This test method covers the enzymatic determination of citrate in both liquid and solid synthetic detergents. The test method is applicable to most detergents containing citrate at a minimum concentration of approximately 5 %. The apparatus to be used in the determination of citrate shall includes interval timer, micropipet, and spectrophotometer. An enzyme system that is based upon the selective cleavage of citrate by citrate lyase (citrate oxaloacetate-lyase; EC 4.1.3.6) shall be employed. One of the products, oxaloacetate, shall be reduced to malate by malic dehydrogenase (L-malate: NAD oxidoreductase; EC 1.1.1.37) with the simultaneous oxidation of reduced (beta)-nicotinamide adenine dinucleotide to (beta)-nicotinamide adenine dinucleotide, oxidized form. The course of the reaction shall be measured spectrophotometrically. The decrease in absorbance at 340 nm caused by the formation of (beta)-nicotinamide adenine dinucleotide, oxidized form, is directly proportional to the concentration of citrate.

1.1 This test method covers the enzymatic determination of citrate in both liquid and solid synthetic detergents. The test method is applicable to most detergents containing citrate at a minimum concentration of approximately 5 % (1-8).

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Material Safety Data Sheets are available for reagents and materials. Review them for hazards prior to usage.