Investigations into Method Improvements for Hexavalent Chromium. Presented by Aaron Rose Thermo Fisher/Dionex Products For 2012 Watercon

Transcription

1 Investigations into Method Improvements for Hexavalent Chromium Presented by Aaron Rose Thermo Fisher/Dionex Products For 2012 Watercon

2 Recent EPA Approvals and Announcements December 22, 2010 Statement from EPA Administrator Jackson regarding her meeting with 10 U.S. senators on Chromium-6 ISO Slide Number 2 Proprietary & Confidential

3 Why the recent flurry of activity? OEHHA's (Office of Environmental Health Hazard Assessment, state of California) initial draft PHG (Public Health Goal) for chromium-6 of 0.06 µg/l was released in August December, The Environmental Working Group released a report indicating that millions of Americans are regularly drinking hexavalent chromium, made famous in the film Erin Brockovich, through their tap water. 31/35 cities tested contained hexavalent chromium. EPA Chief Lisa Jackson appeared before the US Senate and ordered quick action to address public concerns Statement from EPA Administrator Jackson regarding her meeting with 10 U.S. senators on Chromium-6 EPA Issues Guidance for Enhanced Monitoring of Hexavalent Chromium in Drinking Water On December 31, 2010, OEHHA released a revised draft PHG of chromium-6 of 0.02 µg/l. 3 Proprietary & Confidential

4 Developed jointly by Dionex and EPA 20 years ago! METHOD #: Recommended for Approval for NPDES (August, 1991) TITLE: Determination Of Dissolved Hexavalent Chromium In Drinking Water, Groundwater And Industrial Wastewater Effluents By Ion Chromatography 4 Proprietary & Confidential

5 EPA Press Release A direct mention of Dionex and AU144 These modifications allow for improved low concentration measurement and are outlined in Dionex Corp. Application Update 144 "Determination of Hexavalent Chromium in Drinking Water by Ion Chromatography" found at AU144_V18.pdf 5 Proprietary & Confidential

6 218.7 vs released August 1991, 400ppt MDL released November 2011, 20ppt MDL *AU Proprietary & Confidential

7 Regulatory Aspects Federally, chromium is regulated as total since 1992 MCLG at 0.1 ppm MCL at 0.1 ppm Analysis by ICP-MS detects both tri and hexavalent forms Assumption that the total number is in the hexavalent form Safe Drinking Water Act requires the EPA to periodically review drinking water regulations, which occurred in March Ongoing risk assessment 7 Proprietary & Confidential

8 Hexavalent Chromium Health effects Trivalent chromium is an essential nutrient, sold as a supplement and relatively non-toxic. Hexavalent chromium is very toxic! September 2010 Draft IRIS Assessment determined Cr(VI) to be a carcinogen Traditional analysis method EPA Method chelation extraction, atomic absorption Positive interference from some metals Cumbersome not automated Modest detection limits (~5 ppb) IC analysis method EPA Method (ASTM Method D ) IC separation of chromate (Cr VI) coupled with postcolumn reaction (diphenylcarbizide) UV-Vis detection (530 nm) 8 Proprietary & Confidential

9 System Configuration for Hexavalent Chromium by EPA Method Eluent Autosampler High-Pressure Nonmetallic Pump Sample Loop IonPac NG1 IonPac AS7 Post column Reagent Mixing Tee Knitted Reaction Coil UV-vis Detector Waste Proprietary & Confidential

10 Summary of Modifications in 1998 Use a lower-sulfate buffer to adjust sample ph Increase sample size to 1000 µl Reduce eluent flow rate to 1 ml/min Reduce PCR flow rate to 0.33 ml/min Increase postcolumn reaction coil to 750 µl New MDL in reagent water is µg/l 15 lower than Proprietary & Confidential

11 Determination of Hexavalent Chromium Using IC with Postcolumn Reagent Addition and UV-Vis Detection EPA Method (ASTM Method D ) No known interferences Automated IC method Original detection limits 0.1 ppb Optimized EPA Method No known interferences Automated IC method Lower detection limits 18 ppt Proprietary & Confidential

12 Relative Chromate Peak Response Effect of Sulfate and Chloride on Hexavalent Chromium Peak Response Using Optimized EPA Method % 100% 80% 60% Sulfate Chloride 40% 20% 0% Anion Concentration (mg/l) 13 Proprietary & Confidential

13 Further Improvements to EPA Eluent Autosampler Sample Loop 1. 2mm AS7 (do not have 2mm NG1) Both work effectively 2. AXP option High-Pressure Nonmetallic Pump IonPac AS7 IonPac AS7 AXP Mixing Tee Knitted Reaction Coil UV-vis Detector Waste Proprietary & Confidential

14 Summary of Modifications Smaller Column format Reduced eluent consumption AS7 has enough capacity for high ionic strength drinking water Options for post column eluent delivery Updates Benefit Value 2mm AXP post column Less Eluent consumed CM control, no flow fluctuations Flexibility Less cost Ease of Use Proprietary & Confidential

15 IonPac AS7 anion exchange column For Separation of a Wide Range of Polyvalent Anions The IonPac AS7 separates a wide variety of polyvalent anions, including polyphosphates, polyphosphonates, and other polyvalent complexing agents such as EDTA and NTA using acidic eluent (eliminating metal interferences) with postcolumn derivatization and UV-Vis detection. A unique polymer packing that provides superior performance for separating ionic and polar compounds that offers high speed, high efficiency, and high loading capacity at moderate backpressures. Useful for hexavalent chromium in environmental matrices such waters and soil extracts 16 Proprietary & Confidential

