Chromatography Forum

Doing a valley to valley integration seemed to increase resolution far more compared to that, when a drop line between the peaks.

Any reason why.

Are you stating the results of a calculation made by your data system? If so, then perhaps the valley-to-valley integration defines a narrower peak width for each peak for your data system than a baseline drop does? I think that would be a faulty calculation because, from what I've read, one should be calculating peak width (for resolution calculation purposes) by drawing the tangents of a peak at 0.6 times the peak height (for a Gaussian peak), so I would think that any sort of interpretation by the data system could be flawed by improper integration parameters. Just a thought, I'm no expert, but I think I may be on the right path.

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Resolution* [Rs, see Selectivity]
The separation of two peaks, expressed as the difference in their corresponding retention times, divided by their average peak width at the baseline. Rs = 1.25 indicates that two peaks of equal width are just separated at the baseline. When Rs = 0.6, the only visual indication of the presence of two peaks on a chromatogram is a small notch near the peak apex. Higher efficiency columns produce narrower peaks and improve resolution for difficult separations; however, resolution increases by only the square root of N. The most powerful method of increasing resolution is to increase selectivity by altering the mobile/stationary phase combination used for the chromatographic separation [see section on Chemical Separation Power].

Selectivity [Separation Factor, σ]
A term used to describe the magnitude of the difference between the relative thermodynamic affinities of a pair of analytes for the specified mobile and stationary phases that comprise the separation system. The proper term is separation factor [σ]. It equals the ratio of retention factors, k2/k1 [see Retention Factor]; by definition, σ is always ≥ 1. If σ = 1, then both peaks co-elute, and no separation is obtained. It is important in preparative chromatography to maximize α for highest sample loadability and throughput. [see section on Chemical Separation Power]

Retention Factor* [k]
A measure of the time the sample component resides in the stationary phase relative to the time it resides in the mobile phase; it expresses how much longer a sample component is retarded by the stationary phase than it would take to travel through the column with the velocity of the mobile phase. Mathematically, it is the ratio of the adjusted retention time [volume] and the hold-up time [volume]: k = tR'/tM [see Retention Time and Selectivity].

Note: In the past, this term has also been expressed as partition ratio, capacity ratio, capacity factor, or mass distribution ratio and symbolized by k'.

Hi Mohan,

From what I understand the peaks in questions are not baseline separated and that’s the reason for the described differences.
It also means that a good portion of the (combined) area lies between the deduced horizontal baseline and the baseline generated by the software when you ask for a “valley to valleyâ€

Are the peaks are the tail of the main peak?

Coincidentally, if it is, that is why we have tended to move away from using resolution in these particular situations. We now use the discrimination factor instead, as this value should not change as much as resolution regardless of integration type.

Thanks Rob... Zoubair may still be successfull with his 1987 invention of the discrimination factor...

It is a good idea and it works...