METAL AND METALLOID PARTICULATES IN WORKPLACE ATMOSPHERES
(ICP ANALYSIS)

1. Introduction

1.1. Scope

1.1.1. This method describes the collection and subsequent analysis of airborne metal and metalloid particulate by Inductively Coupled Argon Plasma-Atomic Emission Spectroscopy (ICAP-AES).

1.1.2. This method provides rapid simultaneous analysis and data reduction for a wide range of elements, eliminating the necessity of separate analyses by conventional atomic absorption techniques.

1.1.3. This method was validated for 13 elements (Be, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, V, and Zn). A total of 20 to 21 elements are analyzed, but 8 of these are determined semi-quantitatively only [Ag, Al, As, Ca, Mg, Se, Si, and Sn (dependent on instrument, Te replaces Si for one instrument]. Other elements can be added to or subtracted from the method. The capability for expanding the analysis to other elements is mainly dependent on laboratory instrumentation and element solubility and stability in the acid matrix used for digestion.

1.1.4. The method is compatible with determining exposures to arsenic in industrial environments. The sample is collected, prepared and screened for arsenic using this method. A portion of the sample is resubmitted and analyzed using the discussed technique (Heated Graphite Atomizer with Zeeman/L'vov Platform) in OSHA Method No. ID-105 (8.1.).

1.2. History

1.2.1. Previous to the introduction of ICAP-AES, samples containing metallic particulates were digested in a variety of ways and analyzed by Atomic Absorption Spectroscopy (AAS) at the OSHA Analytical Laboratory.

1.2.2. A first generation plasma source and spectrometer (Jarrell-Ash Model 975 Atomcomp) was then used by the OSHA Analytical Laboratory. The analytical procedure for this instrument is described in OSHA Method No. ID-125 (8.2.).

1.2.3. Procurement of new inductively coupled plasma (ICP) instruments, computers, and software allowed samples to be determined using later technology. This technology includes more sophisticated computer systems for data reduction and instrument control.

1.2.4. Currently, three different ICP instruments at the OSHA Salt Lake Technical Center (OSHA-SLTC) are used to apply this method:

Jobin-Yvon (JY) Model 32 (Instruments SA, Edison, NJ)
Jarrell-Ash Model 975 Atomcomp* (Thermo Jarrell-Ash Corp., Franklin, MA)
Applied Research Lab. (ARL) Model 3560 (ARL, Sunland, CA)

These instruments are further referred to as ICP1, ICP2, or ICP3, respectively.

The Jarrell-Ash system was upgraded with a new computer, generator, and software in 1989.

This method is applicable to any simultaneous spectrometer. This method was validated using ICP1 and the data is presented in a backup report (8.3.). An additional evaluation was performed using ICP3 (8.4.).

2. Detection Limits and Working Ranges (8.3.)

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Note:

This method was evaluated before changes to OSHA PELs occurred in January, 1989. The evaluation was based on the Transitional PELs listed in Table 1 and also found in reference 8.5. The method should be applicable to the Final Rule PELs listed in Table 1 and found in reference 8.6.

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2.1. OSHA Permissible Exposure Limits (PELs) (8.6.) for the elements screened and validated are listed in Table 1. Detection limits and working ranges are in Table 2. All reported detection limits were calculated for 50-mL solution volumes.

2.2. The optimum working range for each element listed in Table 2 extends several orders of magnitude above each detection limit.

3. Method Performance (8.3.)

3.1. The precision and accuracy data for the 13 validated elements using ICP1 are listed in Table 3. These values are based on six samples at each concentration level tested. Solutions of the 13 elements were spiked on mixed-cellulose ester filters. These samples were then digested and analyzed using procedures mentioned in this method and in reference 8.3.

3.2. Nine of the thirteen elements reported in Table 3 were spiked at 0.5, 1, and 2 times the PEL*, assuming a 120-L air volume (*Transitional PELs). Spikes for manganese were calculated assuming a 30-L air volume. Approximately 200-L air volumes were assumed for Pb, Ni, and Sb.

