics)

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In analytical chemistry, interference is a systematic error in which the measurement signal is impaired by another component of the sample. If the ingredients of the sample are responsible for measurement problems, we speak of matrix effects instead .

Methods which serve to interference (even in classical wet chemistry disorder ) to eliminate or reduce to as interference suppression , in the quantitative analysis as a correction referred to. The exact procedure for interference suppression depends on the analysis technology used .

In addition to the substances to be determined, analytical samples contain a large number of accompanying substances (sample matrix), some of which are known and some are unknown. These can falsify results in a variety of ways. In qualitative analysis , components interfere with

  • show the same or similar behavior as the substances to be detected,
  • change their properties through chemical reactions ( precipitation , complex formation , redox or acid-base reaction ) with the substances to be detected and thus influence the detection or
  • cover the detection reaction due to another reaction or property.

In quantitative analysis, other phenomena such as the change in activity coefficients due to the sample matrix also play a role.

Examples

In neutral to basic solutions, carbonates interfere with the chloride detection with silver nitrate solution. With Ag + ions they also give a white precipitate that dissolves in ammonia, simulating chloride. Conversely, ammonium salts prevent precipitation under these conditions through the formation of ammonia and can thus lead to a false negative result. In both cases, interference is eliminated by prior heating with dilute nitric acid , whereby carbonate is expelled and ammonia is completely protonated.

Cadmium in the H 2 S group can be detected by precipitating a yellow sulfide precipitate after the other ions of the H 2 S group have been separated off. Even traces of other ions of the H 2 S group that have been carried over give deep brown to black precipitates which cover the yellow precipitate.

See also

Individual evidence

  1. ↑ Entry on interference in analysis . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.I03089 Version: 2.3.3.