Analytical Methods (v.8, #42)

Front cover (7559-7560).

Contents list (7561-7566).

The human body is amazingly chirally selective, and consequently enantiopure drugs are essential for treating disease. Nearly 50% of drugs are chiral wherein pharmacological activity resides with the eutomer (pharmacologically active enantiomer) whereas the distomer (inactive/less potent/equally potent/different pharmacological activity/toxic enantiomer) metabolizes by a different pathway and creates unnecessary burden on the body. A teratogenic (toxic) isomer in a racemic drug creates side-effects, genetic diseases, or may cause death in the case of high dosage. Nowadays, market approval of enantiopure drugs has increased exponentially whereas it has tremendously decreased for racemic and achiral drugs. An expensive process is the main drawback in obtaining enantiopure drugs. Different methods such as chromatography, spectroscopy, and thermal analysis are available for optical purity determination. However, only a few chromatographic methods are useful on an industrial scale. In the present review, racemic resolution and optical purity determination methods are discussed with examples. In addition to this, eutomers and distomers of different drugs containing a single chiral center are also reported.

Synthesis of high-quality metal nanoparticle (NP) decorated graphene (GN) with uniform and controllable nanostructures has attracted considerable attention due to its excellent electronic structure and optical properties. Herein, we develop a facile and robust process for tailoring hexanethiol (SH)-modified Ag NP-decorated graphene nanomaterials (Ag/GN-SH) by coupling in situ reduction and the covalent assembly technique. The as-prepared Ag/GN-SH combines adequate Raman “hot spots” among the high-density Ag NPs and the excellent adsorption performance of GN, making it an excellent surface-enhanced Raman scattering (SERS) substrate for highly selective and sensitive detection of PAHs. Moreover, the Ag/GN-SH can be used as a solid-phase extraction (SPE) adsorbent for qualitative and quantitative detection of PAHs in seawater from their discriminant SERS peaks. The Ag/GN-SH-based SPE-SERS is effective over a wide range of concentrations (0.1 nM to 0.5 mM) for PAHs, with tens of pM detection limits [signal to noise ratio (S/N) = 3], and the detection concentration deviation is less than 15% between the SPE-SERS and GC-MS. This study not only offers a new method for on-site removal of PAHs but also provides a strategy for simultaneous multiplexed detection of PAHs.

Whole blood analysis using microfluidic plasma separation and enzyme-linked immunosorbent assay devices by Hisashi Shimizu; Mariko Kumagai; Emi Mori; Kazuma Mawatari; Takehiko Kitamori (7597-7602).
In this study, a microfluidic plasma-separation device that realizes the whole blood analysis of C-reactive protein (CRP) using one drop of blood is developed. A small, fast, and easy-to-operate blood-testing device is desirable for point-of-care testing, home medical care, and medical cost reduction. Recently, significant advances have been made in analytical instrumentation, and an enzyme-linked immunosorbent assay (ELISA) of a 1 μL plasma sample has previously been realized. Moreover, recent developments in microfluidics have led to the miniaturization of analytical instruments. However, analytical centrifuges that are conventionally used for the separation of plasma and blood cells are very large and cumbersome to combine with microfluidic devices. Therefore, we propose a plasma-separation device combining microfluidics and membrane filtering. Herein, the proposed plasma-separation device is applied to whole blood analysis using one drop of blood. Specifically, the device is designed and fabricated to realize high plasma-separation efficiency via the evaluation of fluidic resistance of a porous membrane. Then, the quality of the plasma separated using the device is evaluated and compared with that of the plasma separated using a conventional centrifuge. Our results reveal that the microfluidic plasma-separation device can efficiently provide a sample for the ELISA of CRP using one drop (50 μL) of whole blood. The total analysis time including plasma separation and ELISA is approximately 25 min.

Rapid discrimination of Enterococcus faecium strains using phenotypic analytical techniques by Najla AlMasoud; Yun Xu; David I. Ellis; Paul Rooney; Jane F. Turton; Royston Goodacre (7603-7613).
Clinical isolates of glycopeptide resistant enterococci (GRE) were used to compare three rapid phenotyping and analytical techniques. Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) were used to classify 35 isolates of Enterococcus faecium representing 12 distinct pulsed-field gel electrophoresis (PFGE) types. The results show that the three analytical techniques provide clear discrimination among enterococci at both the strain and isolate levels. FT-IR and Raman spectroscopic data produced very similar bacterial discrimination, reflected in the Procrustes distance between the datasets (0.2125–0.2411, p < 0.001); however, FT-IR data provided superior prediction accuracy to Raman data with correct classification rates (CCR) of 89% and 69% at the strain level, respectively. MALDI-TOF-MS produced slightly different classification of these enterococci strains also with high CCR (78%). Classification data from the three analytical techniques were consistent with PFGE data especially in the case of isolates identified as unique by PFGE. This study presents phenotypic techniques as a complementary approach to current methods with a potential for high-throughput point-of-care screening enabling rapid and reproducible classification of clinically relevant enterococci.

Physiological performance factors of a catalase-based paired microelectrochemical biosensor, developed for real-time neurochemical monitoring of hydrogen peroxide (H2O2), were determined in the in vitro environment. The excellent ascorbic acid (AA) rejection characteristics and high sensitivity of the paired H2O2 sensor were assessed and verified. The highly suitable response time of the H2O2 sensor was demonstrated and the limit of detection of this sensor was calculated as ca. 0.075 μM. The H2O2 sensor was selective over the electroactive substance Mercaptosuccinate which is used in vivo to disrupt the enzymatic degradation of brain H2O2. The H2O2 sensing element of this paired design was impervious to an acidic/basic shift in environmental pH (6.5/8.0) relative to physiological levels (7.4). The influence of a temperature transition (ca. 23 °C to 37 °C) and a physiological temperature fluctuation expected to be found in vivo (1–4 °C), on the response of the paired H2O2 sensor was deemed negligible and consistent with other amperometric methods. The enzymatic component of the paired H2O2 sensor was found to be stable over a 14 day period of continuous ex vivo brain tissue exposure.

Characterization of TLR4/MD-2-modified Au sensor surfaces towards the detection of molecular signatures of bacteria by Kaveh Amini; Iraklii I. Ebralidze; Nora W. C. Chan; Heinz-Bernhard Kraatz (7623-7631).
Lipopolysaccharides (LPSs), also known as endotoxins, can be fatal even at low concentrations. As a result, the development of novel methodologies for LPS detection has been continuously in the focus of research. Biosensors, which employ a bio-recognition element on a transducer surface, are on the cutting edge of these novel technologies. In this report, Au surfaces modified with TLR4/MD-2 through Lip-NHS linkers with an ultimate potential application as biosensors for LPS detection have been characterized and investigated using X-ray photoelectron spectroscopy, quartz crystal microbalance and electrochemical techniques. Also the interaction between TLR4/MD-2 immobilized on Au surfaces with LPSs has been studied to evaluate the possibility of LPS detection.

Direct quantitative analysis of cocaine by thin layer chromatography plus a mobile phone and multivariate calibration: a cost-effective and rapid method by Flávia Tosato; Thalles R. Rosa; Camilo L. M. Morais; Adriano O. Maldaner; Rafael S. Ortiz; Paulo R. Filgueiras; Kássio M. Gomes Lima; Wanderson Romão (7632-7637).
The detection and quantification of trace amounts of illicit substances such as crack-cocaine continues to be important for law enforcement and clinical medicine. Conventional methods available for crack-cocaine and adulterant detection include chromatography and presumptive testing. Here, we report a simple and inexpensive approach that employs a cell phone which images of thin-layer chromatography (TLC) plates were acquired to directly quantify cocaine and phenacetin in illicit samples seized in Brazil from 2012. Integration of a mobile application with a cell phone enabled immediate processing of TLC results, which eliminated the need for a bulky and expensive spectrometer. Partial least squares (PLS) regression was built using the RGB image system from the TLC plates containing cocaine (0.50 to 16.00 mg mL−1) and phenacetin (0.00 to 14.00 mg mL−1) as adulterants, acquired from a cell phone camera. The RMSEP values obtained for cocaine and phenacetin models were, respectively, equal to 1.60 and 1.36 mg mL−1, and their precision was respectively equal to 6.22 and 7.14%. No statistical difference was observed at a confidence level of 95% for both analytes calculated by the proposed method and those found by the reference method using gas chromatography with flame ionization detection (GC-FID), proving the reliability of the imaging method as an alternative approach for these assays.

