Phase ratio, film thickness and column internal diameter

7 Phase ratio, film thickness and column internal diameter 

Phase ratio, is defined as the volume occupied by the mobile phase (carrier gas) relative to the volume occupied by the stationary phase per unit length. In WCOT columns /3 is the ratio of the internal radius, r (mm), to the 

Since the distribution ratio, K, remains constant for a given stationary phase, temperature and carrier gas velocity the retention ratio, k, will vary directly with film thickness and inversely with the internal diameter dc = 2r). Retention times can therefore be manipulated by selecting alternative i.d. columns or a different film thickness, therefore retention time (i) increases as column i.d. decreases and (ii) increases as film thickness increases. 

8 Performance of wall coated open tubular columns 

The fundamental criteria for assessing a column s capabilities relate to its separating capabilities in terms of the retention characteristics, column efficiency and the stationary phase at OPGV, and temperature cycle. Retention characteristics of a component are indicated by its retention ratio, k (k = t f /tM)- Dead time, is an indication of the OPGV and is readily determined by introducing a sample of methane onto the column. Column efficiency, N or Veir, can be calculated using data from the chromatogram 

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