Measurement & Lab Testing

This page collects the measurement and laboratory terms that appear on meter displays, analysis reports and buyer specifications. Each entry explains what the term means and what the figure it refers to actually describes.

aflatoxin

A family of mycotoxins produced mainly by moulds of the genus Aspergillus, typically on plant material that has been held warm and damp. Laboratories usually report the individual forms, commonly labelled B1, B2, G1 and G2, together with a combined total, each measured as a concentration per unit of sample weight.

Certificate of Analysis (COA)

A results sheet issued by a laboratory for one specific sample or batch. It identifies the material tested, the sample reference, the analytical methods used and the value measured for each parameter examined. A COA reports what that laboratory found on that sample, so it is a record of measurement rather than a statement covering a whole product line.

colony forming unit (CFU)

The counting unit used in microbial analysis. A prepared sample is spread on growth medium and each visible colony that develops is taken to have grown from one viable cell or cluster of cells, so results are reported as colony forming units per gram or per millilitre. It counts organisms able to grow, not total cells.

electrical conductivity (EC)

A measure of how readily a solution carries an electric current, which rises as more dissolved mineral salts are present. Growers read it from a handheld or inline meter, usually in millisiemens per centimetre or microsiemens per centimetre, to describe the overall strength of a nutrient solution or the salt level held in a substrate.

foreign matter

Anything present in a sample that is not the plant material the sample is supposed to consist of, such as soil, stones, insect fragments, hair, packaging debris or parts of a different plant. It is assessed by physical examination and sieving rather than by instrument, and reported as a proportion of sample weight.

Gas Chromatography-Mass Spectrometry (GC-MS)

An analytical technique combining gas chromatography, which separates the compounds in a vaporised sample, with mass spectrometry, which identifies each one from the mass of its fragments. The pairing is used for volatile and semi-volatile substances, including solvent residues and many crop protection compounds.

heavy metals (Pb, As, Cd, Hg)

In analytical reporting, the group of metallic and metalloid elements checked in plant material and in growing inputs, most often lead (Pb), arsenic (As), cadmium (Cd) and mercury (Hg). They can enter a crop from soil, irrigation water, fertiliser inputs or processing equipment, and are measured as a concentration in the sample rather than seen.

High-Performance Liquid Chromatography (HPLC)

An analytical technique that separates the compounds in a liquid sample by pumping it under pressure through a packed column, so that each compound leaves the column at its own characteristic time and can be measured. It is used for constituents that are stable in solution and do not need to be turned into vapour.

homogeneity testing

Analysis that checks whether a batch is uniform, by taking several samples from different points in the lot and comparing the results. Where the figures agree, a single sample can reasonably stand for the batch; where they differ, the batch is mixed and one result describes only the portion that was sampled.

Liquid Chromatography-Mass Spectrometry (LC-MS)

An analytical technique combining liquid chromatography, which separates the compounds in a liquid sample, with mass spectrometry, which identifies each one from the mass of its fragments. It suits substances that are not easily vaporised and is widely used for residue screening at very low concentrations.

microbial testing

Laboratory analysis that counts or identifies the micro-organisms present in a sample, such as bacteria, yeasts and moulds. The sample is prepared and cultured, or analysed by molecular methods, and the result is reported per unit of sample weight. Different parameters answer different questions, so one report normally lists several separate microbial figures.

moisture content

The proportion of a sample's weight that is water, found by weighing the material, drying it under defined conditions and weighing it again. It answers how much water is present in total, while water activity answers how much of that water is available; dried goods are often described by both figures together.

mycotoxin

A toxic compound produced by certain moulds as they grow on plant material. Mycotoxins are chemical substances rather than living organisms, so they remain after the mould that made them has died, and they are measured by chemical analysis rather than by a microbial count. Different moulds produce different mycotoxins.

ochratoxin

A mycotoxin produced by certain Aspergillus and Penicillium moulds growing on stored plant material, with the form called ochratoxin A the one usually analysed. Because it develops during storage rather than in the field, it is commonly tested alongside the aflatoxins on dried material within the same analytical panel.

pesticide screening

Laboratory analysis that looks for residues of crop protection products in a sample. The laboratory works from a defined list of compounds, so a screen reports only the substances on that list; anything applied that is not on the panel will not appear. Results are usually expressed as a concentration per unit of sample weight.

potency testing

Laboratory analysis that measures how much of a named active constituent a sample contains, usually reported as a percentage of dry weight or in milligrams per gram. The figure describes the particular sample analysed, so results vary between batches, between individual plants and between the different plant parts submitted for testing.

residual solvents

Traces of the solvents used during an extraction or purification step that remain in the finished material. They are measured by chemical analysis and reported as a concentration per unit of weight for each named solvent. The parameter applies to processed extracts; unprocessed dried plant material is not normally screened for it.

total aerobic count (TAC / TAMC)

A microbial parameter reporting the number of bacteria able to grow in the presence of oxygen that were recovered from a sample, expressed in colony forming units per gram. It is a broad indicator of the overall bacterial load carried by the material, and it does not identify which species are present. Pharmacopoeial monographs call the same parameter total aerobic microbial count (TAMC), so a laboratory report may carry either abbreviation for it.

total dissolved solids (TDS)

An expression of how much dissolved material a solution contains, reported in parts per million or milligrams per litre. Most grower meters do not weigh the solids directly; they measure electrical conductivity and convert it using a fixed factor, and because that factor differs between meter standards the same solution can read differently on two devices.

total yeast and mold (TYM)

A microbial parameter reporting the combined number of yeasts and moulds recovered from a sample, expressed in colony forming units per gram. It reflects the fungal load on the material as a whole and does not separate harmless field fungi from species that produce toxins; identifying particular organisms needs its own analysis.

UV-Visible Spectroscopy (UV-Vis)

An analytical technique that measures how much ultraviolet and visible light a sample absorbs at given wavelengths. The amount absorbed relates to the concentration of the absorbing compounds present. It is quicker and less costly than chromatography but cannot separate a mixture, so it reports a combined response rather than individual compounds.

water activity (aw)

The ratio of the water vapour pressure of a material to that of pure water at the same temperature, expressed on a scale from 0 to 1. It describes how much of the water present is free and available to micro-organisms, which is not the same thing as how much water the material contains in total.