Page:NIOSH Manual of Analytical Methods - 1615.pdf/3

 METHYL tert-BUTYL ETHER: METHOD 1615, Issue 2, dated 15 August 1994 - Page 3 of 4 c.

10.

Inject 24 µL of the 0.741 µg/µL stock solution, 7 and 19 µL of the 7.41 µg/µL solution, 7, 11, and 14 µL of the 29.62 µg/µL stock solution onto the tubes near the glass wool plug and draw clean air through the tubes at 0.1 L/min for 1 to 2 minutes. d. Seal tube with plastic caps. Allow to stand overnight. f. Prepare a graph of DE vs. mg of MTBE recovered. Analyze three quality control blind spikes and three analyst spikes to ensure the calibration curve and DE are in control.

MEASUREMENT: 11.

12.

Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 1615-1. Inject sample aliquot manually using solvent flush technique or with an autosampler. NOTE 1: If the sample 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 factor in the calculations. NOTE 2: The given conditions are recommendations for the determination of MTBE in gasoline. An initial temperature lower than 0 °C will produce better peak resolution but longer analysis time. Measure peak area.

CALCULATIONS: 13.

14.

Determine the mass, mg (corrected for DE) of MTBE found in the sample front (W f) and back (W b) sorbent sections, and in the average media blank front (B f) and back (B b) sorbent sections. NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of MTBE in the air volume sampled, V (L):

EVALUATION OF METHOD: A calibration curve in the concentration range 0.74 to 111 mg/mL MTBE in carbon disulfide indicated a linear correlation with a coefficient of 0.9998 and s r of 3.3% [1]. Other calibration curves at lower concentrations, covering the recovery/stability range, i.e. 9.3 to 426 µg/mL MTBE in CS 2, indicated linear correlation coefficients >0.998. The LOD and LOQ values varied between 19 to 22 µg/mL and 36 to 73 µg/mL, respectively. A six-level, 31-day storage stability study, conducted at -7 °C, in the range 17.8 to 415 µg MTBE in gasoline spiked on 400 mg charcoal tubes, indicated recoveries of 99.0 ± 4.3% for the first day, 93.2 ± 2.0% for the 17th day, 91.9 ± 7.1% after 23-day storage and 89.0 ± 5.2% after 31-day storage. A five-day room-temperature stability study at 415 µg MTBE in gasoline spiked in 400 mg charcoal tubes indicated a 100.0 ± 4.6% recovery. Four charcoal tubes spiked with 415 µg MTBE in gasoline had air drawn for six hours at 100 mL/min and then were stored at -7 °C for five days indicating 103.6 ± 9.0% recovery. No sample loss occurred due to breakthrough at the 415-µg per sample MTBE level. Charcoal tubes which were spiked with 10 mg MTBE in gasoline and which had 6 to 78 L of air drawn through them did not indicate any breakthrough of MTBE. Light hydrocarbons i.e. n-butane, and isopentane, which are not retained by the charcoal, did break through.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94