Water/Wastewater
3.0 ×105
2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0
0.2 0.6 1.0 1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2 4.6 5.0 5.4 5.8 6.2 6.6 7.0 7.4 7.8 8.2 8.6 9.0 9.4 9.8 10.2 Acquisition time (min)
Figure 1: UHPLC extracted ion chromatogram (EIC) with the Agilent 1290 Infinity LC System, for the 11 analytes of EPA Method 538. Quinoline - 8 levels, 8 levels used, 8 points, 8 points used, 0 QCs
7.0 ×105
6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
-0.5 0
-4 -2 02468 10 12 14 16 18 20 22 24 26 Fenamiphos sulfone - 8 levels, 8 levels used, 8 points, 8 points used, 0 QCs
2.8 ×105
2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
-0.2 0
-4 -2 02468 10 12 14 16 Figure 2: Calibration curves for quinoline and fenamiphos sulfone A. Reservoir water
181.0 & 97.0, 181.0 & 139.0 Ratio = 52.6 (125.9%)
×102 6 4
2 0
3.5 4.0 DIMP (181&97) 4.5 Acquisition time (min) 5.0 ×102
2.5 2.0 1.5
1.0 0
3.5 4.0 4.5 Acquisition time (min)
No confirmatory ion (89.9)
5.0 18 20 22 24 26 28 Concentration (µg/L) B. Drinking water
181.0 & 97.0, 181.0 & 139.0 Ratio = 89.9 (215.1%)
C. Internal standard
+MRM (195.0 & 99.0) Drinking water s ×104
1.50 1.75
1.25
0.75 1.00
0.25 0.50
0 3.5 4.0 4.5 Acquisition time (min)
Figure 3. Analysis of the reservoir water prior to treatment (A.) and treated water (B.) for the pesticide DIMP using the modified Method 538. DIMP is detected using the 181!97 transition as the quantifier ion, and the 181!139 transition as the qualifier ion. In the case of the drinking water, the qualifier (confirmatory) ion is not present, result- ing in a quantifier to qualifier ion ratio that is much too high, indicating the absence of DIMP in the drinking water. The deuterated DIMP internal standard is shown in C.
5.0
4.153 min DIMP d-14
Reference 1.
30 32 34 36 38 40 42 44 46 48 50 52 54
y = 5555.506481x + 420.547499 R2
= 0.99997710
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 (Figure 3). The treated drinking water contained no detectable organophosphate pesticides. Thus, the method was found to be reliable and useful for the analysis of drinking water contaminants, as well as rapid and sensitive.
Conclusions
Running EPA Method 538 on the Agilent 1290 Infinity LC System and the Agilent 6460 Triple Quadrupole LC/MS System with Jet Stream Technology shortens time-to- results by almost a factor of three, and increases reliability of the method by adding a second transition. In addition, the detection limits and adaptations conform to the requirements of this method [1].
28 Concentration (µg/L) Testing of Drinking Water Samples 30 32 34 36 38 40 42 44 46 48 50 52 54
y = 13867.611595x + 884.428417 R2
= 0.99995441
49
The limits of detection (LODs) for the 11 analytes varied from 1 ng/L for aldicarb sulfoxide, which was the most sensitive compound, to 500 ng/L for acephate, which was the least sensitive compound (Table 6). The wide variation in LODs reflects the ability of each analyte to form ions in electrospray. The most polar analytes such as acephate and methamidophos were the least sensitive, while fenamiphos sulfone, and thiofanox were some of the most sensitive compounds and also the most hydrophobic. The LODs for 9 of the 11 compounds were lower than those posted in Table 5 of Method 538, and the MRLs for the same nine compounds were also equal to or lower than those listed in Table 5. Quinoline in particular is much more sensitive using the Agilent 6460 Triple Quadrupole LC/MS System with Jet Stream Technology because it is a stable compound (PNA) with a nitrogen heteroatom. Thus, this adaptation of Method 538 meets the criteria for a sensitive method for organophosphate pesticides in drinking water.
The extra MRM transition used in this adaptation of Method 538 is an important component of a valid method for water quality analysis of pesticides in water samples. The European Union (EU) specifications for unequivocal identification by mass spectrometry require two transitions, and this procedure has become an unofficial standard worldwide.
Figure 2 shows the excellent linearity that was achieved with the direct injection method for two of the analytes, quinoline and fenamiphos sulfone. In fact, the R2 values are ≥0.9999 for all compounds in this method.
J.A. Shoemaker, 2009, EPA Method 538: Determination
of selected organic constituents in drinking water by direct aqueous injection-liquid chromatography/tandem mass spectrometry, EPA/600/R-09/149, 40p.
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www.envirotech-online.com AET Annual Buyers’ Guide 2012
Counts
Responses
Responses Counts
Methamidophos Acephate
Quinoline Aldicarb sulfoxide Oxydemeton-methyl
Dicrotophos Counts
DIMP Aldicarb
Fenamiphos sulfoxide Fenamiphos sulfone
Thiofanox
Counts
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