Water/Wastewater EPA Method 538:
Determination of Selected Organic Contaminants in Drinking Water by Direct Aqueous Injection with the Agilent 6460 Triple Quadrupole LC/MS System
A new method from the U.S. EPA (538) on 11 selected organic contaminants in drinking water by direct aqueous injection liquid chromatography/mass spectrometry/mass spectrometry has been developed using UHPLC and the Agilent Model 6460 Triple Quadrupole LC/MS System. One advantage of the EPA method is that solid phase extraction is no longer needed for sample preparation. This means that the analysis time is reduced by at least half. Furthermore, run time was cut by almost two-thirds by the use of UHPLC, and the method provided excellent linearity (R2≥0.9999) for all analytes, with limits of detection from 1 to 500 ng/L. LC conditions
EPA Method 538 was tested on several samples from river, reservoir and drinking water sources. The method detected only DIMP in one of the samples taken from a reservoir prior to drinking water treatment.
Pesticides and other organic contaminants in drinking water pose potential human health risks. Agricultural and industrial uses of these chemicals are major sources of such contamination. To ensure the quality of drinking water in the US, the Environmental Protection Agency (EPA) has a number of monitoring requirements. EPA Method 538 has been developed and implemented for the determination of selected organic contaminants in drinking water, most of which are organophosphate pesticides.
EPA Method 538 involves analysis of water by direct aqueous injection and liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS). The method measures the presence of 11 target analytes, using five deuterated internal standards. The analytes are separated and identified by comparing the acquired transition ions and retention times to calibration standards obtained under identical LC/MS/MS conditions. The concentration of each analyte is determined by internal standard calibration following standard procedures. Because the method requires no sample extraction, it is rapid and inexpensive relative to other LC/MS/MS methods.
This application note describes an Agilent implementation of EPA Method 538, which is demonstrated with the Agilent 1290 Infinity LC System and an Agilent 6460 Triple Quadrupole LC/MS System using Jet Stream technology. The 10-minute UHPLC chromatographic analysis is more than twice as fast as the original EPA Method 538, saving time and solvent costs. The method was modified by adding a second transition for all analyte ions for confirmation, which satisfies the European Union (EU) specifications for unequivocal identification by mass spectrometry. This gives an even greater assurance of correct identification than prescribed by the EPA. The utility of the method was demonstrated using local water samples.
Author Details: Imma Ferrer and Michael Thurman
Center for Environmental Mass Spectrometry
University of Colorado in Boulder,
Web:
www.agilent.com/chem
Experimental Reagents and Standards
All standard solutions (100 µg/mL) were purchased from Accustandards (New Haven, CT). The deuterated standards were obtained from Cambridge Isotopes (Cambridge, MA). HPLC grade acetonitrile and methanol were obtained from Burdick and Jackson (Muskegon, MI, USA). Formic acid was obtained from Sigma-Aldrich (St. Louis, MO, USA). Individual stock
Column
Column temperature100 µL Injection volume Mobile phase
Run time Flow rate Gradient
Agilent ZORBAX C-18 Eclipse Plus, 2.1 x 50 mm, 1.8 µm (p/n 959757-902)
25 °C 100 µL
A = Acetonitrile B = 0.1% acetic acid in water 10 min
0.4 mL/min
90% B at time 0, and hold for 1.7 min. Gradient to 100% B at 10 min.
MS conditions
Sheath gas temperature Sheath gas flow Gas temperature Desolvation gas flow rate Nebulizer pressure Capillary voltage Nozzle voltage Delta
350o C
11 L/min 250 °C 10 L/min 45 psi 4000 V 0 V
200 V Table 1: LC and MS Instrument Conditions
solutions (1 µg/mL) were prepared in pure methanol and stored at -18 °C. From these solutions, working standard solutions were prepared by dilution with acetonitrile and water.
Instruments
The method was run on the 1290 Infinity LC System with a 100 µL sample loop, coupled to the 6460 Triple Quadrupole LC/MS System with Jet Stream Technology. The instrument conditions are listed in Table 1.
Sample Preparation
Method 538 calls for a 40 mL water sample, preserved with sodium omadine and ammonium acetate. Remove a 950 µL
www.envirotech-online.com AET Annual Buyers’ Guide 2012
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