Article pubs.acs.org/JAFC
Determination of Triazine Herbicides in Drinking Water by Dispersive Micro Solid Phase Extraction with Ultrahigh-Performance Liquid Chromatography−High-Resolution Mass Spectrometric Detection Dawei Chen,† Yiping Zhang,‡ Hong Miao,*,† Yunfeng Zhao,† and Yongning Wu† †
Key Laboratory of Food Safety Risk Assessment, Ministry of Health, China National Center for Food Safety Risk Assessment, Beijing 100021, China ‡ Third Institute of Oceanography State Oceanic Administration, Xiamen 361005, Fujian, China S Supporting Information *
ABSTRACT: A novel dispersive micro solid phase extraction (DMSPE) method based on a polymer cation exchange material (PCX) was applied to the simultaneous determination of the 30 triazine herbicides in drinking water with ultrahigh-performance liquid chromatography−high-resolution mass spectrometric detection. Drinking water samples were acidified with formic acid, and then triazines were adsorbed by the PCX sorbent. Subsequently, the analytes were eluted with ammonium hydroxide/ acetonitrile. The chromatographic separation was performed on an HSS T3 column using water (4 mM ammonium formate and 0.1% formic acid) and acetonitrile (0.1% formic acid) as the mobile phase. The method achieved LODs of 0.2−30.0 ng/L for the 30 triazines, with recoveries in the range of 70.5−112.1%, and the precision of the method was better than 12.7%. These results indicated that the proposed method had the advantages of convenience and high efficiency when applied to the analysis of the 30 triazines in drinking water. KEYWORDS: dispersive micro solid phase extraction, water, triazine, high-resolution mass spectrometry
■
INTRODUCTION Triazine herbicides have been applied to soil and absorbed by the roots of seedling weeds for 50 years. Triazine herbicides and their degradation products have caused great concern because they are of high toxicity and persist in water, soil, and organisms.1,2 As a consequence of the proven carcinogenic and endocrine-disturbing action of these herbicides,3 the monitoring of such herbicides in food has become an important aspect of environmental and health safeguarding. Triazine herbicides, especially atrazine and simazine, are commonly detected in natural waters. For this reason, the U.S. Environmental Protection Agency (EPA) set the maximum allowable level of atrazine at 3 μg/L in water for human consumption;4 a maximum level for each individual herbicide at 0.1 μg/L and 0.5 μg/L for mixtures of pesticides is also set by the European Union (EU).5 In consideration of the low concentration levels of those herbicides in water samples, reliable, sensitive, efficient, and inexpensive methods for monitoring water quality are highly demanded. Generally, triazines are routinely identified and quantitated by gas chromatography−nitrogen phosphorus detection (GCNPD),6,7 high-performance liquid chromatography−ultraviolet detection (HPLC-UV),8,9 gas chromatography−mass spectrometry (GC-MS)10,11 and liquid chromatography−mass spectrometry (HPLC-MS),12,13 where a preconcentration step is usually needed. Sample pretreatment plays a very important role in chemical residue analysis, especially in the trace analysis of the compounds in drinking water samples. Historically, the preconcentration of the compounds from drinking water samples mainly relies on the use of liquid−liquid extraction (LLE) and solid phase extraction (SPE) techniques.14,15 © XXXX American Chemical Society
Nevertheless, the main disadvantages of LLE are that it is time-consuming and requires a large number of organic solvents. SPE offers a high enrichment factor and reduces organic solvent usage and exposure. However, the SPE method requires multiple steps and is still time-consuming, laborious, and relatively expensive. Moreover, some unavoidable difficulties are encountered when SPE is applied to extract trace target compounds from large-volume water samples. A large amount of time is consumed when an SPE column is used for the extraction because of the high backpressure. Although SPE disk procedures have also been used for the preconcentration of triazines in water samples with a larger surface area than the SPE column to obtain fast flow rates,16,17 the cost is still relatively expensive. To overcome these problems, extensive efforts have been made to develop some new rapid, efficient, economical, and miniaturized sample preparation methods. Recently, dispersive micro SPE (DMSPE) has been widely developed as a miniature model of SPE because of the use of micro amounts.18−22 Compared to the traditional SPE, DMSPE shows some advantages, including a short time requirement, less solvent consumption, and the absence of complex equipment. In DMSPE, an extract was added to the tube with the solid sorbent, so the extraction procedure relies only on shaking and centrifugation. Magnetic carbon nanotubes (CNTs), graphene, and metallic nanoparticles, as frequently used solid sorbent materials, are widely applied in such a Received: August 12, 2015 Revised: October 19, 2015 Accepted: October 21, 2015
A
DOI: 10.1021/acs.jafc.5b03973 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry
Figure 1. Structures for the 30 triazines (1−30).
procedure.23 Additionally, the cation exchange polymer material, as another kind of solid sorbent material, can rapidly adsorb the alkaline chemical substances directly with their chemical selectivity and has been usually used in the SPE method,24,25 but little is known about the application in DMSPE. In this regard, polymer cation exchange (PCX), as a high molecular weight polymer, was evaluated in DMSPE during residue analysis of triazine herbicides. Currently, HPLC-MS and GC-MS, especially triple-quadrupole mass spectrometers (QqQ-MS), are more widely used in the analysis of triazines in comparison with GC-NPD or HPLC-UV in order to obtain a higher characterization ability.26−31 Although the QqQ-MS provides sensitive detection in multiple reaction monitoring mode, this approach has some drawbacks and limitations. For example, the simultaneous analysis for multiple substances is restricted due to the limited scan time. In addition, a complicated optimization procedure of acquisition parameters is required for each compound. The use of high-resolution mass spectrometers (HRMS), such as TOF and Orbitrap, is of great help to reduce the complex optimization procedure of acquisition parameters and benefits from the advantages of the higher specificity and qualitative ability with more detailed structural information.32,33 This work shows an ultrahigh-performance liquid chromatography coupled with a Q-Orbitrap high-resolution mass spectrometry method based on the DMSPE procedure using PCX sorbent for the simultaneous analysis of the 30 triazines in drinking water.
■
27; terbuthylazine, 28; terbutryn, 29; trietazine, 30) (>96.5% purity), and two individual internal standard solutions (100 mg/L for atrazine2-hydroxy-d5 and cyromazine-d4) were all obtained from Dr. Ehrenstorfer (Augsburg, Germany). Individual stock solutions (1000 mg/L) of the 30 triazines were prepared in methanol. Multicompound intermediate and working solutions (1 mg/L and 100 μg/L) of the 30 compounds were prepared by diluting the individual stock solutions with appropriate amounts of acetonitrile. A mixed internal standard stock solution (1 mg/L for atrazine-2-hydroxy-d5 and cyromazine-d4) was prepared by diluting each internal standard solution with appropriate amounts of acetonitrile. All standard solutions were stored in screw-capped glass tubes at −20 °C. Sample Collection and Preparation. Two tap water samples and 10 bottled water samples were collected from different locations and local markets of Beijing (China) and were selected for the determination of the target triazines using the proposed method. Fifty milliliters of water was accurately measured into a 50 mL Eppendorf tube with 35 mg of PCX sorbent. Fifty microliters of formic acid was added to the tube to obtain the concentration of 0.1%. The mixture was vortexed for 90 s and then poured off into the 50 mL syringe with a 0.22 μm nylon syringe filter. The extraction solution was passed through the syringe filter and discarded. Then, the PCX, enriched with the analytes, was eluted with 3 mL of ammonium hydroxide/acetonitrile (2:98, v/v). The collected elution was transferred into a vial for UHPLC-HRMS analysis. Chromatographic Conditions. The chromatographic analysis was determined by UHPLC using the Ultimate 3000 system (Dionex, Sunnyvale, CA, USA). An HSS T3 (100 mm × 2.1 mm i.d., 1.8 μm) analytical column (Waters, Milford, MA, USA) was selected for chromatographic separation with the column oven temperature set at 40 °C. The gradient elution procedures were performed with two eluants in a 0.3 mL/min flow rate. Eluant A consisted of a mixture of 4 mM ammonium formate and 0.1% of formic acid in water; eluant B was acetonitrile with 0.1% formic acid. The solvent gradient adopted was as follows: 0 min, 10% B; 0−2 min, 20% B; 2−3 min, 35% B; 3−5 min, 45% B; 5−10 min, 50% B; 10−12 min, 100% B; 12−12.1 min, 10% B; 12.1−15 min, 10% B. The injection volume was set at 5 μL. Mass Spectrometry Conditions. The detection analysis was performed using a Q-Exactive mass spectrometer (Thermo Fisher Scientific, Bremen, Germany) equipped with a heated ESI source. All of the experiments were operated in the positive electrospray ionization (ESI+) mode. The operating parameters were as follows: spray voltage, 3.5 kV; temperature of ion transfer capillary, 325 °C; Slens RF level, 55 V; sheath gas, auxiliary gas, sweep gas, 40, 10, 0 (arbitrary units), respectively. The mass calibration of the instrument was performed every 3 days using the calibration solutions to obtain a mass accuracy value of
