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Buprenorphine and its metabolites are routinely monitored to assess patient compliance with drug detoxification programs or as pain killers. A rapid method for the simultaneous analysis of buprenorphine, norbuprenorphine, and glucuronides in urine using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed. Urine samples were diluted in water containing formic acid 0.1% and directly injected into the UHPLC-MS/MS system without any sample pretreatment. Quality control (QC) samples, prepared using 20 different urine matrices, fortified at 3 concentration levels, were quantified using four deuterated internal standards. The accuracy values obtained spanned from 90 to 114% with repeatability lower than 10% also in the inter-day between batch experiments. Matrix effects (ME), evaluated before correction with internal standards using Matuszewski procedure, mainly affected the analysis of buprenorphine glucuronide. The use of deuterated internal standards (IS) for each analyte was necessary to compensate for ME and was essential in the determination of glucuronides. The method was applied to 30 real urine samples from patients under a detoxification therapy. Duplicate analyses were performed with the presented method and compared with another method which involves a standard hydrolysis procedure. Real sample results were compared showing a good performance agreement, with differences between the two methods lower than ±20% in the quantification results.

DiSTeVA, Universita` degli Studi di Urbino ‘‘Carlo Bo,’’Piazza Rinascimento, 6, 61029 Urbino, ItalyReceived 13 July 2010; received (revised) 22 November 2010; accepted 22 November 2010Published online 8 March 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/mas.20329This review article will give an up-to-date and exhaustiveoverview on the efficient use of electron ionization (EI) tocouple liquid chromatography and mass spectrometry (LC–MS) with an innovative interface called Direct-EI. EI is basedon thegas-phase ionization of the analytes, and it is suitable formany applications in a wide range of LC-amenable compounds.In addition, thanks to its operating principles, it preventsunwelcome matrix effects (ME). In fact, although atmosphericpressure ionization (API) methodologies have boosted the use ofLC–MS, the related analytical methods are sometime affectedby inaccurate quantitative results, due to unavoidable andunpredictable ME. In addition, API’s soft ionization spectraalways demand for costly and complex tandem mass spectrom-etry (MS/MS) instruments, which are essential to acquire an‘‘information-rich’’ spectrum and to obtain accurate quantita-tive information. In EI a one-stage analyzer is sufficient for aqualitative investigation and MS/MS detection is only used toimprove sensitivity and to cut chemical noise. The technologyillustrated here provides a robust and straightforward accessto classical, well-characterized EI data for a variety ofLC applications, and readily interpretable spectra for a widerange of areas of research. The Direct-EI interface canrepresent the basis for a forthcoming universal LC–MSdetector for small molecules. # 2011 Wiley Periodicals, Inc.,Mass Spec Rev 30:1242–1255, 2011Keywords: LC–MS; nano-HPLC; electron ionization; Direct-EI interface; matrix effects

The purpose of this article is to underline the possibility of efficiently using electron ionization (EI) in liquid chromatography (LC) and mass spectrometry (MS). From a historical perspective, EI accompanied the first attempts in LC-MS but, owing to several technical shortcomings, it was soon outshined by soft, atmospheric pressure ionization (API) techniques. Nowadays, two modern approaches, supersonic molecular beam LC-MS and direct-EI LC-MS, offer a valid alterative to API, and preserve the advantages of EI also in LC-MS applications. These advantages can be summarized in three crucial aspects: automated library identification; identification of unknown compounds, owing to EI extensive fragment information; inertness to coeluted matrix interferences owing to very unlikely ion–ion and ion–molecule interactions in the EI gas-phase environment. The direct-EI LC-MS interface is a simple and efficient solution able to produce high-quality, interpretable EI spectra from a wide range of low molecular weight molecules of different polarity. Because of the low operative flow rates, this interface relies on a nano-LC technology that helps in reducing the impact of the mobile phase on the gas-phase environment of EI. This review provides an extensive discussion on the role of EI in LC-MS interfacing, and presents in detail several performance aspects of the direct-EI LC-MS interface, especially in terms of response, mass-spectral quality, and matrix effects. In addition, several key applications are also reported.

A major limitation in quantitative analysis with electrospray ionization mass spectrometry (ESI-MS) is represented by the so-called matrix effects in which the matrix coextracted with the analytes can alter the signal response, causing either suppression or enhancement, resulting in poor analytical accuracy, linearity, and reproducibility. In the direct electron ionization liquid chromatography-mass spectrometry (direct-EI LC-MS) interface the ionization process is based on electron impact ionization, and it occurs in the gas phase and is not influenced by coeluted matrix compounds. In this work we quantitatively evaluated matrix effects on enriched environmental and biological samples, with different extraction procedures, using ESI and direct-EI LC-MS. As expected, the samples analyzed with direct-EI were not affected by matrix composition, whereas with ESI we observed either signal suppression or enhancement, depending on the sample nature.