16 Post Column Delivery Options Pneumatic delivery - pressurized chamber that uses pressure to deliver reagent Advantages less pressure pulsation. Disadvantages Not software controlled Requires monitoring to maintain accurate flow rate Standalone Pump Reliable flow rate SW controlled Second pump of a Dual Pump Dual piston pump Flexibility for additional applications SW controlled 17 Proprietary & Confidential

17 Cr(VI) 2mm using ICS-2100 with AXP HIW same as DIW Excellent column capacity 3.3 mau Column: IonPac AS7 (2 x 50 mm), AS7 (2 x 250 mm) Eluent: 250 mm (NH 4 ) 2 SO 4, 100 mm NH 4 OH Flow: 0.36 ml/min Inj. Vol: Post Column Reagent: 1000 ml 2 mm diphenylcarbazide 10% methanol 1N sulfuric acid Reaction Coil: 125 ml UV Cell: Semi micro (PEEK), 2.5 ml 0.1 mg/l Cr(VI) in DI water 0.1 mg/l Cr(VI) in HIW A Signal offset Minutes B 18 Proprietary & Confidential

18 Cr(VI) Analysis using 2 mm format 2.5 mau C B A Column: IonPacNG1 (2 x 50 mm), AS7 (2 x 250 mm) Eluent: 250 mm (NH 4 ) 2 SO 4, 100 mm NH 4 OH Flow: 0.36 ml/min Inj. Vol: 1000 µl Post Column Reagent: 2 mm diphenylcarbazide 10% methanol 1N sulfuric acid Reaction Coil:125 µl A) DI water blank B) µg/l Cr(VI) in DI water C) Sunnyvale, CA drinking water Minutes 19 Proprietary & Confidential

19 Format Chromate Conc. (µg/l) Detection Limit comparison between Post Column Pumps PC-10 MDL* (µg/l) AXP MDL* (µg/l) DP MDL* (µg/l) 4 mm NA NA 2mm SAME Detection using different post column delivery! 20 Proprietary & Confidential * MDL = (Std. Dev.) x (t s, 99 ), where t s,99 = 3.14 for n = 7

20 Format comparison Format Chromate Conc. (µg/l) Method Detection Limits for Chromate Based on a 1000 µl Injection Std. Dev. (µg/l) RSD (%) MDL* (µg/l) 4 mm mm ppt detection with 2 mm Format! Proprietary & Confidential * MDL = (Std. Dev.) x (t s, 99 ), where t s,99 = 3.14 for n = 7

21 Method improvements for EPA for DW The smaller 2mm column saves cost be using less eluent. The IonPac AS7 has sufficient capacity for a large loop injection of high matrix DW to resolve anions from Cr(VI). Post column pumps Easier to control Low pulsation Improve system easy of use Combined this gives 1ppt detection 22 Proprietary & Confidential

22 Investigations of Chromate Analysis in Soils Challenge: 2 Step process EPA 3060a extraction EPA 7199 analysis similar to EPA Extraction also removes anions and metals in the soil sample redox, ph, sulfides, Mg2+, Fe2+ affect extraction, oxidation and reduction between Cr(III) and Cr(VI). Analysis step Preservation buffer Eluents 23 Proprietary & Confidential

23 Comparison of NH4 and LiOH eluent for Cr(VI) extracted from NIST mau 0 A) NH4OH eluent B) LiOH eluent Column: IonPac AS7 Eluent A: 250 mm (NH 4 ) 2 SO 4, 100 mm NH 4 OH Eluent B: 78 mm LiSO 4, 100 mm LiOH Post Column Reagent: 2 mm diphenylcarbazide 10% methanol 1N sulfuric acid 0 10 Minutes LiOH is a weaker eluent Wider peak area resulting in lower sensitivity Double the run time 24 Proprietary & Confidential

24 Disadvantages of LiOH as a Preservation buffer and Eluent LiOH/LiSO4 is not a buffer Lithium hydroxide isn't available as a concentrated solution and contaminated to various degrees with carbonate, compromising reliability of the buffer. LiOH costs roughly 5x that of a comparable quality sodium hydroxide. Li 2 SO 4 costs roughly 2x that of a comparable quality grade of Na 2 SO 4. Lithium salts are moderately toxic while sodium and ammonium salts are not. 25 Proprietary & Confidential

25 Results of Cr(VI) extracts from NIST 2700 Eluent NIST Standard Soil (550 mg/kg per ICP- MS) Level of Cr(VI) as CrO42-(mg/kg) Level of Cr(VI) as CrO42- (mg/kg) (total from 2 extractions) NH 4 OH and (NH 4 ) 2 SO 4. LiOH and Li 2 SO NA No difference between NH4 and LiOH Eluents. Second extraction resulted in more Cr(VI) suggests that extraction is inefficient 26 Proprietary & Confidential

26 Analysis Cr (VI) of NIST Standard SRM 2701 Comparison of the ph between Eluents before and after Post column Mixing NH4SO4 Eluent NH4SO4 Eluent + PCR reagent LiOH Eluent LiOH Eluent + PCR reagent No Difference in ph to affect the overall reaction of Cr(VI) with the post column reagent 27 Proprietary & Confidential

27 Analysis Cr (VI) of NIST Standard SRM 2701 Comparison of Absorbance using NH4SO4 and LiOH eluents Eluent conc. of Cr(VI) standard (ppb) Absorbance Ammonium Hydroxide conc. of Cr(VI) standard (ppb) Absorbance Lithium Hydroxide Equivalent Results using either Eluents and no chromatography 28 Proprietary & Confidential

28 Conclusion Improvements to EPA are sufficient for the proposed MDL and Public Health Goals from CA. EPA / 7199 can also be used for Cr(VI) from soil samples. Discrepancies with known standards are due to poor extraction efficiencies and known metals that interfere with Cr(VI) extraction. 29 Proprietary & Confidential