1.RV Knorr docked at Woods Hole, MA (WHOI)Jennifer, Jack, Greg and Carrie on board RV KnorrRV Knorr is known for supporting the WHOI andFrench researchers who discovered the wreck of the Driscoll & Cutter with PID-based arsenic GCs on1RMS Titanic in 1985board the RV Knorr

2. Introduction Over one third of the arsenic in theatmosphere comes from man-madesources, notably fossil fuel combustionand copper smelting, while the rest isfrom natural sources such as volcanoes Arsenic can cause bladder, lung, andskin cancer in humans (NationalAcademy of Science 1999) PID Analyzers, LLC 2 3. Arsenic Rule Although EPA regulations are set for total Asconcentrations in drinking water; the standard is 10 partsper billion ppb (http://water.epa.gov/lawsregs/rulesregs/sdwa/arsenic/regulations.cfm),the element can exist in different oxidation states (+V,+III, -III) and inorganic and organic forms within a givenoxidation state (e.g., As+V as arsenate, AsO43- ordimethyl arsinate, (CH3)2AsO2 -); these all have differentbioavailability and toxicity (e.g., Sanders, 1979). Therefore, the chemical speciation of As in natural waterscan be just as relevant as its total concentration.PID Analyzers, LLC3 4. Arsenic contamination in food & juice Arsenic contamination in foods or juices canoccur from As contaminated water or soil A number of techniques have been used for thedetermination of As; some of these are quitecomplex and expensive as shown in the next slide A relatively new technique, photoionization (PID)has been used since the 1980s for the analysis ofAs compounds in sea water; we will discuss thattechnique in this paperPID Analyzers, LLC 4 5. Instrumentation for theAnalysis of ArsenicTypeDetection Limit (ug/L)Cost ($)ICP-MS1.4200,000ICP-OES 880,000GFAAS 880,000HGAAS 0.560,000 ASV130,000PID 112,000GC-PID0.07520,000 PID Analyzers, LLC5 6. Hydride Generation The simplest and most common method for converting Asin solution to a measurable species is hydride generation(formation of AsH3 (g) with Na BH4 as a reducing agent)and using pH adjustment for speciation. As III is converted to arsine using a TRIS-HCl buffer-pH 6.2with NaBH4 reducing agent in the presence of sulfanilamide(0.5 mL of a 2% solution) to remove nitrite interference. Forthe PID only method and AsH3,as As III, the gas from hydridegeneration flows through the PID. The PID has enoughsensitivity so that it does not have to be concentrated.PID Analyzers, LLC6 7. Hydride generation continued The AsH3 is cryogenically trapped, and then determined viaGC with a 2 m Carbopak B-HT packed column (1/8 FEPTeflon tubing) at 25 C and PID. The results for Hydride generation at 0.5 M HCl and GC/PIDdetection produces the concentration of As(III + V) As(V) isthen the difference between the two separatedeterminations. The detection limit for inorganic As is 0.075ug/L and precision at 40 ug/L is better than 5% (relativestandard deviation, RSD) (12). The standard additionsmethod of calibration can be used to improve the accuracy. A chromatogram of a low level (ppb) arsenic sample isshown in the next slide PID Analyzers, LLC 7 8. Low ppb Levels of AsH3 by GC PIDPID Analyzers, LLC 8 9. Photoionization The PID uses a 10.6 eV lamp to ionize arsine(g) generated by reduction with NaBH4. WhenAsH3 absorbs a photon, it forms a positive ionAsH3+ plus an electron (e-).PID Analyzers, LLC 9 10. Photoionization continued The positive ions are collected in an ionizationchamber where the bias electrode pushes theions to the collection electrode and thecurrent collected is proportional to theconcentration over a range of 107 from ppb to%. The schematic of the PID is shown in thenext slide. PID Analyzers, LLC10 11. PID for Arsenic SpeciesSchematic of PIDPhoto PID PID Analyzers, LLC 11 12. Calibration Curve for AsH3- PID Calibration Curve As in Water- PID2000y = 29.427x - 25.0181500 AsH3 ReadingR2 = 0.99831000 500 0 0 1020 30 40 50 60-500 ug/L As in waterPID Analyzers, LLC12 13. Comparison of the Precision of VariousInstrumental Techniques for Arsenic Technique DL (ug/L)RSD %PN-T-MIP 500 4.8GF-3F-MP50 1.8HG-CT-3F-MIP 0.8 6.7HG-GFT-3F-MIP0.4 4.5HG-PID Driscoll (2006)110HG-GC-PID Cutter (1991)>0.075