GC response consistency

[badrul]

Hai everyone..I have a question that has been bothering me for quite sometimes now. I've involved in pestcide residue analysis for 2 years and until today I am still confused about GC signal response (area). Is it just me or that the GC response always keep changing and not consistent. For example, when I inject 1 ppm of analyte today, the response would not be the same when I inject the same analyte concentration, let say a month later. Is this normal? Can anyone give me what is the cause for this? Thank you..

[willnatalie]

Depended on what you are using to detect the analytes.

[badrul]

I'm using GC-ECD to detect pyrethroid pesticides

[Earl C]

ECD response will always change as more samples are injected due to the detector becoming dirty from sample matrix and losing sensitivity. With all GCs as you inject more and more samples you can lose sensitivity due to contamination of the injection port, column or detector; this inevitably leads to the need to perfrom maintenace and recalibrate. In my experience ECDs always lose response over time.

[Jumpshooter]

It's quite normal to see variances in the peak area response on your injections of the "same sample" over different days. Myriad causes such as, these occur over time: changes in the standard sample integrity, mild fluctuations in the electrical current that feeds your GC can produce daily variations in the electrical conductivity of your Detector. However, the main thing that should show consistenci is the Response is the calibration. On day 1 it ought to be linear, and on day 2 it ought be linear between different spike levels/or dilutions of you std.

[zhangfu]

Hai everyone..I have a question that has been bothering me for quite sometimes now. I've involved in pestcide residue analysis for 2 years and until today I am still confused about GC signal response (area). Is it just me or that the GC response always keep changing and not consistent. For example, when I inject 1 ppm of analyte today, the response would not be the same when I inject the same analyte concentration, let say a month later. Is this normal? Can anyone give me what is the cause for this? Thank you..

is the signal always increase or decrease?

[Yuva]

This is normal is ECD. Over the period of time response will decrease. This mainly oxidation on the Radioactive Ni. One of the source of the oxygen is from Carrier Gas. Use the highest quality carrier Gas Nitogen. Use Good Oxygen Filter in the carrier gas line and change it in regulator interval.

Decrease in the sensitivity is can be brought back by Backing the ECD. There are three different procedure for Backing.

1. Keep ECD temperature at 425 over night.
2. Keep injecting Hexane continues.
3. Connect the Hydrogen Gas at the Make Gas Line, set the make gas flow to 60 ml/min, and set the ECD temperature to 400 C and live it over night. This is the best backing..

[fionateo]

my ECD will always have increasing signal for around 2 days if I power off and on the instrument for 2 days. The ECD is cool down before off.

Anybody know what caused this?

I tried to bake ECD again when I on it again each time. but it still take very long.
are other users always keep ECD on and never off it?