APCI quantification

Factors may be classified as quantitative when they take particular values, e.g. concentration or temperature, or qualitative when their presence or absence is of interest. As mentioned previously, for an LC-MS experiment the factors could include the composition of the mobile phase employed, its pH and flow rate [3], the nature and concentration of any mobile-phase additive, e.g. buffer or ion-pair reagent, the make-up of the solution in which the sample is injected [4], the ionization technique, spray voltage for electrospray, nebulizer temperature for APCI, nebulizing gas pressure, mass spectrometer source temperature, cone voltage in the mass spectrometer source, and the nature and pressure of gas in the collision cell if MS-MS is employed. For quantification, the assessment of results is likely to be on the basis of the selectivity and sensitivity of the analysis, i.e. the chromatographic separation and the maximum production of molecular species or product ions if MS-MS is employed. 

Sidwell and Zondervan [10] used LC-MS with APCI detection for the identification and quantification of extractable antioxidants from food-contact plastic materials. Identification is based on the presence of the molecular ion (M + FI)+, (M—H) , other key ions or on further ion breakdown (MSn) transitions. The following antioxidant/stabiliser types were examined hindered phenols,... 

Exact mass Retent. Primary ion for time (mins) quantification +/- 0.1 m/z (-ve APCI) Confirmatory ions MS2 or other quantification ions +/— 0.1 m/z — ve APCI... 

Ornelas-Paz JJ, Yahia EM and Gardea A. 2007. Identification and quantification of xanthophyll esters, carotenes and tocopherols in the fruit of seven Mexican mango cultivars by liquid chromatography-APcI+-time of flight mass spectrometry. J Agric Food Chem 55 6628-6635. 

Fig. 2.5.13. Ion current traces of APCI-FIA-MS(+) examinations of compound interferences performed in multiple ion detection mode applied for quantification of pure AE blend (A AE b,d,f recorded between 0 and 4.0 min), pure quat (B a), betaine (B c) and FADA (B e) blend (cf. B Selected compounds a,c,d recorded between 4.0 and 8.5 min). In mixtures of AE with quat, betaine or FADA, respectively, all constituents were determined by MID (cf. C Mixture AE/quat (a,b), AE/betaine (c,d), and AE/FADA (e,f) (recorded between 8.5 and 14.0 min, respectively). Ions recorded in MID mode for quantification AE (all ions starting at m/z 306 + A 44 and ending at 966), quat m/z 214 and 220, betaine m/z 184, 212, 240, 268, 285, 296, 313, 324 and 341, FADA m/z 232, 260,...

API-MS methods have been successfully applied to the quantification of M2D-C3-0-(E0)n-Me, with reliable and reproducible results obtained after online HPLC separation [29,30]. The method was used to quantify recoveries of the surfactant from the surface of plant foliage and from solid substrates under controlled laboratory conditions. Extension of the method to environmental samples has not been investigated. The entire linear dynamic range for HPLC-APCI-MS was not determined, but linearity was observed within the required... 

Results obtained for the application of HPLC—APCI—MS to the quantification of M2D—C3—O—(EO ) —CH3 recoveries from Chenopo-dium album plant foliage are shown in Table 2.8.5, as compared with HPLC-LSD analysis [29], The improvements in the sensitivity and reproducibility were obtained with the use of HPLC—APCI—MS as the analytical method and the HPLC—APCI—MS method also enabled detection of the n = 3 M2D-C3-0-(E0) -CH3 molecule. 

An industrial blend of ASs presented with its general structural formula in Fig. 2.11.4 was examined to elaborate a method for their quantification in trace amounts. ASs (CraH2n+i-0-S03) only were applied as surfactants in special applications. Moreover, these compounds are the basis of synthesis in the production of AES and therefore the trace analysis of AS in AES is an important task to estimate impurities. Applying APCI-FIA-MS(-), the overview spectrum in Fig. 2.11.5(a) containing [M - H] ions at mlz 265 and 293 was obtained. The mixture then was separated by RP-Cig and recorded by ESI-MS( —). The same [M - H] ions could be recognised that belonged to... 

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. 

For sensitive quantification in LC-MS analysis of non-ionic surfactants, selection of suitable masses for ion monitoring is important. The nonionic surfactants easily form adducts with alkaline and other impurities present in, e.g. solvents. This may result in highly complicated mass spectra, such as shown in Fig. 4.3.1(A) (obtained with an atmospheric pressure chemical ionisation (APCI) interface) and Fig. 4.3.2 (obtained with an ESI interface). 

Fig. 4.3.4. Effect of composition of a technical mixture used for calibration in the quantification of APEO concentrations of influents and effluents from a wastewater treatment plant. (A) LC-ESI-MS (B) LC-APCI-MS.

A method has been reported for the quantification of five fungicides (shown in Figure 5.39) used to control post-harvest decay in citrus fruits to ensure that unacceptable levels of these are not present in fruit entering the food chain [26], A survey of the literature showed that previously [27] APCI and electrospray ionization (ESI) had been compared for the analysis of ten pesticides, including two of the five of interest, i.e. carbendazim and thiabendazole, and since it was found that APCI was more sensitive for some of these and had direct flow rate compatibility with the HPLC system being used, APCI was chosen as the basis for method development. 

With the development of sophisticated ionization techniques including electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), HPLC-MS techniques have been successfully applied to the online analysis of ginsenosides in extracts and biological fluids (Fuzzati, 2004). In terms of sensitivity and specificity, an MS detector is better than UV or ELSD. Among the various MS methods, the HPLC-MS-MS (or just LC-MS-MS) technique is to date the most sensitive method for detection and quantification of ginsenosides. 

Column size is another important consideration. For equipment designed for most routine laboratory HPLC situations the relative sensitivity of APTelectrospray instruments is better at low flow rates (0.2-0.8 mL/min) whereas the relative sensitivity of APCI instruments is enhanced at high flow rates (0.5-2 mL/min). As a result, small columns are appropriate for API-electrospray/MS and, if only one or two compounds of interest are found in a particular sample, high-resolution separations are not necessary. For APTelectrospray analysis of complex samples, 150 mm x 4.1 mml.D., 3 pm columns (flow 0.5-1.0 mL/min) are usually sufficient. For drug quantification involving analysis of single or low numbers of compounds, small columns such as 30 mm x 2.1 mm I.D., 3.5 pm columns (flow rate 0.2-0.4 mL/min) provide sufficient separation and a saving in both column cost and solvent utilization. The reduced injection volume required for the small columns often results in better resolution and increased sensitivity. 

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

Liquid chromatography-APCI-MS with NI and PI was used for the trace determination of several OPPs in groundwater. The limit of quantification varied between 5 and 37 ng/L in PI. Under the NI mode of operation, only the parathion group (both parathions and fenitrothion) had a better sensitivity than with the PI mode, with quantitation limit of 5-15 ng/L, whereas the rest of the pesticides had 2-4 times higher limits as compared to those in PI mode (52). 

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. 

Tremblay, P., Groleau, P. E., Ayotte, C., Picard, P., and Viel, E. (2008). High-throughput screening and quantification of doping agents in urine using LDTD-APCI-MS/MS. In... 

Yu, K., Di, L., Kems, E. H., Li, S. Q., Alden, P., and Plumb, R. S. (2007). Ultra-performance liquid chromatography/tandem mass spectrometric quantification of structurally diverse drug mixtures using an ESI-APCI multimode ionization source. Rapid Commun. Mass Spectrom. 21 893-902. 

Another LC-APCI-MS method has been developed and validated by Zhang et al. for the identification and quantification of zaleplon in human plasma using estazolam as an IS. After the addition of estazolam and 2.0 M sodium hydroxide solution, plasma samples were extracted with ethyl acetate and then the organic layer was evaporated to dryness. The reconstituted solution of the residue was injected onto a prepacked Shim-pack VP-ODS C18 (250 mm x 2.0 mm i.d.) column and chromatographed with a mobile phase comprised methanol-water (70 30) at a flowrate of 0.2 ml/min. 

LLE liquid-liquid extraction, SPE solid phase extraction, LPME liquid-phase microextraction, ESI electrospray ionization, APCI atmospheric pressure chemical ionization, SSI sonic spray ionization, Q quadrupole, QqQ triple quadrupole, TOF time-of-flight, IT ion trap, IS internal standard, CV coefficient of variation, MRE mean relative error, LOD limit of detection, LLOQ lower limit of quantification... 

Beyer J, Peters FT, Kraemer T, Maurer HH (2007) Detection and validated quantification of toxic alkaloids in human blood plasma - comparison of LC-APCI-MS with LC-ESI-MS/MS. J Mass Spectrom 42 621-633... 

Kurilich, A.C. Britz, S.J. Clevidence, B.A. Novotny, J.A. 2003. Isotopic labeling and LC-APCI-MS quantification for investigating absorption of carotenoids and phyl-loquinone Som kale (Brassica oleracea). J. Agric. Food Chem. 51 4877-4883. 

In this regard, our laboratory demonstrated a method for the quantification of STI571 and its main metabolite, CGP 74588, in human plasma using a semi-automated PPT method and a relatively rapid LC/APCI/MS/MS analysis. The assay exhibited an excellent linearity from 4.00 to 10,000 ng/mL in human plasma. The method was utilized for the analysis of thousands of clinical samples. Furthermore, the method was routinely amenable to analysis of STI571 and CGP 74588 in cerebrospinal fluids (CSF), gastrointestinal stromal tumor (GIST) biopsy specimens, and toxicokinetic studies (data not shown). 

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