1,721,109 research outputs found
Atmospheric pressure photoionization mass spectrometry
No full textAtmospheric pressure photoionization (APPI) is the last arrival in the family of atmospheric pressure ionization (API) methods to couple mass spectrometry (MS) to liquid-phase separation techniques. The basic idea was to further extend the fields of application of liquid chromatography (LC)–MS to those molecules that are not, or are poorly amenable, to electrospray (ESI) or APCI. The present review explores the literature. After a short introduction with an historical background and the premises for its development, we describe the technique, its physical principles, and the factors that affect its efficiency. The review also presents a survey of applications in different fields
Piano di risanamento e tutela dalle esposizioni ai campi elettromagnetici del Comune di Aprilia
No full textIl Piano di risanamento e tutela dalle esposizioni ai campi elettromagnetici del Comune di Aprilia, è stato redatto nel 2002 su incarico del comune di Aprilia. Si compone di una relazione di piano, di alcuni studi di settore (Percezione sociale del problema "elettrosmog"; Misurazioni sul campo dei valori di c.e.m; Esperienze di reti di monitoraggio esposizione c.e.m.; Programmi di sviluppo degli enti gestori di telefonia mobile; Regolamenti comunali in materia di tutela alla esposizione ai c.e.m.; Quadro normativo di riferimento), di tavole di indagine e di progetto, di un Regolamento comunale per la verifica di compatibilità territoriale dei sistemi radio elettrici ad elevata frequenza (100 Khz - 300 GHz)
direct determination of the ratio of tetrahydrocortisol+allo-tetrahydrocortisol to hydrocortisone in urine by lc-ms-ms
No full textThe 11β-hydroxysteroid dehydrogenase (11β-HSD) is responsible for the interconversion of both the hormonally inactive cortisone and the active cortisol. This enzyme activity, which has implications in the pathogenesis of numerous diseases, is reflected in the ratio of tetrahydrometabolites of cortisol (allo-tetrahydrocortisol and tetrahydrocortisol) to those of cortisone (tetrahydrocortisone). Several methods have been proposed in the literature to determine such a ratio in urine. Most of them require tedious and extensive extraction and derivatization steps and make use of gas-chromatographic techniques, including gas chromatography coupled to mass spectrometry (GC–MS). We present here an alternative approach for the direct determination of such a ratio in urine by using liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS–MS), based on a minimal sample treatment. Actually, the limit of detections (LODs) for pure standards in water permitted a simple dilution of the urine samples prior to the analysis, hence, an accurate optimization of the high performance liquid chromatography (HPLC) separation was needed in order to get rid of the severe influence of the urine matrix on the ionization efficiency. Besides, the nature of some interfering species was deeply investigated, as well as the suitability of some commercial deuterated steroids as internal standards. All these led to the final method, which was based on a HPLC separation on a C8 column and a ternary gradient water/methanol/acetonitrile. In parallel, an appropriate sample preparation was set up, which consisted of an enzymatic hydrolysis of the conjugated species and a followed 1:20 dilution. Preliminary measurements on real urine samples were performed as well
Linear alkylbenzensulphonic acids (LAS) oxidation by H2O2 and O2: an investigation by gas- and liquid-chromatography coupled with mass spectrometry
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