Page:NIOSH Manual of Analytical Methods - 5040.pdf/4

 ELEMENTAL CARBON (DIESEL PARTICULATE): METHOD 5040, Issue 3, dated 15 March 2003 - Page 4 of 5 7. Analyze three quality control blind spikes and three analyst spikes to ensure that instrument calibration is in control. Prepare spike as follows: a. W ith 10-:L (or other) syringe, apply an aliquot of OC standard solution directly to filter portion taken (step 5) from a precleaned filter. For best results, the precleaned filter punch should be cleaned aga in in the s am ple oven p rior to applica tion of the aliquot. NOTE: W ith sm all aliquots (e.g., # 10 :L), disperse standard solution over one end of filter portion to ensure standard is in laser beam. To prevent possible solution loss to surface, hold the portion off the surface. Larger volumes can easily penetrate to the underside of the filter portion. b. Allow wate r to eva pora te and an alyze spikes with sa m ples and blank s (steps 9 and 10 ). NOTE: A pronounced decrease in filter transmittance during the first temperature step of the analysis indicates water loss. Allow portions to dry longer if this occurs. Spiked punches also can be dried in the oven, if desired. For quick drying, the ‘clean oven’ comm and on the menu can be selected and canceled after about 4 seconds. The time allowed may depend on instrument, but oven temperatures should be below 100 °C to avoid boiling the solution. This approach is con venient and prevents p otential adsorption of organic vapors in laboratory air. 8. De term ine instrum ent blank (results of ana lysis with fre shly clea ned filter portion ) for each sam ple se t.

MEASUREMENT: 9. Adjust analyzer settings according to manufacturer's recomm endations (see instrument operation manual and background information in ref. [2]). Place sample portion into sample oven. NOTE: F orm s of carbon that are difficult to oxidize (e.g., graphite) may require a longer period and higher temperature during the oxidative mode to ensu re tha t all EC is removed (the EC peak should never m erge with the calibra tion pe ak). Adju st time and tem pera ture a cco rdingly. A m axim um tem pera ture a bove 94 0 °C sho uld no t be required. 10. Determine EC (and OC ) m ass, :g. Analyzer results are reported in units :g/cm 2 of C. The reported values are normally based on a sample portion of about 1.5 cm 2, which is the area of the standard punch provided by the manufacturer. If the portion area used differs from the value entered in the ocecpar.txt file, m ultiply the result by 1.5 (or value in ocecpar.txt file) and divide the product by the actual area analyze d to obtain the are a-correcte d re sult (i.e., reported re sult x 1.5/po rtion area = correcte d re sult in
 * g/cm 2). This is m ost easily done in the data spreadsheet. Alternatively, the correct results will be obtained

with the data c alculation pro gram if the portion area is entered in the param ete r file (oc ecpar.txt), but th is approac h is cum bersom e when punche s of different areas are used because correct results will not be obta ined for all pu nch sizes.

CALCULATIONS: 11. Mu ltiply the repo rted (o r area-corrected ) EC resu lt (:g/cm 2 ) by filter deposit area, cm 2, (typically 8.5 cm 2 for a 3 7-m m filter) to ca lculate total m ass, :g, of EC on each filter samp le (W EC). Do the same for the blanks an d calculate the m ass foun d in the average field blank (W b). The m ass of OC is calculated similarly, but the mean O C field blank m ay underestimate the amount of OC contributed by adsorbed vapor. A quartz filter placed beneath the sample filter can provide a better estimate of the adsorbed OC. [2] 12. Calculate the EC concen tration (C EC) in the air volume sam pled, V (L):

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition