VOLATILE ACIDS by Ion Chromatography: METHOD 7907, Issue 1, dated 20 May 2014 - Page 4 of 6
16. 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: 17. Set the ion chromatograph to recommended eluent flow rate (e.g., 1.5 mL/min) and recommended pressure ( e.g., 1.1 x 105 kPa), and other conditions as specified by the instrument manufacturer. 18. Inject a sample aliquot, e.g., 25-µL, into the chromatograph, and measure the peak heights of the chloride, bromide and nitrate peaks (at retention times of approx. 5 min, 9 min and 12 min, respectively). If the peak height exceeds the linear calibration range, dilute with eluent, reanalyze and apply the appropriate dilution factor in calculations. CALCULATIONS: 19. Calculate the mass concentration of each anion, C (mg/m3), in the air volume sampled, V (L): C ={
(C 1*V 1 * Fd ) − (C 0*V 0 ) } * Fc V
where: C0 = mean concentration, in mg/L, of anion in the field blank test solutions; C1 = concentration, in mg/L, of anion 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 = conversion factor to convert from anion to acid concentration Fc = 1.0284 for chloride, 1.0126 for bromide, and 1.0163 for nitrate EVALUATION OF METHOD: On impregnated quartz fiber filters, greater than 95 % recovery of hydrochloric and nitric acid was found four weeks after sample collection, and no breakthrough was observed at sample loadings of up to 2.5 mg HCl or 5 mg HNO3 [3,4,11]. Mean analytical recovery determined from the analysis of spiked filters has been found to be in the range of 97 to 100% for HBr, HCl and HNO3 [3,11]. The component of the coefficient of variation of the method that arises from analytical variability, determined from the analysis of filters sampled at a dynamic test gas apparatus, was 0.8% to 1.3% for hydrogen chloride and 1.1% to 8.8% for nitric acid; and as determined from the analyses of spiked samples of hydrogen bromide, this value was 0.8% to 1.4% [3]. The method has been independently verified for all three acids, in accordance with applicable performance criteria [11,12]. An interlaboratory study with 5 participants found negligible biases and good agreement for hydrogen chloride and nitric acid at concentrations between 0.6 and 8 mg/m3 for HCl and 0.8 and 10 mg/m3 for HNO3 [6]. The back-up data and user check reports are references 6 and 11 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 NIOSH Manual of Analytical Methods (NMAM), Fifth Edition
