Occupational Safety and Health Administration Analytical Laboratory: OSHA Analytical. Methods Manual (USDOL/OSHA-SLCAL Method No. ID-107). Cincinnati, OH:
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Withdrawn Provided For Historical Reference Only 1 of 9 Note: OSHA no longer uses or supports this method (November 2019). SULFUR DIOXIDE IN WORKPLACE ATMOSPHERES (BUBBLER) Method Number: ID-104 Matrix: Air OSHA PEL Sulfur Dioxide (Final Rule Limit): 2 ppm (Time Weighted Limit ) 5 ppm (Short -Term Exposure Limit) Sulfur Dioxide (Transitional Limit): 5 ppm (Time Weighted Limit) Collection Device: A calibrated personal sampling pump is used to draw a known volume of air through a midget -fritted glass bubbler containing 10 to 15 mL of 0.3 N hydrogen peroxide. Recommended Air Volume: 15 to 60 L Recommended Sampling Rate: 1 L/min Analytical Procedure: Samples are directly analyzed with no sample preparation by ion chromatography as total sulfate. Detection Limit Qualitative : 0.0041 ppm (60 -L air volume) Quantitative : 0.010 ppm (60 -L air v olume) Precision and Accuracy Validation Level : 2.5 to 10.0 ppm (60 -L air volume) CVT 0.012 Bias -0.046 Overall Error ±7% Method Classification: Validated Method Chemist: Ted Wilczek, Edward Zimowski Date (Date Revised): 1981 (December, 1989 ) Commercial manufacturers and products mentioned in this method are for descriptive use only and do not constitute endorsements by USDOL -OSHA. Similar products from other sources can be substituted. Branch of Inorganic Methods Development OSHA Techn ical Center Salt Lake City, Utah
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Withdrawn Provided For Historical Reference Only 2 of 9 Note: OSHA no longer uses or supports this method (November 2019). 1. Introduction This method describes the collection and analysis of airborne sulfur dioxide (SO 2) using midget -fritted glass bubb lers (MFGBs) in the workplace. It is applicable for both short -term (STEL) and time weigh ted average (TWA) exposure evaluations. 1.1 History An earlier method used by OSHA involved collecting SO 2 in 0.3 N hydrogen peroxide (H 2O2) which converted SO 2 to sulfuric acid. The amount of SO 2 in the air is determined in the laboratory by volumetric titration of the sulfuric acid with barium perchlorate and a Thorin indicator (8.1.). The titration is susceptible to interferences from volatile phosphates and metals (8.1.), and the end point is difficult to determine. Also, a report indicated the chl oride ion has an adverse effect on the endpoint (8.2.). Method no. ID -104 has replaced the titration with ion chromatography (IC). A method using a solid sorbent sampling media and analysis by IC was recently evaluated (8.3.); however, the sorbent materia l appears prone to contamination. 1.2 Principle Sulfur dioxide is collected in a MFGB containing 0.3 N H 2O2. The H 2O2 converts the SO 2 to sulfuric acid (H 2SO4) according to the following equation: SO2 + H2O2 ———> H2SO4 The H 2SO4 is analyzed a s sulfate using a slightly basic eluent and an ion chromatograph equipped with a conductivity detector. 1.3 Advantages and Disadvantages 1.3.1 This method has adequate sensitivity for measuring workplace atmosphere concentrations of SO 2 and is less affec ted by interferences found in the barium perchlorate titration method. 1.3.2 The method can be fully automated to improve analytical precision. 1.3.3 Collected samples are analyzed by means of a quick instrumental method, since no sample preparation is r equired. 1.3.4 Humidity does not affect the collection efficiency. 1.3.5 The sulfuric acid formed is stable and non -volatile. 1.3.6 A disadv antage is the sampling device. The use of bubbler collection techniques may impose inconveniences for industrial hygiene work. There is the possibility of spillage during sampling, handling, and during transportation to the lab. 1.4 Potential sources of occupational exposure to SO 2 (8.4., 8.5.) Sulfur dioxide is used in industry as a(n): intermediate in the manu facture of sulfuric acid bleaching agent disinfectant fumigant solvent refrigerant food preservative reagent in the manufacture of magnesium, sodium sulfite, and other chemicals
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Withdrawn Provided For Historical Reference Only 3 of 9 Note: OSHA no longer uses or supports this method (November 2019). Sulfur dioxide is also an industrial by -product and can be generated from man y industrial processes. These include the smelting of sulfide ores, the combustion of coal or fuel oils containing sulfur as an impurity, paper manufacturing, and petroleum refining (8.4.). 1.5 Physical Properties: Sulfur dioxide (CAS No. 7446 -09-5) is a colorless, nonflammable gas with a characteristi c, strong and suffoca ting odor. It is intensely irritating to the eyes and respiratory tract. It is soluble in water, methane, ethanol, chloroform, ethyl ether, acetic acid, and sulfuric acid (8.4., 8.5.). Physical Constants Chemical Formula: SO2 Formula Weight: 64.07 Boiling Point: -10.0 °C Melting Point: -72.7 °C Vapor Density: 2.3 (air =1) 2. Range and Detection Limit (8.6.) This method was evaluated over the range of 2.5 to 10.0 ppm (atmosphe ric conditions of 640 mmHg and 24 oC). Total air sam ple volumes of 60 L were used. The analytical portion of the evaluation was conducted using a model 10 ion chromatograph with a 3 x 500 -mm separator and 6 x 250 -mm suppressor columns. The following res ults were obtained using this equipment. 2.1 The sensitivity of the method for the instrumentation used during t he validation study was 1.5 µS/cm/µg as sulfate ion. A 100 µL injection of a 10 µg/mL solution of sulfate gave a 27 -mm chart deflect ion on a 500 -mV chart recorder. The ion chromatograph was set on a range of 30 µS/cm. 2.2 The qualitative detection limit of the analytical method was 0.013 µg of SO 2 per injection (200 -µL sample injection) or 0.65 µg SO 2 in a 10 -mL sample volu me. 2.3 The quantitative limit was 0.033 µg SO 2 per 200 -µL injection or 1.7 µg SO 2 in a 10 -mL sample volume. The coefficient of variation of replicate determinations of standards at this level was less than 0.10. 3. Method Performance (8.6.) This method was evaluated in 1981 using commercial analytical equipment mentioned in Section 2. Advances in ion chromatographic and sampling instruments should enable users to obtain similar or better results than those mentioned below. 3.1 The coefficient of variation (CV T) for the overall sampling and analytical method in the range of 2.5 to 10 ppm (640 mmHg and 24 °C) was 0.012. 3.2 In validation experiments, this method was capable of meas uring within ±25% of the true value (95% confidence lev el) over the validation range. The bias was -0.046 and overall error was ±7%. 3.3 The collection efficiency was 100% for the 0.3 N H 2O2 sampling solution. 3.4 A breakthrough test was conducted at a c oncentrat ion of 9.4 ppm. No breakthrough occurred after 240 min at a sampling rate of 1 L/min. 3.5 In storage stability studies, the average recovery of samples analyzed after 31 days were within 1% of the average recovery of samples analyzed immediatel y after collection.
