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 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

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

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

LABORATORY METHOD FOR Cr(VI) 1.Sample onto PVC filters] 2.Hot plate extraction using pH ~8 buffer 3.Ion chromatography to isolate Cr(VI) 4.Post-column derivatization with 1-5 Diphenylcarbazide 5.Visible detection of Cr-DPC complex

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

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)

FIELD METHOD FOR Cr(VI) 1.Sample onto PVC;[ MCE or PTFE ok if analyzed promptly.] 2.Ultrasonic extraction 3.SAE-SPE to isolate Cr(VI) 4.Elute, acidify, and react Cr(VI) with DPC 5.Measure Cr-DPC complex with portable UV/Vis

Cr(VI) REACTION WITH DPC: NH-NH-C 6 H 6 / O=C+ Cr(VI) \ NH-NH-C 6 H 6 Diphenylcarbazide 9 9 N - N - C 6 H 6 // * C-O-Cr (H 2 O) 4 \ ! N = N - C 6 H 6 Diphenylcarbazone - Cr(III) complex DPC Cross-reactants: Mo, Mg, Hg, V

Cr(VI) ANALYTICAL METHODS COMPARISON ______________________________________________ Parameter Lab Methods Field Method Extraction:NaOH/Na 2 CO 3 *(NH 4 ) 2 SO 4 /NH 4 OH HotplateUltrasonic bath Cr(VI) sep’n.:Ion chromatographySPE Eluent:(NH 4 ) 2 SO 4 /NH 4 OH(NH 4 ) 2 SO 4 /NH 4 OH Detection:Cr-DPC (540 nm)Cr-DPC (540 nm) LOD/LOQ:0.02/0.07 F g/m /0.30 F g/m 3 ___________________________________________ *NIOSH: degas; OSHA: ppt’n. for Cr(III) º Cr(VI)

METHOD PERFORMANCE– IRMM CRM 545 ( Cr[VI] in welding fume on filters) _____________________________________________ Analytical Method n % Recovery (+/-RSD) NIOSH 7605(lab) OSHA ID-215 (lab) NIOSH 7703 (field) _____________________________________________

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

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 ~ hrs. –Field method alleviates sample instability problems

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

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

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.

ACKNOWLEDGMENTS CDC/NIOSH U.S. Air Force Jin Wang Ellen England Jim Boiano David Marlow Marjorie Wallace Karl Sieber Jensen Groff

y = x r 2 = Cr VI Concentration (  g /m 3 ) OSHA ID-215 Cr VI Concentration (  g/m 3 ) NIOSH 7605 Facility 1 Facility 2 The slope is not significantly different from unity Comparison of Hexavalent Chromium Concentrations by Sample Cluster: OSHA ID-215 and NIOSH 7605

y = x r 2 = Cr VI Concentration (  g/m 3 ) NIOSH 7605 Cr VI Concentration (  g/m 3 ) NIOSH 7703 Facility 1 Facility 2 The slope is not significantly different from unity Comparison of Hexavalent Chromium Concentrations by Sample Cluster: NIOSH 7605 and 7703