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In general, conventional chromatography is a slow method of analysis. For application reasons (such as control analysis, reaction monitoring, etc.), it may be beneficial to shorten analysis times. To reduce these times, use a shorter column, as retention times are proportional to column length (Table 2.1). Due to decreased efficiency, the phase ratio β must be increased by choosing a thinner stationary phase film (ID = 100 μm, film = 0.1 μm, β = 250). Hydrogen must be used as the carrier gas (see Van Deemter curve). The last factor that we can easily regulate is the oven temperature (the higher it is, the shorter the analysis). Be aware, however, of the first peaks appearing, since good separation requires a lower temperature. Therefore, the solution is a temperature gradient. Devices allow for ramps that can go up to 100°C/min. For volatile compounds and with various column designs, covered with a heat‐resistant outer sheath, the temperature can be increased more sharply (200°C/20 s). As a result, retention times are reduced significantly (Figure 2.16). This type of fast chromatography, sometimes called high‐speed GC, finds its main use in control analyses.

Table 2.1 Comparison of conventional, fast and ultra‐fast GC set‐ups.

GC type	Ramp (°C/min)	Analysis time (min)	Peak width (s)	Column length (m)	Internal diameter (μm)
Conventional	Conventional oven (1–20)	~30	5–10	15–100	250–320
Fast chromatography	Conventional oven (20–100)	5–10	0.5–5	5–15	100–250
Ultra‐fast chromatography	Resistive heating (60–1,200)	~1	0.05–0.2	2–5	50–100

Figure 2.16 ‘Ultra‐fast’ chromatogram. Left, separation of several aromatic compounds (‘fast’ chromatography according to a document from Thermo Electron Corp.); right, example of a chromatogram obtained under ‘ultra‐fast’ chromatography conditions according to a document from Aviv Analytical.

The detector must be able to follow the rapid variations in concentration almost immediately, i.e. at the moment of each analyte’s elution. For detection by mass spectrometry, there is good reason to be attentive to the sweep speed of the m/z ratio; a slow sequential sweep may lead to a situation in which the concentration in the ionization chamber is not the same from one end of the recording to the other. TOF‐MS (Time‐of‐Flight Mass Spectrometry) does not suffer from this drawback.