Simultaneous Determination of Paraquat and Diquat in Environmental Water Samples by HPLC-MS/MS Richard Jack, Xiaodong Liu, Leo Wang, and Chris Pohl OT70806_E 08/13S 1 The world leader in serving science
Outline Introduction Stationary Phase Design Chromatographic Evaluation Liquid Chromatography-Mass Spectrometry (LC-MS) Result Summary 2
Paraquat (Pq) and Diquat (Dq) Paraquat (Pq) Diquat (Dq) Nonselective, nonsystematic contact herbicides Environmental and safety concerns Toxic to humans through contact (e.g., oral, respiratory, dermal) Moderately hazardous: LD 50 ~35 mg/kg for humans Banned or restricted in several European countries and in Japan Regulation The U.S. EPA regulation: < 20 μg/l for Dq in drinking water European Union (EU) s general rule for pesticides in drinking water (98/83/EC): <0.1 μg/l of each individual pesticide <0.5 μg/l for the total concentration Food safety concerns in developing countries 3
Analytical Methods Colorimetric spectrophotometry Enzyme-linked immunosorbent assay (ELISA) Liquid scintillation counting (LCS) High-performance liquid chromatography (HPLC) wide acceptance Ion-exchange column postcolumn derivatization fluorescence detection Reversed-phase (RP) column ultraviolet (UV), photodiode array (PDA), or MS 4
U.S. EPA Method 549.2 An HPLC method for the determination of diquat and paraquat in drinking water sources and finished drinking water Summary of the method Off-line SPE RPLC/ion-pairing UV or PDA detection Detection limit: 0.72 μg/l for Dq; 0.68 μg/l for Pq Challenges Poor reproducibility Time consuming Complex mobile phase: water, phosphoric acid, acetonitrile, heptane or hexane sulfonic acid (ion-pairing agent), and diethylamine (DEA) Separation and peak shape 5
An Improved Method Specialty column good separation and peak shape Special mobile phase additive Challenges Poor reproducibility Time consuming Complex mobile phase Incompatible with MS 6
A Method Not Requiring Ion-Pairing Agent RP/anion-exchange/chargeexchange/trimode column No ion-pairing agent required On-line SPE Challenges High-concentration buffer (not MS-friendly) Peak shape 7
LC/MS Greater Sensitivity w/o Sample Preparation Specialty RP column No sample enrichment LOQ: 0.1 μg/l for diquat and 5 μg/l for paraquat (10 µl) Challenges Heptafluorobutyric acid (HFBA) as ion-pairing agent not desirable for MS High aqueous mobile phase (95%) lower sensitivity Minutes 8
UHPLC HILIC Column Off-Line SPE LC/MS UHPLC HILIC column Off-line sample preparation (20x) LOQ: ~40 ppt for diquat and paraquat (10 µl ) Challenges Dipuat and paraquat coelution High buffer concentration lower sensitivity 9
Objective To develop a method for determination of diquat and paraquat: Retain k > 2 Resolve Behave LC-MS-Compatible Simple Fast Sensitive Rs > 2 (Dq/Pq) As < 1.5 (UV) No ion-pairing agent Solvent > 50% (v/v) Buffer concentration <50 mm Isocratic method <5 min Better than reported 10
Nanopolymer Silica Hybrid (NSH) Technology Surface Bonding Electrostatically Driven Self-Assembly Benefits: Bare Silica Surface Modified Silica Nanopolymer Silica Hybrid Versatile chemistry platform Cation-exchange and anion-exchange function simultaneously Distinctive spatial separation of the anion-exchange and cation-exchange regions, which results in maximum flexibility in method development. Chromatography can be easily optimized by adjusting mobile phase buffer concentration, ph, and solvent content concurrently or independently. Ideal selectivity for simultaneous separation of basic, neutral, and acidic analytes Separation of hydrophilic ionic and ionizable analytes without ion-pairing reagent 11
Stationary Phase Design Nanopolymer bead (WCX) to retain and separate Dq and Pq Bonded WAX phase for symmetrical peak shape Dq/Pq Phase Retention Mechanism: WCX: Carboxylate WAX: Tertiary amine RP: Alkyl Silica Substrate: 3 µm, high-purity, spherical, porous Surface Area 100 m 2 /g Pore Size 300 A Operating Pressure limit 4000 psi Operating flow rate range 0.3 0.9 ml/min for 3mm i.d. 0.15 0.45 ml/min for 2.1 mm i.d. ph range 2.5 7.0 12
