Page:NIOSH Manual of Analytical Methods - 7906.pdf/4

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