MSACL 2018 US Abstract

Topic: Troubleshooting

Autosampler Tray Troubleshooting Tales

Kristine Van Natta (Presenter)
Thermo Fisher Scientific

Authorship: Joe Di Bussolo, Kristine Van Natta & Ed Goucher
Thermo Fisher Scientific, San Jose, CA

Short Abstract

From our experiences supporting customers over the years, many instances of bad results from LC-MS batches have been caused by problems in and around the systemís autosampler tray. Bad results include abnormally low sensitivity, almost no chromatographic peaks for some specimens and chromatographic results that donít match the intended specimen injections. These problems have been caused by specimen vials with gas-tight caps that have been cooled by the autosampler, specimen vials with micro-inserts that have air trapped at their bottoms and incorrect placement of microtiter plates in the tray holder. Sample preparation procedures must include detailed instructions to avoid such problems.

Long Abstract

Problem

Problem 1

Abnormally low chromatographic peak areas for all analytes from each autosampler vial in a batch.

Problem 2

Almost no chromatographic peak from some injections in a batch.

Problem 3

Chromatographic results do not match the intended specimen injection in a batch.

Method Information

Method 1

∑ Pipette 500 µL of prepared specimens (blanks, calibrators, quality controls (QCs) and samples) into labeled 2 mL glass autosampler vials and cap with gas-tight screw or crimp caps.

∑ Place vials into autosampler tray and place tray into autosampler tray holder cooled to 5įC.

∑ Make 50 µL injections into HPLC column and elute analytes into mass spectrometer ion source.

∑ Evaluate results.

Method 2 information

∑ Pipette 100 µL of prepared specimens into 150 µL glass vial inserts of labeled autosampler vials.

∑ Cap and place each vial into autosampler tray and place tray into autosampler tray holder.

∑ Make 25 µL injections into HPLC column and elute analytes into mass spectrometer ion source.

∑ Evaluate results.

Method 3 information

∑ Pipette 200 µL of prepared specimens into corresponding wells of microtiter plate.

∑ Cover and place the plate into autosampler tray holder.

∑ Make 25 µL injections into HPLC column and elute analytes into mass spectrometer ion source.

∑ Evaluate results.

Troubleshooting Steps

Troubleshooting Steps 1

Observed volumes of specimen actually withdrawn from vials were much less than 50 µL due to lowering of vialsí air space pressure as vials cooled. Repeat injections gave improved results as vialsí air space pressure returned to atmospheric pressure. Repeat injections after removing caps gave accurate results.

Troubleshooting Steps 2

Observed autosampler withdrawing air instead of specimen from some vials. Close inspection of vials revealed air trapped at bottom of glass vial inserts. In some cases, no air gaps were found in vials that failed proper injections. Observed autosampler needle pressing the vial insertís bottom, preventing accurate withdraw of the specified injection volume.

Troubleshooting steps 3

Observed results from the first few injections looked more like samples rather than the expected blanks and calibrators. Checked position of microtiter plate and saw that it was missed-positioned so that the second row of wells rather than the first row were sampled. Careful placement and double-checking placement of the plates prevented reoccurrence of this problem.

Outcome

Outcome 1

Replacing gas-tight caps with snap caps or screw caps with pre-slit septa allowed vialsí air space pressure to equilibrate with atmospheric pressure as the vials were cooled, which prevented inaccurate withdraw of the specified injection volume.

Outcome 2

Tapping vials after capping released air from bottom of glass inserts and inspecting each vial to ensure air is no longer trapped before placement into autosampler tray prevented sampling air instead of specimen. Carefully resetting the needle penetration into the vial insert to avoid touching its bottom prevented inaccurate sample withdraw. This also helped prevent withdrawing precipitated particles.


References & Acknowledgements:


Financial Disclosure

DescriptionY/NSource
Grantsno
SalaryyesThermo Fisher Scientific
Board Memberno
Stockno
Expensesno

IP Royalty: no

Planning to mention or discuss specific products or technology of the company(ies) listed above:

no