Live Webinar : How to be more Successful with your ACQUITY QDa Detector?

Transcription

1 Live Webinar : How to be more Successful with your ACQUITY QDa Detector? Q&A Transcript Q - How do you generate multiple charges reproductively? A - If you use the same settings on the ACQUITY QDa, generating multiple charged ions is only dependent on the eluent composition. It is therefore important to prepare your eluent in a reproducible way. Q - Is there a database of mass spectra in EMPOWER? A - Yes, there is a MS spectra library functionality within Empower. Q- Detector saturation: will we have a message when we have saturated the detector or do we have to check the spectral data? A - There is no specific message when the detector is saturated. Detector saturation does not always negatively impact your data however if the sample is very concentrated it may not be possible to differentiate between the "main" analyte peak and its isotopes. When this happens the mass assignment may appear to be inaccurate as the software has difficulty establishing where the apex of the spectral peak is. Q - How often should we run the start up with the calibration? A - Normally, you would not need to run the calibration check. The QDa is stable over a long period of time (1 year). If you want to be sure or are working in a regulated environment, every time. Q - Why does the additional pump on the performance model increase sensitivity? A - The performance ACQUITY QDa has besides the bigger pump, also a bigger orifice (the opening of the MS) which allows more ions enter the MS. As we let more ions into the MS we need a bigger pump to maintain the vacuum. As we let in more ions, the sensitivity is increased.

2 Q - Is there a way of knowing whether you have multiple charge species present? A - When you have single-charged ions, the first 13C isotope is 1 mass unit from the mono-isotopic mass (molecular ion). When you have double-charged species, the first 13C isotope is 1/2 mass unit from the mono-isotopic mass. Q - Does switching on the front button also start the pumps? A - Yes. Q - Can Empower do a 3D plot like it can with PDA data? A - Empower can present a 3D plot very much like the PDA data, although the peaks are very much narrower in the m/z dimension than they would be in the wavelength dimension. A contour plot is also produced and is often more useful. Q - Can you scan positive and negative at the same time? A - Yes.

3 Q - We have been using QDa for 2 years and we managed to handle all situations. A new one arose regarding the turbo pump and its maintenance. We contacted the local office and they told that each year Oil cartridge should be exchanged. Can you send me PM? A - Yes, we have informed the local service organisation who will contact you. Q - For probe temperature, what would you recommend increasing it to if you are running at higher flow rates (1 to 2ml/min)? A - The probe temperature should be set to 600 in the Advanced Mode of the instrument method editor. When operating at these high flow rates, especially with largely aqueous mobile phase, be sure that the vent drain is directed sloping down and is flowing freely. If liquid accumulates in the drain tube, it can trigger a vacuum error. Q - Is it possible to switch between LC and waste for not overwhelming the MS with uninteresting matrix? Our SQD can only switch one now? A - The QDa does not have an integral divert valve due to space restrictions. It may be possible to divert some flow via the column manager module depending on your configuration. Q - Does a combination Water/ACN without additive work? A - You can expect to see signal with a purely water/can mobile phase. Electrospray ionization, however, works better with a more conductive mobile phase. A low concentration of a volatile acid or salt will give a larger and more stable signal. Q - I want to increase the M H Signal and lower the fragmentation signals. How can I do this? A - The cone voltage setting has the largest influence on the amount of fragmentation. I would use a setting of 15 volts for my first injection, and then make a series of runs at a series of progressively lower cone voltage in steps of 2 volts. A somewhat higher range is typically used for negative ionization mode. Q - Can we perform low level quantifications? A - This is difficult to answer as the question is what are low levels. With the standard ACQUITY QDa, you are normally more sensitive than the quantification levels you can achieve with a PDA.

4 Q - What is the reason for the detection limit at 1250 Da? Is it a limitation in the software or instrument hardware? A - The m/z range upper limit is set at 1250 to ensure that isotopic resolution of all detectable analytes is achieved at the maximum scanning speed (10,000 Da/s) of the instrument. It's a question of consistently providing quality spectral data. Q - I am using AccQTag Ultra, with the solvents included in the kit. Can these solvents be used with QDa? A - Yes, the eluents provided for the AccQ-Tag Ultra Method is compatible with Electrospray Ionization. Choose a lower cone voltage to minimize fragmentation. Observation of a signal at is the symptom that cone voltage should be lower. Q - What is the difference between standard and performance QDa detector? A - The difference between standard and performance QDa is a bigger orifice (entrance of the MS) and a larger pump (rotary). This leads to a sensitivity increase (5-7). Please be aware that this is compound dependent. Q - How much more sensitivity is there between Standard and Performance? A - In general there is about a factor of 5-7 difference between standard and performance (performance being the more sensitive). Please be aware that this is compound dependent! Q - Do we expect (MSMS) similar to this QDa in future? Just by adding fragmentation cell and a second quadrupole? A - Nothing imminent is planned. Q - Should we leave the unit on even if there is no analysis? A - The ACQUITY QDa has been designed to turn it off when you do not need it. So if you are not using it for a longer period (over night/weekend) then we recommend to turn it off as after about 20 minutes after turning it on you can use it again. (We recommend to use the same off/on process as you would use with a PDA detector).

5 Q - With QDa, is it possible to quantify 2 compounds with the same retention time? A - Yes it is absolutely possible to quantify 2 (or more) compounds with the same retention time. With Single Ion Recording you define the m/z value you want to monitor over which retention time, and that can be the same retention time. The maximum amount of compounds you can quantify at the same retention time will depend on the mass range you selected. Q - How to differentiate between 3 and 4 ions? A - The difference between 3 and 4 ions can be calculated from the 13C isotopic pattern. When you have singly charged ions, the first 13C isotope is 1 mass unit from the mono-isotopic mass. (molecular ion). When you have doubly charged species, the first 13C isotope is 1/2 mass unit from the mono-isotopic mass. If you have triply charged species, the first 13C isotope is 1/3 mass unit from the mono-isotopic mass etc. Q - Is there a recommended solvents/additives mixture for UPC2? A - When using QDa with UPC2, a make-up flow is needed. A good starting point therefore is MeOH with 2% water. You can use the same additives as you normally use when doing UPLC-MS analysis, as has been discussed during the webinar, e.g ammonium formate, ammonium acetate etc. Q - What is the recommended probe temperature when using UPC2? A - The recommended probe temperature is 600 C or higher. Also, using UPC2, a higher gas flow might be useful to get better sensitivity. As this depends on your flow, exact numbers are difficult to give. Q - What is better? To keep the QDa on standby or to shut it down for different periods of time? (over night/weekend etc) A - This is up to user preference and how long you wish to wait. It takes approximately 6 minutes for the QDa to be in a ready state from OFF (20 minutes if you run a calibration check upon start-up). For optimal sensitivity (note, this is not always needed for qualitative work), it is recommended to wait 30 to 45 minutes. The benefit of switching off is obviously the reduction in your electricity bill and lab cooling requirements.

6 Q - By scanning in SIR do we see all the fragments on the desired product? A - The name SIR means single ion recording, this means you are monitoring 1 m/z. If you look at the SIR function with the m/z of interest you will not be able to see fragments. However, you can define a full scan acquisition function parallel to the SIR function(s) you have defined. In the full MS results you might be able to see fragments (depending on the compound, cone voltage etc). Q - You spoke about PDA and MS data. Can the delay between the two detectors be set up to align chromatograms? and where? A - Both the 3D and any extracted or SIR 2D channels can be offset for alignment in the processing method on the Smoothing/Offset tab. Q - How can I use isotopic peaks at large unknown molecules? A - As the ACQUITY QDa has unit resolution, it will be difficult to distinguish isotopic patterns at high charge states. If you need that, the better MS instrument to use would be the Waters high resolution XEVO G2-XS QTOF. Q - How can you identify large unknown molecules? Is there a kind of action plan? A - The question is a bit what do you mean by identify and what is large? As you might recall from the webinar, larger molecules can be identified as long as the m/z ratio is below The ACQUITY QDa is capable of identifying known large molecules, as you normally have standards available, so you know retention time and preferable charge state. If you want to identify unknown large molecules the better instrument to use is a high resolution instrument like the Waters XEVO G2-XS QTOF. Q - How can I be sure there are sulphur and/or silica atoms in the molecules? A - Sulphur has an isotopic pattern of 94 sulphur 32 and 4% sulphur 34. This pattern you can see in your isotopic distribution of your molecular ion ([M+H]+ as the second isotope would be higher than expected on basis of only 13C isotopes. The same applies for Silica, as there you have 3 isotopes with distribution: 28Si:29Si: 30Si = 100:5:3. Q - How can I know where a functional group is placed in a (large) molecule? A - With the ACQUITY QDa you might be able to see a fragment which corresponds to either a functional group of interest and/or the loss of the functional group. If you are interested in structural elucidation, a high resolution mass spectrometer like the WATERS XEVO G2-XS QTOF would be the better choice to use.

7 Q - What is the lowest cone voltage possible? A - The cone voltage can be set as low as 1volt. We have seen a very few analytes where that setting was optimal, but a higher setting gives better sensitivity with little fragmentation. Q - Why is the capillary voltage much lower than in the SQD2 (3kV instead of 0.8kV)? A - As with many of considerations around the source (probe position, gas flows) the capillary voltage has been defaulted and ranges set to values which will provide the best combination of sensitivity and robustness. On instruments such as the SQD2 it is very easy for new users to accidentally set capillary voltage parameters and probe positions which can result in short term sensitivity gains but poor robustness. The QDa has been designed to ensure new users and expert users can achieve the same level of instrument performance consistently Q - If I measure SIR of two masses, there is a different in response. If I measure this in one function together or in two functions separately. Why? A - It may not be possible to answer this question without seeing how the methods have been configured. It could be due to a difference in overlapping time regions and consequently a change in dwell time spent on the transition in the two examples you provided. If you would like further input you could send screenshots of your QDa methods. Q - We use as additive FA (ph=3). Is the ph too low and what is a better additive? A - Formic Acid at PH-3 is perfect for positive ionisation. For negative ionisation a higher PH is better, so the use of a buffer would be advised. Q - When the QDa is in standby what is the recommended flow? A - When the QDa is in standby it is not recommended to run any LC flow into source. If you are not acquiring data on the QDa for an extended period of time it is recommended to disconnect the QDa and have the PDA/TUV eluent go to waste.

8 Q - It is better as you said to use negative mode for acidic compounds (like carboxylic acid), but these compounds are often better eluted on C18 column with acidic additives (HCOOH for example) which so reduces the response, correct? What is the best solution? A - The best solution is to use a post-column addition of base to neutralize the acidic mobile phase. I typically use ammonium hydroxide. I make my post column reagent at 5 times the molar concentration of acid in the mobile phase. The flow rate of the post column pump is then 20% of the flow through the column so that I am mixing equimolar amounts of acid and base into the source. For negative ionization, I will usually use a post-column reagent that is 50% water and 50% isopropanol to further enhance the ionization. Q - How to get a more robust system when running a lot of different applications? A - The experience with the ACQUITY QDa is that the system is very robust. This is mainly due to the patented reversed cone sample aperture. We have customers who use the ACQUITY QDa in open access environment who do not see any robustness issues. Depending on the applications you are running, you might want to consider changing the sample aperture preventively.