Page 101 - Multidimensional Chromatography

Orthogonal GC–GC 93

Figure 4.10 Representation of the transformation of data from a single-column data string
to a matrix form, based on the sampling frequency and modulation time. The data points
acquired for each modulation period are placed in a separate row of the matrix. The matrix
data are then in a suitable format to read into an appropriate plotting package such as the
‘Transform’ program.

about 11 s, indicating that it was ‘wrapped-around’ twice. The sterol was located at
3 s in the 2D space, i.e. two wraparounds 8 s, plus 3 s. The first eluting sterol had
2
2
a t R time of about 3 s, while the others had t R times of about 4, 6 and 7 s as their
retentions increased. The latter two peaks therefore appeared in the 2D space at
about 2 s and 3 s. If the sterols were eluted during the temperature programme
2
ramp, they would appear with a relatively constant t R time, since the decreasing
volatility of the later sterols are compensated by the increased temperature at which
they enter the second column.
In a novel experiment where a programmable temperature vaporizer (PTV)
injector was used to continually supply dodecane sample into the first column, and
presenting the retention on the second column for the dodecane during a tempera-
ture programmed analysis, it was possible to generate an isovolatility line for the
second column which looked somewhat like a long tail extending through the sepa-
ration space (26). Its retention decreased as the oven temperature increased, as was
predicted. In some studies, in contrast, stationary phase bleed does not seem to trace
out such a retention reduction. Presumably, since bleed comprizes highly volatile