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Different sample injection modes: Standard & Bracketing

PostPosted: Tue 17 Mar 2015 09:31
by Interchim
Different sample injection modes: Standard & Bracketing and their methods

With the AutoSampler, you can perform 2 different injection modes, with two distinct methods for each mode. The details are given below:

- "Standard mode"
The sample can, or not, be bracketed between two air bubbles to avoid any edge effects with the mobile phase.
This is the standard mode used by all analytical injectors for example.
The sample is conveyed through the tubing to the loop "trapped" between two small air bubbles.

Two methods are available for "standard" mode:

* Method 1 (no lead, rear, DMSO): outer needle rinse (3 times), then inner needle rinse - bubble - sample - bubble - outer needle rinse - carrier solvent.
* Method 2 (lead, rear, no DMSO): outer needle rinse (3 times), then inner needle rinse - bubble - rear - outer needle rinse (3 times) - bubble sample - outer needle rinse (3 times) - lead - bubble - outer needle rinse (3 times) - carrier solvent

- Bracketing mode:
This mode is used to add, upstream and downstream of this "bubble-sample-bubble" train, a solvent segment (DMSO) different from the solvent used as a carrier or for rinsing.
An air bubble is also added to the ends of these solvent segments.

Two methods are available for Bracketing mode:
* Method 1 (no lead, rear, DMSO): outer needle rinse (3 times) then inner needle rinse - bubble - DMSO - outer needle rinse (3 times) - bubble - sample - bubble - outer needle rinse (3 times) - DMSO - bubble - carrier solvent (reverse phase)
* Method 2 (lead, rear, DMSO): outer needle rinse (3 times) then inner needle rinse - bubble - rear - outer needle rinse (3 times) - bubble - DMSO - outer needle rinse (3 times) - bubble - sample - bubble - outer needle rinse (3 times) - DMSO - bubble - lead - bubble - outer needle rinse (3 times) - carrier solvent (reverse phase)

The carrier solvent pushes the sample through the puriFlash injection loop.
Physically, this additional solvent and the carrier solvent will be in two containers (beaker, bottle, etc.) on the AutoSampler tray.
Conventionally, this is a solvent with high solubilisation power, such as DMSO.
The advantage is that this allows injection onto a Water/Acn stabilised column of, for example, a sample solubilised in an X phase and insoluble in this solvent composition.
The sample can thus be pushed into the column preceded and followed by DMSO, thus allowing the sample to pass through the sinter without crystallising.
The aim is to position the sample after the sinter in the silica.
The first elution step is thus performed to elute the DMSO with a high water content, or ideally in acidic water.