HYD RO CAR BO NS, BP 36-216 °C : MET HO D 150 0, Issue 3, dated 15 M arch 200 3 -Page 3 of 8 c. Inject a know n am ount of stock solution (5 to 25 µL) directly onto the front sorbent section with a microliter syringe. d. Allow the tubes to air equilibrate for several m inutes , then cap the tub es a nd a llow to stand overnight. e. Deso rb (steps 5 through 7 ) and analyze with standards and blank s (steps 11a nd 12). f. Prepare a graph of DE vs. µg analyte recovered. 10. Analyze at leas t three qua lity control blind spik es a nd three a nalyst spike s to ins ure th at the calibration grap h an d DE graph are in c ontro l.
MEASUREMENT: 11. Set the gas chromatograph according to the manufacturer's recomm endations and to the conditions given on pag e 15 00-1 . Inject a 1-µL aliquot manually using a solvent flushing technique or with an autosam pler. NOTE: If the pea k area is abo ve the linear ra nge of the working standard s, dilute w ith solve nt, reanalyze and apply the appropriate dilution factor in the calculations.
Analyte n-pentane solvent (CS2)
Approximate Retention Time (min) 7.5 9.6
n-hexane cyclohexane
13.0 16.1
cyclohexene
16.8
n-heptane
17.7
methylcyclohexane
18.9
n-octane
21.6
n-nonane
24.9
n-decane
27.8
n-undecane 30.5 n-dodecane 32.9 NOTE: Retention tim es m ay vary slightly due to column manufacturer and age of column, and be influen ced by other GC ins trum enta l param eters . 12. Measure the peak area.
CALCULATIONS: 13. Determine the mass, µg (corrected for DE), of analyte found in the sam ple front (W f) and back (W b) sorbent sec tions, and in the average m edia blank front (B f) and back (B b) sorbent sections. NO TE: If W b > W f / 10, report breakthrough and possible sample loss. 14. Calculate the concentration, C, of analyte in the air volume, V(L), sampled:
NO TE : :g/L = m g/m 3
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
