Page:NIOSH Manual of Analytical Methods - 2562.pdf/3

 1,1,2,2-TET RAC HLO RO ETH ANE : MET HO D 256 2, Issue 1, dated 15 M arch 200 3 - Page 3 o f 4

10.

c. Cap the tube. Allow to stand for 24 hours. d. Deso rb (steps 5 through 7 ) and analyze with working standards (steps 11 and 12). e. Prepare a graph of DE vs. µg 1,1,2,2-tetrachloroethane recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are w ithin the lim its set b y the qu ality assu ranc e po licy and a re co nsistent with the results given in the section entitled “Evaluation of Method”.

MEASUREMENT: 11.

12.

Set gas chromatograph according to manufacturer’s recomm endations and to conditions given on page 25 62-1. Inject sam ple aliquot m anually using solvent flush techn ique or with an autosam pler. NOTE: If peak area is above the linear range of the working standards, dilute an aliquot of the desorbed liquid with CS 2, reanalyze and apply the appropriate dilution fa cto r in calculations. Measure peak area.

CALCULATIONS: 13.

14.

De term ine the m ass, :g (corrected for DE) of 1,1,2,2-tetrachloroethane found in the sample front (W f) and back (W b) sorbent sections an d 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. Calculate conce ntration, C, of 1,1,2,2-tetrachloroethane in the air volume sam pled, V (L):

NO TE : :g/L / m g/m 3

EVALUATION OF METHOD: NMAM 1019, Issue 1 and Issue 2: The 4 th edition Method 1019 is 2 nd edition NMAM Method S124 in the 4 th edition format. Method S124 was issued on May 9, 1975 [5], and validated with generated atmospheres which were calibrated by gas chromatography [6]. Average recovery was 106 % at 5 pp m. Breakthrough did not occur after sampling 4 h at 0.185 L /m in from an atm osp here con taining 101 m g/m 3 in dry air. Desorption efficiency for SKC Lot 104 petroleum-based charcoal was 0.83, 0.87, and 0.88 at 160, 320, and 640 µg 1,1,2,2-tetrachloroethane per sample, resp ective ly. Lower recoveries w ere o bse rved for coco nut shell charcoal (S KC Lot 105). In subsequent work, 1,1 ,2,2 -tetrachloroethane was observed to degrade rapidly into trichloroethylene during storage on Pittsburgh activated carbon: 19% converted during one day and 63% converted during eight days at ambient conditions [7]. Therefore, the analyte is sensitive to the sorbent type; only the recomm ended sorbent sh ould be used. B reak through at high rela tive hum idity w as not tes ted, nor was sam ple sta bility. NMAM 2562, Issue 1 Initial work to update the NMAM method 1019 resu lted in an average reco very of 88.4% over a ran ge o f 38.1 to 253 .8 µg from the petroleum cha rcoal [1]. In order to see if the overall desorption efficiency of 1,1,2,2tetrachloroethane could be improved at these lower levels, the sorbent was changed from petroleum charcoal to Anaso rb CM S. Deso rption efficiency using Ana sorb CMS (SKC Lot 1879) was 91, 85, 88, and 91% at 38, 76, 165, and 254 µg 1,1,2,2-tetrachloroethane per sample, respectively. The limit of detection was found to be 0.6 µg per sam ple. A recovery of 87% was obtained at a level of 165 µg a fter storage for 28 days at am bient conditions [1].

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition