Veronica Termopoli

Overcoming Matrix Effects in Liquid Chromatography−Mass Spectrometry

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.

Single-step LC/MS method for the simultaneous determination of GC-amenable organochlorine and LC-amenable phenoxy acidic pesticides.

Water pollution by organochlorine pesticides (OCPs) is considered as an analytical challenge, since these persistent and nonbiodegradable pollutants are not amenable by liquid chromatography coupled to atmospheric pressure ionization mass spectrometry (LC/API-MS). This represents a significant constraint in multiresidue analysis of real samples, when high polar, poorly volatile compounds are present as well. This paper reports the development of an innovative single-step method for the simultaneous determination of OCPs and polar pesticides belonging to the class of phenoxy acids in water samples. The method is based on an off-line solid-phase extraction (SPE) procedure with Carbograph 4 followed by liquid chromatography coupled to a direct electron ionization mass spectrometer (LC/direct-EI-MS). The direct-EI capability of acquiring high-quality EI spectra and operation in selected ion monitoring mode allowed a precise quantification of OCPs and phenoxy acids in a single chromatographic run without derivatization. The instrumental response was characterized by excellent sensitivity, linearity, and precision. The SPE recovery rates in river water gave values equal or better than 80% for most of the compounds. The method limits of detection (LODs) span from 0.002 to 0.052 microg/L, allowing the detection of the selected pesticides at the limits required by the European Union (EU) legislation for drinking water.

Electron ionization in LC-MS: recent developments and applications of the direct-EI LC-MS interface.

AbstractThe 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. FigureRange of HPLC amenable compound classes by LC-EIMS

The Rapid Measurement of Benzodiazepines in a Milk-Based Alcoholic Beverage Using QuEChERS Extraction and GC–MS Analysis

Benzodiazepines (BDZs) are widely used as tranquilizers and anti-depressive drugs in common clinical practice. However, their ready availability and their synergistic effects with alcohol make them attractive for criminal intentions. To prove criminal action for legal reasons, it is often necessary to analyze beverage residues from a crime scene. Milk-based alcoholic drinks (whiskey creams) are gaining popularity due to their lower alcohol content pleasant taste. However, the complexity of this sample, containing proteins and fatty acids, can mask the presence of drugs or other substances in standard analysis methods. These characteristics make whiskey creams highly suitable for illicit purposes. In this study, eight BDZs, including diazepam, chlordiazepoxide, clobazam, flunitrazepam, bromazepam, flurazepam, nitrazepam and clonazepam, were extracted from whiskey cream using the Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method and analyzed using GC-MS. The QuEChERS protocol can efficiently separate most of the matrix from the target compounds while maintaining acceptable recoveries. The presented method is simple and rapid and has been validated in terms of precision, accuracy and recoveries. Limits of detection and limits of quantitation were in the range of 0.02-0.1 and 0.1-0.5 µg/mL, respectively. Whiskey cream beverages, fortified with commercial drugs at 20 µg/mL, were extracted and analyzed demonstrating the applicability of the method in forensic analysis.

Rapid LC-MS method for the detection of common fragrances in personal care products without sample preparation

An LC‐MS method for the analysis of personal care and household products without sample preparation is presented. The method takes advantage of the Direct‐electron ionization (EI) LC‐MS interface for the quantitation of principal components, as well as for the identification of unknown or undeclared ingredients. The technique has proven its inertness toward matrix effects and the electron ionization allows quantitation and library identification. Commercially available products (shower gel, perfume, and hand cream) were diluted with methanol and injected directly into a nano‐LC column. Limonene, linalool, and citral were selected as target compounds because of their use as fragrances in toiletry and detergent products. These and all other fragrances are commonly determined with GC‐MS analysis, prior to sample cleanup, a procedure that can lead to analytes loss. The selected compounds are not detected with ESI because of their poor or very low response. Figures of merit and validation studies were executed and special attention was devoted to matrix‐effects evaluation, because a sample preparation procedure is not involved. No matrix effects were observed, and the repeatability was excellent even after several weeks of operation. Products composition was investigated in full scan mode to determine the presence of unknown or not listed ingredients.

A new liquid chromatography-mass spectrometry approach for generic screening and quantitation of potential genotoxic alkylation compounds without derivatization

One of the crucial tasks of pharmaceutical industry is to quantify the potential genotoxic impurities (PGIs) coming from the process of drug production. The European Medicines Agency (EMEA) imposes analytical testing limits in the order of μg/g, depending on drug dosage and exposure period, that means the need of a sensitive and selective method of analysis. Liquid chromatography coupled to electrospray ionization mass spectrometry (LC-ESI-MS) has been demonstrated as the most versatile approach to detect PGIs in complex matrices. However, time consuming derivatization processes are needed to enhance sensitivity and selectivity, and to overcome matrix effects (ME) that may arise from active pharmaceutical ingredients (APIs) or excipients. We propose the use of the Direct-EI LC-MS as an alternative approach to detect and quantify PGIs in drug formulations. The Direct-EI LC-MS interface is based on electron ionization (EI) which is well suited for the detection of low molecular weight compounds of different polarity, without derivatization and with no sign of ME. The method has been successfully applied to the detection of PGIs belonging to the class of alkylation agents. Calibration experiments show satisfactory linearity and precision data. Recoveries in low enriched samples spanned from 55 to 82%, and were not affected by ME. The method limits of detection (LODs), varying from 0.13 to 1.5 μg/g, were satisfactory for the quantitation of the target PGIs at the level required by regulatory agencies.

