Recent development in derivative ultraviolet/visible absorption spectrophotometry: 2004–2008

Integration of a Raman spectroscopic platform based on online sampling to monitor chemical reaction processes

During the pharmaceutical synthesis process, it is essential to control the reaction time to avoid by-product formation and the reduction of yield. In this study, a Raman spectroscopic platform based on online sampling was integrated to collect Raman spectra in real time and realize process monitoring. Considering its attractive features of strong light transmittance and resistance to acids, alkalis and high temperatures, polyfluoroalkoxy (PFA) tubes rather than cuvette-type flow cells or similar devices were used to transfer solutions and as a flow cell for collecting Raman spectra, therefore not requiring an in situ Raman probe, and significantly reducing the cost of equipment. The peristaltic pump is controlled by the sampling software to realize automatic sampling, and it automatically pushes the reaction solution back into the reaction vessel after the spectra are collected. Taking the aspirin synthesis reaction as an example, the platform was employed to monitor the chemical reaction in real-time. The internal standard method was adopted to minimize the interference of spectral oscillation and baseline drift during online monitoring. The characteristic peak of the PFA tube at 731 cm-1 was selected as the internal standard peak, which formed the relative intensity ratio R with the characteristic peak of the product acetylsalicylic acid at 1606 cm-1. The endpoint of the reaction was identified based on the trend of the relative intensity ratio with the reaction time. The results indicate that the method is feasible for monitoring the aspirin synthesis reaction and provides a research basis for real-time monitoring of other pharmaceutical processes.

Application of Odd-Order Derivatives in Fourier Transform Nuclear Magnetic Resonance Spectroscopy toward Quantitative Deconvolution

When Fourier transform (FT) spectrum peaks are overlapped, primary maxima of odd-order derivatives can be used to evaluate their independent intensities. We studied the feasibility of higher odd-order derivatives on Lorentzian peak shape and magnitude peak shape. Simulation studies for FT nuclear magnetic resonance (NMR) spectroscopy demonstrated good results toward quantitative deconvolution of overlapping FT spectrum peaks. Although it is not so desirable to deconvolute special line shapes such as Gaussian, Voigt, and Tsallis profiles, the odd-order derivatives exhibit a bright future compared to even-order derivatives. An application example of practical NMR spectroscopy with ethylbenzene isomers is presented. White Gaussian noises were added to the simulated spectra at two different signal-to-noise ratios (20 and 40). Kauppinen's denoising and smoothing algorithms can effectively remove interference of the noise and help to have good deconvoluting results using the odd-order derivatives. We compared features of our approach with popular deconvolution sharpening algorithms and conducted a comparison study with Kauppinen's Fourier self-deconvolution. Our approach has a better dynamic range of peak intensities and is not sensitive to the sampling rates. Other common deconvolution methods are also discussed briefly.

Lysozyme-sensitive plasmonic hydrogel nanocomposite for colorimetric dry-eye inflammation biosensing

Detection of lysozyme levels in ocular fluids is considered crucial for diagnosing and monitoring various health and eye conditions, including dry-eye syndrome. Hydrogel-based nanocomposites have been demonstrated to be one of the most promising platforms for fast and accurate sensing of different biomolecules. In this work, hydrogel, electrospun nanofibers, and plasmonic nanoparticles are combined to fabricate a sensitive and easy-to-use biosensor for lysozyme. Poly(L-lactide-co-caprolactone) (PLCL) nanofibers were covered with silver nanoplates (AgNPls), providing a stable plasmonic platform, where a poly(N-isopropylacrylamide)-based (PNIPAAm) hydrogel layer allows mobility and good integration of the biomolecules. By integrating these components, the platform can also exhibit a colorimetric response to the concentration of lysozyme, allowing for easy and non-invasive monitoring. Quantitative biosensing operates on the principle of localized surface plasmon resonance (LSPR) induced by plasmonic nanoparticles. Chemical, structural, thermal, and optical characterizations were performed on each platform layer, and the platform's ability to detect lysozyme at concentrations relevant to those found in tears of patients with dry-eye syndrome and other related diseases was investigated by colorimetry and UV-Vis spectroscopy. This biosensor's sensitivity and rapid response time, alongside the easy detection by the naked eye, make it a promising tool for early diagnosis and treatment monitoring of eye diseases.

Recent Advances in the Synthesis and Analysis of Atorvastatin and its Intermediates

Atorvastatin, a lipid-lowering drug that is widely used in the treatment of cardiovascular diseases, has significant clinical significance. This article focuses on the synthetic procedures of atorvastatin, including Paal-Knorr synthesis and several new synthetic strategies. It also outlines chemical and chemo-enzymatic methods for synthesizing optically active side chain of atorvastatin. In addition, a comprehensive overview of the analytical monitoring techniques for atorvastatin and its metabolites and impurities is reported, alongside a discussion of their strengths and limitations.

Screening of neoplastic diseases by statistical analysis of urine fluorescence spectroscopic data. Application of multivariate techniques for enhancing classification

The composition of human fluids is modified during the course of neoplastic diseases. Urine analysis offers the advantage of being a noninvasive method for which samples are easily and routinely collected from patients. In this work, urine fluorescence spectra recorded upon excitation at 405 nm were obtained from healthy volunteers and individuals with different oncologic pathologies. A large number of indexes, i.e., parameters obtained from spectral data which assist spectral features characterization, were developed to classify healthy and pathological populations. The discrimination ability of simple predictive indexes, obtained from spectra pretreated with different normalization procedures and by taking their derivatives, was statistically assessed. In addition, multivariate methods, such as principal component analysis and multivariate curve resolution by alternating least squares, were used to develop more elaborate indexes for distinguishing between healthy and pathological populations. All indexes were systematically evaluated on a statistical basis by in lab-developed routines capable of detecting outliers, judging the normal distribution of the indexes, evaluating variance homogeneity, testing the difference between the means of healthy and pathological populations, as well as performing a receiver operator curve analysis to assess the classification power of each index. Those indexes with the best performances were further combined to perform a linear discriminant analysis, which yielded a powerful classification algorithm with an area under the receiver operator curve of 0.986, a sensitivity of 97.7%, a specificity of 100%, and an overall accuracy of 98.8%. The present study shows that the statistical analysis of urine fluorescence data with a proper combination of multivariate techniques bears a high potential to develop massive screening tests for the early detection of oncologic pathologies.

Effect of ultraviolet light-emitting diode processing on fruit and vegetable-based liquid foods: A review

Ultraviolet light-emitting diode (UV-LED) technology has emerged as a non-thermal and non-chemical treatment for preserving liquid fruit and vegetable foods. This technology uses ultraviolet light to interact with the food at different wavelengths, solving problems related to product stability, quality, and safety during storage. UV-LED treatment has been shown to affect microbe and enzyme inactivation, and it increases and improves retention of bioactive compounds. Moreover, computational simulations are a powerful and relevant tool that can be used optimize and improve the UV-LED process. Currently, there are a limited studies of this technology in liquid fruit and vegetable-based foods. This review gathers information on these food type and shows that it is a promising technology for the development of new products, is environmentally friendly, and does not require the addition of chemicals nor heat. This is relevant from an industrial perspective because maintaining the nutritional and organoleptic properties ensures better quality. However, due to the scarce information available on this type of food, further studies are needed.

Rapid Detection of Different Types of Soil Nitrogen Using Near-Infrared Hyperspectral Imaging

Rapid and accurate determination of soil nitrogen supply capacity by detecting nitrogen content plays an important role in guiding agricultural production activities. In this study, near-infrared hyperspectral imaging (NIR-HSI) combined with two spectral preprocessing algorithms, two characteristic wavelength selection algorithms and two machine learning algorithms were applied to determine the content of soil nitrogen. Two types of soils (laterite and loess, collected in 2020) and three types of nitrogen fertilizers, namely, ammonium bicarbonate (ammonium nitrogen, NH4-N), sodium nitrate (nitrate nitrogen, NO3-N) and urea (urea nitrogen, urea-N), were studied. The NIR characteristic peaks of three types of nitrogen were assigned and regression models were established. By comparing the model average performance indexes after 100 runs, the best model suitable for the detection of nitrogen in different types was obtained. For NH4-N, R2p = 0.92, RMSEP = 0.77% and RPD = 3.63; for NO3-N, R2p = 0.92, RMSEP = 0.74% and RPD = 4.17; for urea-N, R2p = 0.96, RMSEP = 0.57% and RPD = 5.24. It can therefore be concluded that HSI spectroscopy combined with multivariate models is suitable for the high-precision detection of various soil N in soils. This study provided a research basis for the development of precision agriculture in the future.

An innovative spectroscopic approach for qualitative and quantitative evaluation of Mb-CO from myoglobin carbonylation reaction through chemometrics methods

In this work, an innovative approach using K-means and multivariate curve resolution-purity based algorithm (MCR-Purity) for the evaluation and quantification of carboxymyoglobin (Mb-CO) formation from Deoxy-Myoglobin (Deoxy-Mb) was presented. Through a multilevel multifactor experimental design, samples with different concentrations of Mb-CO were created. The UV-Vis spectra of these samples were submitted to K-means analysis, finding 3 clusters. The mean spectra of the clusters were extracted and it was possible to detect 2 totally differentiable groups through peaks 423 and 434 nm, which are wavelengths related to the Mb-CO and Deoxy-Mb components, respectively. The spectral data were subjected to MCR-Purity analysis. The MCR-Purity result successfully described the analyzed reaction, explaining more than 99.9% of the variance (R²) with a LOF of 1.43%. Then, a predictive model of MbCO was created through the linear relationship between MCR-Purity contributions and known concentrations of MbCO. The performance parameters of the created predictive model were R²CV = 0.98, RMSECV = 0.58 and RPDcv = 7.8 for the training set, and R²P = 0.98, RMSEP = 0.7 and RPDp = 6.8 for the test set. Thus, the predictive model presented an excellent performance considering that the Mb-CO variation is comprised between 0 and 21 µM. Therefore, these results demonstrate that the application of the proposed strategy to the analysis of spectral data presenting overlapping bands is feasible and robust.

Selective Laser Sintering of a Photosensitive Drug: Impact of Processing and Formulation Parameters on Degradation, Solid State, and Quality of 3D-Printed Dosage Forms

This research study utilized a light-sensitive drug, nifedipine (NFD), to understand the impact of processing parameters and formulation composition on drug degradation, crystallinity, and quality attributes (dimensions, hardness, disintegration time) of selective laser sintering (SLS)-based three-dimensional (3D)-printed dosage forms. Visible lasers with a wavelength around 455 nm are one of the laser sources used for selective laser sintering (SLS) processes, and some drugs such as nifedipine tend to absorb radiation at varying intensities around this wavelength. This phenomenon may lead to chemical degradation and solid-state transformation, which was assessed for nifedipine in formulations with varying amounts of vinyl pyrrolidone-vinyl acetate copolymer (Kollidon VA 64) and potassium aluminum silicate-based pearlescent pigment (Candurin) processed under different SLS conditions in the presented work. After preliminary screening, Candurin, surface temperature (ST), and laser speed (LS) were identified as the significant independent variables. Further, using the identified independent variables, a 17-run, randomized, Box-Behnken design was developed to understand the correlation trends and quantify the impact on degradation (%), crystallinity, and quality attributes (dimensions, hardness, disintegration time) employing qualitative and quantitative analytical tools. The design of experiments (DoEs) and statistical analysis observed that LS and Candurin (wt %) had a strong negative correlation on drug degradation, hardness, and weight, whereas ST had a strong positive correlation with drug degradation, amorphous conversion, and hardness of the 3D-printed dosage form. From this study, it can be concluded that formulation and processing parameters have a critical impact on stability and performance; hence, these parameters should be evaluated and optimized before exposing light-sensitive drugs to the SLS processes.

Investigation of some univariate and multivariate spectrophotometric methods for concurrent estimation of Vancomycin and Ciprofloxacin in their laboratory prepared mixture and application to biological fluids

Four simple, rapid, accurate and precise spectrophotometric methods were established and validated in accordance with ICH Q2 (R1) guidelines for the simultaneous determination of Vancomycin (VNC) and Ciprofloxacin (CPR) in their raw materials, laboratory prepared mixtures and pharmaceutics. Method A depends on using first derivative spectrophotometry (D¹) where VNC and CPR were resolved at 243.6 and 262.0 nm, respectively. Concerning method B, it is based on utilizing first derivative of ratio spectra (DD¹) where determination was performed at the peak maxima at 244.0 nm and 258.0 nm for VNC and CPR, respectively. Two chemometric models were applied for the quantitative analysis of both drugs in their laboratory prepared mixtures, namely, partial least squares (PLS) (method C) and artificial neural network (ANN) (method D). For univariate methods linearity range for both drugs was in the range of 3-30 and 1-10 μg/mL for VNC and CPR, respectively. Multivariate calibration methods using five level, two factor calibration model for the development of 25 mixtures were also applied for the simultaneous estimation of the two drugs in their laboratory prepared mixture using spectral region from 200.0 to 300.0 nm using interval 1 nm. The suggested methods have been successfully extended to the assay of the two studied drugs in laboratory-prepared mixtures and pharmaceuticals with excellent recovery. First derivative spectrophotometry (D¹) was also applied for the assay of both analytes in spiked human plasma with good recovery. No interaction with common pharmaceutical additives has been observed which indicate the selectivity of the method. The results obtained were favourably compared with those obtained applying the reported methods. The methods are validated in compliance with the ICH Q2 (R1) guidelines and the measured accuracy and precision are assessed to be within the accepted limits.

Development of a low-cost colorimeter and its application for determination of environmental pollutants

Herein, a novel colorimeter based on the Beer-Lambert law was designed for detection of environmental pollutants in water with a high precision, simple, and miniaturized device using a tetracycline-Eu³⁺ complex, cadmium reduction, diazotization, 1,10-phenanthroline, and periodate oxidation. The newly developed colorimeter could detect many environmental pollutants including tetracycline, nitrate, nitrite, Fe, and Mn, which were used to evaluate its performance. Simultaneously, a modified algorithm was applied to extend the linear response range. The colorimeter was comprised of an Red Green Blue Light Emitting Diode (RGB LED) light, focusing len, 3D printed stand for the cuvette, and light-sensitive photodiode detector. Microcontroller Arduino Uno processing technology was used to form a stable integrated structure. With the use of a novel algorithm, the device exhibited a wide linear response, ranging from 0-20, 0-17, 0-0.3, 0-1.75, and 0-15 mg/L for tetracycline, N-NO₃^-, N-NO₂^-, Fe, and Mn, respectively, and low limits of detection (0.88, 0.34, 0.031, 0.08, and 0.47 mg/L for tetracycline, N-NO₃^-, N-NO₂^-, Fe, and Mn, respectively). The advantages of high precision and low cost allow the novel design to be used for the detection of environmental pollutants.

UV spectrophotometric methods for quantitative determination of masitinib; extraction of qualitative information

Masitinib is an orally administered selective tyrosine kinase inhibitor. It has emerged as a promising drug for multiple diseases including cancer and inflammation in either human or veterinary medicine. Five new and simple UV spectrophotometric methods were developed for its determination in bulk and in pharmaceutical tablets. These methods are based on measuring the absorbance of masitinib in either zero order or first, second, third or fourth derivative spectra. Measurements are optimized so as to minimize excipients' interferences. The methods are suitable for micro-analysis of masitinib. The proposed methods were validated according to the ICH-Q2(R1) guidelines and was successfully applied for determination of masitinib in laboratory prepared tablet. The presented methods are simple, fast, cost-effective and suitable for routine pharmaceutical analysis. Moreover, two derivative spectrophotometric-based methods were developed for identification of masitinib, the derivative ratio method and log-A derivative method. The impact of the developed methods on the environment was assessed by both analytical Eco-Sale and the Green Analytical Procedure Index (GAPI). The present work proves how derivative spectrophotometry could greatly extract qualitative and quantitative information from UV spectra.

Method Transfer Evaluation for Digital Derivative Spectrophotometry Through its Resolution Parameter Comparison of Different Computer Programs

The application assessment of different programs was performed with equivalence tests for method transfer pro second-order derivative spectrophotometry. The digital second-order derivative spectra were calculated on different instruments; GBC Scientific Equipment Cintra 20 (Cintral v.2.6 and Spectral v.1.70 software programs) and Thermo Scientific Evolution 300 (VISIONPro software) were analyzed using the amplitude A/B ratio (A = ²D_265,263; B = ²D_263,261). Amplitude A/B ratio is the resolution parameter for derivative spectrophotometry prescribed in European Pharmacopoeia. The obtained values for A/B ratio were either very similar or significantly different among programs: 0.669 (Cintral v.2.6), 0.549 (Spectral v.1.70), 0.556 (medium indirect VISIONPro), 0.557 (one-step Savitzky-Golay 7 VISIONPro), 0.689 (two-step Savitzky-Golay 7 VISIONPro). Method transfer was possible between Spectral v.1.70 and VISIONPro (medium indirect and one-step Savitzky-Golay 7), but the values obtained in Cintral v.2.6 were not comparable to the other programs. The absorbance data exported from both instruments were additionally calculated in OriginPro8 which provided almost the same mean A/B values (0.627 Cintral v.2.6; 0.624 VISIONPro), confirming that the two instruments recorded the same zero-order spectra. The calculation of resolution parameter could be used for verification of program comparison, which would enable transfer between sender and receiver laboratory. The accordance between program algorithms was confirmed when acceptable differences for values of resolution parameter (A/B ratios) were achieved.

Second derivative analysis of synthesized spectra for resolution and identification of overlapped absorption bands of amino acid residues in proteins: Bromelain and ficin spectra in the 240-320 nm range

We establish the origin and formation of peaks in UV absorption spectra of proteins by applying the second derivative analysis to (i) spectra of the native protein, (ii) to its model spectra "synthesized" as a sum of partial free amino acid spectra and (iii) to absorption spectra of the free amino acids. We show that the bromelain peaks at 248.2, 253.2, 258.4 and 264.2 nm are due to phenylalanine maxima; the predictable peak at 279.6 nm (which is almost coincident with the extremum of the zero-order spectrum at 279.4 nm) is mainly due to tyrosine maximum, while the peaks at 274.6 and 290.6 nm are due to tryptophan maximum; 268.0 nm peak to the superposition of tyrosine and phenylalanine maxima, and 283.4 nm peak to the superposition of tyrosine and tryptophan maxima. Similar results are obtained for ficin: the peaks at 248.4, 253.0 and 258.8 nm are formed by the phenylalanine maxima, the predictable peak at 264.4 nm accords with the corresponding bromelain 264.2 nm peak; the 279.4 nm peak almost coincides with the zero order spectrum peak (279.6 nm), but it is expressed stronger than that of bromelain due to a different ratio of tyrosine to tryptophan side groups. The peaks at 273.4 and 290.6 nm are associated with tryptophan, the 268.0 nm peak being mainly due to tyrosine (and fractionally to phenylalanine); and the 283.8 nm peak belongs to tyrosine and, to a greater extent, to tryptophan. We demonstrate that the amino acid residues of tryptophan, tyrosine and phenylalanine undergo correspondingly the largest, intermediate and the lowest positive (red) wavelength shift in the zero-order protein absorption spectrum with respect to the model (synthesized) spectrum. The difference appearing in the positions of the bromelain and ficin absorption band peaks is determined by superposition of relative contributions from amino acid residues. This superposition is resulted from (i) linear combination of amino acid residues spectra and (ii) their different (non-uniform) wavelength shifts as functions of microenvironment of these residues' chromophores. The proposed approach to the analysis of the protein absorption spectra with the help of "synthesized" spectra can be transferred to other objects studied in analytical and organic chemistry of high molecular compounds containing monomer units with various chromophores.

Potassium bromate: Effects on bread components, health, environment and method of analysis: A review

Potassium bromate, is an oxidizing agent and one of the best and cheapest dough improvers in the baking industry. Due to its positive effects it plays a major role in the bread-making industry. Potassium bromate has significant effect on food biomolecules, such as starch and protein, as it affects the extent of gelatinization, viscosity, swelling characteristics as well as gluten proteins; it removes the sulfhydryl group and leads to the formation of disulfide linkages and thus improves the bread properties. However, there are many reports elucidating its negative impact on human health. It is deemed as a potential human carcinogen by IARC and classified under class 2B. Due to this, countries across world have either partially or completely banned it. Numerous techniques have evolved to determine the concentration of potassium bromate in bread. This review explains in detail, the effects of potassium bromate on biomolecules, human health, environment and various methods of analysis.

Development of UV spectrophotometry methods for concurrent quantification of amlodipine and celecoxib by manipulation of ratio spectra in pure and pharmaceutical formulation

Recently, the United States Food and Drug Administration approved a new oral dosage preparation of amlodipine besylate (AML) and celecoxib (CEL) for the management of hypertension and osteoarthritis. However, no simultaneous estimation procedures for these two analytes have been described. Hence, two simple, accurate, and precise ultraviolet spectroscopic procedures that manipulated the ratio spectra were established for concurrent quantification of AML and CEL using ethanol as a solvent. The first method involves determining the peak-to-trough amplitude difference of the ratio spectra of AML and CEL. The second method involves determining the peak amplitude of the ratio first derivative (Δλ 4 nm) spectra of AML and CEL at 334.2 nm and 254.2 nm, correspondingly. Both methods showed linearity in the range of 1–6 μg mL-1 for AML and 5–40 μg mL-1 for CEL with an excellent correlation coefficient (<0.999). The proposed procedures were validated by following the International Conference on Harmonization guidelines for accuracy, precision, selectivity, recovery, and stability studies. It is evident from the low %RSD and %RE that both analytical procedures were found to be accurate and precise, respectively. The percent recovery of AML and CEL from the formulation was found to be 99.79% and 99.34% using the ratio-difference method and 100.13% and 99.70% using the ratio first-derivative method, with a low percent relative standard deviation. Further, the proposed techniques permit concurrent quantification of AML and CEL in different concentration ratios without interference from each other; hence, these techniques can be adopted for regular quality-control studies.

The impact of the order of derivative spectra on the performance of pattern recognition methods. Classification of medicinal plants according to the phylum

Data pre-processing is an important strategy in chemometrics and related fields because in many cases the transformation of data has a great effect on the performance of the method (model). However, a careful examination of the literature clearly points out that only very few systematic studies are dedicated to the effect of the derivative spectra on the performance of the pattern recognition methods. This comprehensive study compares the impact of the order of derivative spectra and other data pre-processing procedures (normalization and standardization) on the performance of cluster analysis, principal component analysis and discriminant analysis applied for characterization and classification of medicinal plants according to their phylum using UV spectra. The efficiency of the pre-processing methods was estimated by comparing the accuracy of classification and prediction measured by internal cross-validation. Derivatization method (1st order) resulted in the best classification (100%) of medicinal plants according to their phylum (Pteridophyte, Magnoliophyte and Spermatophyte) as compared to other pre-processing methods (normalized spectra-71.4%, standardized spectra-76.2% and original spectra-78.6%).

Multicomponent spectrometric analysis of drugs and their preparations

Pharmaceutical preparations may contain a single ingredient or multi-ingredients as well as excipients. In multicomponent systems, specific analytical methods are required to determine the concentrations of individual components in the presence of interfering substances. Ultraviolet and visible spectrometric methods have widely been developed for the analysis of drugs in mixtures and pharmaceutical preparations. These methods are based on ultraviolet and visible multicomponent analysis and chemometrics (multivariate data analysis). The commonly used chemometric methods include principal component analysis (PCA); regression involving classical least squares (CLS), partial least squares (PLS), inverse least squares (ILS), principal component regression (PCR), multiple linear regression (MLR), artificial neural networks (ANNs); soft independent modeling of class anthology (SIMCA), PLS-discriminant analysis (DA); and functional data analysis (FDA). In this chapter, the applications of multicomponent ultraviolet and visible, derivative, infrared and mass spectrometric and spectrofluorimetric methods to the analysis of multi-ingredient pharmaceutical preparations, biological samples and the kinetics of drug degradation have been reviewed. Chemometric methods provide an efficient solution to calibration problems in the analysis of spectral data for the simultaneous determination of drugs in multicomponent systems. These methods facilitate the assessment of product quality and enhance the efficiency of quality control systems.

Ultrasonic assisted synthesis of magnetic Ni-Ag bimetallic nanoparticles supported on reduced graphene oxide for sonochemical simultaneous removal of sunset yellow and tartrazine dyes by response surface optimization: Application of derivative spectrophotometry

The magnetic Ni-Ag bimetallic nanoparticles supported on reduced graphene oxide (Ni-Ag NPs/rGO) was synthesized and characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), field emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM). Subsequently, this magnetic hybrid material as a novel adsorbent was applied for the sonochemical simultaneous removal of sunset yellow and tartrazine dyes in combination with first-order derivative spectrophotometric method to resolve the overlap between the spectra of these dyes. With magnetic properties, the adsorbent could easily be collected from aqueous solution using an external magnetic field. The parameters including initial concentration of each dye, adsorbent dosage and sonication time were studied by Box-Behnken design (BBD) and response surface methodology (RSM), while pH was studied by one-at-a-time approach. According to Box-Behnken design based on desirability function (DF), the best experimental conditions was set as initial sunset yellow concentration 10 mgL^-1, initial tartrazine concentration 8.5 mgL^-1, adsorbent dosage 0.045 g and sonication time of 15 min. The equilibrium data was fitted to different isotherm models and the results revealed the suitability of the Langmuir model. The maximum sorption capacity calculated from the Langmuir model was 28.57 and 26.31 mg g^-1 for sunset yellow and tartrazine, respectively. Kinetic data revealed that the adsorption process followed a pseudo-second-order model. The reusability of the magnetite nanoparticles revealed about 8% decrease in the removal efficiency within four consecutive runs.

Development of mini-spectrophotometer for determination of plasma glucose

This work demonstrates a novel compact spectrophotometer, "Mini-spectrophotometer", designed for plasma glucose detection. Unlike conventional spectrophotometer, a light source of the mini spectrophotometer is replaced by a light-emitting diode (LED), and a fabricated polymer-based microwell is used as a cuvette. To validate the downsizing spectrophotometer prototype, the efficiency and reliability for glucose determination are investigated. Using a certain light intensified from LED, the within-run precision of mini-spectrophotometer is found to be 3.9-8.4% while the between-run precision is 6.7-10.8%. The linearity for the quantification of glucose was up to 500 mg dL^-1 and the recovery 99.1 ± 3.4% is obtained. The sensitive and selective detection of glucose has been observed; with limit of detection (LOD) of 13.5 mg dL^-1 and limit of quantification (LOQ) of 46.2 mg dL^-1, respectively. Hemoglobin and triglyceride at high concentration slightly interferes with the proposed instrument. From comparative studies, there are no significant differences between the glucose concentration measured by mini-spectrophotometer and Shimadzu (r² = 0.9862) or CECIL spectrophotometer (r² = 0.9853). Using Passing-Bablok regression analysis, the results obtained from mini-spectrophotometer are in close agreement with the two conventional spectrophotometers. Furthermore, using microwell, the sample volume and reagent used in the process can be reduced. The in-house developed mini-spectrophotometer is capable of detecting plasma glucose while maintaining a compact system, demonstrating the potential of high performance, cost-effective, and portable spectrophotometer for clinical chemistry analysis in small routine, research, and teaching medical laboratory technologist.

Concentration cell-based potentiometric analysis for point-of-care testing with minimum background

One of the most critical problems of point-of-care testing is how to reduce the interference of background, especially under resource-limited conditions when sample pretreatment is not available. In this work we report a potentiometric method for point-of-care testing with minimum background. The method is based on the principles of a concentration cell which is a type of galvanic cells. It is an electrochemical cell having two carbon electrodes. The potential of each electrode is determined by ratio of a redox couple (i.e. Fe(CN)₆^4-/3-) on the electrode surface. On one electrode, the adsorbed enzyme catalyzes the oxidation of analyte by Fe(CN)₆^3- which produces Fe(CN)₆^4-. The shift of the potential was because of the analyte as well as the background. In the other channel, no enzyme was present so that the shift of the potential, if any, is owing to the background. By measuring the potential difference between the two electrodes (i.e. voltage of the concentration cell), analyte can be quantitatively determined with most of the background eliminated. As the proof-of-concept analyte, blood glucose is quantitatively detected using a voltammeter with acceptable selectivity and accuracy. Noble metal electrodes that are indispensable for conventional electrochemical sensing are not required. All these features simplify the fabrication procedure and reduce the cost for the detection. Therefore, we believe it is promising for electrochemical point-of-care testing.

Simultaneous determination of Brilliant Green and Crystal Violet dyes in fish and water samples with dispersive liquid-liquid micro-extraction using ionic liquid followed by zero crossing first derivative spectrophotometric analysis method

In this study, dispersive liquid-liquid micro-extraction using ionic liquid (IL-DLLME) combined with zero crossing first derivative spectrophotometric method was applied to quantitative determination of triphenylmethane dyes in binary mixtures. The 1-methyl-3-octylimidazolium hexafluorophosphate [OMIM][PF₆] ionic liquid was used to extract Brilliant Green (BG) and Crystal Violet(CV) dyes from aqueous solutions. The amplitude of the zero crossing first derivative spectra at 670 nm and 532 nm were selected for the determination of BG and CV, respectively. Significant factors influencing the extraction of BG and CV such as sample pH, kind of extraction solvent, amount of extractant, extraction and centrifuging times and ionic strength were investigated. Under the optimal conditions, the calibration curves for the simultaneous determination of both dyes were found to be linear in the range of 10-500 μg L^-1 with detection limits (LODs) of 2.7 μg L^-1 and 1.4 μg L^-1 for BG and CV, respectively. The relative standard deviation (RSD%) for five replicate simultaneous determinations of BG and CV were 4.7% and 1.7%, respectively. Extraction efficiencies of the BG and CV dyes in the presence of interfering ions were also investigated. Sample preparation based on the quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction combined with the IL-DLLME method and zero crossing first derivative spectrophotometric detection was applied for the simultaneous analysis of BG and CV in fish and water samples with quantitative recoveries.

Chemometric simultaneous determination of Sofosbuvir and Ledipasvir in pharmaceutical dosage form

Partial least squares (PLS), different families of continuous wavelet transform (CWT), and first derivative spectrophotometry (DS) techniques were studied for quantification of Sofosbuvir (SFB) and Ledipasvir (LDV) simultaneously without separation step. The components were dissolved in Acetonitrile and the spectral behaviors were evaluated in the range of 200 to 400nm. The ultraviolet (UV) absorbance of LDV exhibits no interferences between 300 and 400nm and it was decided to predict the LDV amount through the classic spectrophotometry (CS) method in this spectral region as well. Data matrix of concentrations and calibrated models were developed, and then by applying a validation set the accuracy and precision of each model were studied. Actual concentrations versus predicted concentrations plotted and good correlation coefficients by each method resulted. Pharmaceutical dosage form was quantified by developed methods and the results were compared with the High Performance Liquid Chromatography (HPLC) reference method. Analysis Of Variance (ANOVA) in 95% confidence level showed no significant differences among methods.

Metal Complexes as Self-Indicating Titrants for Acid-Base Reactions in Chloroform

The paper reports an unprecedented spectrophotometric determination of amines in chloroform, in which amines are not transformed into colored derivatives. This result has been achieved by exploiting the acid-base properties of the tight-ion-paired metal complexes [(HR₂DTO)Pt(H₂R₂DTO)][Cl], which are able to donate a HCl molecule to an amine, giving rise to an ammonium salt and to the neutral complexes [(HR₂DTO)₂Pt]. The circumstance that [(HR₂DTO)Pt(H₂R₂DTO)][Cl] and [(HR₂DTO)₂Pt] species show different absorptions in the visible region of the electromagnetic spectrum enables the aforementioned platinum complexes to behave as self-indicating titrants in the spectrophotometric determination of aliphatic amines, which are known to be UV-vis transparent. The new method has been tested by determining a series of fatty amines in the bulk and gave excellent results. The limits of applicability of this method (pK_a > 4) were found by testing a series of benzodiazepines.

The similarity and variability of the iridoid glycoside profile and antioxidant capacity of aerial and underground parts of Lamiophlomis rotata according to UPLC-TOF-MS and multivariate analyses

Lamiophlomis rotata (L. rotata) is a Tibetan medicinal herb used for centuries that contains iridoid glycosides (IGs), which are pharmacologically active ingredients and can be used for quality control. The IG profiles of the underground and aerial parts of the plant were determined by UPLC-TOF-MS to evaluate the similarity and variability of the different herbal parts listed in the Chinese Pharmacopoeia. Twenty-six IGs were detected in the total ion current (TIC) profile of L. rotata, and twenty-two of these were identified by comparing the retention times and mass spectra of the compounds to those of authentic standards. Among these compounds, five IGs with the same molecular formula (C17H26O11) were identified for the first time by mass spectrometry based on their different hydroxyl group-substituted positions. The aerial part has a similar chemical profile to that of the roots. The difference between the two parts was determined by multivariate statistical analysis of the UPLC-TOF-MS data of 24 specimens. Sesamoside was explored as the most characteristic marker to distinguish the two parts of L. rotata. To further estimate the distinction between the two parts, the content of total IGs and the antioxidant capacity were investigated in samples from different locations. The aerial parts showed a high content of total IGs and high antioxidant capacity, although not higher than those of the roots. The results also suggest the dosage should be increased when the aerial parts are used as crude medicinal materials instead of the underground parts.

Design of novel and modified dual optode membrane based on carbon dots for both ultratrace copper(ii) and cobalt(ii): derivative spectrophotometric and central composite design study

A selective, accurate and highly sensitive optical chemical sensor (optode) for the simultaneous determination of copper(ii) and cobalt(ii) without any prior separation or purification ion sensing was developed.

Estimation of water quality by UV/Vis spectrometry in the framework of treated wastewater reuse

The aim of this study is to investigate the potential of ultraviolet/visible (UV/Vis) spectrometry as a complementary method for routine monitoring of reclaimed water production. Robustness of the models and compliance of their sensitivity with current quality limits are investigated. The following indicators are studied: total suspended solids (TSS), turbidity, chemical oxygen demand (COD) and nitrate. Partial least squares regression (PLSR) is used to find linear correlations between absorbances and indicators of interest. Artificial samples are made by simulating a sludge leak on the wastewater treatment plant and added to the original dataset, then divided into calibration and prediction datasets. The models are built on the calibration set, and then tested on the prediction set. The best models are developed with: PLSR for COD (R_pred² = 0.80), TSS (R_pred² = 0.86) and turbidity (R_pred² = 0.96), and with a simple linear regression from absorbance at 208 nm (R_pred² = 0.95) for nitrate concentration. The input of artificial data significantly enhances the robustness of the models. The sensitivity of the UV/Vis spectrometry monitoring system developed is compatible with quality requirements of reclaimed water production processes.

Investigation of different spectrophotometric and chemometric methods for determination of entacapone, levodopa and carbidopa in ternary mixture

New, simple, accurate and sensitive UV spectrophotometric and chemometric methods have been developed and validated for determination of Entacapone (ENT), Levodopa (LD) and Carbidopa (CD) in ternary mixture. Method A is a derivative ratio spectra zero-crossing spectrophotometric method which allows the determination of ENT in the presence of both LD and CD by measuring the peak amplitude at 249.9nm in the range of 1-20μgmL^-1. Method B is a double divisor-first derivative of ratio spectra method, used for determination of ENT, LD and CD at 245, 239 and 293nm, respectively. Method C is a mean centering of ratio spectra which allows their determination at 241, 241.6 and 257.1nm, respectively. Methods B and C could successfully determine the studied drugs in concentration ranges of 1-20μgmL^-1 for ENT and 10-90μgmL^-1 for both LD and CD. Methods D and E are principal component regression and partial least-squares, respectively, used for the simultaneous determination of the studied drugs by using seventeen mixtures as calibration set and eight mixtures as validation set. The developed methods have the advantage of simultaneous determination of the cited components without any pre-treatment. All the results were statistically compared with the reported methods, where no significant difference was observed. The developed methods were satisfactorily applied to the analysis of the investigated drugs in their pure form and in pharmaceutical dosage forms.

UV spectrophotometry for monitoring the performance of a yeast-based deoxygenation process to treat ships' ballast water

This study assessed the usefulness of UV spectrophotometry for the monitoring of a yeast-based deoxygenation process proposed for ships' ballast water treatment to prevent the transfer of aquatic invasive species. Ten-day laboratory experiments using three treatment concentrations and different water types were conducted and resulted in complete oxygen depletion of treated waters. The treatment performance and quality of treated waters were determined by measuring the UV-visible absorbance spectra of water samples taken over time. Samples were also used for laboratory analysis of water quality properties. The UV absorbance spectra values were strongly correlated (r = 0.96) to yeast cell density in treated waters. The second-order derivative (D (2)) of the spectra varied greatly over time, and the spectrum profiles could be divided into two groups corresponding to the oxygenated and anoxic phases of the treatment. The D (2) value at 215 nm was strongly correlated (r = 0.94) to ammonia levels, which increased over time. The D (2) value at 225 nm was strongly correlated (r > 0.97) to DO concentration. Our results showed that UV spectrophotometry may provide a rapid assessment of the behavior and performance of the yeast bioreactor over time by quantifying (1) the density of yeast cells, (2) the time at which anoxic conditions were reached, and (3) a water quality index of the treated water related to the production of ammonia. We conclude that the rapidity of the technique confers a solid advantage over standard methods used for water quality analysis in laboratory and would permit the direct monitoring of the treatment performance on-board ships.

Inter-laboratory verification of European pharmacopoeia monograph on derivative spectrophotometry method and its application for chitosan hydrochloride

Inter-laboratory verification of European pharmacopoeia (EP) monograph on derivative spectrophotometry (DS) method and its application for chitosan hydrochloride was carried out on two generation of instruments (earlier GBC Cintra 20 and current technology TS Evolution 300). Instruments operate with different versions of Savitzky-Golay algorithm and modes of generating digital derivative spectra. For resolution power parameter, defined as the amplitude ratio A/B in DS method EP monograph, comparable results were obtained only with algorithm's parameters smoothing points (SP) 7 and the 2nd degree polynomial and those provided corresponding data with other two modes on TS Evolution 300 Medium digital indirect and Medium digital direct. Using quoted algorithm's parameters, the differences in percentages between the amplitude ratio A/B averages, were within accepted criteria (±3%) for assay of drug product for method transfer. The deviation of 1.76% for the degree of deacetylation assessment of chitosan hydrochloride, determined on two instruments, (amplitude (1)D202; the 2nd degree polynomial and SP 9 in Savitzky-Golay algorithm), was acceptable, since it was within allowed criteria (±2%) for assay deviation of drug substance, for method transfer in pharmaceutical analyses.

Improved quantitative analysis of spectra using a new method of obtaining derivative spectra based on a singular perturbation technique

Spectroscopy is often applied when a rapid quantitative analysis is required, but one challenge is the translation of raw spectra into a final analysis. Derivative spectra are often used as a preliminary preprocessing step to resolve overlapping signals, enhance signal properties, and suppress unwanted spectral features that arise due to non-ideal instrument and sample properties. In this study, to improve quantitative analysis of near-infrared spectra, derivatives of noisy raw spectral data need to be estimated with high accuracy. A new spectral estimator based on singular perturbation technique, called the singular perturbation spectra estimator (SPSE), is presented, and the stability analysis of the estimator is given. Theoretical analysis and simulation experimental results confirm that the derivatives can be estimated with high accuracy using this estimator. Furthermore, the effectiveness of the estimator for processing noisy infrared spectra is evaluated using the analysis of beer spectra. The derivative spectra of the beer and the marzipan are used to build the calibration model using partial least squares (PLS) modeling. The results show that the PLS based on the new estimator can achieve better performance compared with the Savitzky-Golay algorithm and can serve as an alternative choice for quantitative analytical applications.