Determination of Formate in Natural Waters by a Coupled Enzymatic/High-Performance Liquid Chromatographic Technique

Article abstract of DOI:10.1021/ac00168a004

An enzymatic method was developed to quantify formic acid in natural water samples at submicromolar concentrations.The method is based on the oxidation of formate by formate dehydrogenase with corresponding reduction of β-nicotinamide adenine dinucleotide (β-NAD⁺) to reduced β-NAD⁺ (β-NADH); β-NADH is quantified by reversed-phase high-performance liquid chromatograhy with fluorometric detection.An important feature of this method is that the enzymatic reaction occurs directly in aqueous media, even seawater, and does not require sample pretreatment other than sample filtration.The reaction proceeds at room temperature at a slightly alkaline pH (7.5-8.5) and is specific for formate with a detection limit of 0.5 μM (S/N = 4) for a 200-μL injection.The precision of the method was 4.6percent relative standard deviation (n = 6) for a 0.6 μM standard addition of formate to Sargasso seawater.Average recoveries of 2 μM additions of formate to seawater, porewater, or rain were 103, 103, and 87percent, respectively.Intercalibration with a Dionex ion chromatographic system showed an excellent agreement of 98percent.Concentrations of formate present in natural samples ranged from 0.2 to 0.8 μM for Biscayne Bay seawater, 0.4 to 10.0 μM for Miami rain, and 0.9 to 8.4 μM for Biscayne Bay sediment porewater.