Derivatization, sample, tandem mass spectrometry

More recently, liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) have been evaluated as possible alternative methods for carfentrazone-ethyl compounds in crop matrices. The LC/MS methods allow the chemical derivatization step for the acid metabolites to be avoided, reducing the analysis time. These new methods provide excellent sensitivity and method recovery for carfentrazone-ethyl. However, the final sample extracts, after being cleaned up extensively using three SPE cartridges, still exhibited ionization suppression due to the matrix background for the acid metabolites. Acceptable method recoveries (70-120%) of carfentrazone-ethyl metabolites have not yet been obtained. 

One of the most powerful techniques used in Upid analysis today is HPLC coupled with mass spectrometry (HPLC/MS). Several mass spectrometric ionization techniques, such as fast atom bombardment (FAB) [23], electrospray ionization (ESI) [29,30], ionspray ionization (ISI) [31], and atmospheric pressure chemical ionization (APCI) [22,30,32] have been used. By using HPLC/MS, one can get information on the molecular structure of the intact lipids, which helps differentiate molecular species within different lipid classes. By using tandem mass spectrometry (MS/MS), identification of molecular species of different sphingolipids can be achieved in an easier and more sensitive way. There are many other advantages of using MS, such as small sample size, minimal sample preparation, and lack of need for derivatization, speeds, and sensitivity. In the literature, sphingolipids of both animal and plant origin were analyzed by MS. 

Because the presence of anatoxin-a and homoanatoxin-a in the environment represents a risk for animals and humans, several analytical methods have been designed to detect these toxins as well as their natural derivatives (Fig. 3.2). GC-MS was first used to detect and quantify anatoxin-a or its A -acetyl derivative [51,52,66]. High Pressure Liquid chromatography (HPLQ coupled to UV detection was also used, although this detectirm method is not veiy sensitive [67]. Thus, to improve the sensitivity, several authors have used pre-derivatization with a fluorophore, which reacts on the amine of anatoxin-a or of homoanatoxin-a, followed by separation by HPLC coupled to a fluorescence detector [56, 68, 69]. However, the derivatization might lead to false positives even if the technique was improved to remove primary amines present in the sample [70] or by crmcentratirm by extraction of anatoxin-a prior to analysis [71,72]. It is now accepted that the best analytical technique relies on the use of HPLC coupled to tandem mass spectrometry (LC-MS, or even LC-MS") without derivatization to avoid... 

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