Page:NIOSH Manual of Analytical Methods - 1618.pdf/3
ISOP RO PYL ET HER : MET HO D 161 8, Issue 2, dated 15 M arch 200 3 - Page 3 o f 4 a. Prepare three tubes at each of five levels plus three media blanks. b. Rem ove and disca rd the back sorbent sec tion of a blank sam pler. c. Inject a known amount of stock solution (1 to 20 µL) directly onto the front sorbent se ction with a microliter syringe. d. Allow the tubes to air equilibrate for several minutes, then cap the tubes and allow 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. g. Analyze a m inim um of thre e qu ality contro l blind sp ikes and three a nalyst spikes to insure that the calibra tion gra ph and D E graph are in control. h. Analyze at least three quality control blind spikes and three analyst spikes to insure that the calibration grap h an d DE graph are in c ontro l.
MEASUREMENT: 10. Set the gas chromatograph according to the manufacturer's recomm endations and to the conditions given on page 1618-1. Inject a 1-µL aliquot manually using a solvent flushing technique or with an auto sam pler. NOTE: If the peak a rea is above the linea r range of the w ork ing sta nda rds, dilute with so lvent, reana lyze and apply the appropriate dilution factor in the calculations. 11. Measure the peak area.
CALCULATIONS: 12. Determine the mass, µg (corrected for D E), o f 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. NOTE: If W b > W f / 10, report breakthrough and possible sample loss. 13. Calculate the concentration, C, of analyte in the air volume, V(L), sampled:
EVALUATION OF METHOD: Issue 1 S368 was issued on April 21, 1976 [3] and validate d over the rang e 99 2 to 4260 m g/m 3 for 3-L air samples from dynamically generated test atmospheres [2]. The isopropyl ether concentrations were verified by G C/F ID analysis. Breakthrough (5% on the backup section) occurred at 26 min when sam pling a test atmo sphere con taining 426 0 m g/m 3 of isoprop yl ether in dry air at a flow rate of 0.19 8 L/m in. Issue 2 The desorption efficiency, at levels ranging from 10 times the LOQ to 0.1 times the REL, was determined by spiking kn ow n am ounts of is opropyl ether (in CS 2) on coconut shell charcoal tubes. The isopropyl ether exhibited acc epta ble de sorption e fficiency recovery resu lts (97.1% - 103 .4%) o ver the 20 to 651 :g range evaluated [1]. Isopropyl ether was evaluated for its storage stability. Sorbent tubes were spiked at approxim ate ly 615 µg and stored at ambient temperature for 7 days, then transferred to a refrigerator at 5° C. Sam ples were analyzed after 7, 14, and 30 days. Average recovery was 101.1%, 98.7%, and 94.8% respectively [1]. For this issue, the analytical range is lowered due to increased sensitivity and resolution with cap illary colum n ch rom atog raph y. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition