Page:NIOSH Manual of Analytical Methods - 2520.pdf/1



METHYL BROMIDE	2520 CH3Br   MW: 94.94   CAS: 74-83-9   RTECS: PA4900000 METHOD: 2520, Issue 2

EVALUATION: FULL

OSHA:	 C 20 ppm (skin) NIOSH:	lowest feasible; carcinogen; Group I Pesticide ACGIH:	 5 ppm (skin) (1 ppm = 3.95 mg/m³ @ NTP)

Issue 1:	15 August 1990 Issue 2:	15 May 1996

PROPERTIES:	 gas; d 1.73 g/mL @ 0 °C; BP 4 °C; VP 189.34 kPa (1420 mm Hg) @ 20 °C

SYNONYMS:	 monobromomethane; bromomethane SAMPLING SAMPLER:	 SOLID SORBENT TUBES (two petroleum charcoal tubes, 400 mg and 200 mg; drying tube, 9-g Na2SO4, necessary at humidity >50%)

MEASUREMENT TECHNIQUE:

GAS CHROMATOGRAPHY, ATOMIC EMISSION DETECTION (GC-AED) monitoring Br, C, and H channels

ANALYTE:

methyl bromide

DESORPTION:

400 mg tube: 3 mL methylene chloride; 200 mg tube: 2 mL methylene chloride

FLOW RATE:	 0.01 to 0.1 L/min VOL-MIN: -MAX:

1 L @ 5 ppm 5 L with drying tube, 1 L w/o dying tube [1]

SHIPMENT:	 ship on dry ice at −10 °C [1] SAMPLE STABILITY:	 six days at −10 °C [1] BLANKS:

2 to 10 field blanks per set ACCURACY

RANGE STUDIED:

INJECTION VOLUME:

1 µL

TEMPERATURE-INJECTION:	 250 °C -TRANSFER LINE/ CAVITY BLOCK:	 250 °C -COLUMN:	 30 °C, 3.5 min; 12 °C /min to 130 °C; hold 1 min CARRIER GAS:

helium

COLUMN:

DB-1 capillary, 30 m × 0.32-mm ID, 1.0-µm film thickness; 1 m × 0.53-mm deactivated fused silica pre-column

CALIBRATION:

brominated compounds in methylene chloride

RANGE:

33.0 to 2687 µg bromine per sample

0.84 to 32.0 ppm (5-L samples)

BIAS:	−5.2% OVERALL PRECISION :	0.089 ACCURACY:

±19.4%

ESTIMATED LOD:	 16.6 µg per sample [1] PRECISION :

0.066 [1]

APPLICABILITY: The working range is 0.84 to 32.0 ppm (3.3 to 126 mg/m³) for a 5-L sample. Ceiling measurement samples may require dilution when analyzed. INTERFERENCES: Water vapor interferes with collection at relative humidities (RH) >50%. To eliminate the interference, precede the sampling train with a drying tube, and limit the sample volume to 5 L. If drying tubes are not available, limit the sample volume to 1 L under humid conditions. OTHER METHODS: This is Method 2520 [2] revised to account for humidity effects, as well as instability of standards and samples. Other researchers [3] have prepared methyl bromide standards gravimetrically and used GC-ECD for analysis. The gravimetric calibration procedure did not give consistent results when compared with the procedure used in this revision of Method 2520. GC-ECD with a Porapak Q capillary column may be an alternative technique to GC-AED, if other bromine standards are used to confirm the concentration of methyl bromide standards.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition