Chromatography Forum

Hi there,

I am encountering the peak area change when I analyze the DEA in TEA (about 0.1%area of DEA in TEA).

I prepared three same conc. DEA in TEA standard. (about 0.1% DEA in TEA),inject them in GC, 1uL, split ratio 30:1, using CP SIL 5CB, 50mx0.53 column.

However, I found that 1st and 3rd preparation peak area is around 250 but the second one is 150. Initial thought is the 2nd preparation is not correct. Then at the second day, repeat the 2nd sample for three times. This time, all three injection gave peak area around 250. This means the sample preparation should not have any issue.

Then could anyone advise me what is the potential cause for this issue?
Many thanks!

Poor injection repeatability is most likely - were both peak areas affected to about the same extent ?

Peter

Peter is correct. An injection error is very likely, not a chemical cause.

Was it a manual injection?

One explanation is If the septum leaked with the withdrawal of the needle.

best wishes,

Rod

Hi
Poor injection and leak in septum are correct issues.
for solve this problem you can use of a internal standard and calculate ratio of this with your result for a corrction factor.
Good Luck .

Hi, thanks guys!

I use auto injection. Oopss....I never check or change new septum before I performed my work...The TEA peak area seems quite consistent.

The syringe is washed 6 times using standard/sample itself before injection.

External standardization is used. Can I calculate RRF of DEA against TEA and then convert %area to %w/w? This seems can give quite consistent results.

Sample is water solution of DEA and TEA or extract by probe ?

Sample is DEA in TEA solvent