Page:NIOSH Manual of Analytical Methods - 1003.pdf/3

 HYD RO CAR BO NS, H ALO GE NAT ED: M ETH OD 1003, Issue 3, dated 1 5 Ma rch 2003 Page 3 o f 7 9. Determine desorption efficiency (DE) at least once for each lot of charcoal used for sampling in the range of interest. Prepare three tubes at each of five concentrations plus three media blanks. a. Rem ove and disca rd back sorbent sec tion of a blank sam pler. b. Inject a known amount (2 to 20 µL) of pure analyte, or calibration stock solution, 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 analyte recovered. 10. Analyze three quality control blind spikes and three analyst spikes to insure that the calibration graph and D E graph are in control.

MEASUREMENT: 11.

12.

Set gas chromatograph according to manufacturer's recomm endations and to conditions given on pag e 10 03-1. Inject s am ple aliqu ot either m anu ally using solve nt flush technique o r with autosam pler. NOTE: If peak area is above the linear range of the working standards, dilute with CS 2, rean alyze and apply the appropriate dilution factor in calculations. Measure peak area.

CALCULATIONS: 13.

14.

Determ ine the ma ss, µg (correc ted for DE), of 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. Calculate conce ntration, C, of analyte in the air volume sam pled, V (L):

EVALUATION OF METHOD: The current laboratory evaluation of the analytes listed in this method included the incorporation of capillary column chrom atography, the improvem ent of LOD/LOQ values, a desorption efficiency study rang ing fro m app roximately 3-5X LOQ to 0.1x the R EL/PEL, and the inclusion of a 30 day sto rage stability study. Most of the analytes evaluated over this range exhibited acceptable recoveries [4]. However four analyte s had unaccepta ble rec overies at th e lowe st level evaluate d [4]. These analyte s included benzyl chloride, chloroform, carbon tetrachloride and chlorobenzene. For these compounds the LOQ was adju sted acc ordingly. All of the a nalytes evaluated during the stora ge s tability study were d eterm ined to be s table a fter 7, 1 4, and 30 days stora ge [4]. Brom oform was m arginally stable a t 30 days [4]. The initial laboratory evaluation was conducted using spiked samples and generated atmospheres and using SKC Lot 105 coconut shell charcoal as the collection media [1]. Results were:

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition