Glossary

Some terms have different definitions in different communities. We have attempted to use as widespread definitions as possible, preferably those that are used in ref 1 and ref 2.

  •  IS 

    Internal standard.

  • Accuracy

    Measurement result accuracy indicates its closeness to the true value.

  • Analytical run

    or simply run:

    Definition 1: A set of samples that are analysed in one batch, during short time. In LC and LC-MS this term typically refers to an automatized sequential analysis of a set of samples, calibrants and QC samples that have been loaded into autosampler.

    Definition 2 (defined by Clinical Laboratory Improvement Amendments (CLIA)): An interval (i.e., a period of time or series of measurements) within which the accuracy and precision of the measuring system is expected to be stable. In laboratory operations, control samples are analyzed during each analytical run to evaluate method performance, therefore the analytical run defines the interval (period of time or number of specimens) between evaluations of control results. Between quality control evaluations, events may occur causing the measurement process to be susceptible to variations that are important to detect.

  • AOAC
  • Bias

    Quantitative estimate of trueness, can be found as measured value difference from the reference value. 

  • CCα

    Decision limit: the concentration level, as determined by the method, at which there is probability α (usually defined as 0.05 or 5%) that a blank sample will give a signal at this level or higher. 

  • CCβ

    Detection capability:  the concentration level of the analyte in sample at which there is probability β (again usually defined as 0.05 or 5%) that the method will give a result lower than CCα, meaning that the analyte will be declared as undetected.

  • CRM

    Certified Reference Material

  • Dynamic range

    The range where the response changes when the analyte concentration is changed but the relationship may be non-linear. If the response is linear it can be specified as a dynamic linear range.

  • False negative

    Results where analyte is declared to be below LoD although it is not.

  • False positive

    Results where the analyte is declared to be present although actually it is below LoD.

  • FDA
  • Heteroscedasticity

    Difference of variance; describes the data where the standard deviation of the signal (y-value) depends on the concentration of the anaylte (x-value).

  • Homoscedasticity

    Homogeneity of variance; describes the data where the standard deviation of the signal (y-value) does not depend on the concentration of the anaylte (x-value).

  • Identity confirmation

    Providing evidence that the analytical signal registered during sample analysis is due to analyte and not any other (interfering) compound.

  • Instrumental LoD

    LoD estimated for the analysis instrument by measuring the analyte from pure solvent without any sample pretreatment.

  • Intermediate precision

    The precision obtained within a single laboratory over a longer period of time (generally at least several months).

  • Linearity

    Methods ability to obtain signals, which are directly proportional to the concentration of analyte in the sample.

  • Linear range

    Range of concentrations where the signals are directly proportional to the concentration of the analyte in the sample.

  • LoD

    Limit of detection: the smallest amount or concentration of analyte in the test sample that can be reliably distinguished from zero.

  • LoQ

    Limit of quantitation: the lowest concentration of analyte that can be determined with an acceptable repeatability and trueness.

  • Measurement uncertainty

    Measurement uncertainty (or simply uncertainty) defines an interval around the measured value CMEASURED, where the true value CTRUE lies with some predefined probability. The measurement uncertainty U itself is the half-width of that interval and is always non-negative. This definition differs from the VIM [ref 6] definition (but does not contradict it) and we use it here as it is generally easier to understand and to relate to practice.

  • Method LoD

    LoD estimated by using matrix matched samples that are put through the whole analysis method (including the sample preparation).

  • MRL

    Maximum residue limit: the maximum allowed concentration limit set for the compound in certain matrices.

  • Precision

    Characterizes the closeness of agreement between the measured values obtained by replicate measurements on the same or similar objects under specified conditions.

  • Prodrug

    A prodrug is a medication or compound that, after administration, is metabolized (i.e., converted within the body) into a pharmacologically active drug (e.g. by ester bond cleavage within prodrug). Inactive prodrugs are pharmacologically inactive medications that are metabolized into an active form within the body.

  • Quasimolecular ion

    Ion formed by protonation or deprotonation of a molecule [ref 52]. Note that another IUPAC terminology source [ref 57] discourages usage of this term and instead, recommends terms "anionized, cationized, deprotonated and protonated molecule".

  • Recovery

    The recovery of an analyte in an assay is the detector response obtained from an amount of the analyte added to and extracted from the biological matrix, compared to the detector response obtained for the true concentration of the analyte in solvent. Recovery pertains to the extraction efficiency of an analytical method within the limits of variability.

  • Repeatability

    Expresses the closeness of the results obtained with the same sample using the same measurement procedure, same operators, same measuring system, same operating conditions and same location over a short period of time.

  • Reproducibility

    Expresses the precision between measurement results obtained at different laboratories.

  • Residual

    The difference between experimental signal and signal calculated according to the calibration function.

  • Robustness

    A parameter used to evaluate constancy of the results to variations of the internal factors of the method such as sample preparation, mobile phase composition, mobile phase flow rate, injection volume, column temperature etc.

  • Ruggedness

    A parameter used to evaluate constancy of the results when external factors such as analyst, laboratory, instrument, reagents and days are varied.

  • Run

    See: analytical run

  • Scedasticity

    The distribution of error terms.

  • Selectivity

    The extent to which other substances interfere with the determination of a substance according to a given procedure.

  • Sensitivity

    The change in instrument response, which corresponds to a change in the measured quantity; the gradient of the response curve.

  • Stability

    Stability (ST%) characterizes the change in the analyte content in the given matrix under the specific conditions and over the period of time.

  • Trueness

    Closeness of agreement between the average of an infinite number of replicate measured quantity values and a reference quantity value.

  • Working range

    The working range is the range where the method gives results with acceptable uncertainty. Working range can be wider than linear range.