Multilinear Mathematical Separation in Chromatography

Chromatography is a powerful and generally applicable method for the analytical separation and quantification of the chemical constituents in complex mixtures because chromatographic separation can provide high selectivity by isolating all analytes from interferences. Multiway analysis based on the multilinear model is an increasingly widely used method for interference-free and fast determination of the chemical constituents also in complex mixtures because multilinear mathematical separation can provide high selectivity by extracting the pure signal of the analyte from the mixed signal of a real sample. By combining chromatographic separation with mathematical separation, multiway calibration method, multiway standard additions method, and multiway internal standard method can be established. Chromatography assisted by multiway analysis can reduce the requirements for complete chromatographic separation, save elution time, and decrease the consumption of the mobile phase, particularly when the peak coelution problem is difficult to solve. This review presents the fundamentals and analytical applications of multilinear mathematical separation in chromatography.

A novel and simple LC–MS/MS quantitative method for dextromethorphan and dextrorphan in oral fluid

Aim: To develop and validate a simple method using LC–MS/MS for determination of dextromethorphan (DXM) and dextrorphan (DT) in human oral fluid. Results: Following protein precipitation, chromatographic separation used a phenyl column with isocratic elution (1 ml/min) of 10 mM ammonium-formate buffer and acetonitrile (65:35; v/v) with 0.1% formic acid. Retention times were 2.6 min for DT and 5 min for DXM. Total run time was 7 min. The intra- and inter-assay deviations (accuracy) for DT (1–100 ng/ml) and DXM (5–1000 ng/ml) ranged from -13.6 to 8.8% and -9.6 to 5.7%, respectively. Precision variations were ≤7.5%. Matrix effect was ≤11.8%. Conclusion: This method may prove helpful for quantification of DT and DXM in oral fluid for either clinical or toxicological purposes.

Angle Distribution of Loading Subspace (ADLS) for estimating chemical rank in multivariate analysis: Applications in spectroscopy and chromatography

Multivariate analyses are increasingly popular to explore the underlying structure of multivariate datasets, which are more and more prevalent in analytical chemistry. However, difficulties can be associated with estimating the number of components for the data with considerable coherence and noise. The method of Angle Distribution of Loading Subspace (ADLS) has been proposed to estimate the number of components for Principal Component Analysis (PCA) and PARAllel FACtor analysis (PARAFAC), which showed some advantages, in particular in the case of datasets with high coherence, over the commonly used methods (scree plot and cross-validation in PCA, and core consistency diagnostics (CORCONDIA) in PARAFAC). In this paper, we systematically improved and applied ADLS to estimate the number of components in different multivariate methods including, Multivariate Curve Resolution (MCR), PARAFAC and four-way PARAFAC. Firstly, we showed that ADLS performed better when estimating the chemical rank for MCR analysis, compared with scree plots. As well as this, we improved ADLS in multi-way analysis (three- and four-way PARAFAC) by calculating the loading subspace in advance using the Khatri-Rao product. The improved ADLS in multi-way analysis provided the correct result for the simulated three-way fluorescence datasets with unevenly distributed coherence at different dimensions, while the previous version of ADLS showed biased results and CORCONDIA / split-half analysis provided relatively unstable results. Moreover, ADLS was used to estimate the chemical rank for a four-way real-life fluorescence dataset analyzed by four-way PARAFAC. In this case the result of chemical rank results from ADLS was more precise and informative compared with CORCONDIA /split-half analysis in four-way analysis.

Simultaneous Determination of Warfarin and Aspirin Contents in Biological Fluids Using Excitation-Emission Matrix Fluorescence Coupled with a Second-order Calibration Method

In the present work, a practical method that combines excitation-emission matrix fluorescence with a second-order calibration method based on an alternating trilinear decomposition (ATLD) algorithm was developed in order to simultaneously and directly determine the contents of warfarin (WAR) and aspirin (ASA) in human plasma and urine samples, even in the presence of unknown interferences. With the pre-estimated component number of 4, the obtained average spiked recoveries were 105.4 ± 7.8 and 104.2 ± 8.3% for WAR, 96.5 ± 2.8 and 91.2 ± 2.3% for ASA in human plasma and urine samples, respectively. Furthermore, the figures of merit were calculated and also inter- and intra-day experiments were performed that proved the proposed method is of great significance to the monitoring of clinical administration and also being a simple sample pretreatment at low-cost.

Potential transducers based man-tailored biomimetic sensors for selective recognition of dextromethorphan as an antitussive drug

A biomimetic potentiometric sensor for specific recognition of dextromethorphan (DXM), a drug classified according to the Drug Enforcement Administration (DEA) as a "drug of concern", is designed and characterized. A molecularly imprinted polymer (MIP), with special molecular recognition properties of DXM, was prepared by thermal polymerization in which DXM acted as template molecule, methacrylic acid (MAA) and acrylonitrile (AN) acted as functional monomers in the presence of ethylene glycol dimethacrylate (EGDMA) as crosslinker. The sensors showed a high selectivity and a sensitive response to the template in aqueous system. Electrochemical evaluation of these sensors revealed near-Nernstian response with slopes of 49.6±0.5 and 53.4±0.5 mV decade(-1) with a detection limit of 1.9×10(-6), and 1.0×10(-6) mol L(-1) DXM with MIP/MAA and MIP/AN membrane based sensors, respectively. Significantly improved accuracy, precision, response time, stability, selectivity and sensitivity were offered by these simple and cost-effective potentiometric sensors compared with other standard techniques. The method has the requisite accuracy, sensitivity and precision to assay DXM in pharmaceutical products.

Simultaneous determination of metoprolol and α-hydroxymetoprolol in human plasma using excitation–emission matrix fluorescence coupled with second-order calibration methods

Background: Metoprolol (MET) is a β1-adrenoceptor antagonist, which is widely used in the treatment of cardiovascular diseases, and α-hydroxymetoprolol (α-OHM) is its hydroxylated metabolite. Owing to their similar structures, optimization of the condition for the chromatography approach, which is in common use for determination, is both time consuming and laborious. Results: A new and effective strategy that combines the excitation–emission matrix fluorescence with second-order calibration methods was developed for simultaneous determination of MET and α-OHM in human plasma. Conclusion: Although the fluorescence spectra of MET and α-OHM overlapped and a large number of unknown and uncalibrated fluorescent components coexisted, the developed method enables accurate concentrations together with reasonable resolution of excitation and emission profiles for the analytes of interest. An additional advantage of the proposed method is that there is no need for separation and sample pretreatment, in addition to lower cost than traditional methods.

Simultaneous determination of chloropheniramine maleate and dextromethorphan hydrobromide in plasma sample by hollow fiber liquid phase microextraction and high performance liquid chromatography with the aid of chemometrics

A simple and high sensitive technique based on three phase hollow fiber liquid phase microextraction (HF-LPME), optimized by using a four-variable experimental design and response surface methodology was performed to evaluate dextromethorphan hydrobromide (DEX) and chloropheniramine maleate (CLP) simultaneously in human plasma. The influence of source phase pH, HCl concentration of acceptor phase, time and salt addition were investigated. Under the optimized conditions analytes were extracted in their neutral form, pH 12.5 and salt concentration 2% (w/v), through a supported liquid membrane (SLM) of hexadecane into the HCl 0.0005 mol L(-1) located inside the lumen of hollow fiber to be back extracted. The mass transfer of the analytes from the donor phase through the SLM into acceptor phase was driven by the pH gradient. Determination was accomplished by UV-high performance liquid chromatography with recoveries 92% and 84% for CLP and DEX, respectively. Linearity was obtained in the range of 0.01-1000 μg L(-1) (R(2)>0.994). The obtained enrichment factors (EFs) were 233-276 for DEX and CLP respectively and limits of detection were 0.003 μg L(-1) with RSDs below 6%. The method proposed acceptable values to determine CLP and DEX in plasma samples sensitively and accurately.