GC022 Plate Height

The plate height, H, is defined as:

H = L / N

Where L is the column length and N is the plate number. H has units of length and is better suited for comparing efficiencies of columns of different lengths. It is also called height equivalent to one theoretical plate (HETP). A good column will have a large N and a small H

Comments

Post a Comment

Popular posts from this blog

GC065 Column Quality Testing: The Grob Test Mix

 Even though fused silica columns were thought to be inert, it has active “hot spots” of silanol groups, and polar compounds, particularly basic amines, can be adsorbed strongly to its surface, producing peak tailing and poor quantitative results. The Grob test can be used to evaluate the effectiveness of the deactivation process. The test proposes a mixture of six classes of compounds, that would probe for any unwanted column adsorption: 1)       Hydrocarbons. They are neutral compounds and always should produce sharp and symmetrical peaks. If not, they indicate a poorly installed column. 2)       Fatty acid methyl esters. Used to determine separation efficiency of the column. Small peak heights indicate adsorption losses in the system. 3)       Alcohols. They interact if there is presence of silanol in the injection port liner or the column, producing reduced peak heights, due to hydrogen bonding. ...
Read more

GC069 Stationary Phases

 Two of the main decisions in setting up a chromatograph for an analysis are the stationary phase and the column temperature program. The selection of the stationary phase is less critical for open tubular columns than for packed columns, because of their much higher efficiency.
Read more

GC068 Guidelines for Selecting Capillary Columns

Rule respect length: Use the shortest useful column. This saves time, it is cheaper. If more resolution is required, consider to reduce the film thickness or the internal diameter. Rules respect internal diameter (i.d.): A)       Megabore (0.53 mm i.d.) are preferred for high carrier flow rates. It allows for simple and direct injection techniques. B)       Medium size columns (0.25-0.35 mm i.d.) are used for good compromise. C)       Narrow columns (0.10 mmd i.d.). Produced increased speed and separation efficiency. Shorter columns are possible, and hence, reduced times. Some limitations: high split ratios needed (500:1). Trace analysis is difficult. Higher carrier gas pressures required. Manipulation and equipment become critical. Rules respect to film thickness: Thick films produce higher retention and is frequently used for analysis of volatiles. Increased capacity; important for GC-MS or FTIR. ...
Read more