Chromatography Forum

Hello all,

Just found these boards and I'm hoping to find some help. I'm relatively new to my current institution and we have a Varian Saturn 2200 Ion Trap GC/MS that is about 10 years old. I've been working out a method to analyze deltamethrin at low concentrations (~2ng/uL) and running full scan is not giving sufficient signal (not surprisingly). I'd like to simply monitor a single ion - what the Agilent instruments refer to as SIM (single ion monitoring) mode. I just can't figure out how to set it up correctly and no one at my institution makes use of the MS/MS or SIS features or is familiar with their use.

I have the manual, but there are so many options, and the options in the manual don't line up with the options on my screen. I'm not looking for theory but for practical instructions. Does anyone have a good source or advice? Any help is greatly appreciated. (I would try and contact Varian, but of course now they are Agilent, so I don't know if I can actually find someone to talk me through it there.) I was quite proficient with the Agilent 6890, and am feeling rather dense that I can't figure this out...

Thanks!

Per this thread: http://chromforum.org/viewtopic.php?f=6 ... ian+bruker you may want to contact Bruker.

Start first with SIS (selected ion storage) and see what happens. Under MS Workstation, in the method editor, change the final data acquisition note from "none" to SIS. Then, when you click the tab below, enter the appropriate ion for storage. This will probably be the ion with highest abundance in your mass spectrum, but if it's a common ion you may also decide to pick the second highest abundance ion from your full scan results to maximize specificity. It might be 181 or 253 m/z for your target chemical depending upon how the full scan results look. The ion trap will isolate the desired ion within a tolerance of usually +/- 3 m/z. Once the results look good, you can increase the lower mass of your overall scanning range and decrease the higher mass accordingly. The trap will be able to acquire data faster at these settings.

MS/MS could be tried next. First, change the the data acquisition type to AMD (automated method development). In the subsequent tabs, I would start with non-resonant waveform excitation before trying any resonant. Enter the parent ion (253 m/z would be good since it hopefully dissociates into 181 m/z). In the final tab you can enter 9 or 10 different voltages. I would start with 20 at the top and increase the value in each subsequent line by say 5 volts. So, essentially, you may need to develop 2 of these AMD methods. Run perhaps a 20-30 nanogram standard with these methods, also ensuring the trap is scanning rapidly by adjusting your sec/scan to a value of 0.40. When you open the results in MS Workstation, ensure you select "merged" or "all" (I can't remember which) when selecting the data file. This will allow you to click across each data point at the peak of interest and you can see how well the higher 253 m/z fragment is dissociating into product ions. Once you have isolated the voltage that works best, you can make a final AMD method and increase the voltage steps in increments of perhaps 0.5 to really "hone in" on the optimal dissociation voltage. Select the voltage that gives substantial (but not complete) dissociation of the 253. Now, when you go back to the method editor, change the AMD option to MS/MS, select "non-resonant" in the secondary tab, and input the voltage value that you are most satisfied with. Adjust your lower scanning range so as to detect as many fragments as desired.

Another option to consider is chemical ionization. Do you have this option on your 2200? You can do CI-SIS, CI-MS/MS and certainly CI-full scan. Good luck!

Thank you both for your quick responses. The details in the second post are exactly what I need and the thread in the first post provides valuable background for me on the Varian/Agilent/Thermo/Bruker mash up.