Page:NIOSH Manual of Analytical Methods - 5521.pdf/4

 ISOCYANATES: METHOD 5521, Issue 2, dated 15 August 1994 - Page 4 of 6 Mobile Phase Acetonitrile Buffer Solution

Isocyanate 2,4-TDI MDI 2,4-TDI HDI NDI

30% 35% 40% 40% 60%

Capacity Factor (k')a

70% 65% 60% 60% 40%

2 4 3 3 3

a

k'= (tr - to) / to, where tr is the retention time of the urea and to is the retention time of an unretained compound. 15.

Measure peak area.

CALCULATIONS: 16. Read from calibration graph the quantity, M (µg per sample), of isocyanate. 17. Calculate the concentration of isocyanate, CM (mg/m3), in the air volume sampled, V (L):

EVALUATION OF METHOD: The stability of 2,4-TDIU in toluene was investigated using groups of six samples stored at room temperature for up to two weeks or at 4 °C for 1 week with the following results: Quantity (µg) 1.9 3.8 1.9 1.9 3.8 3.8

Storage Period (days) 0 0 7 7 7 14

Storage Temperature room room room 4 °C room room

Percent Recovery, 95% Confidence Interval 99 98 78 88 67 70

± ± ± ± ± ±

11 4 7 7 6 11

The data demonstrate sample instability at room temperature (about 22 °C) and suggest that the samples are somewhat unstable even at 4 °C. Estimates of the limits of quantitation (LOQs) (expressed in terms of the quantity of diisocyanate per sample) were made from the electrochemical detector calibration curves used for the analysis of field samples or control samples: 2,4-TDI, 0.5 µg [1, Sequence 6043]; 2,6-TDI, 0.7 µg [1, Sequence 6043]; MDI, 0.3 µg [1, Sequence 6019]; HDI, 1 µg [5]; NDI, 0.6 µg [1, Sequence 6878-C]. The corresponding limits of detection (LODs) were: 2,4-TDI, 0.2 µg; 2,6-TDI, 0.2 µg; MDI, 0.09 µg; HDI, 0.3 µg; NDI, 0.2 µg.

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