SPECTROPHOTOMETERS Application note: A09-008A Quantitative determination of glucose in an energy drink, apple juice and wine

Introduction The rate of an enzyme reaction varies with substrate concentration; therefore this can be used to determine the amount of substrate present. Measurement of such a reaction requires the determination of the amount of product produced or the disappearance of substrate consumed. With many assays this cannot always be done directly, therefore the reaction may be coupled to a second enzyme that can convert one of the products into a measurable substance. One such example is the coupling of reactions to dehydrogenases that use nicotinamide adenine dinucleotide (NAD + ) or the reduced form, NADH, as coenzymes. NADH can be readily measured in a spectrophotometer at 340nm or by fluorimetry with excitation at 340nm and emission at 460nm.