= 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.<Classification and Use of Terms for Amplification and Related Reactions by D. T. Burns and others>[1999 Recommendations, p.1332, Introduction and classification scheme.]{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>.
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