APCI metabolites

The complementary nature of APCI and ESI, APCI for less polar compounds (Phase I metabolites) and ESI for more polar compounds (Phase II metabolites). 

Currently, HPLC/fiuorescence is still the most common technique for the determination of residues of oxime carbamates. With the introduction of ESI and APCI MS interfaces, HPLC/MS analysis for oxime carbamates in various sample matrices has become widespread. However, for a rapid, sensitive, and specific analysis of biological and environmental samples, HPLC/MS/MS is preferred to HPLC/MS and HPLC/fiuorescence. With time, improved and affordable triple-quadrupole mass spectrometers will be available in more analytical laboratories. With stricter regulatory requirements, e.g., highly specific and conclusive methods with lower LOQ, HPLC/MS/MS will be a method of choice for oxime carbamates and their metabolites. 

Applications APCI-MS is often more widely applicable than ESI-MS to the analysis of classes of compounds with a low molecular weight, such as basic drugs and their metabolites, antibiotics, steroids, oestrogens, benzodiazepines, pesticides, surfactants, and most other organic compounds amenable to El. LC-APCI-MS has been used to analyse PET extracts obtained by a disso-lution/precipitation procedure [147]. Other applications of hyphenated APCI mass spectrometric techniques are described elsewhere LC-APCI-MS (Section 7.33.2) and packed column SFC-APCI-MS (Section 73.2.2) for polar nonvolatile organics. 

In off-line coupling of LC and MS for the analysis of surfactants in water samples, the suitability of desorption techniques such as Fast Atom Bombardment (FAB) and Desorption Chemical Ionisation was well established early on. In rapid succession, new interfaces like Atmospheric Pressure Chemical Ionisation (APCI) and Electrospray Ionisation (ESI) were applied successfully to solve a large number of analytical problems with these substance classes. In order to perform structure analysis on the metabolites and to improve sensitivity for the detection of the various surfactants and their metabolites in the environment, the use of various MS-MS techniques has also proven very useful, if not necessary, and in some cases even high-resolution MS is required. 

Several methods, applying MS-MS techniques, for the identification and characterization of APEOs and their metabolites, alkylphenoxy carboxylates (APECs) and alkylphenols (APs) in environmental liquid and solid samples and industrial blends are reported. APCI-MS-MS... 

Fig. 2.6.10. APCI-FIA-MS-MS(+) (CID) daughter ion mass spectrum of selected [M + NH4]+ parent ion (mjz 340) of potential carboxylated non-ionic surfactant metabolite of precursor NPEO prepared by chemical synthesis structure of short-chain NPEC CgHi9-C6H4-0-(CH2-CH2-0)-CH2-C00H fragmentation behaviour under CID presented in the inset [28],... 

When an industrial blend of C13-AE surfactants CraH2ra+iO-(CH2-CH2-0) H was biodegraded with different biocoenoses in lab scale reactors, different degradation pathways were observed applying biocoenoses of different WWTPs. Besides a mixture of precursor compounds reduced in concentration, metabolites were also observed by APCI and ESI-MS(+) as [M + NH4]+ ions, which were then confirmed by MS-MS. The AE blend CnH2n+10-(CH2-CH2-0) H (.n = 13 x = 1-16) with equally spaced ions (Am/z 44) at m/z 262, 306,... 

A PPG biodegradation product as metabolite of PPG generated by metabolisation of AP could be observed and verified by MS-MS(+) when WWTP effluents were examined by APCI-FIA-MS(+) and selected compounds were identified by FIA-MS-MS(+). In the SPE effluent extracts, two ions at m/z 266 and 324 were observed, which... 

Despite the fact that physico-chemical and chemical degradations were not possible, the isolation of persistent metabolites of the CnF2n+i-(CH2-CH2-0)m-H compound generated by (3 and w oxidations of the terminal PEG unit of the non-ionic blend was reported, but environmental data about this type of compound are still quite rare [49]. TSI(+) ionisation results of the industrial blend Fluowet OTN have been reported in the literature [7,51]. Actual data of non-ionic fluorinated surfactants were applied using ESI- and APCI-FIA-MS(+) and -MS-MS(+), which reported the biodegradation of the non-ionic partly fluorinated alkyl ethoxylate compounds C F2 fi-(CH2-CH2-0)x-H in a lab-scale wastewater treatment process. 

While fast atom bombardment (FAB) [66] and TSI [25] built up the basis for a substance-specific analysis of the low-volatile surfactants within the late 1980s and early 1990s, these techniques nowadays have been replaced successfully by the API methods [22], ESI and APCI, and matrix assisted laser desorption ionisation (MALDI). In the analyses of anionic surfactants, the negative ionisation mode can be applied in FIA-MS and LC-MS providing a more selective determination for these types of compounds than other analytical approaches. Application of positive ionisation to anionics of ethoxylate type compounds led to the abstraction of the anionic moiety in the molecule while the alkyl or alkylaryl ethoxylate moiety is ionised in the form of AE or APEO ions. Identification of most anionic surfactants by MS-MS was observed to be more complicated than the identification of non-ionic surfactants. Product ion spectra often suffer from a reduced number of negative product ions and, in addition, product ions that are observed are less characteristic than positively generated product ions of non-ionics. The most important obstacle in the identification and quantification of surfactants and their metabolites, however, is the lack of commercially available standards. The problems with identification will be aggravated by an absence of universally applicable product ion libraries. 

