Dear fellow researchers, I would like to see phenols such as catechin, epicatechin, quercetin, rutin, ferulic acid, caffeic acid and p-coumaric acid at low microgram per litre quantities in fullscan mode. We will be quantifying using MRM's but would like to set up our system in such a way that we would also detect unknown phenols similar in structure to the above phenols in fullscan mode. Could you please provide me with papers refering to such work? I have found a few already but would like to find more. There seems to be a lot of controversy concerning the use of triple-quadrupoles for such kind of work, but we will need to do it eventhough it might not be as easily do-able using a triple quadrupole as it would be using a TOF. At the moment our diode-array can see several unknown phenol peaks which our MS is not able to detect in scan mode. Therefore it is not possible to easily determine the M-H ion in order to do daughter ion scanning on it. We have decided to do scans at several cone voltages in order to increase the probability of seeing all the unknowns in MS fullscan that the diode array is seeing.
Dear Dr.Rossouw,
Most of the flavonoid glycosides/aglycone methods in HPLC-UV do separate the phenolic acids (phenylcarboxylic type) as well as procyanidins. Depending on the sample matrix, one needs to fine-tune separation and detection conditions. Below article gives a good overview. You could possibly extend it for quantitation by MRM's.
A Screening Method for the Identification of Glycosylated
Flavonoids and Other Phenolic Compounds Using a
Standard Analytical Approach for All Plant Materials
Long-Ze Lin, and James M. Harnly
J. Agric. Food Chem., 2007, 55 (4), 1084-1096
Hope this is useful.
Thank you Dr. Govindaraghavan, I am sure this will be helpful. This is highly appreciated.
Dear Manda, I guess the peaks you're detecting in DAD will be glycosilated forms of phenolic compounds. Your approach of conducting experiments with different cone voltages seems to be the best in order to get a full coverage of existing phenolics, but at an expensive cost in analysis time. If you're conducting an exploratory analysis then it is good to have an idea on the amount of every compound in the sample. Do have an idea on the contribution of "unknown" phenolics to your sample? If you have a large number of samples to analyse then I guess at some point you'll have to balance what is relevant. Hope this helps, Ana
Thank you Dr. Reis and apologies for not answering previously. We are not completely sure of the level of phenolics in our samples. We will need to do a lot of screenings before we will know. What I have noticed is that there are many unknown compounds as well. I might have to speak to a friend who does QTOF to do the initial screenings for us and then target those using QQQ. In the end that might be the easiest solution. In a way I am a bit disappointed with this, because I was hoping to do the screenings myself on the QQQ but the sensitivity of the instrument is terrible. I know there is a major metal ion contamination problem with the LC-QQQ system which we are trying to correct. So, hopefully our low sensitivity problem will then also just disappear.
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