# Chromium, Hexavalent by Ion Chromatography (7605)

​CHROMIUM, HEXAVALENT by Ion Chromatography Cr(VI)
MW: 52.00 (Cr); 99.99 (CrO3 )
METHOD: 7605, Issue 1
CAS: 18540-29-9
PROPERTIES:
Issue 1: 15 March 2003
oxidizing agent
Vary depending upon the compound; chromate commonly used, “chrome six.”
SAMPLING SAMPLER:
RTECS: GB6262000
EVALUATION: FULL
OSHA : 0.1 mg/m3 (as CrO3 ) NIOSH: 0.001 mg/m3 /10 h; carcinogen ACGIH: 0.050 mg/m3 (as Cr, soluble); some insoluble chromates are human carcinogens
SYNONYMS:
7605
FILTER (5.0-:m PVC membrane)
FLOW RATE: 1 to 4 L/min
MEASUREMENT TECHNIQUE:
Ion chromatography with post-column derivatization and UV detection.
ANALYTE:
CrO4 -2 -diphenylcarbazide (DPC) complex 5 mL 2% NaOH- 3% Na2 CO3 . Dilute to 25 mL after heating.
VOL-MIN: -MAX:
1 L @ 0.05 mg/m3 400 L
EXTRACTION:
SHIPMENT:
Routine. Can be shipped cold when deemed necessary.
INJECTION VOLUME:
100 :L
COLUMN:
Dionex NG1 Guard, HPIC- AS7 Separator or equivalent
MOBILE PHASE:
250 mM (NH4 )2 SO4 /100 mM NH4 OH
FLOW RATE:
1.0 mL/min; 0.7 mL/min post column
POST-COLUMN REAGENT:
2.0 mM DPC + 10% MeOH +1N H2 SO4
DETECTOR:
540 nm
CALIBRATION:
Standard solutions of K2 Cr2 O7 in NaOH-Na2 CO3 buffer
OVERALL PRECISION (Ö r T ): 0.07
RANGE:
0.05 to 20 :g per sample
ACCURACY:
ESTIMATED LOD: 0.02 :g per sample [3]
SAMPLE STABILITY:
BLANKS:
Stable for 2 weeks at room temperature. Stable for 4 weeks if stored in refrigerator. 2 to 10 field blanks per set
ACCURACY RANGE STUDIED:
0.05 to 120 :g Cr(VI) [1,2]
BIAS:
-1.6% [2]
± 17.4% (0.6 - 960 :g/m3 ) [1]
PRECISION ( þ r ):
0.015 @ 0.5 to 5 :g/sample [3]
APPLICABILITY: The working range is 0.00025 to 0.1 mg/m3 for a 200-L air sample. This method can be used for the determination of Cr(VI) using 2% NaOH - 3% Na2 CO3 for extraction. INTERFERENCES: Possible interferences are iron, copper, nickel, and vanadium; 10 :g of any of these causes an absorbance equivalent to approximately 0.02 :g Cr(VI) due to formation of colored complexes. Interference due to reducing agents (e.g., Fe, Fe++) is minimized by alkaline extraction (step 5). OTHER METHODS: Method 7703 is a field portable method for Cr(VI). OSHA Method W4001 is for the measurement of Cr(VI) in wipe samples [4]. OSHA Method ID-215 is for measurement of Cr(VI) and employs precipitation to reduce Cr(III) oxidation. [5]. A similar air method is ISO 16740 [6]. EPA Method 218.6 is for water matrices [7]. Method 7604 is also specific for hexavalent chromium, using ion chromatography, but has a higher detection limit than 7605.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​CH RO MIUM , HEX AVA LEN T: Me thod 7605, Issue 1 dated 15 M arch 200 3 - Page 2 o f 5 REAGENTS:
EQUIPMENT:
1. Sulfuric ac id, con c. (98 % w/w).* 2. Am m onium hydroxide, conc. (28 %).* 3. Am monium sulfate monohydrate, reagent grade. 4. Sodium carbonate, anhydrous. 5. Sodium hydroxide, reag ent grade .* 6. Me than ol, HP LC grad e.* 7. 1,5-Diphenylcarbazide, reagent grade. 8. Potassium dichromate or potassium chromate.* Dry at 100 °C and store in a desiccator. 9. Post-C olum n Derivatizing Reage nt: Diphenylcarbazide solution. Dissolve 500 mg 1,5-diphenylcarbazide in 100 mL HPLC-grade methanol. W hile stirring, add 500 mL water containing 28 mL of conc. sulfuric acid. Dilute to a final volume of one liter with water. This reagent is stable for 4 - 5 days. Prepare in one-liter quantities as needed. 10. Cr(VI) standard, 1000 :g/mL. Dissolve 2.829 g po tass ium dichrom ate in d eionized water to m ak e one liter, or use com m ercially ava ilable solution. NOT E: 3.731 g K 2CrO 4 can also be used. 11. Calibration stock solution, 1.0 :g/m L. Dilute 1000 :g/m L Cr(VI) s tand ard 1 :100 0 with deionized water. 12. Filter extraction solution, 2% NaOH-3% Na 2CO 3. Dissolve 20 g NaOH and 30 g Na 2CO 3 in deionized water to mak e one liter of solution. 13. Eluent (mobile phase); 250 mM amm onium sulfate/200 mM amm onium hydroxide. Dissolve 33 g am m onium sulfate in approximately 500 mL distilled water and add 6.5 m L co nc. am m onium hydroxide. Dilute to one liter with distilled water and mix. 14. Nitrogen, pre-purified.
