Walk-Up LC/MS Changes

Post date: Jul 17, 2019 8:6:56 PM

Starting Monday July 22nd 2019, many changes will be made to both the

Welch and NHB walk-up LC/MS instruments.

This has been something we have wanted to do for a while and with the new MS detector recently installed in Welch, we decided this would be a good time to start fresh. Unfortunately, with a constant stream of graduate students coming and going, there is never a great time to make big changes and any changes will inevitably affect some of you and the experiments that you have been running. If you are worried these changes will cause a problem with the methods you have been running, please come and talk to us and we will do our best to address your concerns.

New Methods

First off, we want to announce that we will be implementing 11 new, clearly labeled standard mass spec methods, as shown below. While many of these are already available in some form, we have found the current list of methods has grown out of control and is very unorganized and confusing. Many of the current methods have been made over the years for individual students, who may or may not still be at UT. We never know when a method can be deleted since students tend to pass their method down through their group. We will still be making individual methods when necessary, but will now have a standard way of labeling them.

These new methods are labeled 01 through 11. All of them are available in NHB, which has a multimode source, but only the ESI methods are available in Welch (see more about this below). We have tried to address students' comments that they would like to have access to ACN methods and neutral methods on both instruments. ACN is only available for ESI LC methods, since it gives very poor sensitivity in APCI and there is not much use for it in FIA.

These are the method names you will see on the instruments when submitting samples. They are further described in the poster below.

Old Methods

-All of the old methods on the NHB LC/MS have been deactivated. Try to use one of the new methods above, but if you have a specific method that you still need, please contact us about it and we can reactivate it.

-Since the new Welch MSD came with new software, the method list needs to be rebuilt. We will have these new methods (above) which should cover the majority of your needs. If you have a specific method that you still need, please contact us about it and we can transfer it from the old computer.

Solvent Changes

We have decided to only use 0.1% formic acid in one of the water eluents (channel A). We do not believe that it is necessary to have it in both the aqueous and organic LC eluents and it will also drastically reduce our formic acid consumption and costs.

-Any current methods on the NHB walk-up LC/MS that use channel B (currently MeOH + FA) will now be using ACN. In most cases, this should not have a negative effect, though you may notice differences in retention times. If this change is a problem on your individual method, you can contact us and we can adjust your method so that it uses the MeOH in channel D.

-Any neutral methods on the Welch walk-up LC/MS will use channel C, which contains 50 mM NH4OAc. This has been the case for some time now, though we are reducing the NH4OAc concentration from 100 mM down to 50 mM to hopefully reduce the amount of white precipitate we find when cleaning the source. If you use any neutral (NA) methods in Welch, you will most likely notice NH4+ adducts of your target. These neutral LC methods (07 and 09) in Welch should be useful to simplify complex polymer samples since the NH4+ generally becomes the main adduct and the appearance of peaks due to H+, Na+, and K+ will be drastically reduced or eliminated. Keep in mind though, that the NH4+ ions can reduce the sensitivity of the instrument to other targets.

Differences Between Welch and NHB LC/MS Instruments

-Since we have noticed a lack of use of the APCI methods and in an attempt to reduce the amount of metal in the source, which has caused tailing on the chromatograms, the Welch walk-up LC/MS will only have an ESI source. This means that out of the 11 methods listed above, only the ESI methods (method numbers 02, 06, 07, 08, and 09) will be available in Welch. The NHB walk-up LC/MS will retain the current multimode (ESI and APCI) source.

-As mentioned above, the solvent channel C in Welch will be H2O + 50 mM NH4OAc, whereas it will just be pure H2O in NHB.

-The NHB LC/MS has an autosampler tray chiller set to 12 degrees C, whereas the Welch LC/MS does not have a chiller.

Thank you for your patience and understanding as we implement these changes, which we believe will enhance and simplify LC/MS usage in the future.

~Kristin and Ian