# Non-Volatile Acids (Sulfuric Acid and Phosphoric Acid) (7908)

NON-VOLATILE ACIDS (Sulfuric Acid and Phosphoric Acid)
Formulae: H2SO4 H3PO4
MW: 98.08 MW: 98.0
METHOD: 7908, Issue 1
CAS: CAS:
7664-93-9 7664-38-2
EVALUATION: FULL
SYNONYMS: H2SO4: hydrogen sulfate, oil of vitriol;
SAMPLER: FILTER, 37-mm diameter quartz fiber; or polytetrafluoroethylene (PTFE), 0.45 µm pore size FLOW RATE: 1 to 5 L/min 15 L 2000 L
SAMPLE STABILITY: Stable for 1 week at about 20 °C and at 4 °C thereafter to 28 days [3] 3 field blanks minimum per set ACCURACY* RANGE STUDIED: 0.005 to 2.0 mg/sample
MEASUREMENT TECHNIQUE:
ION CHROMATOGRAPHY (IC) with conductivity detection
ANALYTES:
Sulfate (SO42-) ion, phosphate (PO43-) ion
EXTRACTION:
Aqueous solution of sodium carbonate / sodium hydrogen carbonate
INJECTION VOLUME:
SHIPMENT: 4 °C
BIAS*:
Issue 1: 10 May 2014
H3PO4: ortho-phosphoric acid
SAMPLING
BLANKS:
WS5600000 TB6300000
PROPERTIES: H2SO4: Liquid, mp = 3.0 °C (98%); 10 °C (100%); bp = 338 °C (98%); 330 °C (100%); VP = < 0.0001 kPa @ 20 °C H3PO4: Solid (often used in an aqueous solution), mp = 42.4 °C; bp = 158 °C; vp = 0.0038 kPa @ 20 °C
U.S. OELs OSHA : 1 mg/m3 (H2SO4 & H3PO4) NIOSH: 1 mg/m3 (H2SO4 & H3PO4); STEL: 3 mg/m3 (H3PO4) Other OELs: [1,2]
VOL-MIN: -MAX:
RTECS: RTECS:
7908
Negligible [3]
OVERALL PRECISION ( SˆrT )*: H2SO4 = 0.086; H3PO4 = 0.106 EXPANDED UNCERTAINTY*: less than 23% for both H2SO4 and
  H3PO4 [6]
50 µL
ELUENT:
2.7 mM Na2CO3/0.3 mM NaHCO3, flow rate 1.5 mL/min
COLUMNS:
Pre-column, anion-exchange column and suppressor column
CALIBRATION RANGE:
H2SO4; 0.2 mg/L to 8 mg/L; H3PO4; 0.8 mg/L to 8 mg/L [6]
ESTIMATED LOD: H2SO4 = 0.002 mg/m3; H3PO4 = 0.003 mg/m3 (1 m3 air volume)[6] PRECISION ( S ): H2SO4 = 0.043; r H3PO4 = 0.032 [3,7]
5 and 6 rather than the traditional NIOSH accuracy criteria. APPLICABILITY: The working range for H2SO4 is (at least) 0.002 to 1.0 mg/sample, for H3PO4 is 0.004 to 1.0 mg/sample for a 420 Liter air sample [3,6]. INTERFERENCES:  Particulate salts of sulfate or phosphate will give a positive interference. OTHER METHODS: This procedure, which is consistent with ISO 21438-1 [6], replaces NIOSH 7903 [8] for the determination of sulfuric and phosphoric acid in workplace air samples by IC. The main advantage of NIOSH method 7908 is that it can allow for the collection of the inhalable fraction of sulfuric and phosphoric acid aerosols by means of the pre-filter (housed within an optional inhalable sampler.)
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​NON-VOLATILE ACIDS (Sulfuric Acid and Phosphoric Acid): METHOD 7908, Issue 1, dated 20 May 2014 - Page 2 of 5
REAGENTS:
EQUIPMENT:
1. Water, deionized (DI), ≥18 MΩ-cm resistivity 2. Sodium carbonate (Na2CO3), anhydrous, American Chemical Society (ACS) analytical grade 3. Sodium hydrogen carbonate (NaHCO3), ACS analytical grade 4. Extraction & eluent stock solution: 0.27 M Na2CO3 / 0.03 M NaHCO3; dissolve 2.86 g Na2CO3 and 0.25 g NaHCO3 in 25 mL of deionized water and swirl to mix. Then bring to 100 mL in a volumetric flask, stopper and mix thoroughly. 5. Extraction & eluent solution: 0.0027 M Na2CO3 / 0.0003 M NaHCO3; transfer 10 mL of 0.27 M Na2CO3 / 0.03 M NaHCO3 stock solution to a 1 L volumetric flask, dilute to the mark with deionized water, stopper and mix thoroughly. 6. Sulfate (SO42-) ion and phosphate (PO43-) ion standard solutions, each 1000 mg/L 7. Calibration stock solution, 100 mg/L (as the anion): Place 10 mL aliquots of sulfate and phosphate standard solution into a 100 mL volumetric flask, dilute to the mark and mix thoroughly.
1. Sampler: filter, 37-mm diameter quartz fiber; or polytetrafluoroethylene (PTFE), 0.45 µm pore size, in cassette filter holder manufactured from acid-resistant (chemically inert) material NOTE: Quartz fiber filters should be binderless and heat-treated. 2. Personal sampling pump, 1 to 5 L/min, with flexible connecting tubing 3. Ion chromatograph, with pre-column (50 mm by 4.0 mm), anion-exchange column (200 mm by 4.0 mm), suppressor column (4 mm) and conductivity detector; and connected to data processing unit 4. Ultrasonic bath 5. Vessels, 10-mL, plastic (e.g., polypropylene), with screw caps 6. Volumetric flasks, 25- to 1000 mL 7. Pipets, 50 to 10000 µL 8. Beakers, 25 to 100 mL 9. Water purification system, to prepare greater than or equal to18 MΩ-cm resistivity deionized water 10. Bottles, polyethylene, 100 mL 11. Syringes, plastic, 5 mL 12. Syringe filter cartridges, with 0.8-µm pore size polytetrafluoroethylene (PTFE) membrane filters 13. Micro-syringes, 50 µL, with 60 mm x 0.6 mm needles 14. Tweezers, PTFE-coated 15. Auto-sampler vials, 2 mL capacity 16. Analytical balance, with capability of weighing to nearest 0.01 mg
SPECIAL PRECAUTIONS: Wear gloves, lab coat, and safety glasses while handling acids. All work should be performed with adequate ventilation for personnel and equipment. It is imperative that acid be added to water in order to avoid a violent exothermic reaction. There is risk of fire and explosion when phosphoric acid has contact with bases, combustible substances, oxidizing agents, reducing agents or water. Avoid physical contact since both sulfuric and phosphoric acid are both corrosive and irritants to eyes, skin, and the respiratory system. These are caustic materials and can react with metals to form flammable hydrogen gas. Do NOT mix with solutions containing bleach or ammonia [9,10]. SAMPLING, SAMPLE TRANSPORT AND STORAGE: 1. Calibrate each personal sampling pump with a representative sampler in-line. 2. Sample at an accurately known flow rate between 1 and 5 L/min for a total sample size of 15 to 1000 Liters. Avoid sampler overloading. 3. Immediately after sampling, remove the filter from the cassette with PTFE-coated tweezers and place it in a 10-mL screw-cap plastic vessel. With about 2 mL extraction
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​NON-VOLATILE ACIDS (Sulfuric Acid and Phosphoric Acid): METHOD 7908, Issue 1, dated 20 May 2014 - Page 3 of 5
