QA

Analyte-

Substance being measured or analyzed.

Titrant-

Standard solution of known concentration added from a burette.

Standard solution-

Solution with a known concentration.

Primary standard-

Highly pure, stable substance that can be weighed to prepare a solution of known concentration.

Calibration curve-

Signal measured for a series of known analyte concentrations, used to determine an unknown concentration.

Standard addition-

Add known quantities of the analyte to the unknown sample

Internal standard-

Add a known, constant amount of a different compound to standards and samples to help correct for measurement variation.

Back titration-

Add an excess of a known reagent to the analyte, then titrate the leftover reagent with a second standard solution.

Endpoint-

Point at which an observable indicator or instrument signals completion.

Equivalence point-

Point at which the reactants have been combined in the stoichiometric proportions required by the balanced reaction.

External standard/calibration curve:

Measure separate solutions of known analyte concentrations, then compare the unknown signal with the curve.

Standard addition:

Add more of the analyte itself to the unknown sample.

Internal standard:

Add a different reference species in a constant amount to standards and samples.

Sensitivity:

How much the measured signal changes as concentration changes. It is represented by the slope of the calibration curve.

Selectivity:

How well a method measures the analyte in the presence of other substances

Quality Assurance (QA)

System of procedures used to ensure analytical data are reliable, accurate, and precise.

Raw Data

Original experimental measurements collected directly from an experiment.

Treated Data

Concentration or amount obtained after applying calibration methods. 

Reported Data

Statistical summary of treated data (mean, standard deviation, confidence interval, etc.). 

Accuracy

How close a measured value is to the true value. 

Precision

How closely repeated measurements agree with one another. 

Selectivity

Ability of a method to measure an analyte in the presence of other substances.

Sensitivity

Ability of an analytical method to detect small changes in analyte concentration.

Specificity

Ability to measure only the analyte of interest without interference.

False Positive

Test indicates analyte is present when it is actually absent.

False Negative

Test indicates analyte is absent when it is actually present.

Method Validation

Process of proving an analytical method is suitable for its intended purpose.

Linearity

Ability of a method to produce results proportional to concentration.

Range

Concentration interval over which a method produces reliable results.

Robustness

Ability of a method to remain unaffected by small procedural variations.

Limit of Detection (LOD)

Lowest concentration that can be detected but not necessarily quantified

Lower Limit of Quantitation (LLOQ)

Lowest concentration that can be quantitatively measured with acceptable precision and accuracy. 

Calibration Curve

Graph relating instrument response to known analyte concentrations.

Standard Addition

Calibration technique where known amounts of analyte are added directly to the sample to account for matrix effects. 

Internal Standard

A different compound added at constant concentration to standards and samples to compensate for analysis variability

Matrix Effect

Interference caused by other components in the sample. (Implied by the use of standard addition.)

Spike Recovery

Percentage of a known added analyte recovered during analysis.