Resolving Power at High Mass
{"Image DocumentName": "Resolving Power at High Mass", "Image ImageDescription": "50 ppt Pb, Bi. A very low concentration profile, 50 ppt in solution, is pictured above for Lead an Bismuth. First of all the profile looks the same whether you have a TOF or a quadrupole but in reality there are differences that will be described momentarily. The Pb, Bi profile represents the most common occurrence of adjacent high mass peaks encountered by the typical mass spectroscopists. Here the resolving power is calculated to be 1270 at 50% peak height. Some right angle TOF systems have higher resolving power such as 1500 at this portion of the spectrum but higher resolution beyond the minimum of baseline separation has no benefit at all. The hidden story of these peaks that look very much like a quadrupole spectra is this. A mass filter will step through typically either 10 or 40 settings to generate a peak profile. If 10 steps are used, each segment of the mass scale is 0.1 AMU wide. The first segment that shows signal increase is the finite m/z setting of the mass filter that allows a few ions through the filter to the detector. The apex of the peak is the setting that allows the most ions through the filter. The peak apex is composed of a mixture ions that appear at other m/z settings as well as those that were screened out. It\u2019s very much like stepping an optical slit across a light beam in a stepwise manner from left to right. First a little light gets through, then more and more until the optimum and then the light diminishes as you pass the optimum. There are many factors that cause slight differences in the apparent m/z of similar ions that result in a spread of m/z within a single AMU.", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}