3.3. The analytical error (AE) at 95% confidence for each element listed in Table 3 was calculated as:

±AE% = 100 × [|Mean Bias| + 2(CV)]

Analytical errors for all elements tested were within ±25%; the greatest value was ±18.1% for V. This element was validated near it's detection limit.

4. Interferences (8.7.)

High temperatures present in the plasma (5,000 to 8,000°C) minimize most chemical and matrix interferences. Interferences do exist, however, and can be categorized as follows:

4.1. Physical interferences such as nebulization and transport effects are influences that determine the rate and particle size in which analytes are delivered to the plasma. These effects are minimized by matching the acid concentrations of samples and standards.

4.2. Chemical interferences are characterized by molecular compound formation, ionization effects, and solute volatilization effects. These effects are not severe in ICP analysis and are minimized by matrix matching and careful selection of operating conditions such as: incident plasma source power, sample uptake rate and plasma observation height.

4.3. Spectral interferences include:

1. Unresolved overlap of molecular band spectra.


2. Overlap of a spectral line from another element.


3. Background from continuous or recombination phenomena.


4. Background from stray light.

4.4. The first effect (a) can be minimized by a careful selection of wavelengths for the reported elements (see Table 4 - three different instruments and their wavelengths are listed). The other types of spectral interferences (spectral overlap and elevated background) are minimized by software which performs interelement corrections. This software assumes a linear relationship between the analyte and interference within the working range limits. A spectral interference correction equation typically used by ICP manufacturers is:

Corrected Concn = Calculated Concn - A_i × CP_i

Where:

Ai	=	Correction factor
CPi	=	Concentration of the interfering element

Samples having analyte concentrations above the working range limits should be diluted into range; interelement corrections may not be accurate above the working range. Experimentally determined interelement corrections for the validated elements are listed in reference 8.3.

4.5. If necessary, supplemental background correction can be performed with additional software supplied by the instrument manufacturer.

5. Sampling

5.1. Equipment

5.1.1. Mixed cellulose ester (MCE) filters (0.8-µm pore size), cellulose backup pads, and cassettes, 37-mm diameter, part no. MAWP 037 AO (Millipore Corp., Bedford, MA). Cassettes, filters (MCE) and backup pads of 25-mm diameter can also be used.

5.1.2. Gel bands (Omega Specialty Instrument Co., Chelmsford, MA) for sealing cassettes.

5.1.3. Sampling pumps capable of sampling at 2 L/min.

5.1.4. Assorted flexible tubing.

5.1.5. Stopwatch and bubble tube or meter for pump calibration.

5.1.6. Scintillation vials, 20-mL, part no. 74515 or 58515, (Kimble, Div. of Owens-Illinois Inc., Toledo, OH) with polypropylene or Teflon cap liners. If possible, submit bulk or wipe samples in these vials for ICP analysis.

5.1.7. Smear tabs, part no. 225-24 (SKC Inc., Eighty Four, PA), or Whatman no. 41 or no. 42 filters (Whatman LabSales Inc. , Hillsboro, OR) for wipe sampling.

5.1.8. Gloves, disposable (for wipe sampling).

5.2. Sampling Procedure - Air Samples

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Welding fumes can be characterized using this method. Collect samples on pre-weighed 37-mm polyvinyl chloride (PVC) filters at 2 L/min flow rate. Conduct the welding fume sampling with the filter cassette located inside the welding helmet (8.8.). If the free-space inside the hood precludes the use of 37-mm diameter cassettes and filters, 25-mm sampling assemblies with pre-weighed PVC filters can be used.

Desiccate and post-weigh each sample and then calculate total welding fume exposure:

net weight in µg air volume in liters

= mg/m3

and determine compliance with the 5 mg/m³ PEL for welding fumes. Submit the samples to the laboratory for welding fume/ICP analysis to further characterize the samples.

