18. a quantitative measure of a chemical or substance with high correction
19. a substance added to standards and sample in a fixed and known amount
20. detection of the concentration of reagent or interested chemical from its reaction with known concentration of reagent
21. a substance whose purity and stability are used to calibrate other standards
22. treatment of a sample with a reagent to prevent interruption of other chemicals in the sample
23. a description of the practical steps involved in an analysis