Comparison of solid phase extraction techniques for herbicides

Solid phase extraction (SPE) procedures were used to determine the recoveries of herbicides typically used in containerized ornamental plant production from water samples. Recoveries from C18 cartridges and disks were compared for each of 12 herbicides with variations in elution solvent and volume of elution solvent tested. Recoveries for nine of the herbicides from the cartridges and disks using acetone as an elution solvent were not affected by SPE matrix. Fluazifop recovery was greater with the disks, while napropamide and oxadiazon recoveries were greater with cartridges. Both cartridges and disks yielded low recoveries (23 to 47%) of benefin and prodiamine. Changing the elution solvent from acetone to acetonitrile resulted in 10% improvement for the recovery of benefin and a three- to four-fold increase in recovery of prodiamine. Acetonitrile decreased recoveries of napropamide, oryzalin, oxadiazon, oxyfluorfen, and pendimethalin from cartridges. For the disks, oxyfluorfen, prodiamine, and trifluralin had increased recovery, while fluazifop, oxadiazon, and simazine had decreased recovery with acetonitrile as the elution solvent. Increasing the amount of acetone eluting solvent increased the recovery of prodiamine and oxyfluorfen while decreasing the recovery of fluazifop, pendimethalin, simazine, and trifluralin. Binding capacities of oryzalin on cartridges and disks averaged 13.2 and 7.8 mg, respectively. The advantage of the disk lies in the greater volume of water that can be processed, while the higher cost and greater variability are disadvantages. Cartridge extraction yielded good recoveries with lower standard deviations, and used less organic solvent. Selection of an SPE extraction method depends upon the herbicides under evaluation, expected levels, and the water volume being processed. Both SPE techniques offer advantages over traditional liquid-liquid extraction methods such as reduced requirements for organic solvent and sample preparation.