Operation Holiday - Integrating Gradients

At work, we had some problems during last year holydays due a basic skill that we lack: calculate the individual amount to mobile phase spent in a gradient analysis.

That's OK if you have some overnight runs but not so easy if you have to prepare 10 or 15L of mobile phase (MP) imaging a 5 day - 2 ml/min, 30 minutes gradient. We didn't want to prepare nothing 1 or 2 L beyond our use.

After think about the problem I found 2 possible solutions:



1-One way wold be the graphical method, dividing the gradient into several triangles and rectangles and integrating them. Basic geometry.



Remember that the area (%B/min) should be divided by 100 to gives the result in ml of B!
If your flow is diferent from 1, multiply by it!

 





  









2-Numeric integration using the trapezoid method.
This is much better, because can be automatized into a simple spreedsheet.

Before I found it I was using a interpolation method to generate the individual concentrations of my gradient between the points described in my SOP/Pharmacopeial monograph.

Following this formula, the spreadsheet calculate the area under the gradient curve between the points you type.
Results are identical

Now we can prepare very precise amounts of MP minimizing the waste!