Chromatography Forum

Hi all,

I have posted before about the problem that I cannot find the chemicals longer than C33. ( https://www.chromforum.org/viewtopic.php?f=3&t=110474 )

I have tried some methods applied before, but some are for HP-1 Column (30 m, 0.32 mm id, and 0.1 um), but I have DB-1MS (30m, 0.25 mm, and 0.25 um) installed on my GC-MS. Thus, I transferred the method for this column. However, I cannot see any peaks after the C33 chemical.

I'm planning to replace the column with HP-1, but I do not have HP-1MS. The column I have is used for GC-FID. However, I do not have any other HP-1 so I want to try this one. I know it may degrade the MS by bleeding too much.

I also tried some methods applied with DB-1MS but I couldn't find the same chemicals. The sample run on FID and I see that the chemicals between C33-C44 have a little amount (peaks are much smaller than, for example, C27 or C48 (I defined C48 with a standard a long time ago). On GC-MS, I could see the ones between C16-33 very clear, but there are only bleeding peaks after C33.

My question is (before installing the HP-1):

Could the problem not related to column type? Could it be related to the machine itself? Should I contact the company (Agilent)? What else can the problem be?

I have to defend my thesis in two months but I cannot even write it properly because I do not have the results. I've been working on GC-MS for months but couldn't find a proper method that can show the ones longer than C33.

I appreciate your help!

The HP-1 and DB-1 are basically the same column as long as the dimensions are the same.

The first place I would look would be the inlet not evaporating the heavier hydrocarbons and getting them on column. I am not sure what the upper temperature limit is for those two columns, but I have used the Restek Rxi-5SilMS columns that can go up as high as 350-360C, if you can take the column that high in temperature maybe you can increase the inlet temperature to the maximum of the column and see if the response for the C33-C45 increase. Also on MS you may see lower response for those heavier analytes than for the lighter ones just due to the way it ionizes the molecules.

Just a quick look shows the higher alkanes with boiling points up to as much as 520C, so those are going to be difficult to get onto the column with the injection port at 325C. You may need to use one of the metal capillary SIM-DIST type columns to get these to the analyzer effectively.

Hi James,

The column's highest temperature is 350-360C and 1-2 samples were run at that temperature but I wasn't able to see the peaks. I do not have any other column with a higher temperature.

I still don't understand how people could identify even C52 chemicals on MS with an HP-1 column. Maybe one day I can find it out.

Thank you for your reply!
Best wishes.

https://www.restek.com/en/products/colu ... lumns/596/

One possibility they are using these columns where you can do a ramp temperature up to 430C. If using a guard column that is not coated with stationary phase you can also take the inlet temperature up that high, if you are using graphite O-rings and special high temperature septa.