Quantitation

Quantitation is the process of determining the amount or concentration of an analyte in a sample. It is distinguished from qualitative measurement by producing a numeric value that reflects quantity, not merely presence or absence. Quantitation underpins decisions in fields such as chemistry, biology, medicine, and environmental science and can aim for absolute or relative quantities.

In analytical chemistry, common strategies include external calibration curves built from known standards, internal standards added to correct for losses or variability, and methods such as standard addition to compensate for matrix effects. Modern quantitation often relies on instrument-specific approaches, including isotope-dilution mass spectrometry for high-precision absolute results. Key performance characteristics include the linear dynamic range, limits of detection and quantitation, accuracy, precision, bias, and measurement uncertainty. Results are usually reported with associated uncertainty and traceability to reference materials when required.

In biomedicine and molecular sciences, quantitation covers gene expression and biomolecule abundance. Techniques include real-time quantitative PCR and digital PCR for nucleic acids, sequencing-based counts normalized to library size (for example TPM or FPKM), and various mass spectrometry approaches for proteins and metabolites. Label-free quantitation and isotope-labeling methods (such as SILAC, TMT, or iTRAQ) are used to compare relative abundances across samples.

Quality assurance, validation, and adherence to standards are important to ensure comparability and regulatory acceptability. Uncertainty, matrix effects, instrument drift, and sampling biases are common sources of error that must be controlled through calibration, controls, and reanalysis.

Applications span clinical diagnostics, pharmacokinetics, environmental monitoring, food safety, and research across life and physical sciences.