Page:NIOSH Manual of Analytical Methods - 5040.pdf/3
ELEMENTAL CARBON (DIESEL PARTICULATE): METHOD 5040, Issue 3, dated 15 March 2003 - Page 3 of 5
SPECIAL PRECAUTIONS: Hydrogen is a flammable gas. Users must be familiar with the proper use of flammable and nonflammable gases, cylinders, and regulators. According to the instrument manufacturer, the instrument is a Class I Laser Product. This designation means there is no laser radiation exposure during normal operation. Weakly scattered laser light is visible during operation, but does not pose a hazard to the user. The internal laser source is a Class IIIb product, which poses a possible hazard to the eye if viewed directly or from a mirror-like surface (i.e., specular reflections). Class IIIb lasers normally do not produce a hazardous diffuse reflection. Repairs to the optical system, and other repairs requiring removal of the instrument housing, should be performed only by a qualified service technician.
SAMPLING: 1. Calibrate each personal sampling pump with a representative sampler in line. NOTE: Both open- an d closed-faced cassettes have been used. Both configurations generally give even deposits. At higher flow rates (e.g., 4 L/m in), small spots occasionally have been observed in the center of the filters when closed-faced cassettes are used. This material likely consisted of impacted diesel agglomerates and/or non-diesel particulate matter. EC results for multiple portions of the filters were in good agreement, so the spots had little analytical impact. Other samplers also can be used (see ref. [2]) provided an even deposit of diesel particulate results. An even deposit is necessary because the sample portion analyzed must be representative of the entire deposit. If the deposit is not homogeneous, the entire sample must be analyzed. An impactor/cyclone may be needed in some cases. [2] 2. Attach sampler outlet to personal sampling pump with flexible tubing. 3. Sample at an accurately known flow rate. Typical rates are 2-4 L/min (note: Lower flows (e.g., 1 L/min) have been used in mines to prevent overloading). 4. After sampling, replace top piece of cassette, if removed, and pack securely for shipment to laboratory. NOTE: Diesel particulate samples from occupational settings generally do not require refrigerated shipment unless there is potential for exposure to elevated temperatures (that is, well above collection temperature). Filter samples normally are stable under laboratory conditions. Some OC loss may occur over time if samples contain O C from other sources (for example, cigarette smoke). Sorption of O C vapor after sample collection has not occurred, even with samples having high (e.g ., 80% ) EC content.
SAMPLE PREPARATION: 5. Place sample filter on a freshly cleaned aluminum foil surface. Isopropyl alcohol or acetone can be used to clean the foil. Allow residual solvent to vaporize from the surface prior to use. Punch out a representative portion of the filter. Take care not to disturb deposited material and avoid hand contact with sample. A needle inserted at an angle is useful for removal of the filter portion from the punch body. Newer instruments have an externally mounted bracket to support the quartz sample holder while the previous sample is removed and a new one is loaded. Through a hole in the side of the standard punch, a needle can be used to push the filter portion from the punch onto the sample holder. Alternative approaches also can be used, depending on the user’s preference, as long as contamination is avoided.
CALIBRATION AND QUALITY CONTRO L: 6. Analyze at least one replicate sample. For sets of up to 50 samples, replicate 10% of the samples. For sets over 50 samples, replicate 5% of the samples. If a filter deposit appears uneven (this should not be the case if the cassette is sealed properly), take a second portion (step 5) for analysis to check evenness of deposition. NOTE: Precision of replicate analyses of a filter is usually better than 5% (1 to 3% is typical).
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition