Comparative Analytical Characteristics of Multicapillary Columns with Different Capillary Diameters

Straight gas-chromatographic multicapillary columns (MCCs) with capillaries of 40 μm diameter (hereinafter 40 μm MCCs) have been known for a long time and are well studied; they are used in portable gas analyzers. Some chromatographic characteristics of the relatively recently developed 25 μm MCCs have also been studied, while commercially available 60 and 80 μm MCCs are poorly studied. In this paper, the main analytical characteristics of 60 and 80 μm MCCs are determined and compared with the characteristics of 25 and 40 μm MCCs. It is shown that the maximum specific efficiency of the columns decreases with increasing column capillary diameter and is approximately 24.8, 18.2, 13.7, and 9.5 thousand theoretical plates (t.p.) per one meter of length for 25, 40, 60, and 80 μm MCCs, respectively. It is found that the height equivalent to a theoretical plate for 60 and 80 μm MCCs does not change much in a wide range of carrier gas (nitrogen and helium) velocities, which allows MCC operation at high carrier gas flow rates without a significant loss of their efficiency. In this case, for all MCCs, the separation rate of peaks with a retention factor of more than 10 exceeds 600 t.p./s, and for peaks with a lower retention factor, it can be several thousand t.p./s, which is significantly higher than for conventional capillary and packed columns. It is found that, for 60 μm MCC and especially 80 μm MCC, very high carrier gas flow rates (up to 1000 cm³/min and more) can be generated at a relatively low pressure drop across the column; therefore they can be used in chromatographic systems requiring high carrier gas flow rates.