By definiton, no peak should elute before your void volume. Either it is from the previous run or it is a system peak.

Your system should having void volume less than 3.85 min

Chakravarthi Jampani,

Please verify this with reduce the amount of organic phase(acetonitrile,Methanol etc) and increase the amount of water.

Regards

Amir

Dear all,

ThankQ for your response towards my Question. Now my Question is after washing column with water,Methanol or New column & Mobile Phase is 100% aqueous, if RT of Analyte is before the void volume. What it regards?

Dear Chakravarthi,

In such cases, selection of column also very important. If you want to Perform your system with 100% aqueous prefer Aqueous column.Good luck.

It may not be peak, please check with PDA detector. Spectra should have cut of below 200 nm. Also it can be peak due to traces of solvent, water contamination or acid traces.

1) I don't think it is peak; unretained material elutes no faster than the void volume. Alternatively, the void volume is smaller than you think it is.

2) I'm assuming you are running a C18 column; if not, please let us know. If this is, indeed, a C18 column, you may have poor results running in 100% water unless you use a column designed for this purpose, as Phani Raj mentioned, because of "phase collapse" which causes variable retention times. This link describes phase collapse (Figure 1): http://www.isco.com/WebProductFiles/Applications/101/Application_Notes/AN76_RediSep_Rf_Gold_C18A_for_Highly_Aqueous_Mobile_Phases.pdf

I realize the link refers to flash chromatography columns but the effect is the same for HPLC.

I concur with previous replies, no analyte can elute earlier than the solvent. Inject KNO3 solution to find out what your void volume is (if using C18). If you still observe peaks before void volume your column is dirty.

Dear Jack and Serhan,

Thanks alot to both of you for your valuable feed back.

If u work with fermentation products it is very likely that such unretained peaks will be observed in consecutive runs. Moreover the peak response will be irregular. Column used should be compatible to 100% aq. mobile phase.

It is the new void volume due to swelling of stationary phase in that composition of mobile phase.

It is possible you changed the void time by column swelling but your sample matrix must be very different from what ever earlier injections you used to determine the void time.  In most cases I think there should be very little difference in void time unless you are injecting very large amounts of sample matrix that will change the solution of sample/mobile phase on the column.

How did you determine the void volume?   I think injecting air (literally inject normal volume from an empty vial) or uracil on a reverse phase system would confirm the retention time of the void volume.  I think injecting air is the best way (maybe inject more than once to convince yourself of void time).   Also a common problem I have seen.....If the peak shape is radically different (very broad) for the peaks that elute before the void volume, it is possible you may have carryover from a previous injection. 

This is an old question, but I wanted to post here in case future people search and find this. The original poster did not include the most important information in their question so it would never be possible to confirm their observation or answer their question directly. The missing information was FLOW RATE. What was the flow rate? It is needed to determine what the estimated Tzero or Column Void Time was. Without it, you can not find the answer. If the flow rate in this example was 1.000 ml/minute, then the most likely calculated Tzero time would have been 2.9 minutes (+/- 10%) which was much earlier than the reported peak Rt (so it was not eluting before the Tzero time).

If the peak really did appear to elute before the predicted Tzero time, then there are a few possible explanations. (1) The calculated or measured Tzero time was in error. (2) Changes to the column packing occurred before or after the injection, resulting in changes to the available pore volume.(3) Contamination or a late eluter peak from a previous analysis. (4) In all cases you have no retention so a new HPLC method is required.

*Determining the HPLC column void volume is one of the very first things you should do when you start to perform HPLC analysis. Once you have identified the column and the flow rate, you next calculate the column dead time so you will know when you have retention of the compound on the column (and then can start to develop a method). This should first be done by calculation (as it is simple and will get you close to the actual value). I have attached a ink to a webpage with the formula and an article explaining how to do this. Once you have calculated the estimated Tzero time, you should next measure it using a pure compound that is not retained on the column (Please refer to the attached article for examples). Another reliable way to check it is to observe the "pressure pulse" peak which will occur on the baseliine early in the run. This occurs when the injection valve is switched and the resulting sharp change in pressure will cause a change in refractive index/absorption at that specific moment in time. This "blip" will be seen at low absorbance values (or low RI values) on the detector's output scale.

"Determination of HPLC Column Dead Volume / Dead Time (T zero)" Article Link attached. http://hplctips.blogspot.com/2011/05/determination-of-hplc-column-dead-time.html

http://hplctips.blogspot.com/2011/05/determination-of-hplc-column-dead-time.html

how about if the main peak is close to void volume or ghost peak? if this peak is acceptable? if this separation is scientifically justified? Thanks for you input in advance.

Mahboubeh, no, not at all. We have scientific metrics to define "retention" and also to define when retention has occurred and what is acceptable retention. "Capacity Factor" or more commonly refereed to as 'K' prime, is used to describe this metric.

For a typical RP/NP HPLC method to have any validity, it must show selectivity for the compound(s) being investigated. In this case, that means that the sample must interact with the column support and not just flow through it. If the sample simply passes through the column with little to no interaction, then you have demonstrated what we refer to as "Flow Injection". In flow injection, no chromatography takes place and you could have achieved the same result by placing your sample in a spectrophotometer (since you did not develop a chromatography method). BTW: We use flow injection when we desire to by-pass the HPLC column and inject a compound directly into a detector (e.g. MS).

Perhaps the two most important fundamental HPLC concepts that a novice chromatographer should master early on are:

(1) How to measure/estimate Column Void Volume. "Determination of HPLC Column Dead Volume / Dead Time (T zero)" Article Link attached. http://hplctips.blogspot.com/2011/05/determination-of-hplc-column-dead-time.html

(2) How to calculate K prime. Without a demonstrated understanding of these two concepts, you can not perform HPLC analysis. "K Prime (also known as: Capacity Factor, Ratio or Retention Factor): One of the Single Most Important HPLC Parameters of All" ; https://hplctips.blogspot.com/2015/06/k-prime-also-known-as-capacity-factor.html

@ William Letter Thank you much for your thorough response. Can you take a look at this:

Article HPLC Method for Estimation of Metformin Hydrochloride in For...

It seems to me they need to verify if this peak is at void volume or not.

Hello: The actual paper that is attached to that post is not the paper referenced by the title. The authors posted the wrong paper so I can not comment on any chromatography questions as none are shown.

Sorry, I had copied the original link but researchGate direct it to its own inventory ! Can you please Copy and paste this on your browser.

HPLC method for estimation of metformin hydrochloride in formulated microspheres and tablet dosage form.

The first link is the correct paper. Thank you for your feedback :)

Sorry, I had copied the original link but researchGate direct it to its own inventory ! Can you please Copy and paste this on your browser.

HPLC method for estimation of metformin hydrochloride in formulated microspheres and tablet dosage form.

The first link is the correct paper. Thank you for your feedback :)

Also, if the analyte is coming very early then it might also indicate that it’s not sticking to the column in which case you should wisely select your column based on the chemical nature of the analyte and the elution nature of the mobile phase used. For example, highly polar molecule will not stick to the column in reverse phase chromatography while using a routine C8 column for which a lot of people prefer HILIC column now a days. And there is also scope of manipulating mobile phase gradient to obtain better chromatography.

Mahboubeh Nejati, let's try doing an analysis of the paper, given the leads William provided in his answers and on his Webpages he linked into the previous answers, and which you should have learned during your analytical education as well.

The column dimension is 250 x 4.6 mm. According to the calculations: t(0) = 2,9 min. The paper lists the Metformine peak at a retention time of 2,3 min. calculating k' results in a negative value... Let's simply keep that as it is. We will attempt an explanation later.

Now, what eluent are the authors using? ACN/phosphate-buffer with a pH of 5.75.

As the authors rightly pointed out Metformin in its salt form is N,N-dimethylimidodicarbonimidic diamide hydrochloride. In other words it can be protonated and becomes a cationic species. The ACN content of 65% as indicated in the paper is pretty high, so that even under such conditions we would create a rather elutropic environment. In other words: Retention for polar and ionic components will be reduced. At this point it becomes clear that component will hardly be retained applying such conditions.

As calibrations are being performed using standard solutions, the figures of merit will look nice, however the major intention of chromatography (retaining the components of interest so that they can be separated from others) was hardly obtained. The big BUT is: As long as their samples will contain nothing else but Metformine it might even work. However, once other components are in the samples, problems will occur.

The idea would be to modify the chromatographic conditions so that we either apply a proper ion pair method (i.e., an acidic eluent with low organic solvent concentration), or apply HILIC. One example you can find here:

https://appslab.thermofisher.com/App/1094/rapid-determination-metformin-using-a-hilic-method

an overview of other methods can be found here:

https://appslab.thermofisher.com/Search?CompoundName=Metformin

Hope this is of some help.

Crossing my fingers,

Detlef.

Sorry, I do not have time to look up the paper, but IF:

the RP column used was 4.6 x 250 mm in size AND the flow rate used was 1.00 ml/min, then we can estimate the column void TIME to be around 2.9 minutes (this is an estimate and it should be measured to obtain the actual value, but it will be close).

Once we know the Column Void volume (and thus the column void TIME), K primes can then be calculated for the observed retention time(s). If the calculated K primes of the sample(s) are less than 1.0, then no useful chromatography has occurred and the method is 100% invalid and unscientific for that sample. *So in this case the K primes are close to 0 so the paper referenced is just another example (one of tens of thousands of published papers) where the authors and any reviewers had no liquid chromatography knowledge or experience at all. They published papers where no chromatography took place and could have replaced the HPLC column with a 25 cm long section of tubing and achieved the same result. The proposed method is NOT specific to the sample and is NOT valid or scientifically useful.

Every week I professionally review articles (or which have already been published) which show no chromatographic retention, none, just like the example paper. This is not a rare case at all (esp in some journals like that one). Such poor quality work shows disrespect to all scientists. Always check any chromatography paper for validity and make sure the authors have correctly applied the fundamentals of chromatography in the work. As you can see, a simple check of the basics just takes a minute to do (and something any student could easily do) and is one of the first things I check when reviewing most RP/NP methods.

No need to ask me if these are valid. That is why I provide the simple tools to do so.

"Determination of HPLC Column Dead Volume / Dead Time (T zero)" Article Link attached. http://hplctips.blogspot.com/2011/05/determination-of-hplc-column-dead-time.html

"K Prime (also known as: Capacity Factor, Ratio or Retention Factor): One of the Single Most Important HPLC Parameters of All" ; https://hplctips.blogspot.com/2015/06/k-prime-also-known-as-capacity-factor.html

Thank you dear Willliam and Detlef for your responses. I appreciate your time and patience.