Simultaneous Determination of 9 Trace Common Nonsteroidal Drugs in Domestic Sewage by Liquid Chromatography Tandem Mass Spectrometry with Solid Phase Extraction

A method for the determination of 9 trace common nonsteroidal drugs, including trimethoprim, chlorpheniramine maleate, isopropyl antipyrine, antipyrine, phenacetin, diphenhydramine, mefenamic acid, diazepam, and ketoprofen, in domestic sewage was proposed by liquid chromatography tandem mass spectrometry (LC-MS/MS) with solid phase extraction. The sewage sample was filtered with 0.45 μm fiberglass filter membrane, and 1.0 L of water sample was collected. 2.5 g of disodium ethylenediaminetetraacetate (Na₂EDTA) was added, shaking for 5 min. The solution was passed through HLB solid phase extraction cartridge at 10 mL·min^-1, which was pre-activated with 5 mL of methanol and 5 mL of water, respectively. Elution was carried out with 5 mL of water and 5 mL of methanol, and the eluate was collected and blown to nearly dryness by nitrogen. The residue was reconstituted in 1.0 mL of 20% (volume fraction) methanol solution, and the solution was mixed by vortexing for 1 min, and passed through 0.2 μm filter membrane. Liquid chromatography separation was performed on a BEH C₁₈ column (100 mm×2.1 mm, 1.7 μm), with a mixture of acetonitrile solution containing 0.1% (volume fraction, the same below) formic acid and 0.1% formic acid solution at different volume ratios as mobile phase for gradient elution, and electrospray ion (ESI) in the positive multiple reaction monitoring (MRM) mode was adopted in MS analysis. Quantification was carried out by matrix spiked working curves. As shown by the results, linear relationships between values of the corresponding peak area and mass concentration of 9 nonsteroidal drugs were found in definite ranges, with detection limits (3S/N) in the range of 0.005-0.060 ng·L^-1. Recovery test was carried out according to the standard addition method, giving results in the range of 86.1%-107%, with RSDs (n=6) of the determined values in the range of 3.0%-7.4% for intra-day precision test and 3.8%-8.4% for inter-day precision test, respectively. This method was used for the analysis of 40 actual domestic sewage samples, and it was shown that 7 compounds including trimethoprim, chlorpheniramine maleate, antipyrine, diphenhydramine, isopropyl antipyrine, ketoprofen and diazepam were detected in domestic sewage, among which the detection rate of diazepam was 100%, and the detection amount of antipyrine was the highest, up to 117.46 ng·L^-1.