Engineer Chemical Analysis key terms

A quantified range around a reported result that is expected to contain the true value, combining contributions from sampling, calibration, repeatability, and bias. It is expressed as an expanded uncertainty with a stated coverage factor.

The property of a result whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons each with stated uncertainty.

A reference material accompanied by a certificate giving one or more property values with uncertainties and stating how they were established. It is used to check bias, calibrate instruments, and demonstrate traceability.

The documented process of proving that an analytical procedure is suitable for its intended purpose by evaluating performance characteristics such as selectivity, linearity, accuracy, precision, range, detection limit, and robustness.

The smallest analyte amount or concentration that can be reliably distinguished from blank noise at a stated confidence level, typically three times the standard deviation of blank measurements divided by the calibration slope.

The lowest analyte level that can be determined with acceptable precision and accuracy, commonly taken as ten times the blank standard deviation divided by the calibration slope and confirmed experimentally.

A plot of instrument response versus known analyte concentration, used to convert sample signals into concentrations. Its slope, intercept, and residual pattern reveal sensitivity, bias, and the linear working range.

A calibration strategy in which known analyte increments are added to portions of the sample itself, so matrix effects cancel. The response is extrapolated back to zero added amount to find the original concentration.

A substance added at constant amount to all standards and samples to correct for variations in injection volume, ionization efficiency, or detector response. It should behave like the analyte but be resolved from it.

A change in analyte response caused by other components of the sample, such as suppression or enhancement of ionization, altered volatility, or overlapping background. It is assessed by comparing solvent and matrix-matched standards.

A portion of material that retains the composition of the whole lot for the properties of interest. Obtaining one requires a defined sampling plan, correct sampling tools, and enough increments to cover heterogeneity.

A documented scheme specifying sampling points, number and size of increments, tools, containers, preservation, holding times, and acceptance criteria. It ensures that collected portions are defensible and suitable for the analytical method.

A sample made by combining several increments or subsamples, either in equal or weighted proportions, to give an average composition of a lot. It reduces the influence of local heterogeneity.

A chronological record documenting who collected, handled, transported, and stored a sample, with dates, times, and signatures. It preserves legal defensibility and shows that no tampering or mix-up occurred.

The maximum permitted interval between sample collection and analysis, set to prevent loss or change of the analyte through volatilization, degradation, adsorption, or biological action. It depends on preservation and container type.

Treatment applied after collection, such as acidification, refrigeration, or addition of a biocide, to keep analyte concentrations stable until analysis. The chosen treatment must not interfere with the analytical method.

Mixing or grinding a sample so that any subsample taken has the same composition as the bulk. It is essential before weighing or extracting, especially for solids and heterogeneous materials.

Selecting a smaller portion from a laboratory sample for analysis. The portion must remain representative, so particle size reduction and thorough mixing usually precede it, and the mass taken must satisfy method requirements.

A highly pure, stable substance used to prepare solutions of accurately known concentration or to standardize other solutions. It should be non-hygroscopic, readily dried, and react stoichiometrically and completely.

A volumetric procedure in which a reagent of known concentration is added until it reacts completely with a measured amount of analyte. The volume consumed, read from a burette, gives the analyte amount.

The theoretical point in a titration at which the amount of added titrant exactly matches the stoichiometric amount of analyte. It is a property of the chemistry, not of the indicator used to observe it.

The observable change, such as a colour shift or a jump in a measured signal, that signals the completion of a titration. It is chosen to fall as close as possible to the true equivalence point.

A quantitative method in which the analyte is converted to a pure, stable solid of known composition, collected on a filter, dried or ignited, and weighed. The mass relates to analyte amount by stoichiometry.

The relationship stating that absorbance is proportional to analyte concentration, path length, and molar absorptivity. Deviations occur at high concentration, with polychromatic light, or when the analyte associates or dissociates.

A wavelength-specific constant describing how strongly a species absorbs light at a given wavelength per unit concentration and path length. It determines the sensitivity of a spectrophotometric measurement.

A functional group or structural feature, such as a conjugated double-bond system or a carbonyl group, that absorbs ultraviolet or visible radiation. Its environment shifts the position and intensity of absorption bands.

A movement of an absorption band to longer wavelength, often caused by conjugation, substituent effects, or a more polar solvent. The opposite movement to shorter wavelength is called a hypsochromic shift.

Describing a vibrational mode that produces a change in dipole moment and therefore absorbs infrared radiation. Modes that change only polarizability are Raman active instead, so the two techniques are complementary.

