20 May / June 2019
Figure 1: VUV absorbance spectra from 125-240 nm for C6 of their respective class across the gasoline range.
compounds of each of the PIONA hydrocarbon class types. The shapes of these spectra are representative
and relying heavily on VUV’s ability to spectrally deconvolve coeluting analytes and quantitate by hydrocarbon class and carbon number during the data processing step (Figure 1).
Data is analysed using a novel automated quantitative method, time interval
deconvolution (TID)[14]. Unlike a typical chromatographic quantitative analysis which sets quantitation windows in which a peak is measured in some capacity, TID divides the entire chromatogram into equal time segments, typically 0.02 minutes wide. For each time interval, the spectra within that
Table 1: Relative response factors for the PIONA hydrocarbon classes and select speciated compounds.
interval are summed, and the summed spectrum is matched against the spectral library (approximately 770 compounds) for the best combination of 1 - 3 spectra (called a tiered search), depending on whether the addition of the second or third component improves the fit metric by a defined amount. In order to speed up the analysis, a given time segment is searched within a user- defined retention index (RI) window (typically ± 25 RI units) in the library [14, 15].
Using this iterative process, the total spectral response for each class/analyte is determined. Quantitative data are calculated without the need for calibration standards. Instead, relative response factors are used to calculate percent mass: for each PIONA class, an experimentally determined average response factor is used; for the individual target analytes, an experimentally determined response factor specific for that analyte is used (Table 1). Further conversion can be made to percent volume using either a class-based average density or an analyte- specific density.
This method operates with a high level of precision. Four ASTM gasoline proficiency samples were run 12 times each and analysed for each PIONA class as well as 9 targeted analytes. All %RSD values are below 6%, with all but four values below 2.5% (Table 2).
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
