Water Security: Detecting Chemical Agents by SERS using NeSSI

Transcription

1 Water Security: Detecting Chemical Agents by SERS using NeSSI Chetan Shende, Atanu Sengupta, Frank Inscore, and Stuart Farquharson Support: EPA: EP-D , EP-D See Us in the Exhibit Hall

2 Challenge: specific, fast, sensitive Specificity identify chemical agents & hydrolysis products No False Positives! Speed monitor poisoned water (batch & continuous) 10 min or less Sensitivity Requirements to protect CN 6 mg/l (6 ppm) HD microg/l (100 ppb) TDG Nerve - 5 microg/l (5 ppb) MPA Part-per-billion is challenging!

3 Analysis: CWA Hydrolysis Products HCN H 2 H CN - HD Cl S Cl H 2 2 HCl + H S TDG H VX P S N DIASH H 2 N + EMPA HS P H H EtH + P N EA2192 S H 2 H 2 ethanol + P H MPA DIASH + MPA GA P N C N H 2 HCN + P N H EDMAPA H 2 ethanol + P N DMAPA H GB P F H 2 HF + P H IMPA H 2 2-propanol + MPA GD P F H 2 HF + P H PMPA H 2 2-pinacolyl + MPA GF P F H 2 HF + P H CMPA H 2 cyclohexanol+ MPA

4 Approach: Surface-enhanced Raman Spectroscopy When a molecule is within a plasmon field, the efficiency of Raman scattering can increase by 1 million times! Sub part-per million detection becomes possible. Chemical contribution can provide additional 10 3 enhancement P N S VX Single Molecule Detection: requires

5 SERS-Active Substrates benzenethiol 10-3 M 10-5 M 10-8 M (~10 ppb)

6 Approach: RTA SERS Sampling Systems 2001: Simple SERS Sample Vials : SERS-Active Capillary More suited to extract and pre-concentrate

7 2007: Functionalized Sol-Gel SERS Capillary PC TC unreduced reduced Std SERS vials 2 nd generation

8 Potassium Cyanide: IR, NR, SERS Infrared (solid) C 2 Raman (saturated solution, 1W, 10 min) 2080 cm -1 SERS (1 mg/ml water 100 mw, 1-min) 2140 cm -1 Wavenumbers (Δcm -1 ) Enhancement Factor ~ 3x10 6

9 SERS: cyanide 2003 (Vial) 2005 (Capillary) 2007 (F-Cap) PPM PPB PPT mw 785 nm, 1-min SERS is Non-linear (Langmuir function)

10 Thiodiglycol (TDG): SERS & NR SERS: 1 mg/ml, 1.5-min 100 mw 785 nm Raman: neat solution, 5-min 300 mw 785 nm Enhancement Factor = 2x10 5

11 SERS: Thiodiglycol 2005 (Capillary) 2007 (F-Cap) PPM PPB mw 785 nm, 1-min

12 SERS: MPA SERS: 0.1 mg/ml, 1-min, 100 mw 785 nm Raman: 1000 mg/ml, 5-min, 300 mw 785 nm 756 PC C P Enhancement Factor = 8x10 5

13 SERS: Methyl Phosphonic Acid 2003 (Vial) 2007 (F-Cap) P-C 760 PPM PPB mw 785 nm, 1-min

14 SERS: Methyl Phosphonic Acid SERS MPA ppb 1000 Peak height Concentration (ppb) 25 ppb

15 SERS: 10 parts-per-billion MPA TDG CN

16 1 ppm SERS: Alkyl Phosphonic Acids

17 SERS: 10 parts-per-billion IpMPA PMPA CMPA EMPA DIASH 80 mw, 785 nm, 1-min

18 SERS: 10 parts-per-billion CEMS CEES HEES 40 mw, 785 nm, 30-sec

19 SERS: 10 parts-per-billion Fonofos Chlorobenzoic Acid Sunset Yellow 80 mw, 785 nm, 1-min

20 Sensitivity: 10 ppb 75 mw of 785 nm 1 min

21 NeSSI for Real-World Sampling Parker-Hannifin

22 NeSSI for Real-World Sampling 3-Way 3-Way Surface Ex- Surface 3-Way Surface SERS Surface Valve Valve Connection tractor Connection Valve Connection Sensor Connection Regulated Water Load Sample Into Extractor (5 min)

23 NeSSI for Real-World Sampling 3-Way 3-Way Surface Ex- Surface 3-Way Surface SERS Surface Valve Valve Connection tractor Connection Valve Connection Sensor Connection Regulated Water Load Sample Into SERS Capillary (10 sec)

24 NeSSI for Real-World Sampling 3-Way 3-Way Surface Ex- Surface 3-Way Surface SERS Surface Valve Valve Connection tractor Connection Valve Connection Sensor Connection Regulated Water Measure SERS Load Next Sample Into Extractor (5 min)

25 Parker-Haniffin Intraflow Sample System

26 Electrical Intraflow Sample System Extractor SERS Capillary

27 Parker-Haniffin Intraflow Sample System F Probe SERS Capillary

28 Software Control for Intraflow System Water Flows through Extractor into Waste Methanol Flows through Extractor And SERS Capillary to Waste

29 User Interface

30 Measurements using NeSSI 10 ppb CN- 100 ppb TDG 75 ppb MPA 50 ppb Sunset Yellow Spiked Water EWS from Kensico, NY water reservoir

31 RTA s RamanPro Advantages: No sample preparation Simple integration via fiber optics Remote analysis, multi-component Complete spectral coverage Wavelength stability Confident spectral subtraction and library search/match Real-time, n-demand analysis Long term stability Temperature and vibration immune Shock resistant 5-hour battery (back-up)

32 Summary: specific, fast, sensitive Specificity identify chemical agents & hydrolysis products No False Positives! Speed monitor poisoned water (batch) 10 min or less 1 minute Sensitivity Requirements CN 6 mg/l (6 ppm) HD microg/l (100 ppb) Nerve - 5 microg/l (5 ppb) Lowest NeSSI Flow Measured! CN 10 microg/l (10 ppb) TDG microg/l (100 ppb) MPA - 75 microg/l (75 ppb) ph dependence MPA, DPA, CN by SERS, SPIE, 5269, (2004) SERS Analyzer for Monitoring Chemical Agents and Their Hydrolysis Products, IJHSE, (2007)

33 Abstract Ensuring safe water supplies requires continuous monitoring for potential poisons. In the case of chemical warfare agents (CWAs) analyzers are needed that have sufficient sensitivity (part-per-billion), selectivity (differentiate the CWA from its hydrolysis products), and speed (less than 10 minutes) to be of value. We have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to meet these requirements by detecting CWAs and their hydrolysis products in water. The expected success of SERS is based on reported detection of single molecules, the one-to-one relationship between a chemical and its Raman spectrum, and the minimal sample preparation requirements. Recently, we developed a simple sampling device designed to optimize the interaction of the target molecules with the SERS-active material with the goal of increasing sensitivity and decreasing sampling times. This sampling device employs a syringe to draw the water sample containing the analyte into a capillary filled with the SERS-active material. Using this approach we have been able to detect many of the primary hydrolysis products of nerve agents at ppb concentrations in 1 minute. These measurements as well as those for other CWAs will be presented, as well as a portable analyzer suitable for continuous water monitoring.