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 spectrophotometrical
ly. 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.
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.