The detection of the aroma and flavour volatile compounds of spices is key in product quality control. Accordingly, it is necessary to develop new electronic sensing systems for food adulteration control and authenticity assessment for protecting customer's health. In this work, the capability of the E-nose and VE-tongue in combination with SPME-GC-MS to correctly discriminate between several cumin samples of different geographical origins and to detect their adulteration, by using unsupervised and supervised chemometric tools, was evaluated. Regarding the aroma profile, eleven volatile compounds were characterized by SPME-GC-MS; all of them were found in cumin powder while only eight are found in cumin seeds. The main volatile compounds detected were β-pinene, m-cymene, γ-terpinene, cuminaldehyde and cuminic alcohol, in different proportions depending on the cumin sample form (seed or powder). In summary, the results obtained are sufficiently encouraging as a starting point for the development of new electronic sensing systems with more improvement in the reliability of the sensor's performance as well as chemometric tools in order to deal with a complex dataset.

Application of capillary ion chromatography and capillary ion chromatography coupled with mass spectrometry to determine methanesulfonate and inorganic anions in microliter sample volumes of Antarctic snow and ice by Estrella Sanz Rodriguez; Meredith Nation; Andrew D. Moy; Mark A. J. Curran; Paul R. Haddad; Pavel N. Nesterenko; Brett Paull (7650-7660).
The high costs associated with logistics and the collection of Antarctic ice-cores demands scientists to extract the absolute maximum data from these precious resources. Typically, the chemical analyses of these valuable ice cores, and/or of ice cores from low snow accumulation sites, requires the ice samples to be as small as possible. Despite having a relatively long history within the research lab, recently, capillary ion chromatography (Cap-IC) has become a commercial reality allowing its use as a new analytical capability for the determination of inorganic and organic ions based upon reduced sample volumes. A quantitative study on the simultaneous determination of organic and inorganic anions, including fluoride, methanesulfonate, chloride, sulfate and nitrate anions in Antarctic ice and snow samples was carried out. The new Cap-IC method necessitated only 40 μL of injection volume to attain the analytical performances required, compared to the usual 1–5 mL. In this work, the Cap-IC was also coupled with mass spectrometry, and optimised for the identification and quantification of methanesulfonate. The limit of detection for methanesulfonate was decreased to 0.07 μg L−1 using a hyphenated technique, being the lowest detection limit reported until now in the literature for any ion chromatography based method. To validate the new analytical methods, a comparative study was performed with statistical evaluation of the anion concentrations obtained for snow pit samples from the Aurora Basin North, East Antarctica site, by three separate ion chromatography based methods, namely, standard ion chromatography, and Cap-IC coupled to either suppressed conductivity or mass spectrometry detection.

