APCI phenols

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,... 

Figures 10 and 11 show the structure of the hindered phenolic antioxidant Irganox 1010 (Ciba) and its negative ion APCI mass spectra, respectively. Separation was achieved under the following LC conditions Column Aqua Cl 8 (Phenomenex) 3 pm, 150x2.00 mm, 15% carbon loading, proprietary end capping. Column Temp 50°C. Injection volume 5 pi.

Liquid chromatography, coupled to the different ionization sources, is generally the technique most used to characterize the phenolic profile in fruit and vegetable products. With regard to the source ionization, it seems that ESI is used more frequently than other sources, such as APCI or APPI. Another important aspect of this technique is the ionization of phenolic compounds. Negative ionization seems to be more suitable... 

While APEO cannot be ionised successfully under negative conditions and consequently for identification MS-MS(—) is not informative, the identification of all anionic APEO derivatives is possible in the negative ionisation mode. For some derivatives, negative as well as positive ionisation can be applied. The loss of the anionic moiety, however, must be taken into account if ionisation is performed in the positive mode. Di-NPEC surfactant homologues submitted to negative CID resulted in the prominent di-alkyl-phenolate ion at m/z 345 (Fig. 2.11.18(a) as shown with the homologue m/z 799 under CID conditions). Therefore, the application of the parent ion scan of m/z 345 in the negative ESI and APCI-FIA-MS-MS mode is very specific for the detection of all anionic derivatives of di-NPEO comparable in... 

Puig et al. [450] determined ng/1 levels of priority methyl-, nitro-, and chloro-phenols in river water samples by an automated on-line SPE technique, followed by liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure chemical ionization (APCI) and ion spray interfaces. 

In particular, the priority pollutant phenols (PPP), identified by EPA since the 1970s are widespread water pollutants that must receive the greatest attention due to their recognized toxicity. For the separation of eleven PPP, an ion-interaction reagent (HR) RP HPLC/UV method has been developed that allows limits of detection lower than 30 J,g in river waters, after LLE in dichlo-romethane and a 500-fold pre-concentration [82]. Through on-line SPE followed by both UV and electrochemical detection [83], 16 priority phenols have been determined in water samples with the LOD value for chlorophenols lower than 1 ng L [84]. LODs at ng L levels were obtained for all the PPPs in samples of river water, employing a relatively small volume of sample through an on-line SPE HPLC/MS method with an APCI source. 

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. 

Recent advances in electrospray ionization (ESI), atmospheric-pressure chemical ionization (APCI), thermospray, and particle beam LC-MS have advanced the analyst toward the universal HPLC detector, but price and complexity are still the primary stumbling blocks. Thus, HPLC-MS remains expensive and the technology has only recently been described. Early commercial LC-MS uses particle beam and thermospray sources, but ESI and APCI interfaces now dominate. Liquid chromatography MS can represent a fast and reliable method for structural analyses of nonvolatile compounds such as phenolic compounds (36,37), especially for low-molecular-weight plant phenolics (38), but the limited resolving power of LC hinders the widespread use of its application for phenolics as compared to GC-MS. 

Carbonyl chloride or acetic anhydride Picolinoyl chloride [64] 4-Nitrobenzoyl chloride [60] Pentafluorobenzoyl chloride [65] Acetic anhydride [66] Both phenolic OH and alcoholic OH LC-ESP/MS/ MS LC-APCI/ MS/MS GC-EP/MS LC-APCP/ MS2... 

Harris C.S. Burt A.J. Saleem A. Le P.M. MartineauL.C. HaddadP.S. Beimett S.A. L. Amason J.T. 2007. A single HPLC-PAD-APCI/MS method for the quantitative comparison of phenolic compoimds found in leaf, stem, root and fruit extracts of Vaccinium angustifolium. Phytochem. Anal. 18 161-169. 

Note that palmitic acid does not have a chromophore and would, therefore, not be visible in the UV trace. In general, negative ion APCI and ESI are sensitive to those compounds that can easily deprotonate (e.g., acids and phenols) or attach a negative ion either in the gas phase or in solution, while positive ion APCI and ESI are sensitive to compounds with relatively high proton affinity (e.g., amines and low oxidation state sulfur compounds). As ESI and APCI can be complementary, so positive ion and negative ion can be as well. Consider Fig. 11 which shows a more... 

M.A. Aramendia, V. Borau, 1. Garcia, C. Jimenez, F. Lafont, J.M. Marinas, F.J. Urbano, Qualitative and Quantitative analyses of phenolic compounds by LC and detection with APCI-MS, Rapid Commun. Mass Spectrom., 10 (1996) 1585. 

O. Jauregui, E. Moyano, M.T. Galceran, LC-APCI-MS for chlorinated phenolic compounds. Application to the analysis of polluted soil, J. Chromatogr. A, 823 (1998) 241. 

Positive-ion APCI was preferred by Petrovic and Barcelo [33] in the analysis of AEO and NPEO, while phenols and (halogenated) NPEC were analysed as deprotonated molecules by negative-ion electrospray ionization. 

The detection and identification of phenolic compounds, including phenolic acids, have also been simph-fied using mass spectrometry (MS) techniques on-hne, coupled to the HPLC equipment. The electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) interfaces dominate the analysis of phenohcs in herbs, fmits, vegetables, peels, seeds, and other plants. In some cases, HPLC, with different sensitivity detectors (UV, electrochemical, fluorescence), and HPLC-MS are simultaneously used for the identification and determination of phenolic acids in natural plants and related food products.In some papers, other spectroscopic instmmental techniques (IR, H NMR, and C NMR) have also been apphed for the identification of isolated phenolic compounds. 

Phenolic compounds Vaccinium angustifolium (lowbush blueberry) HPLC-DAD-APCI-MS 87... 

A study was carried out for LEE by the Soxhlet method and microwave-assisted extraction for the determination of the priority phenols in soil samples. Recoveries varied from 67 to 97% with RSD between 8 and 14% for LEE, and >70% for the MAP, except for nitrophenols that underwent degradation when the latter method was applied. LOD was from 20 ngg for 2,4-dimethylphenol to 100 ngg for pentachlorophenol. The best detection method for EC was atmospheric pressnre chemical ionization MS (APCI-MS). The most abnndant ions obtained by this detection method were [M — H] for the lowly chlorinated phenols and [M — H — HCl] for tri-, tetra- and pentachlorophenols . 

The determination of phenols was preferentially performed using GC-MS with analytes in underivatized or derivatized form, but LC-MS methods were also developed. API methods for the analysis of phenols in aqueous matrices were applied [315, 316, 317]. APCI-LC-MS was found to be more sensitive than ESI application despite the possibility of improving ESI-sensitivity by a post-column addition of diethyla-mine [317]. Detection limits were observed with 0.02-20 ng injected onto the column. The determination of alkylphenols and bisphenol A as compounds with endocrine disrupter potential was also performed by ESI-LC-MS from aqueous [318, 319] and sediment samples with detection limits in the low pg L range [346]. 

No signal by negative ESI or negative APCI. This indicates the absence of acidic or phenolic functional groups. 

Developments in LC-MS have probably been greater than in GC-MS though that too has seen significant advances. LC-atmospheric pressure chemical ionization (APCI)-mass spectrometry has become particularly important and has found numerous applications in the determination of, for example, industrial mass chemicals such as dyes, aromatic sulfonates, surfactants, and complexing agents, and also trace compounds such as drugs, endocrine-disrupting compounds, toxins, phenols. 

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