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Withdrawn Provided For Historical Reference Only 4 of 9 Note: OSHA no longer uses or supports this method (November 2019). 4. Interferences 4.1 The presence of other particulate sulfate compounds and sulfuric acid in the air will interfere in the analysis of sulfur dioxide. These two interferences can be removed by the use of a modified prefilter. 4.2 Sulfur trioxide gas (SO 3), if present in a dry atmosphere, can give a positive bias in the SO 2 determination. 4.3 Any substance that has the same retention time as the sulfate ion with the ion chromatographic operating conditions as described in t his method is an interference. If the possibility of an interference exists, changing the separation conditions (colum n length, eluent flow rate and strength, etc.) may circumvent the problem. 4.4 When other substances are known or suspected to be present in the air sampled, the identities of the substances should be transmitted with the sample. 5. Sampling 5.1 Equipment 5.1.1 Hydrogen peroxide (30% H 2O2), reagent grade or better. 5.1.2 Collection solution, 0.3 N H 2O2. Carefully dilute 17 mL of 30% H 2O2 solution to 1 L with deionized water. 5.1.3 Personal sampling pumps capable of sampling within ±5% of the recommended flow rate of 1 L/min are used. 5.1.4 Midget -fritted glass bubblers (MFGBs), 25 -mL, part no. 7532 (Ace Glass Co., Vineland, NJ). 5.1.5 Shipping vials: Scintillation vials, 20 -mL, part no. 74515 or 58515, (Kimble, Div. of Owens -Illinoi s Inc., Toledo, OH) with polyp ropylene or Teflon cap liners. Tin or other metal cap liners should not be used. 5.1. 6 A stopwatch and bubble tube or meter are used to calibrate pumps. 5.1. 7 Various lengths of polyvinyl chloride (PVC) tubing are used to con nect bubblers to the pumps. 5.1. 8 If particulate sulfate or sulfuric acid is suspected to also be in the atmosphere, a modifi ed prefilter assembly is used. This assembly consists of: 1. Sampling cassettes, polystyrene, 37 -mm. 2. Mixed -cellulose ester (MCE) filters, 37 mm. 3. Support rings, cellulose, part no. 225 -23 (SKC Inc., Eighty Four, PA). Rings can also be made fr om 37 -mm cellulose backup pads. Place a half -dollar in the center of the pad and then cut the outer ring formed. Place this ring in the cassette to provide support for the MCE filter. 5.2 Sampling Procedure 5.2.1 Calibrate the sampling pump with a MFGB containing about 10 to 15 mL of collection solution in -line.
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Withdrawn Provided For Historical Reference Only 5 of 9 Note: OSHA no longer uses or supports this method (November 2019). 5.2.2 Place 10 to 15 mL of collection solution in an MFGB. Connect the MFGB to a calibrated sampling pump and then place the sampling device in the breathing zone of the employee . 5.2.3 If particulate sulfate or sulfuric acid are suspected to be present, attach the modified prefilter (Section 5.1.8.) to the MFGB with PVC tubing so that sampled air enters the cassette first. Minimize the amount of tubing from the filter to the MFG B. 5.2. 4 Sample at a flow rate of 1 L/min. For STEL determinations, sample for at least 15 min. For measurements of TWA exposu res, sample from 60 to 240 min. Take enough samples to cover the shift worked by the employee . 5.2. 5 Transfer the collection solution into a 20 -mL glass scintillation vial. Rinse the bubbler with 2 to 3 mL of unused collection solution and transfer the ring s into the sample vial. Place the Teflon – or polypr opylene -lined cap tightly on each vial and seal with vinyl or waterproof tape around the caps to prevent leakage during shipment . 5.2. 6 Prepare blank solutions by taking 10 to 15 mL of the unused collection solution and transfer to individual 20 -mL glass vials . Seal vials as mentioned in Section 5.2.5 . 5.2. 7 Request sulfur dioxide analysis on the OSHA 91A form. If sulfuric acid is also suspected in the sampled atmosphere and a prefilter assembly was used, the MCE filter can be submitted for sulfuric acid analysis . 5.2. 8 Ship the samples to t he laboratory using appropriate packing materials to prevent breakage . 6. Analysis 6.1 Precautions 6.1.1 Refer to instrument and standard operating procedure (SOP) manuals (8.7.) for proper operation . 6.1.2 Observe laboratory safety regulations and practices . 6.1.3 Sulfuric acid ( H2SO 4) can cause severe burns. Wear protective eyewear, gloves, and lab coat when using concentrated H2SO 4. 6.2 Equipment 6.2.1 Ion chromatograph (model no. 2010i or 4500, Dionex, Sunnyvale, CA) equipped with a conductivity detector. 6.2.2 Automatic sampler (model no. AS -I, Dionex) and 0.5 mL sample vials (part no. 038011, Dionex). 6.2.3 Laboratory automation system: Ion chromatograph interfaced to a data reduction and control system (model no. AutoIon 450, Dionex). 6.2.4 Micromembrane suppressor (model no. AMMS -1, Dionex). 6.2.5 Anion separator column (model no. HPIC -AS4A, Dionex) w ith pre -column (model no. HPIC -AG4A, Dionex). 6.2.6 Disposable syringes (1 mL) and syringe pre -filters, 0.5 um pore size, (part no. SLSR 025 NS, Millipore Corp., Bedford, MA). (Note: Some syringe pre -filters are not cation – or ..
