IPC-ESI

In the analysis of nucleotide-activated sugars, structural information was gained via IPC-ESI-MS and IPC-NMR. The NMR spectrometer was equipped with a flow cell a stop-flow valve allowed precise parking of the peak of interest to perform the NMR scan [123]. 

A very sensitive and specific IPC-ESI-MS method for determining cyclamate was used to monitor the content of the artificial sweetener in foods [34], Similarly, IPC proved valuable for controlling the separation of complex mixtures of betacyanin and decarboxylated betacyanin food colorants via gradient elution [35]. 

Since alterations in global DNA methylation are implicated in various pathobio-logical processes, a gradient IPC-ESI-MS/MS method with a volatile IPR was used to determine cytosine and 5-methylcytosine in DNA quantification relied on stable isotope dilution [58], Muscular dystrophies caused by various mutations in the dystrophin gene are amenable to easier prenatal diagnosis via a multiplex polymerase chain reaction (PCR)/IPC assay [59]. Some guidelines for the analysis of genomic DNA by IPC-ESl-MS can be found in Reference 60. 

An IPC-ESI-MS/MS method allowed the simultaneous determination of neomycin and bacitracin in human and rabbit sera [79] and the analysis of aminoglycoside antibiotics in human plasma [80]. IPC was recently validated for the estimation of bulk and formulated gatifloxacin [81]. The IPC determination of norfloxacin in diverse matrices worked as a stability indicating method [82], A CI2 stationary phase with embedded polar group successfully achieved IPC baseline tetracycline separation simply by using a phosphate as the IPR [83], A practical IPC method for the quality control of fosfomycin calcium and its related substances was recently suggested [84],... 

An IPC-ESI-MS/MS method using volatile perfluorinated carboxylic adds as IPRs added directly to the sample solution (not incorporated into the mobile phase) was developed for the quantitative assay of methadone in human plasma. This cost-effective strategy enhanced the efficiency of separation and minimized ion suppression because no IPR was present in the eluent [103]. Table 13.1 lists other potential uses of IPC in the pharmaceutical and clinical analysis fields. 

Ionic modifiers in the IPC eluent can provide a charge for neutral molecules so that they become detectable via the ESI interface. Conversely, counter ions reduce the charge state of an oppositely charged analyte or even convert it to the opposite polarity. If they are polycharged, for example, ESP and ESP modes were comparatively evaluated for the detection of nucleotides that are negatively charged. It was straightforward to use the ESP mode that detects the [M - H]"ion (with low levels of sodium and potassium adducts present), but ESP was a viable alternative because the volatile N,N-dimethylhexylamine IPR yields ion-pairs with the nucleotides. The most abundant relevant ion was the adduct between the compound and... 

ESI is the most common interface since IPC and MS were coupled initially. By 2008, most applications IPC-MS used the ESI interface [58,68-82] because analytes amenable to IPC are usually already ionic in the column effluent that enters the interface. Examples of APCI-MS applications [83,84] include two-fold use of both interfaces [85] they gave similar results in the determination of polyunsatured fatty acid monoepoxides [86]. For determining mono- and di-sulfonated azo dyes, ESI proved to give the best performance in terms of sensitivity and reproducibility [83]. Joining negative APCI-MS and ESI-MS unambiguously identified several acidic oxidation products of 2,4,6-trinitrotoluene in ammunition, wastewater, and soil extracts [61]. 

Analysis of Cer, hydroxy Cer, and GluCer by ESI-MS and ESI-MS/MS is described in details in Chapter 7. But the analysis of IPC and GIPC, which is special to plant lipidomics relative to animal lipids, is discussed below. 

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