 Chemical amplification

In analytical chemistry, chemical amplification uses a chemical reaction or reaction sequence to make a small analyte quantity easier to measure. The final measured species need not be the original analyte. IUPAC's classification includes both chemical multiplication reactions and other chemical means of increasing or facilitating the measured response.^[ref]

For an original ideal assay, suppose each analyte molecule initiates production of ten absorbing reporter molecules from added reagents. With complete conversion and the same final volume, a spectrophotometer sees ten times the reporter concentration that a one-reporter-per-analyte procedure would produce. Under the Beer-Lambert law, the corresponding reporter absorbance is ten times as large if the reporter and optical path are unchanged. This is a stipulated stoichiometric model, not a claim about a particular reagent system. The added material supplies the extra reporter molecules; chemical amplification does not create matter.

The analytical benefit depends on what else grows. An original pre-reaction sample containing a target contribution of two arbitrary amount units and a contaminant contribution of one unit gives signals 20 and 10 after tenfold amplification if both follow the same chemistry. The target-to-contaminant ratio remains 2. Increasing detector response is therefore different from improving chemical selectivity or the signal-to-noise ratio. A chemical amplification blank measures response produced without the intended analyte contribution, including contributions from reagents and handling.

A practical experiment compares reacted standards, reagent blanks and samples under matched reaction time, reagent amounts and final volume. Measurement calibration must include the reaction's actual gain and its variability. Increasing gain can make an otherwise weak signal measurable while also increasing sensitivity to contamination, incomplete chemical reaction or reagent depletion. A larger signal alone does not establish a lower limit of detection.