|We are introducing usefulness of semi-microcolumn such as follows compared to the use of a column (4.6φ mm) with some precautions.
1) Only a small amount of a mobile phase
2) Analysis is performed only with a
small amount of a sample.
3) Detection sensitivity is increased.
However, in the actual practice, some precautions are needed in hardware and software aspects.
Concerning hardware aspects, you seem to have used a system applicable to microcolumns from the content of your question. However, as another
precaution, peak shapes and retention times vary whether an autoinjector is used or the sample is injected manually.
In Fig. 1, we show the examples of analysis of polyaromatic hydrocarbons (PAHs). Use of an autoinjector results in poor finish of a peak and prolongation
of the retention time of a component eluted in the early stage. These are attributed to the volume of a sample loop attached to the autoinjector
indicating that even a factor not raising issues in the ordinary use may become problematic in the use in the range of low flow volume. In view
from software, the key point is “which solvent a sample is dissolved in and how much it is injected” and these effects are also visible remarkably
in the peak shapes of components eluted in the initial stage.
|◆Fig. 1 Effect of the sample injection method◆
In Fig. 2, differences in chromatograms when PAHs are dissolved in solvents of different polarities and injected in the same volume are shown. Dissolution of a
strongly hydrophilic and freely water-soluble sample in water or an nitial solvent of a mobile phase is not so problematic. However, when a strongly hydrophobic
sample such as PAHs is dissolved in a solvent with more potent elution capacity than the mobile phase, importance is attached to “which solvent the sample is
dissolved in” and dissolution in a potent elution solvent in particular must be avoided as it may lead to broadening of a peak. Even when a sample is dissolved in
the same solvent, injection of a minimum amount results in improvement of a peak shape.
As mentioned above, we explained precautions during use of a semi-microcolumn. Semi-microcolumn is extremely useful analytical tool provided that it is used with
thorough understanding of its characteristics and differences from general-purpose columns.
|◆Fig.2 Effect of the sample diluent and the amount of injection◆