Rapid detection of 11 common drugs in domestic sewage by pulsed direct current electrospray ionization mass spectrometry

Drugs and their metabolites are ubiquitous in various environmental media， including water bodies， soil， sediment， and air. These substances pose significant risks to human and animal safety and have emerged as a new category of pollutants. Accurate detection of the content of drugs in the environmental matrix can not only timely and objectively grasp the usage status， spatial distribution characteristics and temporal change patterns of drugs in a certain area， but also precisely assess the impact of long-term low-level exposure on the ecological environment. Currently， monitoring domestic sewage has emerged as a significant tool for tracking drugs use in various countries globally. Data obtained from domestic sewage samples for drugs detection can provide an objective， real-time， accurate， and effective reflection of local drug use patterns. Mass spectrometry has the advantages such as high specificity， high sensitivity and high quantitation accuracy and is mostly used for the analysis of domestic sewage samples. However， laboratory mass spectrometry methods involve complicated and time-consuming sample preparation processes， along with stringent environmental requirements， making them impractical for on-site rapid analysis. Consequently， there is an immediate need for the development of detection methods that are broad-spectrum， rapid， and capable of high throughput. In recent years， direct ionization mass spectrometry technology has been widely applied in on-site rapid detection and analysis work due to its characteristics such as avoiding complex chromatographic separation processes， fast analysis speed， high matrix tolerance， the ability to directly ionize analytes in complex matrix samples， and no（or only very little） sample pretreatment required. Direct ionization mass spectrometry is now playing an essential role in scientific research， environmental monitoring and public security. Pulsed direct current electrospray ionization mass spectrometry（pulsed-DC-ESI-MS） is a portable detection platform， which can be used for the accurate， rapid， on-site， batch， and sensitive analysis of picoliter level samples. In this research， a novelty method of pulsed-DC-ESI-MS was developed to achieve rapid detection of 11 drugs in domestic sewage. The drugs analyzed include methamphetamine（MA）， amphetamine（AM）， 3，4-methylenedioxymethylamphetamine（MDMA）， 3，4-methylenedioxyamphetamine（MDA）， morphine（MOR）， 6-monoacetylmorphine（6-MAM）， ketamine（KET）， norketamine（NKET） cocaine（COC）， benzoylecgonine（BZE）， and codeine（COD）. The sewage samples were extracted using the Oasis PRiME MCX solid-phase extraction（SPE） column. The extraction solution was blowing to nearly dry with nitrogen and then redissolved with 200 μL methanol and vortex for 0.5 min. The redissolved sample solution was filtered through a 0.22 μm organic filter membrane and analyzed by pulsed-DC-ESI-MS. The methodological validation results indicated that the 11 drugs had a good linear relationship within their respective linear ranges. The correlation coefficients（<italic>r</italic>²） were all ≥0.998 6， the limits of detection（LODs） and quantification（LOQs） were 0.01‒0.5 μg/L and 0.05‒5 μg/L， respectively. At three spiked levels， the recoveries of 11 drugs ranged from 88.0% to 107.6%， the intra- and inter-day precisions were both ≤8.5%. This method has a fast detection speed， greatly improving the detection efficiency， and is suitable for the rapid detection and analysis of common drugs in domestic sewage.