What Is Dwell Time? Ms/ms
You may change the dwell time in the settings dialogue.Press the 'All the settings' when starting the program. Then you may choose the dwell time separately for:. pressing the keyboard button. pause between keyboard button presses.
fixation on other items (toolbar, zoom window). pause between fixation on other itemsIf you cannot press the 'All the settings' button when the program is starting because of disability and/or decided to change the settings when the program runs, you may use the program's onscreen keyboard to start the dialogue.
The amount of time that elapses between when a user clicks on a search result and then returns to the SERP from a website. #top10seocompany 2018 #bestseocompany #digitalmarketing company www.gvate. Popular Answers ( 2) Remember that the stated dwell time is NOT the actual dwell time; you have dead time in the detector when you jump from ion to ion. Also make sure that you start your ion window at least 6-10 seconds prior to the start of your peak elution, as there is processing dead time when you switch ion groups.
Parameters That Influence MS Quantitation1. Number of Points Across the Chromatographic Peak 2. Spray Stability 3. Peak Shape 4. Chromatography 5.
Internal Standard 7. Mass Resolution.
Numberof Points Across the Chromatographic Peak. Youneed at least 15 to 20 points across a chromatographic peak forgood quantitation.
If youhave fewer points you will not be able to describe the peakadequately and may lose information, for example you maymiss the top of the peak. Also reproducibility is negativelyaffected with fewer points and you will observe RSD’s increasingto unacceptable values. Onecan increase the number of points across the peak by scanningfaster however data quality is sacrificed. If you increase thenumber of points across the peak you must increase your scanspeed, so the time you look at your mass of interest is shorter. Ashorter dwell time negatively affects s/n. Theoretically the s/nincreases with the square root of the increased dwell time.
SprayStability. Spraystability influences signal intensity. A wildly fluctuating sprayalso affects peak shape. These poorly shaped peaks give very badRSD’s and bad calibration curves. For the integrator it is verydifficult to determine the beginning and ending of the peak. Spraystability is influenced by several parameters:i. Poorly mixed solvents.If you use premixed solvents or buffers, be sure that the solvents arewell mixed before starting the assay.
In addition sudden solvent changeswill negatively affect spray stability.ii. Old solvents. Unlike cognac, whisky and some wines HPLC solventsdo not age very well. Intime they absorb salts from their glass containers. They can also formradicals which give spikes and poor spray stability.iii. Badly cut capillaries.Broken or poorly cut capillaries lead to sputtering and sprayinstability.
Also with a poorly cut capillary it is possible that thesprays goes off on an angle and is not aligned optimally with the MSentrance.iv. Polyamide Tail. Somesolvents used for HPLC cause the polyamide coating from the capillariesto weaken and get longer than the fused silica. You can observe this bylooking at the end of the fused silica capillary. If you see a“tail” hanging off the capillary you should take care of it. Thisleads to sputtering and unstable spray. There are two ways to preventthis 1.) Cut the capillary regularly or 2.) Burn the polyamide coatingaway for 1 or 2 cm.
Be careful when you burn the capillary. There areflammable liquids around and the fused silica becomes extremely brittleand becomes difficult to handle once burned.
PeakShape. Badchromatographic peak shapes are difficult to integrate. Peaktailing or leading makes it difficult for the integrator todetermine the beginning or end of the peak. Also it is verydifficult to do the integration reproducibly on irregular peaks.The same applies for split peaks. Try to get nice sharp peaks evenif sensitivity is not required. “Blobs” are not nice to lookat and are difficult to integrate.
Chromatography. Itis true that ms or ms 2 can surmount somechromatographic problems, but remember, good chromatography willgive you better quantitation and calibration curves. Itis better to separate your peaks with the LC than with the MS.
Ifyou separate them on the column you have more time per componentso you can use longer scan times resulting in better s/n ratios.Better s/n ratios are easier to integrate and give you betterRSD’s. Tryto avoid too many co-eluting peaks. Co-elution might causecompetition effects during the ionization.
If compound Aco-elutes with compound B which is much more basic the morebasic compound B will “steal” protons from compound Aand so suppress it making your assay less sensitive. Tryto reconstitute the samples in the inorganic solvent. This willcause the compounds to stack on the front of the column and giveyou sharper peaks. Don’tforget about chromatography just because you have a massspectrometer. Additives.
Useonly volatile modifiers. Nonvolatile buffers, acids and bases willdecrease your sensitivity by a factor 10 to 100, and they can giveunstable sprays. TFAsuppresses MS signal. When you must use TFA, use as little aspossible. Minimizethe use of ion pairing reagents.
If necessary make sure they arevolatile and at low levels. Internalstandard.
Theuse of an internal standard will enhance the reproducibility andprecision of your data. With mass spectrometry we can use the bestinternal standard available, the compound it self.
We can use the stable isotopic labeled compound. Thesecompounds are chemically the same and behave the same. The labeledstandard should be “far” enough away from the non-labeled toavoid signal contribution of the abundance of the natural isotopesto the signal of the internal standard. If the compound and thestandard are not separated adequately by mass, this will result inquadratic standard curves and sample interference. MassResolution. Howcan mass resolution help you? If you have a co-elution of near isobariccompounds, high resolution can help you separate them,if the resolution is high enough.
If you do MS 2 it isimportant that you have the possibility of high resolution withms1 and ms2 not only in the ms2 mode. You need the high resolution in ms1for high resolution precursor ion selection.
If you don’t havethis capability you can get a mixed product ion spectrum that willlead you to the wrong conclusions or wrong quan and calibration curve results. Isobariccompounds are compounds with the same nominal mass but with adifferent molecular formula. N 2 and CO both havethe same nominal mass of 28 amu. With a low resolution instrumentthese two compounds can not be separated.
What Is Dwell Time Ms/ms Mean
Actually themass of N 2 is 28.006148 and the exact mass of CO is 4 the mass difference is0.01123336. Copyright © 2004-2016 IonSource All rights reserved. Last updated: Tuesday, January 19, 2016 02:48:41 PM021706.