Full scan acquisition technique

In El-MS, the major ions formed from PBDEs are the and the [M — 2Br], which can be used for its identification and quantitation. This ionization technique facilitates the analysis of BDE congeners in the presence of possible coeluted compounds (such as PCBs). EI-LRMS is not routinely used for the PBDE analysis, because of its relatively low sensitivity, especially for the analysis of higher brominated BDE congeners (hepta- to deca-DBE). However, this ionization mode allows the acquisition of full scan spectra, thus offering a multiple choice in ion selection than ECNI mode. Yet, ECNI is more selective towards aromatic brominated compounds. 

Liquid chromatography-time-of-fiight (TOF)-mass spectrometry has also been established as a valuable technique for the routine control of the wholesomeness of food. In this sense, TOF techniques can record an accurate full-scan spectrum throughout the acquisition range and have resulted as an excellent tool for the unequivocal target and nontarget identification and confirmation of food contaminants [105,106]. 

In contrast to the full scan, these acquisition modes require more information on the compounds under investigation. Especially for SRM mode acquisitions, information on the product ion(s) of the respective compounds is [16] necessary to perform an analysis. These techniques provide higher sensitivity, but information can be lost as unexpected metabolites remain undetected. Therefore, these methods are suitable only for the detection and quantification of known (or at least predicted) metabolites, even though a precursor ion scan or neutral loss scan can detect a large range of possible metabolites. However, as some metabolic reactions lead to an altered fragmentation pattern, there is still the chance that some products are missed. 

Full scan analysis of an average substance concentration to determine the selective ions (SIM masses, two to three ions/component) chose more potential SIM ions as finally required as special matrix conditions are to be taken into account. Chose SIM masses with highest S/N ratio. Determination of the retention times of the individual components. Establishment of the data acquisition interval (time window) for the individual SIM descriptors, or use the retention timed SIM technique with a symmetrical acquisition window centered to the compound retention time. Test analysis of a low standard (or better, a matrix spike) for optimization (SIM masses, separation conditions). 

Negative chemical ionization high-resolution gas chroma-tography/mass spectrometry with on-column injection (NCI HRGC/MS) provides sensitivity and selectivity for the detection of nitro-aromatics. The limit of detection is approximately 50 pg for the mono-nitro-aromatics and di-nitro-pyrenes in the full mass scan data acquisition mode. The limit of detection can be improved, if necessary by using selected ion monitoring techniques. 

It should be emphasized that these performance differences between the two designs are subtle and should not detract from the overall benefits of the TOF approach for ICP-MS. As mentioned earlier, a scanning device such as a quadrupole can only detect one mass at a time, which means that there is always a compromise between number of elements, detection limits, precision, and the overall measurement time. However, with the TOF approach, the ions are sampled at the same moment in time, which means that multielement data can be collected with no significant deterioration in quality. The ability of a TOF system to capture a full mass spectrum, approximately three orders of magnitude faster than a quadrupole, translates into three major bene-hts—multielement determinations in a fast transient peak, improved precision, especially for isotope ratioing techniques, and rapid data acquisition for carrying out qualitative or semiquantitative scans. Let us look at these in greater detail. 

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