Paracetamol (N-acetyl-4-amino-phenol) is a popular antipyretic and analgesic medication which has few side effects and little toxicity when used in recommended dose. After ingestion of an overdose quantity of paracetamol, the accumulation of toxic metabolites may cause severe and even fatal hepatotoxicity and nephrotoxicity. In addition, p-aminophenol is the hydrolytic product of paracetamol and has high toxicity. It may be involved in the pharmaceutical preparation of paracetamol as a synthetic intermediate or a degradation product of paracetamol. Therefore, establishing an appropriate analytical method to research the stability of the medication is quite important and necessary. In this work, a kinetic alkaline degradation process of paracetamol was investigated by online two-way dimensional UV-Vis kinetic spectroscopy combined with the chemometric method Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS). The extracted concentration profiles and pure spectra of the reacting species in the reaction were obtained. These profiles indicated that there are two intermediates in the process. The possible degradation pathway and reaction mechanism of the paracetamol was postulated based on the MCR-ALS results, and the rate constants of every reaction step were resolved through subsequent model-fitting. To validate these results, a comparative offline measurement method with high performance liquid chromatography was implemented experimentally. Moreover, an ab initio calculation was also performed to evaluate the estimated reaction mechanism theoretically in energy terms.

•We proposed an analytical method to identify rice of several geographical origins.•It included spectra acquisition, baseline removal and multivariate analysis.•We proposed a Raman scheme for rapid detecting rice adulteration with paraffin.Rice has played an important role in staple food supply of over approximately one-half of the world population. In this study, Raman spectroscopy and several multivariate data analysis methods were applied for discrimination of rice samples from different districts of China. A total of 42 samples were examined. It is shown that the representative Raman spectra in each group are different according to geographical origin after baseline correction to enhance spectral features. Moreover, adulteration of rice is a serious problem for consumers. In addition to the obvious effect on producer profits, adulteration can also cause severe health and safety problems. Paraffin was added to give the rice a desirable translucent appearance and increase its marketability. Detection of paraffin in the adulterated rice samples was preliminarily investigated as well. The results showed that Raman spectroscopy data with chemometric techniques can be applied to rapid detecting rice adulteration with paraffin.

Citrus fruits are of great interest because they contain flavonoids which are health promoting substances. Hesperidin, nobiletin and tangeretin are flavonoid glycosides that occur naturally in citrus. In the present study, a reversed-phase high-performance liquid chromatographic method has been developed for the rapid separation and determination of hesperidin, nobiletin and tangeretin in different fresh citrus fruit juices and commercial citrus beverages. Furthermore, principal component analysis was applied to their chromatographic profiles. Classification of orange, mandarin and hybrid was achieved. The possibility of estimating the approximate juice content of commercial beverages based on their PC1 values was attempted. These results demonstrated that the combination of HPLC and chemometrics offers a feasible and efficient approach for quality evaluation of citrus fruits and beverages.

Soft modeling (SM) methods can be used to resolve spectroscopic data from complicated reaction processes with unknown kinetics, with the exception of data containing a component for which there is no spectroscopic information available, such as an intermediate that does not absorb in the UV–visible region. In this work, modified SM methods were developed to resolve these undetectable components. Based on the mass balance principle, the mass balance error (MBE) method was first applied to determine whether the undetectable component existed. Next, the evolving error analysis (EEA) method was developed to search the local mass balance region (LMBR) where the concentration of the non-absorptive component was low enough to be neglected. In the LMBR, the concentration profiles of all absorptive components were scaled according to least squares regression. Subsequently, more reliable results were obtained using the evolving time region iteration (ETRI) method. Based on the mass balance principle, the concentration profile of the undetectable component was resolved for the entire time period. Both simulated and experimental data from an autocatalytic reaction were used to demonstrate the feasibility of the proposed method. In the autocatalytic oxidation of sodium oxalate by acidic potassium permanganate, the product Mn(II) was determined to be non-absorptive. Using the methods described above, the pure spectra of three other absorptive components and the scaled concentration profiles of four Mn species, including two intermediates, were all resolved. As a result, the mechanism of the reaction was more clearly described.

Rank annihilation factor analysis combined with the optimization of kinetic parameter is adopted to resolve the two-way kinetic-spectral data measured online from chemical reactions. To a multi-step reaction whose intermediate process is complicated and reaction order is fractional, the reaction order and rate constant of the first step can be determined without the knowledge of the kinetic model of the reaction. Taken a three-step reaction as an example, the synthetic data has been resolved and its effectiveness was proved. When the approach is applied to the analysis of practical reaction systems such as alkaline hydrolysis of phenyl benzoate, oxidization of sodium bromide by potassium permanganate and electro-degradation of sunset yellow, reliable results are obtained.

Paracetamol (N-acetyl-4-amino-phenol) is a popular antipyretic and analgesic medication which has few side effects and little toxicity when used in recommended dose. After ingestion of an overdose quantity of paracetamol, the accumulation of toxic metabolites may cause severe and even fatal hepatotoxicity and nephrotoxicity. In addition, p-aminophenol is the hydrolytic product of paracetamol and has high toxicity. It may be involved in the pharmaceutical preparation of paracetamol as a synthetic intermediate or a degradation product of paracetamol. Therefore, establishing an appropriate analytical method to research the stability of the medication is quite important and necessary. In this work, a kinetic alkaline degradation process of paracetamol was investigated by online two-way dimensional UV-Vis kinetic spectroscopy combined with the chemometric method Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS). The extracted concentration profiles and pure spectra of the reacting species in the reaction were obtained. These profiles indicated that there are two intermediates in the process. The possible degradation pathway and reaction mechanism of the paracetamol was postulated based on the MCR-ALS results, and the rate constants of every reaction step were resolved through subsequent model-fitting. To validate these results, a comparative offline measurement method with high performance liquid chromatography was implemented experimentally. Moreover, an ab initio calculation was also performed to evaluate the estimated reaction mechanism theoretically in energy terms.