1. Sam pler: polyvinyl chloride (PVC) filter, 5.0-:m pore size , 37-m m diam ete r in polystyrene cas sette filter holder. NOTE: Som e PVC filters promote reduction of Cr(VI). Check each lot of filters for recovery of Cr(VI) standard. 2. Personal sa m pling pum p, 1 to 4 L/m in, with flexible connecting tubing. 3. Vials, scintillation, 20-mL glass, PTFE-lined screw cap.** 4. Forceps, nonmetallic. 5. Gloves, polypropylene or latex. 6. Liquid chromatography apparatus consisting of au tosa m pler; pu m p; NG1 (Dionex Corp.) or equivalent guard column; HPIC-AS7, 4 x 250-mm (Dionex Corp.) separator column (or equivalent); post-column rea gent delivery system, 2.2-m PEEK™ tubing m ixing/re action loop w ith 1 m in a wa ter ba th at 32 °C ± 3 °C ; and UV detector. 7. Filtration apparatus, PTFE luer-lock filter (Gelman IC Acrodisc or equivalent)/syringe. 8. Bea kers , borosilicate, 50 -m L.** 9. W atch glass.** 10. Volum etric flasks , 25-, 100-, and 10 00-m L.** 11. Oven at 107°C, not to exceed 115°C. NOTE: H ot plate can be used. A n ultrasonic bath can be used instead of oven or hot plate. 12. Micropipettes, 10-:L to 0.5-mL. 13. Pipettes, T D 5-m L.** 14. Bagge d refrigera nt.
rinse thoroughly before use.
SPECIAL PRECAUTIONS: Many chrom ate com pounds are suspected hum an carcinogens [8]. All sample preparation should be performed in a hood. Concentrated acids and bases are toxic and corrosive. W hen working with concentrated acids and bases, wear protective clothing. Amm onium hydroxide is a respiratory irritant. Methanol is flamm able and toxic.
SAMPLING: 1. Calibrate the sampling pump with a representative sampler in line. 2. Sam ple at a n ac curately kn own flow ra te in the rang e 1 to 4 L/m in for a sam ple size of 1 to 400 L. Do not excee d 1 m g total dust loading on the filter.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​CH RO MIUM , HEX AVA LEN T: Me thod 7605, Issue 1 dated 15 M arch 200 3 - Page 3 o f 5 3. Filters can be left in the cass ettes for shipping to the lab, b ut to m inim ize sample contamination during shipping, rem ove the filter from the cassette within one hour of completion of sampling and place it in a vial to be shipped to the laboratory. Handle the filter only with gloved hands and nonmetallic forceps. Discard the backup pad. As a precaution, it is recomm ended to ship the samples with bag ged refrige rant.
SAMPLE PREPARATION: 4. Don a clean pair of disposable plastic gloves (to pre vent s am ple contamination). Using forceps, transfer the PVC filter to a 50-mL beaker, and add 5.0 mL filter extraction solution, 2% NaOH/3% Na 2CO 3. Start m edia blank s at this point. NOTE 1: If significant amounts of Cr[III] are expected to be present in the samples, either (a) degas the sodium hydroxide/sod ium carb ona te extraction so lution by bubb ling nitrog en throug h it for 5 m in. before p roceed ing, or (b) us e a precipitation re age nt [1]. NOT E 2: If only soluble chromates are o f interest, use am m onium sulfate buffer in p lace of ca rbon ate extra ction s olution [9, 10]. 5. Cover the beaker with a watchglass and heat it to near the boiling point (100°C to 115°C) in an oven with occasional swirling for 45 min. Do not boil the solution. Longer heating times (up to 90 minutes) may be necessary for some samples (e.g., paint spray). Do not allow the solution to evaporate to d ryness because hexavalent chromium may be lost due to reaction with the PVC filter and/or co-collected aerosol constituents. An indication that hexavalent chromium has been lost in this manner is a brown-colored PVC filter. NOTE: A ho t plate, heate r block, or ultrasonic bath can also b e us ed fo r this ste p [9, 11 ]. a. Cool the solution and transfer it qu antitatively with distilled water rinses to a 25-mL volumetric flask. Bring to volume with distilled water. NOTE: If the solution is cloudy, filter an aliquot through a PTFE luer lock filter attached to a syringe. b. Transfer an aliquot of the solution to the appropriate vial for the chromatograph’s autosampler and analyze (steps 9 through 13).
CALIBRATION AND QUALITY CONTRO L: 6. Calibrate daily with at least six working standards. Transfer 5 mL of extraction solution to each of a series of 25-mL volumetric flasks. Pipet known volumes (0 to 5 m L) of calibra tion sto ck solution (1.0 :g/m L) into the volumetric flasks. For higher standards, pipet 10 - 20 :L of the 1000 :g/mL concentrated stock and bring the volume to 25 mL with distilled water. These working standards contain 0 to 20 :g Cr(VI) per sample. 7. Analyze the working standard s together with blanks and sam ples (steps 9 through 1 3). 8. Prepare a calibration g raph [instrum ent re spo nse vs. :g Cr(VI)].
MEASUREMENT: 9. Set wavelength on the detector to 540 nm. 10. Set the liquid chromatograph to manufacturer's recomm endations and parameters given on page 7605-1. W ith a mobile phase flow rate of 1.0 mL/m in., a post-colum n reagent flow rate of 0.7 mL/min., and a 2.2-m post-column tube, the derivative retention time should be approximately 3.7 - 4.7 minutes. NOTE: If the ins trum ent re spo nse for the sam ples is higher tha n the standard s, dilute using a 1:5 dilution of extraction solution:water to maintain a constant ionic strength; repeat the analysis; and m ultiply the measured concentration by the app ropriate dilution facto r. Alternatively, inject a sm aller volum e and m ultiply by the appropriate factor. 11. After the analysis is complete, flush the entire system with ASTM Type II water for at least one hour at 1.0 mL/m in. with all columns on line. Rem ove the columns and continue flushing for an additional two hours. Flush the autosampler with several injections of water. Leaving the columns in line while the system is idle is not recomm ended.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​CH RO MIUM , HEX AVA LEN T: Me thod 7605, Issue 1 dated 15 M arch 200 3 - Page 4 o f 5 CALCULATIONS: 12. From the calibration graph, determine the mass of C r(VI) in e ach sam ple, W (:g), and in the average blank, B (:g). 13. Ca lculate con cen tration, C (m g/m 3), of Cr(VI) in the air volume sam pled, V (L):
NO TE : :g/L = m g/m 3
EVALUATION OF METHOD: This method was evaluated in the laboratory with spiked filters and a certified reference material containing a known loading of Cr(VI). This c ertified reference material (CRM ) is European Comm ission, Institute for Reference Materials and Measurements EC/IRMM) CRM 545, Cr(VI) and Cr(total) in welding dust loaded on a glass fiber filter [12]. This method was evaluated for extraction efficiency over the concentration range of 0.15 - 5 :g/sample testing two brands of filters, SILICAL® and G LA-5000™[3]. In these experiments, test atmospheres were no t generate d; inste ad, C r(VI) as the dichromate was fortified on the face of the sam ple filters, then 240 L of air with 35% relative humidity was pulled through at 1 L/min. A 30-day storage study using both types of filters was conducted at 1.5 :g/sample (30x LOQ) at ambient room temperature and 4 °C. The average recovery of the sto red sam ples w as 94.8% . The estim atio n of the lim it of detec tion and lim it of quantitation (LO D/LOQ ),were de term ined ana lyzing a se ries of liquid sta nda rds . The LO D and L OQ , 0.02
    g/sample and 0.07 :g/sa m ple respe ctively were ca lculated by Burk art's m etho d [13].
To fully evalua te this m etho d, a field-stud y was con duc ted in w hich side-by-side sam ples were tak en to m easure exposures to Cr(VI) during spray-painting and electroplating operations. Th ese sam ples were analyzed subsequently by 4 different methods (NIOSH Method 760 5, 7703, 7300 and OS HA ID-215) [1 ]. NIOSH m etho d 73 00 w as u sed to measure total chromium. The results from the other 3 methods correlated very well showing no statistical difference among the 3 methods. Recoveries of 98.4 (+ 3.4) % were obtained for C RM 545 (n = 6) [2].
REFERENCES: [1]
[2] [3]
[4]
[5]
[6] [7]
Boiano JM, W allace ME, Sieber W K, Groff JH, W ang J, Ashley K [2000]. Com parison of three sampling and analytical methods for the determination of airborne hex avalent ch rom ium . J Environ M onit 2: 329333. Ashley K, Andrews RN, Cavazos L, Dem ang e M [2001]. Ultrasonic extraction as a sample preparation technique for elemental analysis by atomic spectrometry. J Anal At Spectrom 16:1147-1153. Foote P, W ickman DC, Perkins JB [2002]. Back-up data report for determination of hexavalent chromium by HPLC with post-column derivatization, prepared under NIOSH C ontract 2000-95-2955., unpublished, Augus t . Eide ME [2 000]. H exavalent C hrom ium , Meth od No . W 4001. Sa lt Lake City, Utah: US Department of Labor (U SDO L), Occ upational Safety and Health Adm inistration (OSH A), Salt Lake T echnical Cen ter. (Septem ber). Ku JC, Eide M [1998]. Hexavalent chrom ium in the workp lace atm osphere, O SH A ID -215. Sa lt Lake City, Utah: US Departm ent of Lab or (U SD OL ), Oc cup ationa l Safe ty and H ealth A dm inistration (O SH A), Sa lt Lake Tech nical Center (1998). ISO [2003]. Method No. 16740 (Draft International Standar d) , M arch, 1999. Reference Num ber ISO/TC146 /SC 2/W G 2N136. Geneva, Switzerland: International Organization for Standardization. Arar EJ, Pfaff, JD, Martin TD [1994]. Method 218.6, Revision 3.3 (199 4). Cincinn ati, Oh io: Environmental Monitoring Systems La boratory, Office of Research and Developm ent, U.S. Environmental Prote ctio n Agency.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition ​CH RO MIUM , HEX AVA LEN T: Me thod 7605, Issue 1 dated 15 M arch 200 3 - Page 5 o f 5 [8] NIOSH [1975]. Criteria for a recomm ended standard: occupational exposure to chro m ium (VI). Cincinnati, OH: U.S. Department of H ealth, E duc ation, a nd W elfare ; National Ins titute for Occupational Safety and Health; DHEW (NIOSH) Publication No. 76-129. [9] W ang J, A sh ley K , Ke nn ed y ER, Neumeister C [1997]. Determination of hexavalent chromium in industrial hygiene sa m ples using ultrasonic extraction and flow injection a nalysis. Ana lyst 122: 13071312. [10] Ndung’u K, Djane N-K, Malcus F, Mathiasson L [1999]. Ultrasonic extraction of hexavalent ch rom ium in solid samples followed by automate d a na lysis using a combination of supported liquid mem brane extra ction a nd u v detection in a flow system . Ana lyst 124: 1367-1372. [11] W ang J, Ashley K, Marlow D, En gland EC , Carlton G [1999]. Field me thod for the determination of hexavalent chromium by ultrasonic and strong anion exchange solid phase extraction. Anal Chem 71: 1027-1032. [12] EC/IRMM [1997]. Certificate of analysis, CR M545: C r(V I) and tota l leacheable Cr in welding dust loaded on a filter. Brussels: Comm ission of the European Comm unities, Institute for Reference Materials and Me asu rem ents . [13] Burka rt JA [1986]. General procedures for limit of detection calculations in industrial hygiene chem istry laboratory. Appl Ind Hyg, 1(3): 153-155 .
MET HOD CO NTRIBUTO RS: Kevin Ashley, NIOSH/DART. Penny A. Foote, DataChem Laboratories, Inc., Salt Lake City, Utah James B. Perkins, DataChem Laboratories, Inc, Salt Lake City, Utah Don C. W ickman, DataChem Laboratories, Inc, Salt Lake City, Utah
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition