Traditional library search, like NIST and PBM (used by Agilent) typically use a pre-filtering algorithm based on pre-selecting a small number of the largest peaks in the spectrum. This dramatically speeds up the search by reducing the total number of library spectra that are fully “matched”. Unfortunately, many time these algorithms don’t work well with mixtures or low signal-to-noise spectra and can filter out exactly the spectrum we are looking for. In some search software, this option can be disabled, but at the cost of speed. Full spectrum search can take over 30 seconds per search, and with hundreds of compounds in the run, well you can see the problem.
CPS is a special library search developed by Cerno to dramatically speed up un-filtered library searching of every spectrum in a library, a requirement for SMD. To accomplish this, the search libraries are saved in a special format (.CPS) and are searched using the advanced vector instructions and liberal memory available in modern computers to dramatically accelerate the search. CPS full library search is typically much faster than a traditional filtered search despite the increased computational load.
CPS search can be used alongside of the traditional NIST search (which GC/ID uses natively) and only runs when Search Mixture Deconvolution (SMD) is required. However, CPS search can also be set to run as the default search. The advantage of using CPS search is that the search pre-filtering, although only occasionally, can eliminate the correct compound with the pre-filter and produce incorrect search results[1], especially for low signal-to-noise spectra. CPS returns search result values about 40 points higher than NIST due to the slightly different algorithm used, but the ranking and accuracy are similar and SMD will perform better for those cases as mentioned above.
Since CPS search uses a different library format, you must import your current NIST format libraries using the “Import CPS Library” tool accessible from the GC/ID “App” page. CPS search by default installs the NIST20 library in CPS format so you don’t need to import that library, but you must have a license for NIST20 on your computer to legally use it. If you possess a legal copy of NIST20 in any format (PBM, NIST, or other) you have a legal license to use the NIST20 CPS library on that computer.
It should also be noted that CPS search runs in a separate application window labeled “Cerno CPS Server”. It automatically starts when CPS is needed and shows the status of the search. It stays open as it keeps the library in memory for speed. You can close the window which will free up memory, but it will be automatically restarted the next time CPS is used.
One of the many powerful features of MassWorks GC/ID.
Find out more from the MassWorks Rx GC/ID brochure .