6.1. Safety Precautions

6.1.1. Arsenic is considered a human carcinogen (8.1., 8.6.). Use extreme care when handling arsenic or arsenic-containing compounds.

6.1.2. All work with concentrated acids is potentially hazardous. Care should be exercised when handling any acidic solutions. Acid solution contact with work surfaces should be avoided. If any acid contacts the eyes, skin, or clothes, flush the area immediately with copious amounts of water. Medical treatment may be necessary.

6.1.3. Always wear safety glasses and protective clothing when using chemicals. Prepare all mixtures, samples, or dilutions in an exhaust hood. To avoid exposure to acid vapors, do not remove any beakers from the hoods until they have returned to room temperature and have been diluted.

6.1.4. Use a pipette bulb, never pipette by mouth.

6.1.5. When scoring glass sampling tubes to remove the sorbent before analysis, score with care. Apply only enough pressure to scratch a clean mark on the glass. Use a paper towel or cloth to support the opposite side while scoring. Moisten the mark with DI H₂O and wrap the tube in cloth before breaking. If the tube does not break easily, re-score. Dispose of glass in a waste receptacle specifically designed and designated for broken-glass.

6.1.6. Consult the Standard Operating Procedure (SOP) (8.12.) and any instrument manuals before using any instrument.

6.1.7. Since metallic elements and other toxic substances are vaporized during HGA operation, it is imperative that an exhaust hood is installed and used directly above the graphite furnace. Always ensure the exhaust system is operating before proceeding with the analysis.

6.1.8. Do not look directly at the furnace during the atomization step or at the emission of an electrodeless discharge lamp.

6.2. Equipment

6.2.1. Atomic absorption spectrophotometer consisting of a(an):

1. Heated graphite furnace atomizer with argon purge system and graphite tubes

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Note:

If samples are analyzed in matrices other than recommended in this method (4% HNO3, 200 µg/mL Ni), or matrix-matching samples and standards is difficult, it is recommended to use an HGA capable of significant resolution of background, such as a Zeeman/L'vov Platform-type HGA (Perkin-Elmer, Norwalk, CT) with pyrolytically-coated graphite tubes.

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2. Pressure-regulating devices capable of maintaining constant argon purge pressure.
3. Optical system capable of isolating the desired wavelength of radiation.
4. Adjustable slit.
5. Light measuring and amplifying device.
6. Display, strip chart, or computer interface for indicating the amount of absorbed radiation.
7. Deuterium Arc Background Corrector (if Zeeman background correction is unavailable).
8. Electrodeless Discharge Lamp (EDL) for arsenic and an EDL power supply (Note: A modulated system is necessary when using a Zeeman HGA.).
9. Automatic sampler.

6.2.2. Glassware

1. Phillips beakers, 125- and 250-mL
2. Volumetric flasks, Class A: 10-, 25-, 50- and 100-mL
3. Pipettes, Class A: Assorted sizes
4. Scintillation vials, 20-mL (for desorbing charcoal)

6.2.3. Forceps.

6.2.4. Exhaust hood and hotplate, or microwave digestion system (model no. MDS-81, CEM Corp., Matthews, NC).

6.2.5. Filtering apparatus consisting of MCE filters, 0.45-µm pore size, 47-mm diameter (cat. no. HAWP 047 00, Millipore Corp., Bedford, MA) and filtering apparatus (cat. no. XX15 047 00, Millipore).

6.2.6. Automatic pipets, adjustable, 0.1 to 5.0 mL range (models P-1000 and P-5000, Rainin Instruments Co., Woburn, MA).

6.2.7. Glass tube scorer, or needle, 21 to 25 gauge - for glass wool, foam, and sorbent from glass tubes. A piece of bent wire can also be used.

6.2.8. Exhaust vent.

6.2.9. Ultrasonic bath (for arsine samples).

6.2.10. Analytical balance (0.01 mg).

6.2.11. Arsine sampling media (for standard preparation if arsine has been collected):   Obtain six sampling tubes each containing 400 mg (front) and 200 mg (backup) sections of activated coconut shell charcoal.

6.3. Reagents (All chemicals should be reagent grade or better.)

6.3.1. Deionized water (DI H₂O) with a specific conductance of less than 10 µS.

6.3.2. Mineral acids (used for digestions and dilution solution preparation)

CAUTION:   Refer to Sections 6.1.2.-6.1.3. before using acids.

1. Hydrochloric acid (HCl), concentrated (36.5 to 38%).
   
2. Nitric acid (HNO₃), concentrated (69 to 71%).

6.3.3. Mineral acids (used for cleaning glassware)

CAUTION: Refer to Sections 6.1.2.-6.1.3. before using acids.

1. Nitric acid, 1:1 HNO₃/DI H₂O mixture: Carefully add a measured volume of concentrated HNO₃ to an equal volume of DI H₂O.
   
2. Nitric acid 10% v/v: Carefully add 100 mL of concentrated HNO₃ to 500 mL of DI H₂O and then dilute to 1 L.

6.3.4. Nickelous nitrate [Ni(NO₃)₂· 6H₂O].

6.3.5. Stabilizer, 1,000 µg/mL Ni solution - Dissolve 5.0 g nickelous nitrate in 100 mL of DI H₂O, add 5 mL concentrated HNO₃, and dilute to 1-L with DI H₂O.

6.3.6. Mixed cellulose ester (MCE) filters, 0.8-µm pore size, 37-mm diameter.

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(Note:

These filters are used for matrix-matching standards with samples. If possible, use the same brand and lot of filters for air sampling and matrix-matching.)

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6.3.7. Diluting solution: Place 20 blank MCE filters in a cleaned 250-mL Phillips beaker and carefully add 100 mL of concentrated HNO₃ and 100 mL of the 1,000 µg/mL nickel solution. Digest this mixture on a hot plate until about 20 to 40 mL of solution remain. Transfer the solution to a cleaned 500-mL volumetric flask, add 2 mL of concentrated HCl, and dilute to volume with DI H₂O.

6.3.8. Standard solution, 1,000 µg/mL arsenic: If possible, use commercially available aqueous standards. Observe expiration dates; if none, properly dispose the standard after 1 year.

6.3.9. If a commercial standard (Section 6.3.8.) is not available, a 1,000 µg/mL solution can be prepared as follows:

1. Sodium hydroxide (NaOH).
2. Arsenic trioxide (As₂O₃).
3. Sodium hydroxide, 10% solution: Dissolve 10 g of NaOH in about 75 mL of DI H₂O. Dilute to 100 mL.

In a cleaned 1-L volumetric flask, dissolve 1.320 g As₂O₃ in 25 mL 10% NaOH. Dilute to volume with DI H₂O, and mix. Dispose of properly after 1 year.

6.3.10. Argon, compressed gas (for HGA tube purges).

6.4. Glassware Preparation

6.4.1. Place the Phillips beakers in an exhaust hood and add approximately 10 mL of a 1:1 HNO₃/DI H₂O mixture in each 125- or 250-mL Phillips beaker. Using a hot plate, apply moderate heat to the beakers until refluxing occurs. Carefully decant the acid mixture into a waste container and allow the beakers to cool before removing from the hood. Rinse the beakers thoroughly with DI H₂O.

6.4.2. Rinse all volumetric flasks with 10% v/v HNO₃ and then rinse thoroughly with DI H₂O.

6.4.3. Allow all glassware to air dry before proceeding.

6.5. Standards

6.5.1. Dilute stock solutions:

Prepare dilute arsenic stock solutions (0.1-, 1-, and 10-µg/mL) by diluting aliquots of the 1,000-µg/mL standard solution with DI H₂O. Prepare the diluted stock solutions on the same day the working standards are prepared.

6.5.2. Working standards:

A dilution scheme using 0.1-, 1-, and 10-µg/mL stock solutions is proposed below.

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Working Standard (µg/mL)	Stock Solution (µg/mL)	Stock solution Aliquot (mL)	Final Volume* (mL)
0.01 0.02 0.05 0.1   0.2   0.5	0.1   0.1 1 1 10   10	10 20   5 10   2   5	100 100 100 100 100 100
*  Diluent is the diluting solution (Section 6.3.7.)

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Dilute all working standards to volume using the diluting solution. This will assure the matrix (acid, sample filter, and nickel content) of the samples (air and wipe) and standards are closely matched. Dispose working standards after 6 months.

6.5.3. Standards for arsine determinations

Remove the 400-mg section of charcoal sorbent from six arsine sampling tubes. Place each 400-mg section in a separate vial. Pipet a 3-mL aliquot from each working standard (prepared in Section 6.5.2.) into each vial such that six standards ranging in concentration from 0.01 to 0.5 µg/mL arsenic are prepared with a charcoal matrix.

6.6. Sample Preparation

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Note:

Always prepare blank samples with every sample set. Prepare an additional blank media sample any time an extra procedure is used (i.e. wiping out the particulate contained inside a cassette with an MCE filter or preparing a contaminated backup pad). If possible, this blank media should be from the same manufactured lot as the prepared filter, tube, or backup pad.

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1. Preparation of air and wipe sample filters
   
   
   1. Open the filter cassette or scintillation vial, carefully remove the sample filter with forceps, and place in a labeled Phillips beaker. Use 125-mL beakers for air samples and smear tabs. If the cassette or vial contains loose dust, carefully rinse the dust into the beaker with DI H₂O. If necessary, wipe out the dust with a clean MCE filter and place this filter in the sample beaker.
      
      
   2. Prepare and analyze backup pads if:
      1. volatile inorganic arsenic species are suspected, or
      2. the backup pad appears to be discolored. Discoloration may be due to leakage of air around the filter during sampling.
         
         
      If analysis of the backup pad is necessary, place each backup pad in a separate beaker.
   
   
   
2. Preparation of bulk samples
   
   
   1. Review any available material safety data sheets to determine safe bulk handling. The data may also offer a clue regarding the aliquot amount needed for adequate detection.
      
      
   2. Measure by volume or weight an appropriate aliquot of any liquid bulk sample. Weigh the appropriate amount of any solid bulk sample.
   
   

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Note:

Aliquot amounts of bulks are dependent on the analytical sensitivity, detection limit, and solubility of the material used. If uncertain, a 20- to 50-mg aliquot of a solid material can be taken as a starting point. Make sure the aliquot taken is representative of the entire bulk sample. If necessary, use a mortar and pestle to grind any nonhomogenous particulate bulk samples in an exhaust hood.

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After measuring, transfer the aliquot to a 250-mL Phillips beaker.

3. Preparation of arsine (charcoal) samples
   
   
   1. Score the tube with a glass tube cutter (also see Section 6.1.5.) and then break open the front section of the tube above the glass wool. An alternative approach to scoring and breaking is to carefully remove the glass wool with a bent wire or needle.
      
      
   2. Carefully transfer each section of the sorbent to separate 20-mL scintillation vials without losing any particles.

6.7. Sample Digestion or Extraction

1. MCE air filters and smear tabs
   
   Place the beakers in an exhaust hood and carefully add 3 to 5 mL concentrated HNO₃ and the appropriate amount of Stabilizer (Section 6.3.5.) as shown below. Place the beakers on a hot plate and heat the samples until the appropriate amount of solution remains as shown below.
   
   

   Air Vol (L)	Stabilizer (mL)	Digestion Vol (mL)
   <200	2.0	0.5
   ³ 200	5.0	1.0
   Smear tabs	5.0	1.0

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Note:

If the sample solution is not clear, add a second portion of approximately 1 to 2 mL of concentrated HNO3. Apply heat until the appropriate digestion volume listed above remains.

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Remove the beakers from the hotplate. Allow beakers to cool, then add 100 µL (~2 drops) of HCl to each and swirl the contents.


2. Polyvinyl chloride filters, or backup pads

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Note:

Polyvinyl chloride (PVC) filters are not routinely used for arsenic sample collection and analysis. In some cases the industrial hygienist will sample for total or respirable dust using PVC filters and also submit these samples for analysis. The PVC filter will not be completely digested using the acid digestion listed in this method; rather, the particulate is acid-extracted from the filter. Perchloric acid should not be used to digest arsenic samples collected on PVC filters or backup pads; low recoveries for arsenic were noted when PVC filters were digested using an H2SO4/HCl/HClO4 acid matrix (8.10.). In addition, graphite tube degradation is greatly accelerated from perchloric acid.

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Place the beakers in an exhaust hood and add the following amount of concentrated HNO₃ to the beakers:

Backup pads		10 to 15 mL
PVC filters		3 to 5 mL

Follow the digestion procedure mentioned above (Section 6.7., MCE air filters and smear tabs) and determine the amount of Stabilizer needed, and digestion volumes. After heating on a hot plate and subsequent cooling, each PVC filter should be thoroughly rinsed with DI H₂O during quantitative transfer of the sample solution.

3. Bulk samples
   
   If necessary, use a microwave digestion system to facilitate digestion [For further information regarding microwave digestion, see the Microwave Standard Operating Procedure (8.13.)].
   
   Add 10 to 30 mL HNO₃, 5 mL of Stabilizer, and place the beaker on a hot plate. Digest the bulk sample until the material dissolves and approximately 1 mL of solution remains. Remove the beakers from the hot plate. Allow beakers to cool, then add 40 µL (~2 drops) of HCl to each and swirl the contents.
   
   
4. Arsine (charcoal) samples
   
   To each scintillation vial add 3 mL of Stabilizer solution (Section 6.3.5.). Cap and sonicate each vial contents for 10 min.

6.7.1. Filtration - any solutions samples containing particulate

Digested samples: If particulate matter is present after digesting, allow the sample to cool, add approximately 10 mL DI H₂O, then filter the solution through a 0.45-µm MCE filter. Save the filtrate for analysis. Repeat the digestion procedure above for the filter containing the particulate.

Arsine samples:   If particulate is present after extraction (i.e. charcoal fines), filter the 3-mL solution through a 0.45-µm MCE filter, and analyze the filtrate.

6.7.2. Dilution - all samples

Digested samples:   Allow all beakers to cool to room temperature in an exhaust hood before proceeding. Carefully add about 5 mL of DI H₂O to each beaker, rinsing down the insides of each beaker. Quantitatively transfer each sample solution to individual volumetric flasks. Dilute to volume with DI H₂O and mix well. Recommended final sample solution volumes are:

Air (³200-L), wipe, and bulk samples		25 mL
Air volumes <200-l		10 mL

Larger dilution volumes can be used for bulk samples; however, the final solution volume should contain 4% HNO₃ and 200 µg/mL Ni.

Arsine samples:   For charcoal samples, further dilution is not necessary.

6.7.3. Samples previously prepared for ICP analysis

For samples already prepared and analyzed using OSHA method no. ID-125G, no additional sample preparation is necessary.

6.8. Instrument Setup and Analysis

6.8.1. Set up the spectrometer and HGA according to the SOP (8.12.) or the manufacturer's instructions. Suggested parameters for two specific instruments are shown in Appendix A.

1. Install an EDL for arsenic and allow to stabilize.
2. Optimize conditions such as lamp position, furnace alignment, etc. as mentioned in the SOP (8.12.).
3. Be sure cooling water is circulating around the furnace before heating it and if deuterium (D₂) arc background correction is used, assure the purge air is circulating around the D₂ components before lighting the D₂ lamp.
4. Only for those samples previously prepared using OSHA Method ID-125G:
   Set up the instrument such that a nickel spike is added to each sample or standard immediately prior to HGA initiation. A 10-µL aliquot of the sample can be injected, then overlay 5 µL of Stabilizer (Section 6.3.5.) on the sample before starting the HGA cycle. Standards prepared in Section 6.5. can be used during analysis of these samples.

6.8.2. Inject an aliquot of a standard into the HGA and measure the absorbance of the standard using peak height or area. The standard concentration should be within the linear range. If possible, compare this absorbance to a value from a previous analysis. Measure other prepared working standards first to assure proper instrument operation.

6.8.3. Analyze samples and blanks. Analyze a standard after every four or five samples. Standards should bracket the sample concentrations. Standard readings should be within 10 to 15% of the readings obtained at the beginning of the analysis.

6.8.4. If any samples exceed the linear range, dilute with diluting solution (Section 6.3.7.) to bring them into the working range.

6.8.5. Cadmium, copper, iron, lead, and zinc can be analyzed in conjunction with the arsenic analysis using an atomic absorption spectrophotometer (air/acetylene flame) and direct aspiration. Analytical conditions for flame analysis of these elements are shown in Appendix B. Additional information can be found in OSHA Method No. ID-121 or instrument manufacturers' manuals.

6.9. Analytical Recommendations

6.9.1. The amount of nickel added to each sample can vary slightly from the standards without producing a significant matrix effect. An excess of nickel always needs to be present. (Note: A common range is to have from 100 to 2,000 µg/mL Ni present in the samples and standards.)

6.9.2. When standards are prepared, analyze the old and new standards and compare results to verify the new standard is correct. If two or more 1,000 µg/mL arsenic solutions are available for standard preparations, rotate the preparation from one stock solution to the next to verify the quality.

6.9.3. Keep a permanent record of all standard preparation and comparison data. Assign and follow expiration dates for all standards.

6.9.4. Always analyze blank samples along with the other samples. Treat blanks in the same fashion as samples, including any filtration steps.

6.9.5. If possible, analyze quality control samples from an independent source. The quality control samples should be freshly prepared if they are derived from liquid spikes on MCE filters.