Pretreatment Methods Suitable for Comprehensive Non-Target Analysis of Dissolved Organic Matter In Urban River Water by High-Resolution LC/MS

Abstract

 In non-target LC/MS analysis, solid phase extraction (SPE) is often adopted for a sample pretreatment method, but recovery rate in SPE varies greatly depending on the samples and cartridges used, and some dissolved organic matter (DOM) are lost before LC/MS. In this study, we tried freeze drying (FD) and large volume injection of untreated samples(LVDI) and 4 SPE methods, namely, styrene divinylbenzene polymers, hydrophilic reversed phase polymers and activated carbon, mixed mode cation exchange polymers and anion exchange polymers, primary secondary amine and strong cation exchange, for urban river water at Omokage Bridge, Kanda River, Tokyo, Japan. We compared these six methods in terms of DOC recovery and the number of DOM detected by LC/MS. As results of experiments, two ion-exchange SPE methods showed significant organic leaching from the SPE cartridges and were not suitable for the non-target analysis. DOC recovery of FD were 82.1% to 92.9% and higher than those of SPE methods. Freeze dried samples (FD) detected about 8000 DOMs, which was twice as many DOMs as those detected in SPE samples. Among all DOM components detected by FD, LDVI and two SPE methods, more than half of them were detected by only single method. There was a clear difference in the interquartile range of LC retention times between different pretreatment methods. To choose a single sample pretreatment method, FD was the best suitable method because it had the highest DOC recovery rate and the highest detected number of DOM components. To accomplish further comprehensive analysis, combination of multiple pretreatment methods was also recomendable.