HYD RO CAR BO NS, AR OM ATIC : MET HO D 150 1, Issue 3, dated 15 M arch 200 3 - page 3 of 7 9. Determine desorption efficiency (DE) at least once for each batch of charcoal used for sampling in the calibra tion ran ge (s tep 8). a. Prepare three tubes at each of five levels plus three media blanks. b. Inject a known amount of DE stock solution (5 to 25 µL) directly onto front sorbent section of each charcoal tube with a microliter syringe. c. Allow the tubes to air equilibrate for several minutes, then cap the ends of each tube and allow to stand overnight. d. Deso rb (steps 5 through 7 ) and analyze together with standards and b lanks (steps 1 1 and 12). e. Prepare a graph of DE vs. µg analyte recovered. 10. An alyze a minimum of three quality control blind spikes and three analyst spikes to insure that the calibra tion gra ph and D E graph are in control.
MEASUREMENT: 11.
Set gas chromatograph according to manufacturer's recomm endations and to conditions given on page 1501-1. Inject a 1-µL sample aliquot manually using the solvent flush technique or with an autosam pler. Note: If peak area is above the linear range of the working standards, dilute with solvent, reanalyze, and app ly the app ropriate dilution facto r in the c alculations. Analyte
a b
Approximate Retention Time (min)
benzenea toluene a ethylbenzene a o-xylenea m -xylenea p-xylenea
3.52 6.13 10.65 12.92 11.33 11.04
cumene b p-tert-butyltolueneb "-methylstyrene b $-methylstyrene b styrene b
18.61 21.45 19.99 20.82 18.33
Separation achieved using a 30-m Stabilwax fused silica capillary colum. Separation achieved using a 30-m Rtx-35 fused silica capillary column.
12.
Measure peak areas.
CALCULATIONS: 13.
14.
Determine the mass, µg (corrected for DE ) of analyte found in the samp le 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. NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate conce ntration, C, of analyte in the air volume sam pled, V (L):
NO TE : µg/L = m g/m 3
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
