Journal of Chromatography A, 1389 (2015) 76–84 Contents lists available at ScienceDirect Journal of Chromatography A jo ur nal ho me pag e: www.elsevier.com/locate/chroma The role of methanol addition to water samples in reducing analyte adsorption and matrix effects in liquid chromatography–tandem mass spectrometry Wei Li a , Yucan Liu a , Jinming Duan a,b,∗ , Christopher P. Saint b , Dennis Mulcahy b a Key Laboratory of Northwest Water Resources, Environment and Ecology, MOE, Xi’an University of Architecture and Technology, 13 Yanta Road, Xi’an 710055, China b Centre for Water Management and Reuse, School of Natural and Built Environments, University of South Australia, Mawson Lakes Campus, SA 5095, Australia a r t i c l e i n f o Article history: Received 7 November 2014 Received in revised form 10 February 2015 Accepted 14 February 2015 Available online 23 February 2015 Keywords: Adsorption effect Matrix effect LC–MS/MS Surface water a b s t r a c t Liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis coupled simply with water filtering before injection has proven to be a simple, economic and time-saving method for analyzing trace-level organic pollutants in aqueous environments. However, the linearity, precision and detection limits of such methods for late-eluting analytes were found to be much poorer than for early-eluting ones due to adsorption of the analytes in the operating system, such as sample vial, flow path and sample loop, creating problems in quantitative analysis. Addition of methanol (MeOH) into water samples as a modifier was shown to be effective in alleviating or even eliminating the negative effect on signal intensity for the late-eluting analytes and at the same time being able to reduce certain matrix effects for real water samples. Based on the maximum detection signal intensity obtained on desorption of the analytes with MeOH addition, the ratio of the detection signal intensity without addition of MeOH to the maximum intensity can be used to evaluate the effectiveness of methanol addition. Accordingly, the values of <50%, 50–80%, 80–120% could be used to indicate strong, medium and no effects, respectively. Based on this concept, an external matrix-matched calibration method with the addition of MeOH has been successfully established for analyzing fifteen pesticides with diverse physico-chemical properties in surface and groundwater with good linearity (r 2 : 0.9929–0.9996), precision (intra-day relative standard deviation (RSD): 1.4–10.7%, inter-day RSD: 1.5–9.4%), accuracy (76.9–126.7%) and low limits of detection (0.003–0.028 g/L). © 2015 Elsevier B.V. All rights reserved. 1. Introduction Liquid chromatography with tandem mass spectrometry (LC–MS/MS) in the multiple reaction monitoring (MRM) mode can provide high selectivity, which makes it possible to inject water samples after only a simple sample pretreatment, such as syringe membrane filtering [1–4]. However, this process may adversely affect detection signal intensity caused by matrix effects and ana- lytes adsorption. Matrix effects are believed to be one of the main issues affect- ing quantitative analysis in mass spectrometry (MS), which are ∗ Corresponding author at: School of Municipal & Environmental Engineering, Xi’an University of Architecture and Technology, 13 Yanta Road, Xi’an 710055, China. Tel.: +86 029 82201354; mobile: +86 15802980070. E-mail address: jinmingduan@xauat.edu.cn (J. Duan). defined as the combined negative effects of all components other than the analytes in samples on the quantitative analysis [5]. Matrix effects by different matrix components have been stud- ied extensively, and are generally thought to be caused by the matrix components being co-eluted with target analytes. This may suppress ionization in electrospray ionization (ESI) processes [6,7]. In the case of membrane filtering pretreatment, matrix effects can hardly be avoided in the LC–MS/MS since complex matrix components (i.e. inorganic ions and low molecular weight organic substances) cannot be removed from the sample solutions [1,3,8]. A comparative analysis between the peak area of an analyte in pure solvent standard solution and that in matrix-spiked standard solution was commonly used to evaluate such matrix effects [9]. Several methods for alleviating or eliminating the matrix effects have been proposed and proven to be successful, including appli- cation of matrix-matched standards, a standard addition method, http://dx.doi.org/10.1016/j.chroma.2015.02.044 0021-9673/© 2015 Elsevier B.V. All rights reserved.