HPLC Products

Autosampler Problems - X-Y Calibration

Some autosamplers use a carousel, with one, two or three rows of vials. This is relatively slow, but eliminated the possibility of X-Y calibration errors.

Other autosamplers use a tray of vials, containing x columns of y rows. In order for the autosampler to be able to find each of these vials without damaging the needle, it needs to know the precise X-Y coordinates of each vial.

This is usually done by specifying the number of rows and columns, and giving the coordinates of the first and last vial in each tray. Calculation of the coordinates is done in Service Mode, as is the input of the results. The exact procedures are different for each autosampler, and it will be necessary to consult the manual, possibly the service manual, for further instructions.

If the X-Y calibration starts to drift, the first indication is that the holes in the vial caps after injection start to drift nearer the edges of the caps. This is a warning which we do well to heed, because it is then only a matter of time before a bent needle is the result. There can be two reasons for the drift in the hole position. Apart from the X-Y calibration, the other possibility is that the needle is beginning to bend. If so it is important to straighten it straightaway, and then to monitor for further problems. If the problem recurrs regularly, replace the needle.

Most autosamplers zero their X-Y coordinates when they are switched on, or when a run begins. You will see the arm go to the back and the left, and the needle raise to the top (the zero Z position). Once this has happened, it is really important not to manually move the arm even a little. Even if you really want the vial underneath its current position!! Moving the arm does not usually register with the autosampler, which then has a completely incorrect location for the needle. The next time it attempts to make an injection it will go to the wrong position, and the needle will probably hit something solid and bend. If the arm is moved accidentally, stop the run sequence, and if necessary, turn off the autosampler and restart it. A needle will usually cost over £100, and it is not worth taking the chance.