Determination of 2,4-dichlorophenoxyacetic acid (2,4-D) in human urine with mass selective detection

Method development and validation studies have been completed on an assay that will allow the determination of 2,4-dichlorophenoxyacetic acid (2,4-D) in human urine. The accurate determination of 2,4-D in urine is an important factor in monitoring worker and population exposure. These studies successfully validated a method for the detection of 2,4-D in urine at a limit of quantitation (LOQ) of 5.00 ppb (parts per billion) using gas chromatography with mass selective detection (GC/MSD). The first study involved the determination of 2,4-D in control human urine and urine samples fortified with 2,4-D. Due to chromatographic interference, a second study was conducted using 14C-2,4-D to verify the recoverability of 2,4-D from human urine at low levels using the GC/MSD method. The second study supports the results of the original data. The 2,4-D was extracted from human urine using a procedure involving hydrolysis using potassium hydroxide, followed by a liquid-liquid extraction into methylene chloride. The extracted samples were derivatized with diazomethane. The methylated fraction was analyzed by GC/MSD. Quantitation was made by comparison to methylated reference standards of 2,4-D. Aliquots fortified at 5-, 50-, and 500-ppb levels were analyzed. The overall mean recovery for all fortified samples was 90.3% with a relative standard deviation of 14.31%.