I've been working in the HPLC-EC detection on 3,4-Dihydroxybenzoic acid. The peak for nM sample has increased almost 100 fold last few days.I prepared fresh stock solution and the problem remains. What I understand is that if the working electrode is contaminated the signal should decrease rather than increase,right? The reference electrode is fine and noise level didn;t change.
Thanks a lot for your help.

I'll assume that there's a reason you didn't want or couldn't use UV detector.

Firstly 3,4-DHB acid as other catechol-related compounds has been detected by EC over the last decades because of their higher sensitivity compared to UV detection.
Secondly, nM concentration is a "high" concentration for EC. Conc. ranging 1-100 pM are usually measured in biological samples.
Rebe ¿could you change any parameter of the ECD as "Sensitivity Factor" or "Range" that affects the output? Because most of the EC detector has a parameter which defines the output range i.e. 0-500 pA, 0-5 nA, 0-500 nA, etc.
Please, you should provide more info regarding hardware and chrom. conditions.

Good Luck

HI, MFB and anonymous, Thank you for your reply. I'm now trying to see what will happen if I use 2,3-DHBA for the system. I may aslo try cell cleaning?
I'm using Decade(Antec Layden) detector and Hypersil C18 column.MP is 95/5Methanol/H2O (pH2.6 citrate buffer). Eox=0.8V, range is 50nA.This is used to measure 3,4-DHBA in a mixture.
Thanks again.

I may be facing a similar problem; see my posting "Signal drift in analysis of glycols" (posted two days ago). I am using a Dionex ED40 electrochemical detector for HPLC analysis of glycols.

Does the apparent concentration increase steadily when the sample is injected more than one time (one right after the other)?

N. Suzuki

Working at +0.8 V (vs. Ag/AgCl ?) you should polish the glassy carbon electrode(important info for ECD you should give us)at least once a week. But, why citrate pH=2.6? Phosphate is better for EC, citrate can be easily contaminated with Fe especially at low pH becaous of its ability to yield complexes from active surfaces of the stainless steel tubing ­and other electroactive compounds. By the way, have you passivated your LC system?

What kind of injection system are you using? If you are using a siringe, have you passivate it? (Prefere siringe with piston with teflon end for ECD).Metals are released from siringe piston and could be revealed by EC detector, I had this problem many years ago with morphine and ECD).