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Withdrawn Provided For Historical Reference Only 6 of 9 Note: OSHA no longer uses or supports this method (November 2019). anion -free. Tests should b e done with blank solutions first to determine suitability for the analyte being determined) . 6.2.7 Miscellaneous volumetric glassware: Micropipettes, volumetric flasks, graduated cylinders, and beakers. 6.2.8 Analytical balance ( 0.01 mg). 6.3 Reagents – All chemicals should be at least reagent grade. 6.3.1 Deionized water (DI H 2O) with a specific conducta nce of less than 10 µS. 6.3.2 Eluent [0.0015 M sodium carbonate (Na 2CO3)/0.0015 M sodium bicarbonate (NaHCO 3)]: Dissolve 0.636 g Na 2CO3 and 0.504 g NaHCO 3 in 4.0 liters of DI H 2O. 6.3.3 Sulfuric acid (H 2SO4), concentrated (98%). 6.3.4 Regeneration solution (0.02 N H 2SO4): Pipet 1.14 mL concentrated H 2SO4 into a 2 -L volumetric flask which contains about 500 mL DI H 2O. Dilute to volume with DI H 2O. 6.3.5 Sodium sulfate (Na 2SO4). 6.3.6 Sulfate stock standard (1,000 µg/mL sulfate): Dissolve and dilute 1.4792 g Na 2SO4 to 1 -L with DI H 2O. 6.4 Standard Preparation Working standards (100, 10, 1.0, and 0.1 µg/mL as sulfate). Make appropriate serial dilutions of the sulfate stock standard with eluent. Prepare these solutions monthly. 6.5 Sample Preparation 6.5.1 Measure and record the total solution volume of each sample with a graduated cylinder. 6.5.2 If the sa mple solutions contain suspended particulate, remove the particles using a pre -filter and syringe (Note: Some pre -filters are not cation or anion free. Tests should be done with blank solutions first to determine suitability of the filter for the analyte being determined). 6.5. 3 Fill the 0.5 -mL automatic sampler vials with sample solutions and p ush a filtercap into each vial. Label the vials. 6.5. 4 Load the automatic sampler with labeled samples, standards and blanks. 6.6 Analysis Set up the ion chroma tograph and analyze the samples and standards in a ccordance with the SOP (8.7.). Typical operating conditions for a Dionex 2010i with a data reduction system are listed below.
