connecting two or more columns

[mr3573]

I connected three columns by universal connector as follow:
1- CPWAX 60M, 0.32
2-CPSIL 8CB 30M, 0.25
3-CPSIL 5CB 60M, 0.25
I needed low temperature for best separation. So first peak appear at about 31’ and peaks not so sharp (the peaks heights are short). Is it related to connector and if I use one long column have same situation or not

[Peter Apps]

You have 150m of column, with two different diameters and two connectors so I would not expect the peaks to be very sharp. Using a single column can only improve matters - are 150m columns available ? Maybe you shouuld think of using a thicker film of stationary phase. What is your inlet pressure, and the flow rate of the carrier gas ?

Peter

[mr3573]

You have 150m of column, with two different diameters and two connectors so I would not expect the peaks to be very sharp. Using a single column can only improve matters - are 150m columns available ? Maybe you shouuld think of using a thicker film of stationary phase. What is your inlet pressure, and the flow rate of the carrier gas ?

Peter

The constant flow is 1 ml/min with initial pressure 18 psi. Actually I want to use a 100m column in replace of those three columns. But not sure to purchase new column.

[Peter Apps]

What are you trying to analyse ?

Peter

[mr3573]

What are you trying to analyse ?

Peter

The analysis is for possibility of some individual diens in benzene. Desired compounds and their boiling points as per MSDS are:
A:2,4 Hexadiene(mixtures of three isomer);82 C
B:1,3 Cyclohexadiene;80 C
C:1,4 Cyclohexadiene;88 C
The original method used column number 1 and 2 in series and connected by usual glass connector. In that case all three compounds appear before benzene but one isomers of A co-eluted with non aromatics presents in benzene and therefore difficult to determination.
I tried to using some combination of columns
1) One polar followed by one non polar (column 1 and 3) not only couldn’t separate isomers’ A but also component C disappeared and I noticed C completely covered by benzene big peak
2)one or two of non polar column – although column number 2 is some polar!-(i.e. column 3 or columns 3 and 2 in series) haven’t been successful.
Best combination was by three columns but in that case height of peak have not been good (25-35 uV for 10 ppm standards)
Some time age I posted question about that in forum but we have not heart cut or switch as recommended in forum.
Sorry for long explanation and not so good English!

[Peter Apps]

I would have advised heart cutting, but you say that you cannot do that.

Rather than trying to do this by the brute force approach of longer and longer columns perhaps a better approach would be to try to find a particular stationary phase that has the selectivity that you need. Try asking the column manufacturers for advice.

Peter