[snov]

Trying to investigate lidocaine in wastewater but haven't found a peak on chromatogram when running through a stock lidocaine standard. Have used methanol/water mixtures and phosphate buffer(pH 4)/acetonitrile ones.  Any ideas on how to proceed?

[Babcock_Hall]

What wavelength of detection are you using, and why did you choose it?  What do you know about the solubility of lidocaine in the mobile phases you have chosen?

[snov]

210 and 260nm on seperate runs. Just going by past examples seen in journals.  I have read that it is mostly insoluble in water and soluble in alcohols. Log Kow is ~ 2.4.

[Arkcon]

Many more things are possible other than mobile phase.  Are you exactly coping journal procedures and seeing nothing?  Is your system working properly for other analyses?

[Babcock_Hall]

I agree with Arkcon, but I have one more question.  How are you preparing the standard?

[kez8zek]

dissolve standard in 60:40 ACN Water. try mobile phase 60% ACN: 40% 25-50mM phosphate buffer ph=6-7. Should be RT<10min

[Arkcon]

This method here is from a column manufacturers website:  https://www.phenomenex.com/Application/Detail/3254?returnURL=/Compound?id=Jetocaine&alias=Jetocaine

That method is different than yours, but not too far away.  If you have that column, you might want to try it.  What level are you at?  How much are you injecting on-column, and can you see something if you inject more?  Are you sure your system is ok? Can you run caffeine, or other test mixture to see that the system is working properly?

[Babcock_Hall]

Lidocaine has a tertiary amine that should protonate in the pH range of your buffer.  My thought would be to use buffer in the preparation of the standard also (so as to protonate the lidocaine), but I will defer to others with greater knowledge of chromatography.