Negative Role of the Environmental Endocrine Disruptors in the Human Neurodevelopment.

The endocrine disruptors (EDs) are able to influence the endocrine system, mimicking or antagonizing hormonal molecules. They are bio-persistent for their degradation resistance in the environment. Our research group has investigated by gas chromatography–mass spectrometry (GC–MS) the EDs presence in 35 brain samples, coming from 27 cases of sudden intrauterine unexplained death syndrome (SIUDS) and 8 cases of sudden infant death syndrome (SIDS), collected by centralization in the last year (2015). More in detail, a mixture of 25 EDs has been subjected to analytical procedure, following standard protocols. Among the target analytes, some organochlorine pesticides, that is α-chlordane, γ-chlordane, heptachlor, p,p-DDE, p,p-DDT, and the two most commonly used organophosphorus pesticides (OPPs), chlorpyrifos and chlorfenvinfos, have been found in seven and three samples, respectively. The analytical procedure used to detect the presence of environmental EDs in cortex samples has been successfully implemented on SIUDS and SIDS victims. The environmental EDs have been found to be able to overcome the placental barrier, reaching also the basal ganglia assigned to the control of the vital functions. This finding, related to the OPPs bio-persistence, implies a conceptual redefinition of the fetal–placental and fetal blood–brain barriers: not real safety barriers but simply time-deferral mechanisms of absorption.

Liquid chromatography-electron ionization tandem mass spectrometry with the Direct-EI interface in the fast determination of diazepam and flunitrazepam in alcoholic beverages

This is the first application based on electron ionization (EI) using a Direct‐EI LC interface and MS/MS to detect unequivocally target compounds in a very small real sample. The determination and quantification of benzodiazepines in very small residues of beverages, collected at the scene of drug‐facilitated crimes are mandatory in legal procedures. A specific and sensitive analytical instrumentation is needed, involving little or no sample preparation. Here, a direct flow injection analysis of alcoholic beverages spiked with commercially available drugs containing diazepam and flunitrazepam is presented. The method proposed is very fast and requires neither sample preparation nor chromatographic separation. Linearity (R2) was between 0.9977 and 0.9992; LOD and LOQ spanned from 0.01 to 0.02 ng/μL and from 0.1 to 0.5 ng/μL, respectively; intra‐ and interday repeatabilities were between 1 and 8%. No matrix effects were observed from the comparison of the linear regression curves obtained in real fortified samples and in pure ethanol. Vodka, whisky, and white wine specimens were fortified with commercial drugs, Valium® and Rohypnol®, at two different concentrations (20 and 50 ng/μL) to simulate the typical amounts found in adulterated real samples and analyzed to demonstrate the method applicability to forensic analyses.

Pesticide exposure during pregnancy, like nicotine, affects the brainstem α7 nicotinic acetylcholine receptor expression, increasing the risk of sudden unexplained perinatal death

This study indicates the impact of nicotine and pesticides (organochlorine and organophosphate insecticides used in agriculture) on neuronal α7-nicotinic acetylcholine receptor expression in brainstem regions receiving cholinergic projections in human perinatal life. An in-depth anatomopathological examination of the autonomic nervous system and immunohistochemistry to analyze the α7-nicotinic acetylcholine receptor expression in the brainstem from 44 fetuses and newborns were performed. In addition, the presence of selected agricultural pesticides in cerebral cortex samples of the victims was determined by specific analytical procedures. Hypodevelopment of brainstem structures checking the vital functions, frequently associated with α7-nicotinic acetylcholine receptor immunopositivity and smoke absorption in pregnancy, was observed in high percentages of victims of sudden unexpected perinatal death. In nearly 30% of cases however the mothers never smoked, but lived in rural areas. The search for pesticides highlighted in many of these cases traces of both organochlorine and organophosphate pesticides. We detain that exposition to pesticides in pregnancy produces homologous actions to those of nicotine on neuronal α7-nicotinic acetylcholine receptor, allowing to developmental alterations of brainstem vital centers in victims of sudden unexplained death.

Application of Liquid Chromatography-Direct-Electron Ionization-MS in an in Vitro Dermal Absorption Study: Quantitative Determination of trans-Cinnamaldehyde

We propose a new analytical approach, based on liquid chromatography (LC) coupled to electron ionization mass spectrometry (EI-MS), using a Direct-EI interface, for dermal absorption evaluation studies. Penetration through the skin of a given compound is evaluated by means of in vitro assays using diffusion cells. Currently, the most popular approach for the analysis of skin and fluid samples is LC coupled to electrospray ionization tandem mass spectrometry (ESI-MS/MS). However, this technique is largely affected by sample matrix interferences that heavily affect quantitative evaluation. LC-Direct-EI-MS is not affected by matrix interference and produces accurate quantitative data in a wide range of concentrations. Trans-cinnamaldehyde was chosen as test substance and applied in a suitable dosing vehicle on dermatomed human skin sections. This compound was then quantified in aliquots of receptor solution, skin extract, cell wash, skin wash, carbon filter extract, cotton swab extract, and tape strip digest. On column limits of detection (LOD) and limits of quantitation (LOQ) of 0.1 and 0.5 ng/μL, respectively, were achieved. Calibration showed satisfactory linearity and precision for the concentration range of interest. Matrix effects (ME) were evaluated for all sample types, demonstrating the absence of both signal enhancement and signal suppression. The Direct-EI absorption profile was compared with that obtained with liquid scintillation counting (LSC), a recognized ME free approach. A good correlation was found with all samples and for the overall recovery of the dosed substance.