The limit of analytical quantitation (LOQ), also sometimes referred to as the ‘limit of analytical determination’, is the lowest concentration of a pesticide residue in a defined matrix for which positive identification and quantitative measurement can be achieved using a specified method.
The limit of analytical quantitation is generally expected to be at the level of 0.05 milligrams per kilogram or less.
The method must be sufficiently sensitive to accommodate pesticides that have low acceptable daily intakes, (for example, an active constituent for which the LOQ is set at 0.002 milligrams per kilogram because the acceptable daily intake is 0.0002 milligrams per kilogram per day). However, the Australian Pesticides and Veterinary Medicines Authority recognises that some matrices may make it difficult to have the LOQ as low as 0.05 milligrams per kilogram (for example, hops).
Evaluation of data to decide on the limit of analytical quantitation
In practical terms, the LOQ is the lowest concentration at which quantitative recoveries can be achieved.
The word ‘quantitative’ in this context is defined as recoveries in the range of 70% to 120%. If substantial recovery data is available, a practical specification is defined as 80% of recovery values at the LOQ to be between 70% and 120%, and all recoveries at the LOQ to be between 60% and 130%.
Recoveries should also be determined at levels at which residues are likely to occur.