The performance of single and multi-collector ICP-MS instruments for fast and reliable 34S/32S isotope ratio measurements by Ondrej Hanousek; Marion Brunner; Daniel Pröfrock; Johanna Irrgeher; Thomas Prohaska (7661-7672).
The performance and validation characteristics of different single collector inductively coupled plasma mass spectrometers based on different technical principles (ICP-SFMS, ICP-QMS in reaction and collision modes, and ICP-MS/MS) were evaluated in comparison to the performance of MC ICP-MS for fast and reliable S isotope ratio measurements. The validation included the determination of LOD, BEC, measurement repeatability, within-lab reproducibility and deviation from certified values as well as a study on instrumental isotopic fractionation (IIF) and the calculation of the combined standard measurement uncertainty. Different approaches of correction for IIF applying external intra-elemental IIF correction (aka standard-sample bracketing) using certified S reference materials and internal inter-elemental IIF (aka internal standardization) correction using Si isotope ratios in MC ICP-MS are explained and compared. The resulting combined standard uncertainties of examined ICP-QMS systems were not better than 0.3–0.5% (uc,rel), which is in general insufficient to differentiate natural S isotope variations. Although the performance of the single collector ICP-SFMS is better (single measurement uc,rel = 0.08%), the measurement reproducibility (>0.2%) is the major limit of this system and leaves room for improvement. MC ICP-MS operated in the edge mass resolution mode, applying bracketing for correction of IIF, provided isotope ratio values with the highest quality (relative combined measurement uncertainty: 0.02%; deviation from the certified value: <0.002%).

Olive oil density characterization through microfluidic detection using acoustic signatures (MIDAS) by C. McIntosh; S. Sherman; M. T. Napoli; K. Turner; B. Bamieh; S. Pennathur (7673-7677).
The fraudulent business derived from olive oil adulteration fuels a multi-million dollar underground economy. Current methods to identify adulteration in olive oils, although very sensitive, are costly and time consuming. We propose a miniaturized platform, which we call MIDAS – microfluidic detection using acoustic signatures – that determines the density of an unknown solution by measuring the time delay of an ultrasound wave traveling within the solution. By post-processing the data using a custom Matlab script that implements a matched filter and an ad hoc pre-filter, we show a sensitivity of 0.36% or 3.2 kg m−3. MIDAS could be used to determine the density of a wide variety of samples, including biological fluids for health monitoring.

Chemical profiles of Robusta and Arabica coffee by ESI(−)FT-ICR MS and ATR-FTIR: a quantitative approach by Radigya M. Correia; Laiza B. Loureiro; Rayza R. T. Rodrigues; Helber B. Costa; Bruno G. Oliveira; Paulo R. Filgueiras; Christopher J. Thompson; Valdemar Lacerda; Wanderson Romão (7678-7688).
This paper reports a method to quantify Robusta coffee in Arabica coffee blends using univariate and multivariate models. Coffee samples were analyzed by negative-ion mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI(−)FT-ICR MS) and by attenuated total reflection Fourier transform spectroscopy in the mid-infrared region (ATR-FTIR). To build the univariate calibration model with ESI(−)FT-ICR MS data, 12 samples of Arabica coffee adulterated with different proportions of Robusta coffee and doped with an internal standard were used. For the ATR-FTIR analysis, a higher variability of adulteration was employed with a total of 23 blend samples, and a partial least squares (PLS) regression model was proposed. The obtained univariate calibration model had limits of detection (LOD) and quantification (LOQ) of 0.2 and 0.3 wt%, respectively, whereas the PLS model with ATR-FTIR data had LOD and LOQ values of 1.3 and 4.3 wt%. Repeatability and intermediate precision for the ESI(−)FT-ICR MS model were 4 wt% and 5 wt%, respectively, and for the model with ATR-FTIR data both were 1.7 wt%. The proposed methodologies also enable the prediction of Robusta coffee adulteration in Arabica coffee commercial samples.

Species identification of ancient leather objects by the use of the enzyme-linked immunosorbent assay by Yi Liu; Yi Li; Runxing Chang; Hailing Zheng; Yang Zhou; Menglu Li; Zhiwen Hu; Bing Wang (7689-7695).
Leather is one of the indispensable necessities in human daily life. However, the identification of ancient leather, especially species identification, is a great challenge for archaeologists and conservation scientists. Fortunately, the non-competitive indirect enzyme-linked immunosorbent assay (ELISA) offers a particularly promising approach for the analysis of ancient leather because of its advantageous properties such as high efficiency, low-cost, and high sensitivity and specificity. This study focuses on the use of a non-competitive indirect ELISA method to identify the species of ancient leather. Three ancient leather samples, which were unearthed from the desert in the Xinjiang area, were characterized using an analytical Oxford ISIS energy dispersive spectrometer (EDS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and ELISA. Two independent indirect ELISAs were established, and the results from the two methods were used in the determination of animal species. It was shown that all the three ancient leather samples were recognized by both anti-collagen-I antibody (ab23446) and anti-collagen-I antibody (ab117119), which indicates that the species of these leathers belong to cow. This is the first study to use an immunological method for the characterization of ancient leather. It is concluded that the ELISA method has the potential to become a powerful analytical tool in the identification of ancient proteinous materials.

Multiscale X-ray fluorescence mapping complemented by Raman spectroscopy for pigment analysis of a 15th century Breton manuscript by K. V. Manukyan; B. J. Guerin; E. J. Stech; A. Aprahamian; M. Wiescher; D. T. Gura; Z. D. Schultz (7696-7701).
We present complementary multiscale X-Ray Fluorescence (XRF) mapping and Raman spectroscopy to analyze pigments in a rare medieval Breton manuscript. Once a codex of 129 parchment leaves in the Bergendal Collection (olim MS 8), the manuscript was sold at auction and then subsequently dismembered page-by-page. The leaves were then disseminated on the open market by the biblioclast. The analysis was performed on 12 illustrated leaves (samples) out of the 92 which were recovered by Rare Books and Special Collections at the University of Notre Dame. The combination of elemental mapping with molecular spectroscopy permits an unprecedented analysis of the illuminations in the manuscript. XRF scanning provides both elemental analysis of large-scale objects as well as microscopic examination of individual pigment particles. The XRF mapping indicates distinctive elemental distributions within specific regions of interest. Raman spectroscopy of these selected areas identifies the molecular composition of the pigments. This combination of analytical techniques provides an in-depth characterization of the Breton manuscript on the macro, micro- and molecular levels. The results from different leaves confirm that pigments and inks of illustrated leaves belong to the same palette. The results also show the pigments utilized in illustrations, text, and borders are identical indicating that the manuscript was prepared in a single setting, by a single artisan or a small number of artisans working closely.

Multivariate optimization of PTV-GC-MS method for simultaneous determination of organometallic compounds of mercury, lead and tin by C. Moscoso-Pérez; V. Fernández-González; J. Moreda-Piñeiro; P. López-Mahía; S. Muniategui-Lorenzo; D. Prada-Rodríguez (7702-7710).
A simple, rapid and inexpensive method using programmed temperature vaporization-gas chromatography-mass spectrometry (PTV-GC-MS) was developed for the simultaneous trace level determination of organometallic compounds of mercury (monomethylmercury, MMM), lead (trimethyllead, TML and triethyllead, TEL) and tin (monobutyltin, MBT; dibutyltin, DBT and tributyltin, TBT). Inorganic tin, mercury and lead species were also determined in the same chromatographic run. Prior to chromatographic separation and detection, a one-step micro liquid–liquid extraction (MLLE) after derivatization was carried out with sodium tetrapropylborate (NaBPr4) in the presence of a small volume of isooctane. Injection conditions were optimized by applying experimental designs (Plackett–Burman design (PBD) and central composite design (CCD)) using an injection volume of 25 μL. PBD was chosen to screen variables affecting the vaporization efficiency (injector heating rate, injection speed, split vent flow, injector isothermal time, injector initial temperature, oven isothermal time, oven initial temperature, and splitless time). Then, the optimum values of the significant factors (injector isothermal time, oven isothermal time and splitless time) were obtained by a CCD. The figures of merit were achieved using selective ion monitoring (SIM) and full scan modes. The instrumental detection and quantification limits were in the range of few μg L−1. Repeatability and intermediate precision in the range of 1.3–20% were achieved for most compounds studied. The accuracy of the method (average analytical recovery percentages) was satisfactory.

Back cover (7711-7712).