ETH YL ET HER : MET HO D 161 0, Issue 3, dated 15 M arch 200 3 - Page 3 o f 4 9. Determine desorption efficiency (DE) at least once for each lot 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. Rem ove and disca rd the back sorbent sec tion of a blank sam pler. c. Inject a known amount (1 to 20 µL) of ethyl ether or a standard solution of ethyl ether in carbon disulfide directly onto the front sorbent section with a microliter syringe. d. Ca p the tube. Allow to stand overnight. e. Deso rb (steps 5 through 7 ) and analyze together with working standards (steps 11 and 12). f. Prepare a graph of DE vs. µg ethyl ether recovered. 10. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and D E graph are in control.
MEASUREMENT: 11. Set gas chromatograph according to manufacturer's recomm endations and to conditions given on pag e 16 10-1 . Inject s am 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 standards, dilute an aliquot of the desorbed sam ple with carbon disulfide, reanalyze , and apply the appropriate dilution fa cto r in the calculations. 12. Measure peak area.
CALCULATIONS: 13. Determ ine the ma ss, µg (correc ted for DE), of ethyl ether found in the sam ple front (W f) and back (W b) sorbent sections, and in the averag e m edia blank front (B f) and back (B b) sorben t sec tions. NOTE: If W b > W f/10, report breakthrough and possible sample loss. 14. Calculate conce ntration, C, of ethyl ether in the air volume sa m pled, V (L):
EVALUATION OF METHOD: Issues 1 and 2 Method S80 was issued on February 14, 1975 [4], and evaluated over the rang e 63 0 to 2500 m g/m 3 at 22 °C and 766 mm Hg for 3-L air samples desorbed in 0.5 mL ethyl acetate [2]. The concentrations were verified by using a total hydrocarbon ana lyzer. Breakthrough (5% on the backup section) occurred at 33 min when sampling a concentration of 247 0 m g/m 3 in dry air at a flow rate of 0.185 L/min., corresponding to a capa city of 15 m g. The average DE was 98% over the range 1.8 to 7.1 mg ethyl ether per sample. Sample storage stability was not determined. Issue 3 The sensitivity of this m etho d for ethyl ethe r was lowered to cover a range from approximately 10 times the LOQ (based upon an improved LOD of 0.2 µg/sample) to 500 times (0.25 REL) the LOQ. The desorption efficiency was tested at four levels over the range of 8 - 428 :g/sample. The average recovery for ethyl ether over this ran ge w as 1 02.5 %. A 30-day storage stability study for ethyl ether was completed during the method developm ent. Th e storage stab ility was d etermined at a level approximately 0.2 REL. The analyte was dete rm ined to be stable for 14 da ys when s tored at 5°C with an average reco very of 90.3% [1].
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