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5.2.1. Place a MCE filter and a cellulose backup pad in each two- or three-piece cassette. Seal each cassette with a gel band.

5.2.2. Calibrate each personal sampling pump with a prepared cassette in-line to approximately 2 L/min flow rate.

5.2.3. Attach prepared cassettes to calibrated sampling pumps (the backup pad should face the pump) and place in appropriate positions on the employee or workplace area. Collect the samples at about 2 L/min flow rates. Minimum sampling times recommended are:

Time Weighted Average Samples	240 min
Short-Term Exposure Limit Samples	15 min*
Ceiling Samples	5 min

The analytical sensitivity of a specific analyte may dictate using a larger sampling sampling time.

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*	When determining compliance with the STEL for beryllium, take 30-min samples.

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Note:

If soluble compounds (i.e. Cr2+, Cr3+, soluble salts of Al, Fe, Mo, Ni, ZnCl2, etc.) are suspected to be present in the sampled air, take separate samples. Request analysis for the specific compound(s). These samples are analyzed using OSHA Method No. ID-121 and not by this method.

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5.2.4. If the filter becomes overloaded while sampling, another filter cassette should be prepared. Consecutive samples using shorter sampling periods should be taken if overloading occurs.

5.2.5. Place plastic end caps on each cassette after sampling.

5.2.6. Attach an OSHA-21 seal around each cassette in such a way as to secure the end caps.

5.3. Sampling Procedure - Wipe Samples

5.3.1. Wear clean, impervious, disposable gloves when taking each wipe sample to prevent sample contamination.

5.3.2. Moisten the wipe filters with deionized water prior to use.

5.3.3. If possible, wipe a surface area covering 100 cm².

5.3.4. Fold the wipe sample with the exposed side in.

5.3.5. Transfer the wipe sample into a 20-mL scintillation vial and seal with vinyl or electrical tape. Securely wrap an OSHA-21 seal length-wise from vial top to bottom.

5.4. Sampling Procedure - Bulk Samples

In order of laboratory preference, bulk samples may be one of the following:

1. a high-volume filter sample,


2. a representative settled dust (i.e. rafter) sample,


3. a sample of the bulk material in the workplace.

Transfer the bulk material into a 20-mL scintillation vial and seal with vinyl or electrical tape. Securely wrap an OSHA-21 seal length-wise from vial top to bottom.

5.5. Shipment

When other compounds or elements are known or suspected to be present in the sampled air, such information should be transmitted with the sample(s) to the laboratory.

5.5.1. Submit at least one blank sample with each set of air or wipe samples. Blank filter samples should be handled in the same manner as other samples, except no air is drawn through the blank.

5.5.2. Send the samples to the laboratory with the OSHA 91A paperwork requesting ICP analysis. If arsenic is also suspected request ICP analysis/arsenic.

5.5.3. Bulk samples should be shipped separately from air samples. They should be accompanied by Material Safety Data Sheets if available. Check current shipping restrictions and ship to the laboratory by the appropriate method.

6. Analysis

6.1. Safety Precautions

6.1.1. Prepare 1:1 H₂SO₄ in DI H₂O cautiously.

1. Use a 1- or 2-L thick-walled, break- and heat-resistant bottle.
2. Wear thick rubber gloves, plastic apron, labcoat, and face shield.
3. Add 500 mL DI H₂O to the bottle.
4. Place the bottle over the drain in a sink which has a slot vent to provide ventilation. Begin running cold tap water over the side of the bottle, being careful not to get any tap water in the bottle. Let the level of water rise in the sink to provide cooling of the bottle.
5. Carefully and slowly begin adding 500 mL concentrated H₂SO₄ to the DI H₂O. Add a small quantity, swirl to mix, and allow contents to cool. Do NOT allow boiling of solution within the container.
6. After the acid has been added, loosely cap the bottle and allow it to remain in the sink with the water running for at least 15 min. Allow the solution to cool to room temperature.
7. A thick-walled beaker, Teflon-coated stirring bar, electronic stirrer and a ventilation hood can also be used to prepare 1:1 H₂SO₄ if precautions are taken to prevent solution overheating and splattering.

6.1.2. Digest all samples within a suitable exhaust hood.

6.1.3. To prevent splattering, add H₂O₂ (30%) to beakers in 2- to 3-drop groups.

6.1.4. Perchloric acid added to organic substances can produce fires and/or explosions. If HClO₄ solutions darken in color while heating, immediately remove beakers from the hotplate and carefully add a small amount of HNO₃. Only use HClO₄ in exhaust hoods designed and reserved for HClO₄ use.

6.1.5. Do not directly view the plasma.

6.1.6. Do not override the rf generator or torch box safety interlocks.

6.2. Equipment

6.2.1. Inductively coupled argon plasma/atomic emission direct-reading spectrometer, cooling unit for torch assembly, computer, and radio-frequency (rf) generator.

6.2.2. Nebulizer.

6.2.3. Automatic sampler.

6.2.4. Peristaltic pumps (optional). Use one pump for automatic sampler rinse. Use the other pump for sample introduction into the nebulizer.

6.2.5. Mass Flow Controller (optional). Use the controller to regulate nebulizer argon flow and sample uptake rate.

6.2.6. Borosilicate glass Phillips beakers, 125- and 250-mL.

6.2.7. Borosilicate glass volumetric flasks, 25-, 50-, 100-, 250-mL, and 1- or 2-L. Use the larger flasks for standard preparation.

6.2.8. Thick walled, 1- or 2-L heat- and break-resistant bottle.

6.2.9. Mixed cellulose ester filters (0.45-µm pore size) and a filtering apparatus. Use this system to remove any insoluble particulates from sample solutions.

6.2.10. Hot plate capable of reaching 300°C.

6.2.11. Volumetric pipets, glass of various sizes.

6.2.12. Analytical balance (0.01 mg).

6.3. Reagents (reagent grade or better)

6.3.1. Deionized water (DI H₂O).

6.3.2. Concentrated sulfuric (H₂SO₄), hydrochloric (HCl), nitric (HNO₃), and perchloric (HClO₄) acids.

6.3.3. Prepare 1:1 H₂SO₄ (V/V) solutions as described in Section 6.1.1.

6.3.4. Sample dilution solution or reagent blank (8% HCl/4% H₂SO₄):

In an exhaust hood, slowly and carefully add 40 mL concentrated H₂SO₄ to approximately 500 mL of DI H₂O contained in a thick-walled, heat- and break-resistant bottle. Gently stir and allow the solution to cool to room temperature. Slowly and carefully add 80 mL conc. HCl, allow to cool, and dilute to 1 L with DI H₂O.

6.3.5. Stock solutions of 1,000 µg/mL for standard preparation of the various elements.

6.3.6. Hydrogen peroxide, (H₂O₂), 30%.

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Note:

Some manufacturers use organotin compounds to stabilize H2O2. Since Sn is one of the elements screened, use H2O2 that does not contain this type of stabilizer.

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6.3.7. Argon - quality as specified by the ICP manufacturer.

6.4. Standard Preparation

Prepare multielement working and control standard solutions (see Table 4 and Table 5 for examples of combinations) using 1,000 or 10,000 µg/mL stock solutions. A control standard is a mixture of elements whose concentrations are within their respective analytical linear ranges and is used to monitor instrumental performance. Whenever possible, prepare the control standard from different stock solutions than those used for calibration standards. The control standard should contain elements and concentrations reflecting what is expected in the majority of the samples, or problem elements.

The final acid concentration of the working and control standards is 8% HCl/4% H₂SO₄. These standards should be stable for at least 6 months.