solution (0.27 M Na2CO3 0.03 M NaHCO3), rinse material from the inside surfaces of the cassette into the vessel. Add additional extraction solution into the vessel until a final volume of 5 mL is reached. 4. Submit at least three field blanks for each set of samples collected per day. Handle these in the same way as the field samples; i.e., place each filter into a vessel, add 5 mL of eluent solution and ship it to the lab along with the remaining samples. 5. Refrigerate all samples that are to be stored overnight (or longer) prior to shipment to the laboratory. Ship all samples to the laboratory in accordance with established chain-of-custody procedures [11]. 6. Refrigerate the samples (4 °C) immediately upon receipt at the lab until ready for analysis. 7. Analyze samples within 4 weeks of receipt. SAMPLE PREPARATION: 8. Remove sample vessels from storage and bring them to room temperature. 9. Sonicate the samples in an ultrasonic bath for at least 15 minutes and allow to cool for at least 30 minutes. 10. Using 5-mL syringes, filter each sample extract solution through a PTFE filter into clean plastic vessels or into autosampler vials (if autosampler used). CALIBRATION AND QUALITY CONTROL: 11. Through dilution of the calibration stock solution in eluent solution, prepare calibration working standard solutions covering the range of approximately 0.2 to 8 mg/L of sulfate and phosphate. Store working standards in tightly sealed polyethylene bottles. Prepare fresh working standards weekly. 12. Calibrate the ion chromatograph with at least six working standards covering the range of 0.2 to 8 mg/L of sulfate and phosphate ion per sample by preparing a calibration graph of anion peak height (mm or µS [micro siemens]) vs. concentration (mg/L). 13. Analyze working standards together with samples, reagent blanks and field blanks at a frequency of at least 1 per 20 samples (3 minimum of each). MEASUREMENT: 14. Set the ion chromatograph to desired eluent flow rate, e.g.,1.5 mL/min, and column pressure, e.g., 1.1 x 105 kPa, and other conditions as specified by the instrument manufacturer. 15. Inject a sample aliquot, e.g., 50-µL, into the chromatograph, and measure the peak heights of the phosphate and sulfate peaks (at retention times of about 9 min and 11.6 min, respectively). If the peak height exceeds the linear calibration range, dilute with eluent, reanalyze and apply the appropriate dilution factor in calculations. CALCULATIONS: 16. Calculate the mass concentration of each anion, C (mg/m3), in the air volume sampled, V (L): (C 1*V 1 * Fd ) − (C 0*V 0 ) C ={ } * Fc V where: C = mean concentration, in mg/L, of anion in the field blank test solutions; 0 C = concentration, in mg/L, of anion in the sample test solution; 1 V = volume, in liters, of the air sample; V = volume, in mL, of the field blank test solutions; 0
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​NON-VOLATILE ACIDS (Sulfuric Acid and Phosphoric Acid): METHOD 7908, Issue 1, dated 20 May 2014 - Page 4 of 5
V = volume, in mL, of the sample test solutions 1 Fd = dilution factor for each sample test solution Fc = conversion factor to convert from anion to acid concentration: Fc = 1.021 for sulfate; Fc = 1.031 for phosphate EVALUATION OF METHOD: Laboratory testing with generated atmospheres of sulfuric acid mist yielded a collection efficiency of greater than 95% over the range 0.5 to 10 mg/m3 of H2SO4 on 0.45 µm pore size PTFE filters [4]. Greater than 95% recovery of sulfuric acid and phosphoric acid was found four weeks after sample collection. On quartz fiber filters, 97 to 100% recovery of sulfuric acid was found four weeks after sample collection, and no breakthrough was observed at sample loadings of up to 1 mg [3]. Mean analytical recovery determined from the analysis of spiked quartz fiber filters has been found to be in the range of 97 to 100% for both acids [3,4]. The component of the coefficient of variation of the method that arises from analytical variability, determined from the analysis of spiked quartz fiber filters, was 0.7% to 3.2% for phosphoric acid and 0.5% to 2.6% for sulfuric acid [3]. An interlaboratory study with 26 participants found negligible biases and interlaboratory relative standard deviations of 12 to 15% for sulfuric acid and phosphoric acid concentrations between 0.05 and 1 mg/m3 [12]. The method has also been field tested for sulfuric acid measurements at sample volumes of up to nearly 2,000 Liters [13]. The analytical figures of merit for the method satisfy performance criteria specified in an applicable consensus standard [14]. The back-up data and user check reports are references 4 and 12 respectively. REFERENCES: [1] ACGIH [2013]. TLVs and BEIs based on the documentation of the Threshold Limit Values for chemical substances and physical agents and Biological Exposure Indices. Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists. [www.acgih.org]. [Data accessed April 2014.] [2] Institut fur Arbeitsschutz der Deutschen Gesetzlichen Unfallversicherung [2013]. GESTIS database on international limit values for hazardous substances (German Social Accident Insurance). Sankt Augustin, FRG: [http://www.dguv.de/ifa/Gefahrstoffdatenbanken/GESTIS-Stoffdatenbank/index-2. jsp]. [Data accessed April 2014.] [3] Breuer D [2002]. Inorganic acid mists (H2SO4, H3PO4). In: Kettrup A, Greim H, eds. Analyses of hazardous substances in air (Deutsche Forschungsgemeinschaft). Vol. 6. Weinheim, FRG: Wiley-VCH. pp. 67-78. [4] Breuer D [1999]. Measurement of vapor-aerosol mixtures. J Environ Monit. 1:299-305. [5] ISO (International Organization for Standardization) [1995]. ISO Guide 98: Guide to the expression of uncertainty in measurement. Geneva, Switzerland: ISO. [6] ISO [2007]. ISO 21438-1: Workplace atmospheres – Determination of inorganic ions by ion chromatography – Part 1: Non-volatile acids (sulfuric acid and phosphoric acid). Geneva, Switzerland: International Organization for Standardization (ISO). [7] Breuer D [2013]. Anorganische säuren, partikulär: phosphorsäure, schwefelsäure (Inorganic acid mists: phosphoric acid, sulfuric acid), in IFA Working Folder, Sheet No. 6173. Berlin, FRG: ErichSchmidt Verlag. ISBN 978-3-503-13084-9. [8] NIOSH [1994]. Acids, inorganic: Method 7903. In: Eller PM, Cassinelli ME, eds. NIOSH Manual of analytical methods, 4th ed., Cincinnati, OH: U.S. Department of Health and Human Services, Center for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH). Publication No. 94-113. [www.cdc.gov/niosh/nmam.] [9] NIOSH [2005]. NIOSH Pocket guide to chemical hazards. Barsan ME, ed. Cincinnati, OH: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2005-149.
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​NON-VOLATILE ACIDS (Sulfuric Acid and Phosphoric Acid): METHOD 7908, Issue 1, dated 20 May 2014 - Page 5 of 5
[10] Furr AK, ed. [1995] CRC Handbook of laboratory safety, 4th ed. Boca Raton, FL: CRC Press. [11] ASTM International [2010]. ASTM D4840: Standard guide for sampling chain of custody procedures. West Conshohocken, PA: ASTM International. [12] Breuer D, Howe A [2006]. Performance of methods for measurement of exposure to inorganic acids in workplace air. J Environ Monit. 8:120-126. [13] Breuer D, Heckmann P, Gusbeth K, Schwab G, Blaskowitz M, Moritz A [2012]. Sulfuric acid at workplaces – applicability of the new indicative occupational exposure limit value (IOELV) to thoracic particles. J Environ Monit. 14:440-445. [14] Comité Européen de Normalisation (CEN) [2012]. EN 482, Workplace exposure — General requirements for the performance of procedures for the measurement of chemical agents. Brussels, Belgium: Comité Européen de Normalisation (CEN). METHOD WRITTEN BY: Dietmar Breuer, Dr. rer. nat., Institute for Occupational Safety and Health of the German Social Accident Insurances, Sankt Augustin, Germany; and Kevin Ashley, Ph.D., NIOSH/DART Disclaimer: Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health. In addition, citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of these Web sites. All Web addresses referenced in this document were accessible at the time of publication.
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition