METHYLCYCLOHEXANONE: METHOD 2521, Issue 2, dated 15 August 1994 - Page 3 of 4 9.
10.
Determine desorption efficiency (DE) at least once for each lot of Porapak Q used for sampling in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. a. Remove and discard back sorbent section of a media blank sampler. b. Inject a known amount (1 to 20 µL) of DE stock solution directly onto front sorbent section with a microliter syringe. c. Cap the tube. Allow to stand overnight. d. Desorb (steps 5 through 7) and analyze together with working standards (steps 11 and 12). e. Prepare a graph of DE vs. mg methylcyclohexanone recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.
MEASUREMENT: 11.
12.
Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 2521-1. Inject a 5-µL sample aliquot manually using solvent flush technique. Do not use an autosampler because of possible plugging of the syringe needle with Porapak Q. NOTE: If peak area is above the linear range of the working standards, dilute with acetone, reanalyze and apply the appropriate dilution factor in calculations. Measure peak area. A retention time of ca. 9 min is expected under these conditions. Acetone elutes before the single peak observed for the methylcyclohexanone isomers.
CALCULATIONS: 13.
14.
Determine the mass, mg (corrected for DE) of methylcyclohexanone found in the sample front (W f) and back (W b) sorbent sections, and in the average media blank front (B f) and back (B b) sorbent sections. NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of methylcyclohexanone in the air volume sampled, V (L):
EVALUATION OF METHOD: Method S375 was issued on February 18, 1977 [2]. The precision and accuracy were determined by analyzing generated atmospheres of 50/50 mixtures of 3- and 4-methylcyclohexanone containing 213, 426, and 852 mg/m 3 at 22 °C and 759 mm Hg using 3-L samples [1,3]. The concentration of methylcyclohexanone was determined using the rate of delivery of a syringe drive system and the flow rates of the dilution air. The stability of the concentrations was monitored with a total hydrocarbon analyzer; no bias was found. Storage stability was determined to be at least seven days at room temperature. Breakthrough of the front section of the Porapak Q tube was not observed after sampling 8.1 L of a test atmosphere containing 852 mg/m 3 at ≥ 80% RH for 185 min at 0.044 L/min. Desorption efficiencies for samples spiked with methylcyclohexanone in the range 0.73 to 2.93 mg per sample were 0.91 to 0.94.
REFERENCES: [1]
Backup Data Report for Methylcyclohexanone, S375, available as "Ten NIOSH Analytical Methods, Set 2," Order No. PB 271-464 from NTIS, Springfield, VA 22161.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
