Page:NIOSH Manual of Analytical Methods - 2556.pdf/3

 ISOP HO RO NE: M ETH OD 2556, Issue 1, dated 1 5 Ma rch 2003 - Page 3 of 4 9. Determine desorption efficiency (DE) at least once for each batch of XAD-4 used for sampling in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. a. Rem ove and disca rd back sorbent sec tion of a med ia blank sam pler. b. Inject a known amount of isophorone directly onto front sorbent section with a microliter syringe. c. Ca p the tube. Allow to stand overnight. d. Deso rb (steps 5 through 7 ) and analyze together with working standards (steps 11 and 12). e. Prepare a graph of DE vs. µg isophorone recovered. 10. Analyze three quality control blind spikes and three ana lyst spikes to insure that the calibration graph and DE graph are in control.

MEASUREMENT: 11. Set gas chromatograph according to manufacturer's recomm endations and to conditions given on page 255 6-1. Inject sam ple aliqu ot m anu ally using solve nt flush technique o r with autos am pler. NOTE: If peak area is above the linear range of the working standard s, dilute w ith diethyl ether, rea nalyze and apply the appropriate dilution factor in calculations. 12. Measure peak area.

CALCULATIONS: 13. Determine the mass, µg (corrected for DE ) of isophorone fo und 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. NOTE: If W b > W f/10, report breakthrough and possible sample loss. 14. Calculate conce ntration, C, of isopho rone in the air volume sa m pled, V (L):

EVALUATION OF METHOD: NIOSH method NMAM 2508 for isophorone reported an average DE recovery of 86% over the high concentration range of 849 to 3400 µg [1]. W hile the results are considered acceptable, at th e lowe r levels encountered in current analyses, the recoveries would most likely fall below those considered acceptable. Therefore, a m eth od developm ent effort was initiated to im prove the re covery an d analysis of isophorone at thes e lower leve ls. In 1987, Levin and Carleborg reported that isophorone was quantitatively recovered from XAD polymer using diethyl ether as the desorption solvent at the 750 µg level [4]. Initial results using this approach were plagued by varying recoveries and poor peak resolution which was so lved by using a Stabilwax-DA fused silica capillary colum n and a base-deactivated inlet liner in th e gc injec tion port. T he base-deactivate d inlet liner should be replaced after 35-40 injections. Additionally, the samples were placed on a rotary mixer fo r 1.5 hours after the addition of the diethyl ether. These changes resulted in an average recovery of 94.1% over the range of 55 to 831µg and the LOD being lowered to 1 µg/sample. Isophorone samples, when spiked at levels 0.15 times the REL, were stable (89% recovery) for 30 days when stored at 5°C.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition