compound rt (min) polarity mrm cone (v) ce (ev) …...bromacil 6.17 esi - 259 > 203 259 > 160...

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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