This situation can be applied to 2D chromatography. If there is a T-piece can two To void volume markers be used to measure that volume for sample to reach the detector. Some research applies HILIC-reverse phase or vice versa what To void volume markers do they use. I am sure that To markers that are suitable for ion exchange columns could apply to mixed mode columns but I do not have experience in ion exchange chromatography adequately.
Alternatively how does one measure void volume without a void volume marker. Would the manufacturer have specifications?.
http://www.sciencedirect.com/science/article/pii/S0021967308014131
This has been discussed many times in the past. A column's Void Volume can be calculated (estimated based on known properties and dimensions) as well as measured using a compound which is not retained. Please refer to the linked article, "Determination of HPLC Column Dead Volume / Dead Time (T zero)," referenced below which covers this topic and includes examples of compound types which can be used as void markers.
Use of a mixed mode column does not change this. All support types found in one tube will still function the same way as they do in separate columns. The dimensions do not change and the measurements/calculations are still the same. Nothing has changed. Remember that in all cases, we are trying to find out how long it takes for a compound to elute out of a column which does not interact at all with the support. NO matter what mechanisms are in place (i.e. size exclusion, ion exchange, pore sizes...) the fact is that you can measure/calculate it. As a matter of fact, this is suppose to be one of the very first things you do (and learn) when you establish an HPLC method as without this most basic and fundamental information you will not have any way of demonstrating that you are using a chromatography method. Most of the critical metrics we use are based on this initial value.
https://hplctips.blogspot.com/2011/05/determination-of-hplc-column-dead-time.html
Thank you again.
I have demands from the supervisor to get work done and a marker for this could be out there. Problems, logistics and troubleshooting the method.
Yes. Porosity is too general a term. We are interested in how much free space remains after the column has been packed at very high pressure with the support. This value varies depending on many things, but can be obtained from the manufacturer or measured (usually by gas). For most silica based HPLC columns with porous supports, the support pore volume is ~ 0.70 (70%). Some are more or less than this value. *I should also note that there are non-porous chromatography supports too.
There are other general ways of determining the Tzero time for any HPLC column system too (true for 1 column or even 6 columns in-series). The pressure change (or RI difference) created when a sample is injected into the flow stream results in a small perturbation in the baseline. This small 'blip' can easily be seen by most UV/VIS and RID type detectors on the baseline. It is yet another way of approximating the time, though again, it needs to be calculated and measured to be sure.
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