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Drinking water
LC-MS/MS ANALYSIS OF ACIDIC HERBICIDES IN
WATER USING DIRECT INJECTION
Authors: Renata Jandova, Euan Ross, Simon Hird, Marijn Van Hulle Waters Corporation, Stamford Av., Altrincham Road, SK9 4AX Wilmslow UK
INTRODUCTION The presence of pesticides in surface and ground waters is of concern globally because of the impact on aquatic ecology but also the potential to contaminate drinking water supplies. Presence of pesticides in European waters
is regulated through different directives. The Drinking Water Directive1 sets a maximum limit of 0.1 μg/l for individual pesticide residues present in a sample (0.5 μg/l for total pesticides). The Water Framework Directive (WFD)2
deals with surface waters, coastal waters, and groundwater. Member States must identify River Basin Specific Pollutants and set their own national environmental quality standards (EQS) for these substances (e.g. 2,4-D: 0.1 µg/l
in France and Germany). In the USA, drinking water is regulated under the Safe Drinking Water Act.3 Through this regulation, EPA established National Primary Drinking Water Regulations (NPDWRs) that set mandatory Maximum
Contaminant Levels (MCL) for drinking water (e.g. 2,4-D: 70 µg/l). Some states have set guidance values at lower concentrations (e.g. 2,4-D: 30 µg/l in Minnosota). Surface and ground waters are regulated under the Clean Water
Act4, which establishes Water Quality Standards (WQS) but these don’t include any acidic herbicides. Although regulations vary from country to country, many look to guidelines established by EU, USA or the WHO.5 Therefore,
there is a need for reliable analytical methods for monitoring acidic herbicides in various types of water. This work describes a rapid and sensitive method for the determination of 20 acidic herbicides in a variety of different types
of water sample, with minimal sample preparation. The method is suitable for checking compliance with regulatory limits in many parts of the world.
References
1. European Commission (1998). Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption. Off. J. Eur. Communities 1998.
2. European Commission (2000). Directive 2000/60/EC of 23 October 2000 establishing a framework for community action in the field of water policy as last amended by Commission Directive 2014/101/EU (OJ No L 311, 31.10.2014, p32).
3. https://www.epa.gov/sdwa. "Safe Drinking Water Act (SDWA)." United States Environmental Protection Agency. Accessed 05 April 201
4. https://www.epa.gov/laws-regulations/summary-clean-water-act. "Summary of the Clean Water Act, 33 U.S.C. §1251 et seq. (1972)." United States Environmental Protection Agency. Accessed 05 April 2018.
5. World health organisation (2017). Guidelines for drinking-water quality: fourth edition incorporating the first addendum. Geneva. Licence: CC BY-NC-SA 3.0 IGO.
Fragile compounds and soft ionization: 2,4-DB, dicamba, MCPB and triclopyr, exhibited fragmentation within the source region under typical settings. Therefore, the temperature of the source block and the desolvation gas was reduced to 120 °C and 300 °C, respectively, which increased the response of the deprotonated molecular ion. These compounds were also acquired in Soft Ionization mode, a function enabled in the MS acquisition file that applies a shallower gradient of voltages to the StepWave XS™ ion transfer optics to reduce fragmentation during transmission of ions to the first quadrupole. Reducing fragmentation can result in significant improvements in sensitivity as shown in Figure 4.
Sensitivity and selectivity of the method: Excellent sensitivity and selectivity was demonstrated by the response for each compound detected from the analysis of drinking and surface water spiked at 0.02 µg/L, which is well below the maximum limits. Figure 2 shows representative example of two MRM chromatograms for drinking and surface water. Laboratories are expected to provide methods with lower limits of quantification (LLOQ) of at least one third of the EQS. The sensitivity observed suggests that detection and quantification of all compounds at lower concentrations should be possible.
RESULTS AND DISCUSSION
CONCLUSION
A method for determination of 20 acidic herbicides, in drinking and surface water, using LC-MS/MS, has been
developed, which is suitable for monitoring waters for compliance with regulatory limits.
This method uses direct injection with no sample preparation so avoids the time, costs and potential losses associated
with techniques such as liquid-liquid extraction (LLE) solid-phase extraction (SPE).
Reducing the temperature in the source and using Soft Ionization mode to optimize StepWave XS™ parameters,
provided significant increases in response for the more “fragile” compounds in the suite of analytes.
In-house validation showed very good linearity and residuals over the concentration range studied and accuracy of the
method was observed to be excellent.
Figure 1: 20 acidic herbicides with their retention times (overlay of two MRM transitions). Standard prepared in drinking water at 0.1 µg/L.
Quantification and Accuracy: Standard solutions, prepared in drinking and surface water at seven concentrations (0.01, 0.02, 0.05, 0.10, 0.20, 0.50 and 1.0 µg/L), were used for bracketed calibration. In all cases, the correlation coefficients (r
2) were >0.99
with residuals of <20% The accuracy and precision of the method was determined from the analysis of spiked water samples. Trueness was found to be within the range 88 to 120%. Repeatability was good with RSDs ≤7% at 0.1 µg/L and ≤20% at 0.02 µg/L (n = 6 per each level). Figure 3 shows the results in detail.
Figure 2: Monitored MRM transitions of selected herbicides in matrix matched standard at 0.02 µg/l in A) drinking water and B) surface water. Quantitative transition is on the top. Figure 4: Enhanced signal for molecular ion of fragile herbicides
achieved with Soft Ionization mode to control the StepWave XS™
METHODS Aliquots of surface water samples (10 ml) were centrifuged and passed through syringe PVDF filter (0.2 µm). Aliquots (1.5 ml) from each water sample were then transferred to deactivated glass vials and acidified (30 µl of 5 % formic acid) prior to analysis. The accuracy (trueness and precision) of the method was assessed by analysis of water samples. Two different samples of drinking and surface waters, previously shown to be blank, were spiked with the compounds of interest at 0.02 and 0.1 µg/l three times; n=6 for each water type at each concentration.
MS parameters UPLC conditions and gradient
min3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00
%
0
100
min
%
0
100
min
%
0
100
min
%
0
100
min
%
0
100
min
%
0
100
2,4-D
219 > 125
219 > 161
Clopyralid
192 > 110
192 > 146
219 > 175
175 > 145
Dicamba
min3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00
%
0
100
min
%
0
100
min
%
0
100
min
%
0
100
min
%
0
100
min
%
0
100
2,4-D
Clopyralid
Dicamba
219 > 161
219 > 125
192 > 110
192 > 146
219 > 175
175 > 145
A) B)
StepWave XS™
Surface water
Figure 3: Trueness (%) and precision (% RSD) from measurements of spiked water samples (n = 6 per each concentration).
Parameter Setting
UPLC System ACQUITY UPLC® I-Class
Column HSS T3 column (1.8µm, 2.1×150 mm)
Column Temp. 40 °C
Mobile phase A 0.02 % formic acid (aq.)
Mobile phase B Methanol (LC-MS grade)
Flow rate 0.4 mL/min
Injection volume 250 µL
Time (min) %A %B
Initial 80 20
9 0 100
12 0 100
15 80 20
Parameter Setting
MS instrument Xevo® TQ-XS
Source Electrospray
Polarity ESI-/ESI+ switching
Capillary voltage 1 kV ESI-/ 2kV ESI+
Desolvation temperature 300 °C
Desolvation gas flow 1000 L/Hr
Source temperature 120 °C
Cone gas flow 150 L/Hr
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
Dicamba MCPB 2,4-DB Triclopyr
Normal mode
Soft ionization mode
Time6.00 6.10 6.20 6.30 6.40 6.50 6.60 6.70
%
0
100
Soft ionization mode
Normal mode
[M-H]- 219 > 175
[M-H]- 227 > 141
[M-H]- 247 > 161
[M-H]- 256 > 198
Compound RT (min) Polarity MRM Cone (V) CE (eV)Clopyralid 2.91 ESI+ 192 > 110
192 > 1463030
3020
Imazapyr 4.19 ESI+ 262 > 149262 > 202
3030
2522
Dicamba 5.45 ESI- 175 > 145219 > 175
2020
55
Fluroxypyr 5.79 ESI- 253 > 233253 > 175
3030
822
Bentazone 5.99 ESI- 239 > 132239 > 175
3030
2520
Bromacil 6.17 ESI- 259 > 203259 > 160
3030
1818
Imazaquin 6.31 ESI+ 312 > 267312 > 199
3030
2025
2,4-D 6.92 ESI- 219 > 161219 > 125
3030
1325
MCPA 7.12 ESI- 199 > 141201 > 143
3030
1313
Compound RT (min) Polarity MRM Cone (V) CE (eV)Ioxynil 7.29 ESI- 370 > 127
370 > 2153030
3230
Dichlorprop 7.66 ESI- 233 > 161233 > 125
3030
1325
Triclopyr 7.49 ESI- 256 > 198254 > 196
2020
1212
Fluazifop 7.74 ESI+ 328 > 282328 > 254
3030
1625
Mecoprop 7.76 ESI- 213 > 141213 > 71
3030
1015
2,4,5-T 7.77 ESI- 253 > 195253 > 159
3030
1525
2,4-DB 8.13 ESI- 161 > 125247 > 161
3030
1015
MCPB 8.17 ESI- 227 > 141229 > 163
2020
1515
Fenoprop 8.37 ESI- 267 > 195269 > 197
3030
1515
Haloxyfop 8.64 ESI+ 362 > 288362 > 272
3030
2532
Time2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50
%
0
100
2.91
7.29
4.19
5.45 5.79
5.99
6.17
6.31
6.92
7.12
7.49
7.66
7.77
7.76
7.74
8.138.17
8.378.64