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]
- Accuracy calculations were determined using references
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
