Chromatography Forum

were running astm d6584 method for analysis of glycerides in biodiesel.

the method recommends a 2-5m guard to extend column life. weve been starting with a 2m guard and clipping it down to say, 1/2 meter before discarding

triglycerides are notorious for gunking up a column, and were using an expensive hi-temp metal column. I dont want to push it and risk column damage by using too short of a guard.

any recommendations? Is there any disadvantage to starting with a longer 5m guard? i imagine since its deactivated the added heat cycling wont really affect anything, all the contamination tends to occur in the first few inches anyway, which gets progressively clipped

thanks!

i am also interested in the answer since i am doing the free and total glycerin test as well. I have a 5m guard column but it is fused silica not metal. It would be nice to be able to cut it into 1m lengths, but i think what i will end up doing is just cut two 2m lengths and try out the 1m length and see if there is any difference.

In my experience, there is no rule, because it depends on the feedstock and process.

If you have a clean feedstock (very little of other lipids, relatively low concentrations of polyunsaturates ), then a guard column may be unnecessary, however it's good insurance. The question is, how confident are you in the consistency and cleanliness of your samples?.

Bruce Hamilton