Page 234 - Multidimensional Chromatography

228 Multidimensional Chromatography

Table 10.3 13 C values of the various components of a natural cis-3-hexen-1-ol fraction
(cf. Figure 10.5) (27)
13
C values (n
5)
No. a Component Conventional GC—IRMS b MDGC-IRMS b
1 Ethyl 2-methylbutyrate – 27.20 0.4
2 trans-2-Hexenal 29.23 0.3 29.71 0.3
3 1-Hexanol 30.91 0.3 32.49 0.2
4 cis-3-Hexen-1-ol 32.95 0.2 34.99 0.4
5 trans-2-Hexen-1-ol 31.09 0.5 31.12 0.3
a
Numbering as shown on Figure 10.5.
b
Values given relative to the universal standard PDB (Belemnitella americana from the Cretaceous Pedee
formation, South California, USA).
Reprinted from Journal of High Resolution Chromatography, 15, S. Nitz et al., ‘Multidimensional gas
chromatography–isotype ratio mass spectrometry (MDGC–IRMS). Part A: system description and tech-
nical requirements, pp. 387–391, 1992, with permission from Wiley-VCH.
isotope mass spectrometer via a combustion interface was employed. The results
confirmed those previously obtained by Nitz et al. (27), as follows:
13
• the C values obtained by MDGC–IRMS are in agreement with those obtained
by GC–IRMS and also elemental analysis measurements;
• the precision of the measurements expressed as standard deviations is signifi-
cantly lower than 0.03‰;
• the results demonstrated the absence of isotope discrimination and systematical
errors due to the MDGC system with live switching by ‘live T-piece’ coupling.
The authors demonstrated the importance that correct use of the MDGC–IRMS
system is essential for the achievement of precise and accurate measurements. Table
10.4 reports the GC–IRMS measurements of some standard reference materials,
obtained with different cut conditions. As can be seen from this table, premature cuts
result in 13 C values which are significantly higher than the true values, while
13
delayed cuts give lower C values. This fact indicates that the beginning of the
13
peak is enriched in C, while the end is depleted.

Table 10.4 GC–IRMS measurements of standard reference materials obtained under
different cut conditions (25)
13
C (‰)
Condition 5-Nonanone Menthol (R)- -Decalactone
Complete cuts 27.84 26.61 30.05
Premature cuts 3.58 14.70 13.09
Delayed cuts 57.06 71.60 91.28
Reprinted from Journal of High Resolution Chromatography, 21, D. Juchelka et al., ‘Multidimensional
gas chromatography coupled on-line with isotype ratio mass spectrometry (MDGC–IRMS): progress in
the analytical authentication of genuine flavor components’, pp. 145–151, 1998, with permission from
Wiley-VCH.