# Particulate Fluorides and Hydrofluoric Acid by Ion Chromatography (7906)

​PARTICULATE FLUORIDES and HYDROFLUORIC ACID by Ion Chromatography MW: F-, 18.998 (HF, 20.01)
METHOD: 7906, Issue 2
CAS (HF): 7664-39-3
RTECS: (HF) MW7875000
EVALUATION: FULL
U. S. OELs  OSHA :       2.5 mg/m3 (fluorides); 3 ppm (HF) NIOSH: 2.5 mg/m3 (fluorides); 3 ppm (HF), STEL (HF): 6 ppm Other OELs:   [1,2]
7906
Issue 2: 20 May 2014
Issue 1: 15 August 1994
HF: gas; mp = -83.1 °C; bp = 19.5 °C; sp. gr. 0.987; VP = 783 mm Hg (104.4 kPa). Fluoride salts liberate HF vapor in the presence of acids.
SYNONYMS: Hydrogen fluoride; hydrofluoric acid;    Sodium fluoride (CAS #7681-49-4) SAMPLING SAMPLER: PRE-FILTER, cellulose nitrate, 0.8 µm pore size, 37-mm diameter, + TREATED FILTER, cellulose nitrate impregnated with Na2CO3, 0.8 µm pore size, 37-mm diameter, separated by a chemically inert spacer
MEASUREMENT TECHNIQUE:
ION CHROMATOGRAPHY (IC) with conductivity detection
ANALYTE:
Fluoride ion (F-)
EXTRACTION:
Aqueous solution of sodium carbonate / sodium hydrogen carbonate
FLOW RATE: 1 to 2 L/min VOL-MIN: -MAX:
15 L 1000 L
INJECTION VOLUME:
50 µL
SHIPMENT: 4 °C
ELUENT:
SAMPLE STABILITY: Stable for at least 14 days (fluorides) / 28 days (HF) if stored at @ 20 °C for 7 days and 4 °C thereafter [1]
8 mM Na2CO3 / 1 mM NaHCO3 flow rate 1.0 mL/min
COLUMNS:
Pre-column, anion-exchange column and suppressor column
BLANKS:
CALIBRATION RANGE:
3 minimum field blanks per set ACCURACY*
RANGE STUDIED: 0.04 to 5.9 mg/m3 (fluorides);
0.30 to 6 ppm (HF)
F-; 0.4 to 8.0 mg/L [3,5]
ESTIMATED LOD: 0.1 mg/L / 0.009 mg/m3 (120 L air volume; as F-) [3] PRECISION ( S ): Fluorides, 0.033; HF, 0.056 [3] r
BIAS*:
Negligible [3]
OVERALL PRECISION*( SˆrT ): Fluorides, 0.074; HF, 0.125 [5,6] EXPANDED UNCERTAINTY*: less than 20% for F-;
less than 22% for HF [4,5]
rather than the traditional NIOSH accuracy criterion. APPLICABILITY:
The working range is (at least) 0.1 to 8 mg/sample for a 250 Liter air sample.
INTERFERENCES: Co-sampled formate and acetate compounds in the work environment can cause a positive interference; thus detection by ion selective electrodes is a suitable alternative if airborne formate and acetate are expected. Cations that form insoluble fluorides, such as Ca2+, Fe3+, and Al3+ can cause negative interferences. Recovery of gaseous HF is reduced at high humidity.
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​PARTICULATE FLUORIDES and HYDROFLUORIC ACID: METHOD 7906, Issue 2, dated 20 May 2014 - Page 2 of 6
OTHER METHODS: This method updates NIOSH 7906 [7] by providing full method accuracy information, and specifies the use of an impregnated filter instead of a treated cellulose pad. The procedure, which is consistent with ISO 21438-3 [6], replaces NIOSH 7903 [8] for the determination of particulate fluorides and gaseous HF in workplace air samples. The advantages of this method are that it can allow for the collection of the inhalable fraction of particulate fluorides by means of the pre-filter (housed within an optional inhalable sampler) and it can provide for lower limits of detection and quantitation for gaseous HF due to higher sampling flow rates. NIOSH 7902 [9] and ASTM D4765 [10] are alternative methods that are recommended for insoluble fluorides, which rely on detection of F- by ion-selective electrode. 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. Filter impregnation solution (0.75 M Na2CO3); Dissolve 7.95 g Na2CO3 in deionized water and swirl to mix. Then bring to 100 mL in a volumetric flask, stopper and mix thoroughly. 5. Eluent stock solution: 0.8 M Na2CO3 / 0.1 M NaHCO3; Dissolve 16.96 g Na2CO3 and 1.68 g NaHCO3 in deionized water and swirl to mix. Then bring to 200 mL in a volumetric flask, stopper and mix thoroughly. 6. Eluent solution: 8 mM Na2CO3 / 1 mM NaHCO3; Transfer 10 mL of 0.8 M Na2CO3 / 0.1 M NaHCO3stock solution to a 1 Liter volumetric flask, dilute to the mark with deionized water, stopper and mix thoroughly. Prepare fresh eluent solution weekly. 7. Fluoride (F-) standard solution, 1000 mg/L 8. Calibration stock solution, 100 mg/mL (as the anion): Place a 10 mL aliquot of fluoride standard solution into a 100 mL volumetric flask, dilute to the mark and mix thoroughly. The solution is stable for at least 4 weeks at room temperature. 9. To prepare the impregnated filter, evenly distribute 120 µL 0.75 M Na2CO3 over the surface of the filter and allow to dry at room temperature for several hours.
1. Sampler: 37-mm diameter cellulose nitrate pre-filter, 0.8 µm pore size, 37-mm impregnated cellulose nitrate filter. The untreated filter collects particulate fluorides, while the impregnated filter collects HF vapor. Arrange the filters serially (with the pre-filter upstream of the impregnated filter) in a 37-mm diameter 3-piece chemically inert cassette filter holder. 2. Personal sampling pump, 1 to 2 L/min, with flexible connecting tubing 3. Ion chromatograph (IC), 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, inert plastic, with screw caps 6. Volumetric flasks, 25- to 1000 mL 7. Pipets, 50- to 10000 µL 8. Beakers, 25- to 100 mL 9. Filtration apparatus, with filter funnel 10. Disposable filters, cellulosic, 0.45 µm pore size 11. Styrene-based sulfonic acid resin cartridges 12. Water purification system, to prepare greater than or equal to 18 MΩ-cm resistivity deionized water 13. Bottles, polyethylene, 100 mL 14. Syringes, plastic, 5 mL and/or 10 mL 15. Syringe filter cartridges, with 0.8-µm pore size polytetrafluoroethylene (PTFE) membrane filters 16. Micro-syringes, 50 µL, with 60 mm x 0.6 mm needles 17. Auto-sampler vials, polypropylene, 0.75 mL capacity.