Organic Solvent Effect 150 Pq mau Pq Pq Dq Pq Pq Dq Dq Dq Pq/Dq 30% MeCN 40% MeCN 50% MeCN 60% MeCN 70% MeCN 75% MeCN Rs 2.45 3.69 5.5 7.5 8.0 8.8 As 1.88/1.18 1.17/1.35 1.15/1.07 1.03/0.98 0.93/0.96 1.08/0.96 Efficiency 1900/2175 3060/3370 4090/4600 5550/5560 6000/4840 6230/5670 Dq 75% MeCN 70% MeCN 60% MeCN 50% MeCN 40% MeCN Column: Mobile Phase: Flow Rate: 0.60 ml/min Inj. Volume: 2 µl Temp: 30 C Detection: Sample: Dq/Pq prototype, 3 µm (3.0 50 mm) MeCN/ 25 mm (total) NH 4 OAc, ph5 UV, 290 nm Dq and Pq (0.1 mg/ml each) 0 Pq Dq 30% MeCN 0 2 4 6 8 Minutes 10 13
Buffer Concentration Effect Pq/Dq 10 mm 15 mm 20 mm 25 mm Rs 10.7 10.3 9.5 8.8 150 Pq Dq k 26.4/46.8 11.8/21.0 6.9/12.2 4.5/7.9 As 1.02/0.96 1.02/0.93 1.03/0.97 1.08/0.96 Efficiency 5900/6160 5860/6170 5760/5770 6230/5670 mau Pq Dq Pq 25 mm 20 mm Dq 15 mm Column: Mobile Phase: Flow Rate: Inj. Volume: 2 µl Dq/Pq prototype, 3 µm (3.0 50 mm) 75/25 v/v CH 3 CN/ various conc NH 4 OAc, ph5 0.60 ml/min Temp: 30 C Detection: Sample: UV, 290 nm Dq and Pq (0.1 mg/ml each) 0 Pq Dq 10 mm 0 5 10 15 20 25 Minutes 14
ph Effect 100 Pq Dq Column: Mobile Phase: Flow Rate: Inj. Volume: 2 µl Dq/Pq prototype, 3 µm (3.0 50 mm) 75/25 v/v CH 3 CN/ 25 mm (total) NH 4 OAc, ph5 0.60 ml/min Temp: 30 C Detection: Sample: UV, 290 nm Dq and Pq (0.1 mg/ml each) mau Pq ph 5 Pq/Dq ph 4 ph 5 Resolution (Rs) 5.1 8.8 Dq Retention (k) 4.7/6.8 4.5/7.9 Asymmetry (As) 1.31/1.18 1.08/0.96 Efficiency 3900/4800 6200/5600 0 ph 4 0 2 4 6 8 10 Minutes 15
LC/MS Configuration Inject / Cleanup Separation Reconditioning 16
MS and Test Matrix Parameters SRM* Scan Events Precursor Quantitative SRM* (CID) Confirmative SRM* (CID) Paraquat 185 169 (27) 170 (17) Paraquat-d 8 193 178 (17) Diquat 183 157 (22) 130 (31) Diquat-d 3 186 158 (22) * Selected Reaction Monitoring Matrix Na + and K + NH + 4 NO - 3 HCO 3 - SO 4 2- Cl - Concn >5000 mg/l 1000 mg/l 200 mg/l 1500 mg/l 2500 mg/l 3500 mg/l 17
Relative Abundance LC-MS-MS: Paraquat and Diquat at 10 ppb 100 NL: 1.19E5 100 NL: 5.46E4 100 NL: 5.47E4 100 NL: 9.67E5 100 NL: 3.11E5 Paraquat: Q-SRM 185 169 Paraquat: C-SRM 185 170 Paraquat-IS 193 178 Diquat: Q-SRM 183 157 Diquat: C-SRM 183 130 Chromatographic Conditions System: Thermo Scientific Dionex UltiMate 3000 Rapid Separation (RS) UHPLC Column: Dq/Pq Mobile Phase: 25% Ammonium Acetate (100 mm, ph 5.0) Flow Rate: Injection: 5 µl Column Temp: 75% Acetonitrile 0.5 ml/min Ambient Mass Spectrometric Conditions System: Thermo Scientific TSQ Quantum Access MAX triple stage quadrupole mass spectrometer Interface: Heated electrospray ionization, Thermo Scientific HESI-II probe Spray Voltage: 1500 V Vaporizer Temp: 400 ºC Sheath Gas Pressure: 70 Aux Gas Pressure: 10 Capillary Temp: 350 ºC Quantitation Mode: SRM 100 NL: 9.98E5 Diquat-IS 186 158 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Minutes Scan Events Precursor Quantitative SRM Confirmative SRM (CID) (CID) Paraquat 185 169 (27) 170 (17) Paraquat-d 6 193 178 (17) Diquat 183 157 (22) 130 (31) DiQuat-d 3 186 158 (22) 18
Area Ratio Quantitation: Diquat from 0.1 to 100 ng/ml Diquat LOQ: 100 ppt (10-µL) or 1 pg 16 Y = 0.0224505+0.152363*X R 2 = 0.9995 W: 1/X 0.1 to 100 ng/ml 1.6 0 0 20 40 60 80 100 Concentration (ng/ml) 0.0 0 1 2 3 4 5 6 7 8 9 10 19
Spike Recoveries ng/ml Replicates Paraquat Diquat Observed % Recovery % RSD Observed % Recovery % RSD 0.50 (n = 3) 0.39 78.0 1.73 0.44 88.0 3.14 Creek Water 5.0 (n = 2) 5.12 102 3.17 5.37 107 1.30 50 (n = 3) 47.2 94.4 0.52 52.1 104 1.04 Heavy Matrix 10 (n = 30) 10.5 105 3.48 9.43 94.3 1.09 20
Summary NSH technology allows for tailoring column chemistry to meet specific needs. A column for diquat and paraquat analysis has been developed Adequate retention k > 2 Excellent resolution Rs > 4 (Dq/Pq) Good peak shape As < 1.5 MS-compatible Simple Fast Sensitive Robust No ion-pairing agent Acetonitrile > 50% (v/v) Buffer concentration < 25 mm Isocratic method 5 min 1 pg (or 0.1 ppb with 10-µL injection) Recoveries in real and synthetic matrices 21
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