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Withdrawn Provided For Historical Reference Only 8 of 9 Note: OSHA no longer uses or supports this method (November 2019). 7.4 Reporting Results Results are reported to the industrial hygienist as ppm sulfur dioxide. 8. References 8.1. National Institute for Occupational Safety and Health: NIOSH Manual of Analytical Methods . 2nd. ed., Vol. 4 (Method No. S308) (DHEW/NIOSH Pub. No. 78 -175). Cincinnati, OH: National Institute for Occupational Safety and Health, 1978. 8.2. Steiber, R. and R. Merrill: Application of Ion Chromatography to the A nalysis of Source Assessment Samples. In Ion Chromatographic Analysis of Environmental Pollutants (Volume 2), edited by J.D. Mulik & E. Sawicki. Ann Arbor, MI: Ann Arbor Science Publishers Inc., 1979. pp. 99-113. 8.3. Occupational Safety and Health Admini stration Analytical Laboratory: OSHA Analytical Methods Manual (USDOL/ OSHA -SLCAL Method No. ID -107). Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0 -936712 -66-X), 1985. 8.4. National Institute for Occupational Safety and Health: Criter ia for a Recommended Standard – Occupational Exposure to Sulfur Dioxide (DHEW/NIOSH Pub. No. 74 -111). Cincinnati, OH: National Institute for Occupational Safety and Health, 1974. 8.5. Fassett, D.W. and D.D. Irish, ed.: Patty’s In dustrial Hygiene and Toxicology . 2nd rev. ed., Vol. 2. New York: John Wiley and Sons, 1963. 8.6. Occupational Safety and Health Administration Technical Center: Sulfur Dioxide Backup Data Report (ID -104). Salt Lake City, UT. Revised, 1989. 8.7. Occupat ional Safety and Health Administration Technical Center: Ion Chromatography Standard Operating Procedure . Salt Lake City, UT. In progress (unpublished).
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Withdrawn Provided For Historical Reference Only 9 of 9 Note: OSHA no longer uses or supports this method (November 2019). Figure 1. Chloride 3 µg , nitrate 20 µg , phosphate 20 µg , sulfate 20 µg. REPORT VOLU11E DILUTION POINTS RATE START STOP AREA FcEJ External Re-r Cornoonent !Łium T 1me hlame L 3 4 5 6 o.n 0.85 1.:JS chlo1″1.dc 2.47 nitrate J.’78 phosphate 5.J7 sult;;te :::1331 : 26:331 j 21331 \ 1 0.27 0.85 1 35 tY::, 16331 i i 1–, Ł -.. i i~71· .1 !.j_:,l I 1,: i i ii; Ii b-·,:-=:-·:;.~,. \;; i_ii ii -Ł-..J Iij Ii I jj ! i . ii~ j i 1331 / U i l . ,_ 1863 ‘5Hz I i 6.21 5001_,(l(r Height Hrea 14::,70313 S10797t)38 460000 2628000 11~6875 8174000 21717447 21J280000 6749818 92956000 15340000 258840000 i \ i \._ j ‘–5.37 -3fiG3~~.——-~~~~,-,-,-,—·= ! ~~—~~-~–,~, i i 0.00 .2.00 4.00 . f:.oc, Minutes
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SULFUR DIOXIDE ( IMP INGER) BACKUP DATA REPORT 1. Procedure: The general procedure for collection and analysis of sulfur dioxide air samples is described in OSHA Method No. ID 104 (11.1). Sulfur dioxide is collected in a midget bubbler containing 0. 3 N hydrogen peroxide in deionized water. The hydrogen peroxide solution converts the sulfur dioxide to sulfuric acid. The amount of sulfur dioxide as sulfate in the hydrogen peroxide solution is determined by ion chromatography. This method has been validated for a 60-liter 60 minute average TWA for the OSHA-Permissible Exposure Level (PEL). The idation of the method for sulfur dioxide consisted of the following experimental protocol: 1.1. Analysis of a total of 18 samples (6 samples at each of three test levels) prepared by spiking with appropriate amounts of sodium sulfate in 0.3 N hydrogen peroxide. These samples represented concentrations of 0.5, 1, and 2 times ttie OSHA PEL, based upon a 60-minute sample c0l11:ctlon at a flow ratP-of 1.0 liter per minute. 1. 2. Analysis of a total of 18 samples (6 samples at each of the three test levels) collected from dynamically ated test atmospheres at 0.5, 1, and 2 times the OSHA PEL standard, based upon a 60-liter sample at a flow rate of 1.0 liter per minute.
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Sulfur Dioxide Backup Data Re!)lH’t 1.3 Determination of the ,:ollection E>fficlency :-rnd breakthrough of the hydrogen peroxidf’ collecting solution uslng midget bubblers at 2 tlmes tlie OSHA PEL stnn