6.5. Sample Preparation

The final acid concentration for the different sample matrices should be 8% HCl/4% H₂SO₄. All of the elements validated are soluble when using the following acid digestion procedures. Other elements not included in the validated element list (Table 3) should be evaluated for solubility and stability before using these procedures.

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Note:

Requests for analysis of compounds which have a PEL that specifically addresses the soluble fraction (i.e. Fe, Ni, Mo, etc.) are analyzed using OSHA Method No. ID-121 and not by this method.

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Filters, backup pads, wipes, and bulks are prepared by the following procedures:

6.5.1. Mixed-cellulose ester (MCE) membrane filters

1. Clean the insides of the 125-mL Phillips beakers by refluxing 1:1 HNO₃ using a hot plate in a ventilated hood. Carefully pour the used 1:1 HNO₃ into an appropriate labeled container. Allow beakers to cool, then rinse several times with DI H₂O and allow to dry. Using forceps, place sample filters in separate labeled and washed beakers (If the backup pad appears contaminated, see Section 6.5.2. below).
2. For samples with air volumes > 400 L:
   Add 4 mL of 1:1 H₂SO₄ to each beaker containing the filter sample.
   For samples with air volumes < 400 L:
   Add 2 mL of 1:1 H₂SO₄.
3. To facilitate the digestion, allow the filters to sit at least an hour in the 1:1 H₂SO₄. Add several drops of H₂O₂ (30%) to each beaker before placing it on the hotplate.
4. Heat the beakers on a hot plate for approximately 10 min. The solutions should turn brown.
5. Cautiously add H₂O₂ in 2- to 3-drop groups until each solution becomes clear, colorless, or slightly yellow (the color is dependent on the concentration and type of analyte present).
6. Heat several more minutes until dense, white fumes of SO₃ just become evident. Remove the beakers from the hotplate and allow to cool.
7. Slowly and carefully add the following amount of concentrated HCl (CAUTION: SPLATTERING MAY OCCUR IF THE HCl IS ADDED TOO RAPIDLY OR THE H₂SO₄ SOLUTION IS STILL HOT):
   

   Acid Volume		Air Volume
   2 mL		< 400 L
   4 mL		> 400 L

8. Rinse the sides of the beakers with DI H₂O and return the beakers to the hotplate. Heat the beakers until near boiling to promote solubilization of all elements present. Remove the beakers from the hotplate and allow to cool.
9. Quantitatively transfer the solutions into volumetric flasks using DI H₂O. For samples having air volumes > 400 L, dilute to 50 mL; volumes < 400 L, dilute to 25 mL.

6.5.2. Backup Pads

1. If the backup pad has been contaminated during collection, digest the pad along with the filter. Also, separately digest and analyze the blank filter with a clean backup pad.
2. Place each contaminated backup pad and corresponding filter into individual beakers. Allow to sit at least an hour in the appropriate amount of 1:1 H₂SO₄ (Section 6.5.1., Step 2). Add 10 mL of concentrated HNO₃ and proceed as in Section 6.5.1., Step 3 above.

6.5.3. Wipe or Polyvinyl Chloride (PVC) Filter Samples

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Polyvinyl chloride filters are not routinely used for sample collection and analysis by ICP. The industrial hygienist may sample for gravimetric determinations of total dust or total welding fumes using PVC filters and also submit these samples for ICP analysis. If perchloric acid is used to digest the PVC filters, confirmation of arsenic content can not be performed using OSHA method no. ID-105 (8.1.). Extract the particulate on the PVC filter using only H₂SO₄, HCl, and H₂O₂ if arsenic is of interest.