Scheidweiler KB, Huestis MA. 2004. Simultaneous quantification of opiates, cocaine, and metabolites in hair by LC-APCI-MS/MS. Anal Chem 76 4358. 

Musshoff et al. [35] developed a method for the enantiomeric separation of the synthetic opioid agonist tramadol and its desmethyl metabolite using a Chiralpak AD column containing amylose tris-(3,5-dimethylphenylcarbamate) as chiral selector and a n-hexane/ethanol, 97 3 v/v (5mM TEA) mobile phase nnder isocratic conditions (1 mL/min). After atmospheric pressure chemical ionization (APCI), detection was carried out in positive-ion MS-MS SRM mode. The method allowed the confirmation of diagnosis of overdose or intoxication as well as monitoring of patients compliance. 

Dams et al. [18] developed a validated quantitative LC-APCI-MS-MS method for simultaneous determination of multiple illicit drugs and their metabolites in oral fluid. This substrate is being increasingly popular for forensic applications as it provides information on recent use, similarly to blood plasma/serum, although it can be obtained with a simple, noninvasive, collection. Sample pretreatment, though limited to protein precipitation with acetonitrile, was sufficient to avoid matrix effect (see Figure 20.2). 

Eight BDZs among the most frequently encountered in forensic toxicology (clonazepam, desal-kylflurazepam, diazepam, flunitrazepam, lorazepam, midazolam, nordiazepam and oxazepam) were determined in whole blood after solvent extraction with butyl chloride and fast isocratic separation using a C18 (100 x 4.6 mm x 5 (tm) column [61]. The mobile phase was composed of phosphate buffer (35mM, pH 2.1) and acetonitrile (70 30, v/v) and the flow rate was 2mL/min. Within less than 4 min of analysis time, the analytes could be successfully determined starting from therapeutic concentrations. Using HPLC coupled with APCI-MS-MS, Rivera et al. [62] set up a method for the detection of 18 BDZ and metabolites after butyl chloride extraction at alkaline pH in 0.5mL... 

Much data on the structure of flavonoids in crude or semipurified plant extracts have been obtained by HPLC coupled with MS, in order to obtain information on sugar and acyl moieties not revealed by ultraviolet spectrum, without the need to isolate and hydrolyze the compounds. In the last decade, soft ionization MS techniques have been used in this respect, e.g., thermospray (TSP) and atmospheric pressure ionization (API). However, the most used methods for the determination of phenols in crude plant extracts were the coupling of liquid chromatography (LC) and MS with API techniques such as electrospray ionization (ESI) MS and atmospheric pressure chemical ionization (APCI) MS. ESI and APCI are soft ionization techniques that generate mainly protonated molecules for relatively small metabolites such as flavonoids. 

The applicability of the APCI interface is restricted to the analysis of compounds with lower polarity and lower molecular mass compared with ESP and ISP. An early demonstration of the potential of the APCI interface is the LC-APCI-MS-MS analysis of phenylbutazone and two of its metabolites in plasma and urine (128). Other applications include the LC-APCI-MS analysis of steroids in equine and human urine and plasma (129-131), the determination of six sulfonamides in milk samples after a simple solid-phase extraction and LC separation (132), of tetracyclines in muscle at the 100 ppb level (133), of fenbendazole, oxfendazole, and the sulfone metabolite in muscle at the 10 ppb level, and of five thyreostats in thyroid tissue at the 1 ppm level (134). 

Over the past two decades, QMF-based quantification assays have become the technique of choice for quantification of drug candidates and their metabolites. Combining a mass spectrometer with LC provides an additional degree of selectivity and makes the combined technique the method of choice for quantitative bioanalysis of drugs and metabolites. Among the mass spectrometer types, QMF are ideal for coupling with LC and atmospheric pressure ionization sources (ESI, APCI, APPI, DART, DESI, etc.) because QMFs have the lowest voltage requirements and vacuum requirements. 

In this chapter, the utility of LC-electrospray ionization (ESI)-MS, LC-ESI-MS/MS, LC-APCI-MS, LC-APCI-MS/MS, and HDX-LC-MS for structural identification of metabolites and derivatives of loratadine and desloratadine is discussed. 

To demonstrate that the proposed methods are suitable for structural elucidation of isomeric metabolites and derivatives in biological matrices, human plasma was spiked with the mixture of DL, 6-OH-DL, 3-OH-DL, /V-OH-DL, and 1-pyridine-/V-oxide-DL. The resulting sample was extracted and analyzed by LC-MS and LC-MS/MS in ESI and APCI modes as described above. HDX was successfully performed online when the extract was injected directly onto the HPLC column without drying and reconstituting the sample in a deuterated solvent. In general, there were no differences between the results obtained for the spiked plasma extract and for the mixture of the standard compounds, which indicates that the LC-MS methods with HDX described here are applicable for the analysis drug-derived material in plasma or other biological matrices. 

For a compound which contains dimethylpyperidine substructure (shown on the left), isomeric metabolites oxygenated at positions 1, 2, and 3 can be easily distinguished without NMR by conducting a single LC-APCI-MS experiment on the TSQ Quantum. Loss of 16 is observed for oxidation at position 1 (/V-oxide), loss of 18 (H20) for aliphatic hydroxylation at position 3, while for aromatic hydroxylation at position 2 no significant in-source fragmentation is observed. 

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