Hello Andrea,

do you have a vague idea of what the degradation products could look like structurally? The recommendation for one or the other detector would be based on this.

Regards

Markus

This sounds like the question from a student who wants us to do his work. An answer to your question requires more information, since appropriate answers require reasonably intelligent questions. (1) Which pesticides? (2) Are the products of interest known? If this is a fishing trip to find the products, then identify them, then develop quantitative methods of analysis, the answer takes a number of technical man years of development work. Start with a literature search.

Andrea: Detector selection is based on the known physical and chemical properties of the compounds you wish to detect. If you do not specify the compounds, then there is no scientific way to determine which detector or detection method is most appropriate. As Scot suggests, if you you wish to do "science", then please research and ask scientific questions.

Dear all, compound is terbuthylazine.

Dear Marcus: thank you.

Dear Scot: 'this sound like an answer of' a person who didn't read the question. Try to do it and you'll discover that your point (2) is meaningless.

Dear William and Scot: I didn't specify the compound as I wanted to understand if technique could be applicable to this class, or if more specific considerations need to be applicable. Hence, William, 'if you wish to do science', avoid hurry in reach your conclusion and express your judgement. Moreover, if you still believe that this is a 'stupid' question, I would like to remind you that your background is very different from that of many other clever people; this doesn't mean that question you pose to each other have to be considered silly.

Marcus and William, I had to answer you as I did, considering that your answers were unpolite. Please, do not continue the fight, as first of all I'm glad of your interest in my question and I would be really happy to have also your advice.

Andrea, you have a great deal to learn about how to both ask and research a question to find answers. I never said you asked a stupid question, but rather an incomplete one that can not be answered in a constructive way. This is important for all questions posed, but perhaps more so when you seek free advice on the web, then fail to provide detailed information or invest in researching the question before posting. To fail to do so would be "unpolite", as you say. That is the point we are making. Our hope is that you learn from your mistakes and become a better student and scientist some day.

There appears to be a significant body of literature on the degradation, so you might study separations and detection with spiked samples. If the material or metabolites are CL containing, an ECD gives great sensitivity. Nearly 50 years ago we (C.S.Giam, R.C.Hall and I ) reported the separation and low level detection of halogenated nitrogen containing herbicides using a thermal reaction zone on the front end of a GC. Article New technique for the determination of picloram and other he...

HPLC is a generally useful separation tool, but it is not the only one. The work I did was before HPLC was commercially or commonly available. When starting out to define sensitivity limits, you might want to try using first some pure samples, and then add some sample matrix. You may well find that you will need a preconcentration step, especially if the samples are soil or run off water. The preconcentration step can increase concentration by orders of magnitude, and this offers commensurate increase in overall assay sensitivity. Sometimes a step gradient after large injections can work; other times it is better to do the preconcentration step separately under different conditions.

Dear William and Scot,

I explained in my previous answer why my question was complete as it was. Only now, after your request of more detail, I can assume that the technique cannot be mostly estended to the class of substances that I mentioned; this was not obvious, as other techniques can be. I understand your first reaction, in light of the number of students that try to find in Research Gate easy and quick answers, but believe me, this is not the case.

I published on Chemosphere a review on Terbuthylazine , after evaluation of two hundred papers. If I am posting here is because I want your also your advice, as experts.

Scot, the paper you adviced seems focused on GC, isn't it? I know some techniques, as GC-MS and HPLC-MS that are suitable, what I do not know if is HPLC-UV could be. William, do you have any advice?

Thank you both,

Andrea

Thanks Scot, Luckily this is just tap water. I've found GC and HPLC-GC reliable in the past, HPLC-GC fester than the former. However, my actual lab has not HPLC-GC but just HPLC-UV. Hence, before to refer to external labs, I wanted to explore this possibility and understand if is/is not possible, why. Thanks for your advice, Andrea

With that set of tools, I'd first establish separations and quantification of known products of the degradation using standard reference materials. I would then do some degradation experiments and find out if the results are below the detection limits. I would then do some external concentration methods and use the hplc as a way to track the efficacy of the various concentration methods. It is pretty easy to get a hundred fold increase in concentration using batch chromatography or sometimes a step gradient for collection after many injections of low level samples. This can give a much higher concentration and a cleaner sample for evaluation, especially when using a somewhat different kind of chromatography-or at least very different kinfs of interactions.

Dear Scot,

with your last information, I think that I have finally identified the best path to follow. Please, let me know if you agreee.

I know most of the intermediates from the very, very narrow literature available, but treatment that I am going to apply is slightly different to those explained in literature; hence, few intermediates not found till now could be detected. I will go to the external lab with just a sample, adding some information on what intermediates I am expecting to see. I can perform by myself in that lab all the right procedure to obtain a reliable GC-MS analysis. Once I'll have the results, I can easily confirm if known intermediates are present, as well as I can see if other peaks have been found. With this background, I can perform another analysis with our HPLC on the same sample, now knowing what I am searching for and, if results abtained are in agreement with GC-MS, I can run the rest of the analyses with our HPLC.

Thank you,

Andrea