Threshold switches forming

Data-dependent acqnisition (DDA) is a mode of operation, where the MS experiment performed in a particular scan is based on the data acqnired in a previons scan. In a simple form, a DDA experiment switches the instrument from full-scan MS acquisition to full-scan product-ion MS-MS when the total-ion intensity or a selected-ion intensity exceeds a preset threshold. This avoids the need to perform two consecutive injections for the identification of unknowns in a mixture first to obtain the m/z values for the intact protonated molecules of the unknowns, and second to acquire the product-ion MS-MS spectra of these unknowns in a time-scheduled procedure, switching between various preselected precursor ions as a function of the chromatographic retention time. The DDA was promoted by Thermo Finnigan upon the introduction of the API-ion trap combinations [44-46]. Similar procedures are available for other commercial ion-trap systems, as well as for triple-quadrupoles, e.g.. Information Dependent Acquisition (IDA) from Applied Biosystems MDS Sciex, Data-directed Analysis (DDA) from Waters, and Smart Select from Bruker. 

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