Isocratic or Gredient

[aniket]

Dear Experts,

We are mainly into rapid screening of PK study samples form animals, we use both HPLC as well as Lc-MS for the same. I prefer gredient methods to isocratic methods, for good peak shape. But there is considerable debate (in my lab) regarding use of gredient in such studie.

So the experts can guide regarding the same, what is the best of kind of method, for such screening,

Thank you,

Aniket
Mumbai, India

[DR]

As usual, it depends.

If the separation is not too challenging, you can probably get faster analysis of multiple samples and make life simpler by using an isocratic method. If the separation is more difficult or peak shape is critical due to unavoidably small amounts of analyte (or the sample doesn't absorb much in the UV etc.), gradient elution may be the only option. The drawbacks are having to equilibrate the column between injections, making 2 mobile phases, keeping careful track of retention times...

[sam.pedraglio]

As DR wrote it depends on your analytes and on your clean-up procedure.
If you're confident than your clean-up is very efficient, you can work in isocratic mode.
If you do a simple PPT to work fast and you have analyte and IS with different polarity it's easier to work in gradient mode. You can use step gradients to make them short but you savetime respect to an isocratic mode and you keep your column clean.