Unwanted radiation reaching the detector at wavelengths outside the selected band, causing negative absorbance errors and loss of linearity at high absorbance. It is a key performance check for spectrophotometers.

A line source in atomic absorption spectroscopy whose cathode is made of or coated with the element of interest, emitting its sharp resonance lines. It provides the element-specific radiation absorbed by atoms in the flame or furnace.

The process of converting analyte in a sample into free ground-state atoms, achieved by flame, graphite furnace, or plasma. Its efficiency strongly influences sensitivity and susceptibility to matrix interference.

A reagent added in graphite furnace atomic absorption to stabilize the analyte to higher ashing temperatures or to volatilize interfering matrix components. Common examples include magnesium nitrate and palladium.

A technique that subtracts non-analyte signal caused by scattering or molecular absorption in atomic spectroscopy. Methods include deuterium lamp correction, Zeeman splitting, and simultaneous measurement of a nearby wavelength.

A reduction in analyte signal in mass spectrometry or chromatography caused by co-eluting matrix components competing for ionization or occupying active sites. It is diagnosed by post-column infusion or standard addition.

The elapsed time between injection and the maximum of a chromatographic peak. It is used for qualitative identification when compared with a standard run under identical conditions, and it must be reproducible.

A measure of chromatographic separation between two peaks, calculated from the difference in retention times divided by the average peak width. A value near 1.5 indicates baseline separation for symmetric peaks.

A number describing column efficiency, derived from retention time and peak width. More plates mean narrower peaks and better separation, though the plate count alone does not guarantee adequate resolution.

The volume in a chromatographic system, including injector, tubing, and connections, where no stationary phase exists. Excessive dead volume broadens peaks and can cause tailing or loss of resolution.

An atmospheric-pressure ionization technique for liquid samples in which a high voltage creates charged droplets that evaporate to release ions. It is suited to polar and macromolecular analytes and is prone to ion suppression.

The relationship linking electrode potential to the activities of species in a redox half-reaction. It underpins potentiometry and explains how an ion-selective electrode response depends on analyte activity.

A sensor whose membrane potential responds selectively to the activity of one ion in solution. Its response is described by the Nernst equation and characterized by slope, detection limit, and selectivity coefficients.

An electrode with a stable, known potential, such as silver/silver chloride, used as the fixed half-cell against which the indicator or working electrode is measured. Its junction must be kept clean and filled.

A thermal technique that records sample mass change as temperature is increased at a controlled rate. It reveals decomposition steps, moisture, and residue content, and requires careful buoyancy and baseline correction.

A thermal method measuring the heat flow difference between a sample and a reference as temperature changes. It detects transitions such as melting, glass transition, crystallization, and polymorphic conversion.

The ratio of analyte signal to the random fluctuation of the baseline. It governs detection capability and is used to estimate detection limits, with a ratio of about three often taken as the detection threshold.

The fraction of a known amount of analyte added to a sample that is measured by the method. Low or high recovery indicates matrix suppression, losses during preparation, or calibration bias.

The completeness, consistency, and accuracy of records throughout the data lifecycle, supported by audit trails, access controls, and secure retention. It ensures that reported results faithfully reflect what was measured.

A secure, computer-generated, time-stamped record of creation, modification, or deletion of data, capturing who did what and why. It allows reconstruction of the analytical record during inspection or investigation.

A ventilated enclosure that draws air away from the operator to control exposure to vapours, fumes, and aerosols. Its face velocity and sash position must be verified, and it is not suitable for biohazards or perchloric acid work.

A document summarizing a chemical's hazards, including toxicity, flammability, reactivity, exposure limits, and required protective measures. It is a primary source for risk assessment and safe handling instructions.

A sealed enclosure with attached gloves that lets an operator manipulate materials in a controlled atmosphere, excluding air and moisture or containing hazardous substances. It is used for air-sensitive reagents and highly toxic compounds.

A sealed vessel containing a drying agent that maintains a low-humidity atmosphere for cooling and storing hygroscopic solids, weighing bottles, and reference materials before weighing.

A substance or signal that changes observably at a chosen point in a titration, such as a pH indicator whose colour depends on protonation. Its transition range should bracket the equivalence point.

A solution whose concentration is accurately known, prepared either from a primary standard or by standardization against one. Its concentration must be corrected for temperature and periodically rechecked.

Introduction of analyte or interference from sampling vessels, caps, or preservatives, causing false positives or biased results. It is controlled by blank containers, material selection, and cleaning protocols.

A mathematical operation converting an interferogram from the time or path domain into a frequency or wavenumber spectrum. It enables rapid, high-throughput infrared and mass spectrometric measurements with high resolution.