INSTRUMENT MAINTENANCE
PRACTICAL TASK P15. GC COLUMN SEPARATION Outline The performance of a chromatography column – its ability to separate substances – can be monitored by the measurement of retention time and peak width. Two calculated parameters are then used to determine performance. These are:  the number of theoretical plates (N)  resolution (R) The background theory to these is covered in Chapter 6 of Advanced Spectro/Chrom notes, and will not be repeated here. Procedure (HP 6850) 1. Inject the ethanol/1‐propanol mix into the instrument, which will be set up ready for use. 2. Allow the two peaks to appear, and stop the run. 3. Record the retention time and width for each peak, and also the column length in metres. Calculations Calculate N for both peaks and report the average. t
N  16 r
 tw
2

 ÷ length 
 t  t r1 
 where tr1 refers to the retention time and tw1 to the width of the first peak to R  2  r 2
 t w1  t w 2 
Reporting Requirements Use the standard Performance Check reporting sheet. Acceptable range N: > 1000/m R: > 1