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​PARTICULATE FLUORIDES and HYDROFLUORIC ACID: METHOD 7906, Issue 2, dated 20 May 2014 - Page 3 of 6
SPECIAL PRECAUTIONS: Acids, particularly HF, are extremely corrosive to skin, eyes, and mucous membranes. HF will attack glass. Plastic labware is recommended. 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 [11,12]. SAMPLING, SAMPLE TRANSPORT AND STORAGE: 1. Prior to sampling, load each clean sampler, first with a sampling (impregnated) filter, then with a prefilter, separating the filters with a spacer. Ensure that the configuration in which the filters are loaded leads to the sampled air passing first through the pre-filter and then through the sampling filter. 2. Calibrate each personal sampling pump with a representative sampler in the line. 3. Sample at an accurately known flow rate between 1 to 2 mL/min for a total sample size of 15 to 1000 L. Avoid sampler overloading. 4. After sampling, remove the filters from the cassette and place them in screw-cap plastic vessels. For the pre-filter portion: With approximately 2 mL eluent(extraction) solution, rinse material from the inside surfaces of the pre-filter portion of the cassette into the vessel. Add eluent solution into the vessels until a final volume of 10 mL is reached. 5. Submit at least three blank untreated filters and three blank impregnated filters as 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 10 mL of eluent solution and ship it to the lab along with the remaining samples. 6. 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 [13]. 7. Refrigerate the samples immediately upon receipt at the lab until ready for analysis. 8. Analyze samples within 2 weeks of receipt. The samples can be stored at room temperature for one week; for longer storage, refrigerate the samples (4 °C). SAMPLE PREPARATION AND MEASUREMENT: 9. Remove sample vessels from storage and bring them to room temperature. 10. Sonicate the samples in an ultrasonic bath for at least 15 minutes and allow to cool for at least 30 minutes. 11. Using 5- or 10-mL syringes, filter each sample extract solution through a PTFE filter and a styrenebased sulfonic acid resin cartridge (follow the manufacturer’s instructions), discard the first two milliliters and place the remaining solution in clean plastic vessels. CALIBRATION AND QUALITY CONTROL: 12. With dilution of the calibration stock solution in eluent solution, prepare calibration working standard solutions covering the range of approximately 0.4 to 8 µg/mL of fluoride. Store working standards in tightly sealed polyethylene bottles. Prepare fresh working standards biweekly. 13. Calibrate the ion chromatograph with at least six working standards covering the range of (at least) 0.4 to 8 µg/mL of fluoride per sample by preparing a calibration graph of anion peak height (mm or µS) vs. concentration (µg/mL). 14. 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). Cellulose nitrate filters demonstrate variable batchdependent blank values, thus media blank correction is essential.
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​PARTICULATE FLUORIDES and HYDROFLUORIC ACID: METHOD 7906, Issue 2, dated 20 May 2014 - Page 4 of 6
MEASUREMENT 15. Set the ion chromatograph to recommended eluent flow rate, (e.g. 1.0 mL/min or approximately 13 MPa pressure), and other conditions as specified by the instrument manufacturer. 16. Inject a sample aliquot (e.g. 50 µL) into the chromatograph and measure the peak height of the fluoride peak. If the peak height exceeds the linear calibration range, dilute with eluent, reanalyze and apply the appropriate dilution factor in calculations. CALCULATIONS: 17. Calculate the mass concentration of fluoride, C (mg/m3), in the air volume sampled, V (L):
C={
(C1*V1*Fd)-(C0*V0) }*Fc V* h
where: C0 = mean concentration, in µg/mL, of fluoride in the field blank test solutions; C1 = concentration, in µg/mL, of fluoride in the sample test solution; V = volume, in liters, of the air sample; V0 = volume, in mL, of the field blank test solutions; V1 = volume, in mL, of the sample test solutions; Fd = dilution factor for each sample test solution; Fc = 1.053 = conversion factor to convert from fluoride to HF concentration (if applicable); η = recovery. EVALUATION OF METHOD: This updates Issue 1, NIOSH 7906 [7], by providing full method accuracy information, and specifies the use of an impregnated filter instead of a treated cellulose pad. The procedure described in issue 2 of NIOSH 7906, which is consistent with ISO 21438-3 [6], also replaces NIOSH 7903 [8] for the determination of particulate fluorides and gaseous HF in workplace air samples. Recovery of 100% ± 2% was found after sample collection for both F- and HF [3,5,6], and no breakthrough of HF was observed from impregnated filters for up to 5 mg fluoride [6,14]. The component of the coefficient of variation of the method that arises from analytical variability, determined from the analysis of spiked filters, was 2.4% to 5.6% for HF and 1.7% to 3.3% for fluorides [3,6]. Laboratory testing with test atmospheres of HF (0.5 to 5 mg/m3) demonstrated quantitative sampling efficiencies (greater than 95%) at relative humidity (RH) of 20% to 60%, but recovery was around 60% at relative humidity of 80%. The recovery of HF as an effect of relative humidity (RH) greater than 60 percent can be calculated as follows (see also Figure 1):
h=
[226.5-(2.0914 * RH)] 100
No effect of humidity (RH from 20% to 80%) was observed on recovery of particulate fluoride over the concentration range of 0.3 to 5 mg/m3. Results for repeatability and reproducibility of the method for test atmospheres of hydrogen fluoride and fluoride aerosol (Relative humidity was approximately 50%) are shown in Table I. The method has been successfully applied in independent investigations [14] and
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​PARTICULATE FLUORIDES and HYDROFLUORIC ACID: METHOD 7906, Issue 2, dated 20 May 2014 - Page 5 of 6
has been promulgated as an International Standard [6]. The back-up data and user check reports are references 3 and 14 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, Gusbeth K [2005]. Hydrogen fluoride and fluorides. In: The MAK-Collection Part III: Air monitoring methods. (Deutsche Forschungsgemeinschaft) Vol. 9. Weinheim, FRG: Wiley-VCH. pp. 105-118. [4] ISO (International Organization for Standardization) [1995]. ISO Guide 98: Guide to the expression of uncertainty in measurement. Geneva, Switzerland: ISO). [5] Breuer D [2006]. Fluoride und fluorwasserstoff (Fluorides and hydrogen fluoride), in BGIA Working Folder, Sheet No. 7512. Berlin, FRG: Erich-Schmidt Verlag. ISBN 3-503-020853. [6] ISO (International Organization for Standardization) [2010]. ISO 21438-3, Workplace air — Determination of inorganic acids by ion chromatography — Part 3: Hydrofluoric acid and particulate fluorides. Geneva, Switzerland: International Organization for Standardization (ISO). [7] NIOSH [1994]. Fluorides, aerosol and gas, by IC: Method 7906. In: Eller PM, Cassinelli ME, eds. NIOSH Manual of analytical methods, 4th ed., Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH). Publication No. 94-113. [www.cdc.gov/niosh/nmam.] [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, Centers 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 [1994]. Fluorides, aerosol and gas, by ISE: Method 7902. In: Eller PM, Cassinelli ME, eds. NIOSH Manual of analytical methods, 4th ed., Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH). Publication No. 94-113. [www.cdc.gov/niosh/nmam.] [10] ASTM International [2008]. ASTM D4765, Standard test method for fluorides in workplace atmospheres by ion-selective electrodes. West Conshohocken, PA: ASTM International. [11] 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. [12] Furr AK, ed. [1995] CRC Handbook of laboratory safety, 4th ed. Boca Raton, FL: CRC Press. [13] ASTM International [2010]. ASTM D4840, Standard Guide for Sampling Chain of Custody Procedures. West Conshohocken, PA: ASTM International. [14] Demange M, Oury V, Rousset D [2011]. Evaluation of sampling methods for measuring exposure to volatile inorganic acids in workplace air. Part 2 – sampling capacity and breakthrough tests for sodium carbonate-impregnated filters. J Occup Environ Hyg. 8:642-651. [15] 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).
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition ​PARTICULATE FLUORIDES and HYDROFLUORIC ACID: METHOD 7906, Issue 2, dated 20 May 2014 - Page 6 of 6
METHOD WRITTEN BY: Dietmar Breuer, Dr. rer. nat., and Petra Heckmann, 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.
FIGURE 1.
HF recovery as function of relative humidity
TABLE 1. Performance evaluation for HF and F- ion measurements from test atmospheres [5] Concentration Analyte Sr1 (n = 6) RSD2(%) U3 (mg/m3) HF 0.25 0.007 3.1 0.22 HF 1.2 0.044 2.8 0.21 HF 2.3 0.026 1.1 0.20 HF 5.0 0.099 2.0 0.11 Fluoride 0.04 0.002 3.8 0.19 Fluoride 0.52 0.006 1.3 0.12 Fluoride 2.95 0.009 0.3 0.11 Fluoride 5.9 0.065 1.1 0.11 1 Standard deviation for 6 test samples 2 Relative standard deviation 3 Expanded measurement uncertainty; k = 2 (calculated in accordance with EN 482 [15])
NIOSH Manual of Analytical Methods (NMAM), Fifth Edition