Page:NIOSH Manual of Analytical Methods - 1450.pdf/3

 EST ERS 1: MET HO D 145 0, Issue 3, dated 15 M arch 200 3 - Page 3 o f 6 9. Determine desorption efficiency (DE) at least once for each lot of charcoal used for sampling in the calibration range (step 8). 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 of analyte 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. mg analyte 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 chrom ato graph acc ording to m anufacturer’s recomm endations and to conditions given on page 145 0-1. Inject sam ple aliqu ot with a utos am pler, or m anu ally using solve nt flush technique. NOTE: If peak area is above the linear range of the working standards, dilute with desorbing solution, reanalyze, and apply the appropriate dilution factor in calculations. 12. Mea sure pea k area. Divide the peak area of analyte by the peak area of internal standard on the same chromatogram.

CALCULATIONS: 13. De termine the m ass, (:g, corrected for DE ) of analyte found in the samp le front (W f) and back (W b) sorbent sec tions and in the average m edia blank front (B f) and back (B b) sorben t sec tions. NO TE: If W b > W f/10, report breakthrough and possible sample loss. 14. Calculate conce ntration, C, of analyte in the air volume sam pled, V (L):

EVALUATION OF METHOD: Previous Evaluation The original methods for S31 (sec-amylacetate), S47 (n-butyl acetate), S46 (sec-butyla cetate ), S32 (t-b utyl acetate), S41 (2 -etho xy acetate ), S35 (ethyl acrylate), S45 (iso am yl aceta te), S4 4 (is obutyl ace tate), S 37 (m eth yl isoamyl acetate), S48 (n-propyl acetate) were issued on December 6, 1974, ex cept for S51 (n -am yl acetate), which was issued on January 17, 1975 [3]. Atmospheres of each compound were generated in dry air by calibrated syringe drive and 10-L air samples were taken [1]. Collection efficiency in humid air and sample storage stability were not tested. Spiked samplers were used to study measurement precision and des orption efficienc y (DE). Current Evaluation Methods for esters (n-amyl acetate, n-butyl acetate, sec-butyl acetate, t-butyl acetate, 2-eth oxyeth yl acetate, eth yl acrylate, isoamyl acetate, isobutyl aceta te, m eth yl isoam yl acetate, n-propyl acetate) were evaluated [5] using analytes fortified on Anasorb CSC sorbent tubes (Lot #2000). Desorption efficiency (DE) and precision are shown in Table 2. Sec -am yl aceta te was evaluated in the previous issue of this method but it was not includ ed in th is current update. Storage stability studies were performed on Anasorb C SC tubes (Lo t #2000) at approxim ate ly 150 µg each analyte/sample. The s am ples were stored for up to 30 days at 4 °C. T he recove ries of 30-day storage are summ arized in Table 2. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition