Page:NIOSH Manual of Analytical Methods - 2555.pdf/3

 KET ON ES I: MET HO D 255 5, Issue 1, dated 15 M arch 200 3 - Page 3 o f 5 b. Inject a known amount (5 to 25 µL) of DE stock solution directly onto the front sorbent section of each Anasorb CMS tube with a microliter syringe. c. Allow the tub es to air equ ilibrate for several m inutes, then cap the ends of ea ch tube a nd a llow to stan d overnight. d. Deso rb (steps 5-7) and a nalyze together with standards and blanks (steps 11 and 12). e. Prepare a graph of DE vs µg analyte recovered. 10. Analyze a minimum of three quality control blind spikes and three analyst spikes to ensure that the calibra tion gra ph and D E 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 2555-1. Inje ct a 1-µ L sam ple aliquot m anually using the solvent flush technique or with an autosam pler. NOTE: If peak a rea is above the linear range of the working standard s, dilute w ith solve nt, reanalyze and app ly the app ropriate dilution facto r in the c alculations. 12. Measure peak areas.

CALCULATIONS: 13. De termine the m ass, µg (co rrected 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. 14. Calculate conce ntration, C, of analyte in the air volume sam pled, V(L):

NOTE: :g/L = m g/m 3

EVALUATION OF METHOD: This method development was based upon a prioritized list of problematic gas chromatographic methods identified in a survey of external users of the NIOS H M anu al of Analytical M ethods. M etho d im prov em ents include the use of capillary column chromatography, lower LOD/LOQ values, improved desorption efficiency (DE) at lower quantitative levels, and a storage stability study conducted at 7, 14, and 30 days. The method also incorporate s the use of a n im proved solid sorbent tu be sam pler (A nasorb CM S) res ulting in improved sample recovery and allowing methyl ethyl ketone and methyl isobutyl ketone to be included in the m ethod without loss of sample recovered from the sorbent tube. Table 4 lists the method evaluation data, the LOD/LOQ values, the range of measurements, and the precisions for each analyte. [2] The average D E dete rm ined fo r ac eto ne was 98.2% (RSD = 0.01 9), for m eth yl ethyl ketone was 98.6% (RSD = 0.017), for 2-pentanone was 99.3% (RSD = 0.01 1), for m eth yl isobutyl ketone w as 96.4% (RSD = 0.011), for 2-hexanone was 100.6% (RSD = 0.013), for diisobutyl ketone was 102.4% (RSD = 0.013), and for cycloh exa non e wa s 95 .4% (RS D = 0.015). The average 30-day storage stability recovery for acetone was 100.7% (RSD = 0.017), for methyl ethyl ketone was 101.7% (RSD = 0.018), for 2-pentanone was 10 1.5% (R SD = 0.028), for methyl isobutyl ketone was 103.8% (RSD = 0.018), for 2-hexanone was 101.4% (RSD = 0.029), for diisobutyl ketone was 103.5% (RSD = 0.019), a nd fo r cycloh exa non e wa s 87 .4% (RS D = 0.009).

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition