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METHYL BROMIDE 2520 - Centers for Disease Control and ... Flipbook PDF
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition METHYL BROMIDE: METHOD 2520, Issue 2, dated 15 May 1996 - Page
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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
METHYL BROMIDE: METHOD 2520, Issue 2, dated 15 May 1996 - Page 2 of 5
REAGENTS:
EQUIPMENT:
1. Eluant: methylene chloride, chromatographic grade.* 2. Methyl bromide, 99.5%.* 3. Calibration stock solution: To 4 mL of methylene chloride, add 12 µL dibromomethane. NOTE: Other brominated compounds may be used if liquid at room temperature. 4. Desorption stock solution: Bubble methyl bromide gas slowly into chilled eluant. Determine the methyl bromide concentration by comparison with calibration standards. 5. Helium, prepurified, 99.995%. 6. Oxygen, ultra purified, as reagent gas for plasma, 30 psi. 7. Air, filtered. 8. Dry ice, flaked, for chilling solvent. *See SPECIAL PRECAUTIONS.
1. Sampler: two glass tubes, each tube, 10-cm long, 8-mm OD, 6-mm ID, containing 20/40 activated (600 °C) petroleum charcoal, first tube 400 mg, second tube 200 mg, held in place with silylated glass wool plugs; drying tube, glass, 9 g sodium sulfate. Tubes are connected in series with short pieces of plastic tubing. Pressure drop across sampler 50% RH. The analytical technique was changed to GC with atomic emission detection (GC-AED). The atomic emission detector monitors individual elements, in this case NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
METHYL BROMIDE: METHOD 2520, Issue 2, dated 15 May 1996 - Page 4 of 5
bromine, independent of the source compound. Calibration can be done with brominated compounds that are liquid at room temperature, thereby eliminating the need for methyl bromide standards. Methylene chloride replaced carbon disulfide as desorption solvent. This revised Method 2520 (issued 5/15/96) for methyl bromide was evaluated at 7.8, 20.0, and 125.0 mg/ m³ (2, 5, and 32 ppm) [1]. Test atmospheres were generated by delivering methyl bromide gas from two diffusion tubes kept at −12 °C into an airstream flowing at 12 L/min. Humidity was added downstream when needed, and airflow passed through two mixing chambers before reaching a sampling manifold. The concentration was monitored with a total hydrocarbon analyzer and confirmed by calibrating against other brominated standards by GC-AED. Three compounds used as calibration standards (dibromomethane, 1-bromopropane, and 1-bromobutane) were chosen as closest in chemical structure to methyl bromide, although a compound-independent response was assumed [6]. A three-compound calibration was used during the development of the GC-AED analytical procedure. Since there was good agreement between the three compounds, the method was written with only one brominated standard, dibromomethane. When challenged with methyl bromide at a calculated concentration of 27 ppm, the capacity of the sampler (a 400-mg petroleum charcoal tube plus a 200-mg petroleum charcoal tube) at 40% RH and 20 °C was 1386.5 µg regardless of flow rate (10.5, 40, or 100 mL/min). However, at 100% RH and 39 °C, the average capacity fell to 298.6 µg. With a 9-g sodium sulfate drying tube in line, the capacity was increased to 651.8 µg (concentration averaged 33 ppm). Even with a drying tube in line, severe breakthrough occurred at the 10-L sample volume (50% was found on the back tube). Without the use of a drying tube, a 1-L sample volume is recommended, based on a 170.6 µg capacity (1.6 L) found at the 40 mL/min rate multiplied by the 0.67 caution factor.
Recovery (%)
Recovery fell below 70% for sample loadings less than 58 µg when carbon disulfide was used for desorption (Figure 1). This would not allow accurate sampling at 2 ppm, the exposure level most frequently encountered. Therefore, alternate desorption solvents were tested. Desorption with methylene chloride improved recovery at the 15-µg level to 76.7%. However, sample stability still fell below 70% after storage for six days at −10 °C regardless of sample level. This stability limitation remains a concern and rapid sample analysis is required.
Methylene chloride Carbon disulfide
Methyl bromide (µg)
Figure 1. Comparison of desorption solvents.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
METHYL BROMIDE: METHOD 2520, Issue 2, dated 15 May 1996 - Page 5 of 5
REFERENCES: [1] NIOSH [1995]. Research into problems with NIOSH method 2520 for methyl bromide. Cincinnati, OH: National Institute for Occupational Safety and Health, DHHS (NIOSH) NTIS Pub. No. PB95-179842. [2] NIOSH [1984]. Methyl Bromide: Method 2520. In: Eller PM, Ed. NIOSH Manual of Analytical Methods, 3rd ed. Cincinnati, OH: National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 84-100. [3] Woodrow JE, McChesney MM, Sieber JN [1988]. Determination of methyl bromide in air samples by headspace gas chromatography. Anal Chem 60:509–512. [4] NIOSH [1984]. Current Intelligence Bulletin 43: monohalomethanes; methyl chloride, methyl bromide, methyl iodide; evidence of carcinogenicity. Cincinnati, OH: National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 84-117. [5] NIOSH [1977]. Methyl bromide: Method S372. In: Taylor DG, Ed. NIOSH manual of analytical methods, 2nd. Ed., Vol. 2. Cincinnati, OH: National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 77-157-C. [6] Yu W, Haung Y, Ou O [1992]. Quantitative characteristics of gas chromatography with microwaveinduced plasma detection. In Uden PC, Ed. Element-specific chromatographic detection by atomic emission spectroscopy, ACS Symposium Series 479, American Chemical Society, pp. 44–61. METHOD REVISED BY: Yvonne T. Gagnon, MRB/DPSE/NIOSH
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition