Page:NIOSH Manual of Analytical Methods - 5026.pdf/3

 OIL M IST, MIN ERA L: MET HO D 502 6, Issue 2, Rev. 15 M ay 1996 - Page 3 of 4 SAMPLE PREPARATION: 4. Using tweezers, transfer each sample or blank filter to a vial. Add 10.0 mL CCl4. Cap and shake vigorously.

CALIBRATION AND QUALITY CONTRO L: 5. Calibrate daily with at least six working standards. a. Add known amounts of stock mineral oil standard to CCl4 in 10-m L volum etric flas ks and dilute to the mark to obtain mineral oil concentrations in the range 5 to 250 µg/mL. b. Analyze with samp les and blanks (step 8). c. Prepare calibra tion gra ph (p eak abs orba nce vs. :g m ineral oil). 6. Determine recovery (R) at least once for each lot of filters used for sampling in the range of interest. Prepare three filters at each of five levels plus three media blanks. a. De pos it a known am oun t of stock m ineral oil standard o nto the filter. Allow solve nt to evaporate. b. Store samples overnight in filter cassettes. c. Prepare and analyze with working standards. d. Prepare a graph of R vs. µg mineral oil recovered. 7. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and R g raph are in control.

MEASUREMENT: 8. Scan each standard solution and each blank or sample filter extract from 3200 to 2700 cm -1 in absorbance mode vs. CCl4 in reference beam. Record absorbance at wavelength of largest absorbance near 2940 cm -1 (± 11.8% ).

CALCULATIONS: 9. Determine the mass, µg (corrected for R), of mineral oil found in the sample (W ) and in the average media blank (B) from the calibration graph. 10. Calculate concentration, C, of mineral oil in the air volume sam pled, V (L)

EVALUATION OF METHOD: The sam pling portion of this m etho d wa s evaluated over the ran ge 2 .5 to 11 .7 m g/m 3 at 22 °C and 755 m m Hg using 100-L air samples of Gulf machine cutting oil with measurem ent by fluo rescence spectrophoto m etry. Mixed cellulose ester filters, 0.8-µm pore size, were used for sampling [1,5]. The overall precision was 0.065 with an average recovery of 98%. The infrared measurem ent method was subsequently evaluated by NIOSH [2,3]. Precision and ac curacy of the infrared and fluoresce nce spe ctrophotom etric techniques are sim ilar.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition