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ANALYTICAL METHODS FOR AIRBORNE HEXAVALENT CHROMIUM

ANALYTICAL METHODS FOR AIRBORNE HEXAVALENT CHROMIUM. Kevin Ashley, Ph.D. U.S. Department of Health and Human Services Centers for Disease Control and Prevention National Institute for Occupational Safety and Health Cincinnati, OH 45226. INTRODUCTION .

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ANALYTICAL METHODS FOR AIRBORNE HEXAVALENT CHROMIUM

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  1. ANALYTICAL METHODS FORAIRBORNE HEXAVALENT CHROMIUM Kevin Ashley, Ph.D.U.S. Department of Health and Human ServicesCenters for Disease Control and PreventionNational Institute for Occupational Safety and HealthCincinnati, OH 45226

  2. INTRODUCTION • New Analytical Methods for Cr(VI) in Workplace Air: • NIOSH 7605 (draft) • Revised lab method • NIOSH 7703 (draft) • New field method • OSHA ID-215 • New lab method

  3. INTRODUCTION (continued) • To be presented: • Overview of the three analytical methods for Cr(VI) • Need for updating: increased sensitivity • Advantages and limitations

  4. INTRODUCTION (continued) • Comparison of the performance of the 3 methods • OSHA vs. NIOSH lab vs. NIOSH field • Field studies – On-site method (NIOSH 7703 [draft]) • Examples from aircraft painting/ maintenance

  5. LABORATORY METHOD FOR Cr(VI) • Sample onto PVC filters] • Hot plate extraction using pH ~8 buffer • Ion chromatography to isolate Cr(VI) • Post-column derivatization with 1-5 Diphenylcarbazide • Visible detection of Cr-DPC complex

  6. ISSUES: • Reduction of Cr(VI) to Cr(III) during sampling/extraction: • Use of PVC filter (rather than MCE) • Acid mist & iron in aerosol problematic • Base treatment of filter to stabilize Cr(VI) • pH ~8 buffer stabilizes Cr species in solution

  7. ISSUES: • Oxidation of Cr(III) to Cr(VI) during extraction: • Minimize by using slightly basic buffer • OSHA uses precipitation agent to cause Cr(III)9 • Cr(III)/Cr(VI) redox equilibrium during extraction: • Ammonium sulfate buffer prevents Cr(III):Cr(VI)

  8. FIELD METHOD FOR Cr(VI) • Sample onto PVC;[ MCE or PTFE ok if analyzed promptly.] • Ultrasonic extraction • SAE-SPE to isolate Cr(VI) • Elute, acidify, and react Cr(VI) with DPC • Measure Cr-DPC complex with portable UV/Vis

  9. Cr(VI) REACTION WITH DPC: NH-NH-C6H6 / O=C + Cr(VI) \ NH-NH-C6H6 Diphenylcarbazide99 N - N - C6H6 // * C-O-Cr (H2O)4 \ ! N = N - C6H6Diphenylcarbazone - Cr(III) complex DPC Cross-reactants: Mo, Mg, Hg, V

  10. Cr(VI) ANALYTICAL METHODS COMPARISON ______________________________________________Parameter Lab Methods Field Method Extraction: NaOH/Na2CO3* (NH4)2SO4/NH4OHHotplate Ultrasonic bathCr(VI) sep’n.: Ion chromatography SPEEluent: (NH4)2SO4/NH4OH(NH4)2SO4/NH4OHDetection:Cr-DPC (540 nm)Cr-DPC (540 nm)LOD/LOQ: 0.02/0.07 Fg/m3 0.09/0.30 Fg/m3___________________________________________*NIOSH: degas; OSHA: ppt’n. for Cr(III) º Cr(VI)

  11. METHOD PERFORMANCE– IRMM CRM 545 (Cr[VI] in welding fume on filters) • _____________________________________________Analytical Method n % Recovery (+/-RSD) NIOSH 7605 (lab) 3 94.2 + 9.9OSHA ID-215 (lab) 3 84.3 + 1.9NIOSH 7703 (field) 6 98.4 + 6.7_____________________________________________

  12. Cr(VI) METHOD CRITERIA • Analytical Figures of Merit: • LODs <10x planned OSHA PEL % • Lab & field methods meet NIOSH accuracy criteria % • Costs: • Lab method estd. $50 per sample (by contract lab) • Field method estd. < $15 per sample (excl. labor) • Lab equipment >> field equipment • Field method throughput < lab method

  13. Cr(VI) METHOD CRITERIA(Lab method vs. field method, cont’d.) • Advantages: • Lab method high throughput, automated • Lab method alleviates need for extra field person • Field method results in ~1.5 - 2 hrs. • Field method alleviates sample instability problems

  14. Cr(VI) METHOD CRITERIA(Lab method vs. field method, cont’d.) • Drawbacks: • Lab results not timely (note construction appls.) • High maintenance on equipment for lab method • Field method more hands-on • More work for IH or need for extra body

  15. SUMMARY • Successful methods for speciation of Cr. • Lab and field methods available • Comparison between methods good • Field method field tested • To be published in NMAM

  16. SUMMARY (cont’d.) • Sampling remains problematic. • Reduction of Cr(VI) during sampling of certain aerosols • New strategies & further study needed • ISO lab draft standard based on NIOSH draft lab method.

  17. ACKNOWLEDGMENTS CDC/NIOSHU.S. Air Force Jin Wang Ellen England Jim BoianoDavid MarlowMarjorie WallaceKarl SieberJensen Groff

  18. Comparison of Hexavalent Chromium Concentrations by Sample Cluster: OSHA ID-215 and NIOSH 7605 1000 y = 1.0353x 2 r = 0.9044 100 CrVI Concentration (g/m3) Facility 1 NIOSH 7605 Facility 2 10 The slope is not significantly different from unity 1 1 10 100 1000 CrVI Concentration (g/m3) OSHA ID-215

  19. Comparison of Hexavalent Chromium Concentrations by Sample Cluster: OSHA ID-215 and NIOSH 7703 1000 y = 1.2058x 2 r = 0.9382 100 CrVI Concentration (g/m3) Facility 1 NIOSH 7703 Facility 2 10 The slope is significantly different (p<0.05) from unity 1 1 10 100 1000 CrVI Concentration (g/m3) OSHA ID-215

  20. Comparison of Hexavalent Chromium Concentrations by Sample Cluster: NIOSH 7605 and 7703 1000 y = 1.1267x r2 = 0.8837 100 CrVI Concentration (g/m3) Facility 1 NIOSH 7703 Facility 2 10 The slope is not significantly different from unity 1 1 10 100 1000 CrVI Concentration (g/m3) NIOSH 7605

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