Triple quadrupole mass analyzer method development

Positive ion thermospray LC/MS and LC/MS/MS methods carried out on a triple quadrupole mass spectrometer have been successfully utilized in our laboratory to elucidate the structures of metabolites of several compounds currently undergoing development as drug candidates. Samples were obtained from both in vivo sources (urine, bile, or plasma) and analyzed directly from the biological fluid or from in vitro enzymatic/chemical methods. In all cases, buffer ionization mode using ammonium acetate in the HPLC mobile phase was employed for ionization of the metabolites of interest. 

Corn-based foods followed by fumonisin B2 (FB2).The problems and risks associated with fumonisin contamination have resulted in the development of precise, reliable and sensitive methods for its determination in corn and corn-based foods (Magan Olsen, 2004, as cited in Silva et al., 2009). Therefore, the quality parameters in the analysis of FBI and FB2 in corn-based products obtained with LC with fluorescence detector have been investigated (Silva et al, 2009). Furthermore, a comparison study between fluorescence detector (FD), mass spectrometry, and tandem mass spectrometry with a triple quadrupole (QqQ) analyzer using an electrospray ionization interface for the determination of fumonisin B1 and B2 in corn-based products has been performed. A comparative study of the three LC detectors, FD, single quadrupole, QqQ for the analysis of fumonisins in corn samples has been performed. The response achieved by the three detectors was sensitive enough to study the maximum contents established by the EU legislation. These LC detectors would be appropriate for quantification purposes but the acquisition of at least two transitions achieved with QqQ provided a univocal identification. 

In terms of the hardware, TRMS methods described in this book use most common types of ion sources and analyzers. Electrospray ionization (ESI), electron ionization (El), atmospheric pressure chemical ionization (APCI), or photoionization systems, and their modified versions, are all widely used in TRMS measurements. The newly developed atmospheric pressure ionization schemes such as desorption electrospray ionization (DESI) and Venturi easy ambient sonic-spray ionization (V-EASI) have already found applications in this area. Mass analyzers constitute the biggest and the most costly part of MS hardware. Few laboratories can afford purchasing different types of mass spectrometers for use in diverse applications. Therefore, the choice of mass spectrometer for TRMS is not always dictated by the optimum specifications of the instrument but its availability. Fortunately, many real-time measurements can be conducted using different mass analyzers equipped with atmospheric pressure inlets - with better or worse results. For example, triple quadrupole mass spectrometers excel at quantitative capabilities however, in many cases, popular ion trap (IT)-MS instruments can be used instead. On the other hand, applications of TRMS in fundamental studies often require a particular type of instrument (e.g., Fourier transform ion cyclotron resonance mass spectrometer for photodissociation studies on trapped ions). 

Since the analytical point of view most of current analytical methods are based on LC-MS/MS, but for some classes of pesticides GC-MS continues being the technique of choice. The use of quadrupole ion trap (QIT) to analyze multiple pesticide residues is limited to several multiclass pesticides in fruit [162], because of the limited number of ions that can be isolated at the same time. For this reason, the use of several time windows is required and this is indeed a strong limitation in practice. The use of hybrid triple quadrupole linear ion trap (QqLlT) mass spectrometer has provided significant contribution to the development of high-sensitive multiresidue analytical methods for pesticide control. An example of application is the method reported by Hernando et al. for the analysis of pesticide residues in olive oil [65]. 

By examining this brief history of the development of instrumentation and methods, it should be clear what parameters define the instrument of choice for analysis of pharmaceutically important molecules. Such an instrument is one capable of performing LC-MS, typically using a reverse-phase HPLC separation and one of the API techniques. MS-MS capability is desirable—using an ion trap, a triple quadrupole, or other tandem mass analyzer instrument. Accurate mass measurement capability is also desirable. These attributes make up a prioritized list of capabilities for the ideal full-purpose instrument to be used in a pharmaceutical research environment. As one progresses through this list, the expense of the instrument increases, the sophistication of the instrument increases, and the intellectual and technological commitment required to do these experiments increases. 

---