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1. Reflux 1:1 HNO₃ in 250-mL (for wipes) or 125-mL (for PVC filters) Phillips beakers, empty and allow to cool. Rinse the beakers several times with DI H₂O and allow to dry.
2. Place each filter or wipe in a separate washed beaker.
3. Add the appropriate amount of 1:1 H₂SO₄ as listed below:
   

   Acid Volume*		Sample Type
   8 mL		Wipe
   4 mL		PVC filter (> 400 L Air Volume)
   2 mL		PVC filter (< 400 L Air Volume)

   
   * Concentrated HCl or 1:1 H₂SO₄

4. Add 10 mL concentrated HNO₃ to each beaker. Place the beakers on the hotplate.
5. Add H₂O₂ in 2- to 3-drop groups. PVC filters and wipes require more H₂O₂ for digestion than MCE filters.
6. If HClO₄ digestion precautions are followed (Section 6.1.4.), 1 to 2 mL of HClO₄ can also be used to complete digestion. Do not add HClO₄ if arsenic analysis is requested or suspected to be present. The samples can not be further evaluated for arsenic content using OSHA method no. ID-105 if HClO₄ is used. The PVC filter will not completely digest if HClO₄ is not added; therefore, thoroughly rinse the filter residue with DI H₂O during quantitative transfer of the sample solution.
7. Allow digested samples to cool and carefully add the same volume of concentrated HCl as the 1:1 H₂SO₄ used in Section 6.5.3., Step 3. above.
8. Rinse the sides of the beaker with DI H₂O and then heat to near boiling.
9. After beakers have cooled to room temperature, dilute digested wipe solutions to 100 mL. Dilute PVC filter solutions to final volumes as stated in Section 6.5.1., Step 9.

6.5.4. Bulks

1. Review any available material safety data sheets to determine safe bulk handling. The safety data may also offer a clue as to the aliquot amount needed for adequate detection of the element(s) of interest.
2. Measure by volume or weight an appropriate aliquot of any liquid bulk sample. Weigh the appropriate amount of any solid bulk sample. Weigh an aliquot of any paint bulk by placing a small amount on a MCE filter, allow to air dry then take the dry weight.

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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 needed, use a mortar and pestle to grind any nonhomogeneous particulate bulk samples in an exhaust hood.

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After measuring, transfer the aliquot to an acid-washed 250-mL Phillips beaker.

3. Add 20 mL of 1:1 H₂SO₄ and digest on a hotplate. Hydrogen peroxide (dropwise) and a few mLs of HNO₃ can be carefully added to break up the matrix.

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Caution:

Do not add the HNO3 to wet bulk materials containing organic solvents. Significant reactions could occur.

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4. Remove the beaker from the hotplate and allow to cool. Carefully add 20 mL of concentrated HCl and then heat the solution to near boiling.
5. Allow to cool and quantitatively transfer to a 250-mL volumetric flask. Dilute to volume with DI H₂O.

6.5.5. Air, wipe, and bulk samples: If particulates are present in any of the sample solutions, filter this solution through a MCE filter (0.45-µm pore size) and then re-digest the particulate and filter. Save the filtrates for analysis.

6.6. Instrument Startup and Calibration

Follow the manufacturer's instructions for instrument start-up and calibration. An example of ICP operating parameters is shown below. These settings will vary from instrument to instrument:

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Gas Used	Argon
Gas Flow (Rotameter settings)	Plasma Nebulizer Auxiliary Plasma	12 - 16 L/min * 0.14 - 0.18 L/min
RF Power	Incident Reflected	1.1 kW < 5 W
Observation Height	Plasma	15 mm above work coil
Integration Time	Peak Signal	3 to 10 s
Wash Time	Automatic Sampler Without Automatic Sampler	60 s 10 s
Number Of Exposures	Standards & Samples	2 to 10
Nebulizer*	Solution Uptake Rate Pressure	0.8 - 1.6 mL/min ~30 psig
Mass Flow Controller	Flow Rate Range	varies*
* This flow will vary depending on the type of nebulizer in use.

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6.6.1. Profile the instrument before beginning the calibration and analysis. Follow the Standard Operating Procedure (SOP) (8.9.) or manufacturer's instructions for computer initialization and profiling.

6.6.2. Obtain a two-point calibration curve by nebulizing the working standards into the plasma and measuring atomic emission intensities. For most instruments, a first-order linear fit of the data is computer calculated and slope and intercept coefficients are obtained. Perform calibrations by following the instrument manufacturer's guidelines.

6.7. Analytical Procedure

For more details regarding analytical procedures, refer to the instrument manufacturer's software manual(s) or the SOP (8.9.).

6.7.1. If necessary, determine detection limits using the manufacturer's software (if available). These limits normally do not significantly change during short time spans. A general rule is to recalculate detection limits when an integral component (nebulizer, torch, mass flow controller, etc.) of the ICP has been replaced or adjusted. A typical calculation of detection limit (DL) is shown:

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DL =

(K × SDI × C) (I - Io)

× S

Where:

S	=	Solution volume in mL
K	=	Degree of confidence (sigma value)*
SDI	=	Standard deviation of reagent blank intensity (Io.)
C	=	Concentration of the calibration standard in µg/mL
I	=	Total intensity of standard containing concentration C
Io	=	Background intensity (reagent blank)

* In most cases, K=2 or 3 for qualitative and K=10 for quantitative determinations.

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6.7.2. Analysis using an automatic sampler is described below:

1. Fill automatic sample vials to the minimum sample volume for one analysis and a potential rerun.
2. Load the automatic sampler with labeled standard and sample vials. A multielement working standard should be analyzed after every 5 to 6 samples. A control standard should be occasionally analyzed to ensure proper instrument operation. If an element or elements contained in the control standard are not within specification (a general rule is to use a value less than ±10 to 15% of the known concentration), the analyst should recalibrate before proceeding with the analysis.
3. Aspirate each sample or standard for approximately 1 min prior to initiating the exposure cycle. This ensures equilibration in the plasma and minimizes carry-over effects.
4. Dilute and reanalyze any samples containing elements (both screened and validated) exceeding the working range (Table 2). Interelement corrections may not be accurate above the working range. Prepare the dilutions by pipetting an appropriate aliquot from the original solution and dilute with 8% HCl/4% H₂SO₄.
5. Based on the calibration curve initially obtained, convert the sample intensities to concentrations. Then, using the air volume, solution volume, dilution factor and sample weight, calculate the concentration for each element analyzed as mg/m³ (air samples), total micrograms (wipes), or percentage of total weight (bulks) using the equations shown below.

6.8. Calculations

6.8.1. Total amount of analyte in the sample:

µg A = (µg/mL A) × (mL S) × (DF)

(1)

Where:

µg A	=	Total µg of analyte in the sample
µg/mL A	=	Measured concentration of analyte in sample solution (derived from calibration curve)
mL S	=	total volume of the solution analyzed
DF	=	amount of dilution applied to an aliquot of the original solution (ratio of final volume divided by the aliquot volume)

6.8.2. The blank value, if any, is subtracted from each sample:

µgc A = µg A - µgb A

(2)

Where:

µgc A	=	µg of analyte, blank corrected
µgb A	=	µg of analyte in blank

6.8.3. For air samples, the concentration of analyte in the sample is expressed in mg analyte per cubic meter for each element or compound analyzed:

mg A/m3 = (µgc A) × (GF) air volume, L

(3)

Where:
GF = Gravimetric Factor

For those elements having a PEL listed as an oxide, the gravimetric factors for the validated elements are:

1.4298 for Fe₂O₃       1.2447 for ZnO       1.7852 for V₂O₅

6.8.4. Convert bulk sample analytes to % composition using:

analyte % (w/w) = (µgc A) (100%) (sample weight) (1,000 µg/mg)

(4)

Where:

µgc A	=	analyte amount (µg)
Sample wt	=	aliquot (in mg) of bulk taken in Section 6.5.4.

7. Reporting Results

7.1. Air sample results are reported as mg/m³. Results for analytes having a PEL as an oxide are reported as mg/m³ of the oxide.

7.2. Wipe sample concentrations are calculated and reported as total micrograms for each element.

7.3. Bulk sample results are calculated and reported as elemental percent by weight (or volume if liquid aliquots were used). Due to differences in sample matrices between bulks and standards, bulk results are approximate for each element determined.

7.4. Determinations of the screened elements or compounds are not routinely reported. Spectral interference corrections for these analytes are not included and validations have not been performed. If a sample has a screened analyte over the PEL, the analyst should contact her/his supervisor. Additional sampling, or if possible, additional analysis of the original sample should be performed to quantitate the potential overexposure.

8. References

8.1. Occupational Safety and Health Administration Technical Center: Arsenic in Workplace Atmospheres (USDOL/OSHA-SLTC Method No. ID-105). Salt Lake City, UT. Revised 1991.

8.2. Occupational Safety and Health Administration Analytical Laboratory: OSHA Analytical Methods Manual (USDOL/OSHA-SLCAL Method No. ID-125). Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.

8.3. Occupational Safety and Health Administration Technical Center: ICP Backup Data Report (ID-125G) by J.C. Septon. Salt Lake City, UT. Revised 1991.

8.4. Occupational Safety and Health Administration Technical Center: ICP Backup Data Report (ARL 3560) by J.C. Septon. Salt Lake City, UT. In progress.

8.5. "Toxic and Hazardous Substances," Code of Federal Regulations Title 29, Pt. 1910.1000, Subpart Z. 1987. pp 676-682.

8.6. "Air Contaminants; Final Rule": Federal Register 54:12 (19 Jan. 1989). pp. 2923-2960 and also 54:127 (5 July 1989). pp. 28054-28061.

8.7. National Institute for Occupational Safety and Health: NIOSH Manual of Analytical Methods, 2nd ed., Vol. 7 (DHEW/NIOSH Pub. No. 82-100). Cincinnati, OH, 1981. Method No. 351.

8.8. United States Department of Labor, OSHA: "Memorandum, Sampling for Welding Fumes" by Patricia Clark, Director Designate, Directorate of Compliance Programs. United States Department of Labor, OSHA, Washington, DC, February 14, 1989. [Memo].

8.9. Occupational Safety and Health Administration Analytical Laboratory: ICP Standard Operating Procedure by J.C. Septon. Salt Lake City, UT. 1988 (unpublished).

Both the detection limits and upper limits were determined using ICP1 (JY-32 ICP). Performance may vary from instrument to instrument. Upper limits are the upper linear range for each element. These were determined using a linear model (8.3.).

The following exceptions were used when calculating spike amounts:

Where:

The ICP instruments are calibrated using a two-point calibration curve with the highest standard for each element listed above. A reagent blank is used as the low standard. Each element calibrated is contained in one of three separate calibration standards (STD SOLN). For example, mixed standard no. 2 is used for Co. This mixed standard also contains Si and Mo.

The three mixed calibration standards were selected because of chemical compatibility and potential interferences. Other combinations of elements or concentrations can be used; however, compatibility and possible interferences have to be considered when combining elements other than the mixtures listed above.

Control standard mixtures are prepared and analyzed as an analytical monitor ICP performance. Some instrument manufacturers have instituted analytical software routines which will evaluate control standard results during the analysis. The control standard listed above is an example which was used for the ISA JY-32 ICP. Alternate control mixtures can be prepared.

To illustrate the control standard concept, 5 µg/mL V is used. For this control standard, V has a limit of ±15% (upper and lower concentration limits of 5.75 µg/mL and 4.25 µg/mL, respectively). If a calculated value greater than ±15% is obtained while analyzing the control standard, the analysis will automatically halt. The ICP operator should then re-calibrate the instrument.