Calibration Curve
Definition
In RIA, a set of standards containing known concentrations of unlabelled analyte that are run alongside test samples. Bound radioactivity is measured for each standard and plotted against concentration to generate a dose-response curve. Unknown sample concentrations are interpolated from this curve. The curve is characteristically sigmoidal when plotted on a log-concentration axis.
- Analytical acceptance threshold
- R² above 0.995 over the working range
- Standard count
- Five to seven per curve
- Radiocarbon reference dataset
- IntCal20
Common questions
How do you know a calibration curve is reliable?+
In analytical work, the curve must have an R² value above 0.995 across your working range. This tells you the instrument's response follows the expected pattern tightly enough to trust concentration readings from unknown samples.
Why is the radiocarbon calibration curve wiggly instead of straight?+
The curve reflects how 14C levels have varied in Earth's atmosphere over time. Flat or wiggly sections mean radiocarbon measurements cluster at the same calendar age range, so you cannot pinpoint the date as precisely during those periods.
How many standards do you need to build a calibration curve?+
Five to seven standards, spread across the range of concentrations you expect to encounter in your cases.
Related terms
- AMS Radiocarbon Dating
- Accelerator Mass Spectrometry measurement of the ratio of carbon-14 to carbon-12 in a sample. It requires milligram-scale samples and produces a raw...
- Bomb-Pulse Dating
- Use of the post-1952 atmospheric 14C spike, produced by nuclear weapons testing, to date biological tissues formed since 1950. Because the spike...
- Bracketing Standards
- Calibration standards or quality control samples injected before, during and after a batch of case samples. They track instrument drift through the...
- Certified Reference Material (CRM)
- A sample with one or more analyte concentrations established by an accredited body and traceable to a national metrology institute. NIST SRM...
- Chemiluminescent Immunoassay (CLIA)
- A non-radioactive immunoassay that uses enzyme-catalysed chemiluminescent reactions to generate the detection signal. CLIA instruments measure light output in relative light units....
- Competitive Binding Assay
- An immunoassay format in which labelled and unlabelled forms of the same analyte compete for a fixed, limiting number of antibody binding...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Dendrochronology
- The science of dating by tree-ring sequences. Each annual ring encodes the growing conditions of that year; matching ring patterns to a...
- Extraction
- The first step in sample preparation. The analyte is pulled out of its original matrix (blood, urine, viscera, soil, paint chip) into...
- Internal Standard (IS)
- A compound chemically near-identical to the analyte, often a deuterated isotopologue (d3-morphine, d5-EDDP, d5-alprazolam, pyrene-d10), spiked into every sample at a known...
- Iodine-125 (125I)
- The radioisotope most commonly used in RIA. It emits gamma radiation, has a half-life of approximately 60 days, and can be covalently...
- Limit of Detection (LOD) and Limit of Quantitation (LOQ)
- LOD is the lowest concentration the instrument can reliably distinguish from blank, defined as three times the standard deviation of the blank...
Explained in these topics
- Radiocarbon and Other Dating MethodsA dataset, currently IntCal20, that maps raw radiocarbon ages onto calendar years by comparing 14C measurements from known-age tree rings, corals, and speleoth...
- Radioimmunoassay: Principles, Uses, and DeclineIn RIA, a set of standards containing known concentrations of unlabelled analyte that are run alongside test samples. Bound radioactivity is measured for each...
- Sample Preparation, Purification and Instrument CalibrationA plot of instrument response (peak area, absorbance, intensity) against analyte concentration, built from five to seven standards spanning the expected case r...