match quality $90% with respect to the experimental spectrum. The similarity of the ten spectra is apparent from visual comparison of library spectra (not shown herein). Examples of different spectra reported
for the same compound within the library is also noted (hits 1&3; 4&8; 5&9; 6&7). Table 1 also shows
that whilst these compounds have similar mass fragmentation patterns, their retention indices are quite different. Thus components may be reliably differentiated based on RI data. The FFC library uses a two-step library matching routine, which is built into the Shimadzu GC–MS software. The first step is a spectrum comparison, which inevitably offers a range of incorrect responses. The second step is a post-search filter using retention indices (with a match window of 65 index units); any match offered in the first step whose retention index is not consistent with the retention index of the unknown component is rejected. By using calculated retention indices and the interactive search filter built into the FFC library, the only possible match offered for the above example would be a-terpinene, which is of course correct identification.
For the calculation of LRI shown in Table 2, a C –C n-paraffin hydrocarbon series was chromatographed independently to the lavender oil samples. Van den Dool and Kratz’s equation [24] was used to calculate linear retention indices by linear interpolation A cubic spline interpolation has also been suggested for the calculation of temperature programmed retention indices [25]. Some debate has arisen over the reproducibility of retention indices, To´th reported random variation in calculated retention indices of a range of volatiles over a 2-month period using a temperature program of 4 K min (using an older type GC and argon as the carrier gas) [26]. Poor reproducibility of LRI was not experienced during the present investigation (nor is it the general experience of this group). Provided a low temperature program rate is used, the difference in the programmed retention index, and the true isothermal retention index generally does not exceed 1% for terpenoid compounds [9]. Jennings determined retention indices using low temperature program rates of 2 K min [9]. Adams similarly used a low temperature programmed rate of 3 K min [8]. The correlation between the calculated retention indices and literature retention indices in Table 2 (for the same stationary phase) confirms that the conditions used were satisfactory for this class of sample
match quality $90% with respect to the experimental spectrum. The similarity of the ten spectra is apparent from visual comparison of library spectra (not shown herein). Examples of different spectra reportedfor the same compound within the library is also noted (hits 1&3; 4&8; 5&9; 6&7). Table 1 also showsthat whilst these compounds have similar mass fragmentation patterns, their retention indices are quite different. Thus components may be reliably differentiated based on RI data. The FFC library uses a two-step library matching routine, which is built into the Shimadzu GC–MS software. The first step is a spectrum comparison, which inevitably offers a range of incorrect responses. The second step is a post-search filter using retention indices (with a match window of 65 index units); any match offered in the first step whose retention index is not consistent with the retention index of the unknown component is rejected. By using calculated retention indices and the interactive search filter built into the FFC library, the only possible match offered for the above example would be a-terpinene, which is of course correct identification. For the calculation of LRI shown in Table 2, a C –C n-paraffin hydrocarbon series was chromatographed independently to the lavender oil samples. Van den Dool and Kratz’s equation [24] was used to calculate linear retention indices by linear interpolation A cubic spline interpolation has also been suggested for the calculation of temperature programmed retention indices [25]. Some debate has arisen over the reproducibility of retention indices, To´th reported random variation in calculated retention indices of a range of volatiles over a 2-month period using a temperature program of 4 K min (using an older type GC and argon as the carrier gas) [26]. Poor reproducibility of LRI was not experienced during the present investigation (nor is it the general experience of this group). Provided a low temperature program rate is used, the difference in the programmed retention index, and the true isothermal retention index generally does not exceed 1% for terpenoid compounds [9]. Jennings determined retention indices using low temperature program rates of 2 K min [9]. Adams similarly used a low temperature programmed rate of 3 K min [8]. The correlation between the calculated retention indices and literature retention indices in Table 2 (for the same stationary phase) confirms that the conditions used were satisfactory for this class of sample
การแปล กรุณารอสักครู่..
