Determination of amoxicillin in pharmaceuticals using sequential injection analysis and multivariate curve resolution

In this study, we report a method for quantifying amoxicillin in pharmaceuticals in the presence of interferents using sequential injection analysis (SIA) with a diode-array spectrophotometric detector and multivariate curve resolution with alternating least squares (MCR-ALS). With a suitable analytical sequence, we can use SIA to generate a pH gradient and, for each sample, obtain a data matrix. We used augmented matrices to resolve the system and obtain the spectra and concentration profiles of the components in the sample.We studied what are the effects of imposing trilinearity at the resolution stage, how to choose the species that will be used for quantification (acid, basic or the sum of the two), and which is the most suitable concentration of the reference standard. Once the optimum conditions were established, we performed the quantification in three amoxicillin-containing pharmaceuticals (flubiotic, augmentine, and clamoxyl). With this method, determination is quick, the reactants and instrumentation are inexpensive, and pretreatment of the sample is unnecessary.     

Determination of amoxicillin in pharmaceuticals using sequential injection analysis (SIA): Evaluation of the presence of interferents using multivariate curve resolution

In this study, we report a method for determining amoxicillin in pharmaceuticals using sequential injection analysis (SIA) with a diode-array spectrophotometric detector. Before determining the amoxicillin, we use multivariate curve resolution with alternating least squares (MCR-ALS) to investigate whether any interferents are present. With a suitable analytical sequence, we can use SIA to generate a pH gradient and, for each sample, obtain a matrix of data that have been analysed by several chemometric techniques based on multivariate analysis: principal components analysis (PCA), simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) and MCR-ALS. In this way we obtain the concentration profiles and spectra of the species in the sample.We studied six pharmaceuticals containing amoxicillin. Two of these pharmaceuticals contained no interferents, one contained an interferent but amoxicillin had a selective spectral area with respect to it, and the other three contained interferents. For the first three samples, we set up a system of univariate calibration, which determines amoxicillin quickly (it can analyse 20 samples/h) using inexpensive instrumentation and reactives.     

Effect of chromatographic parameters and detector settings on the response of HILIC-evaporative light-scattering detection system using experimental design approach and multicriteria optimization methodology

Four polar compounds, i.e. pantothenic acid, inositol, taurine and caffeine were used as probe solutes in conjunction with chemometric methods to find out meaningful implications of chromatographic conditions and detector settings on the system performance. Putting a premium on the conditions of hydrophilic interaction liquid chromatography (HILIC) and settings of evaporative light-scattering detection (ELSD), we scrutinize the importance of certain factors on signal-to-noise ratio and its variability. The application of a central composite design reveals that caffeine, which sublimes, differentiates from the relatively thermosensitive pantothenic acid as well as from inositol and taurine, which are thermostable, do not sublime and have high melting points. It seems that prior knowledge of solute characteristics is critical to estimate the chromatographic response as a function of chromatographic conditions and detection settings. Reducing the responses to just one by combining them “ad hoc”, results in an overall desirability function, which brings out the global optimal chromatographic conditions and detector settings.     

Fluorimetric determination of aminocaproic acid in pharmaceutical formulations using a sequential injection analysis system

A sequential injection analysis (SIA) methodology for the fluorimetric determination of aminocaproic acid in pharmaceutical formulations is proposed. The developed analytical procedure is based on the derivatisation reaction of the aminocaproic primary amine with o-phthalaldehyde (OPA) and N-acetylcysteine (NAC) and fluorimetric detection of the formed product (λ_ex = 350 nm; λ_em = 450 nm). The implementation of a SIA flow system allowed for the development of a simple, fast and versatile automated methodology, which exhibits evident advantages regarding the US Pharmacopoeia 24 (USP 24) reference procedure. By combining the SIA time-based sample insertion with a subsequent zone sampling approach, which permitted to select for detection of a well-defined sample zone, it was possible to implement an on-line dilution strategy that enabled the expansion of the analytical working range of the methodology, and thus its application in dissolution studies, without manifold re-configuration.Linear calibration plots were obtained for aminocaproic acid concentrations up to 6 × 10⁻⁵ mol l⁻¹. The developed methodology exhibit a good precision, with a R.S.D. < 2.0% (n = 15) and the detection limit was 2.5 × 10⁻⁷ mol l⁻¹. The obtained results complied with those furnished by the reference procedure with a relative deviation lower than 1.2%. No interference was found.     

Simultaneous potentiometric and fluorimetric determination of diclofenac in a sequential injection analysis system

Two independent methods for the determination of diclofenac were simultaneously implemented in an automated analytical system, based on the concept of sequential injection analysis, providing real-time assessment of results quality. The potentiometric detection was carried out with an ion-selective electrode based on a cyclodextrin while for the fluorimetric determination the sample was previously subject to in-line irradiation with UV light. The potentiometric and photochemical-fluorimetric determinations exhibited linear working ranges of 5×10⁻⁶ to 1×10⁻² and 1×10⁻⁶ to 1×10⁻⁴ mol dm⁻³, respectively. Relative standard errors of 0.5% for the potentiometric determination and 0.6% for the photochemical-fluorimetric determination were obtained after 10 consecutive injections of a 5×10⁻⁵ mol dm⁻³ diclofenac standard solution. The sampling rate was about 32 samples h⁻¹. Both methods were applied in the analysis of pharmaceutical formulations. The quality of results obtained was evaluated by comparison to the reference method, with no statistically significant differences for a 95% confidence level.     

Spectrophotometric determination of sulphate in automotive fuel ethanol by sequential injection analysis using dimethylsulphonazo(III) reaction

A sensitive SIA method was developed for sulphate determination in automotive fuel ethanol. This method was based on the reaction of sulphate with barium-dimethylsulphonazo(III) leading to a decrease on the magnitude of analytical signal monitored at 665 nm. Alcohol fuel samples were previously burned up to avoid matrix effects for sulphate determinations. Binary sampling and stop-flow strategies were used to increase the sensitivity of the method. The optimization of analytical parameter was performed by response surface method using Box-Behnker and central composite designs. The proposed sequential flow procedure permits to determine up to 10.0 mg SO₄²⁻ l⁻¹ with R.S.D. <2.5% and limit of detection of 0.27 mg l⁻¹. The method has been successfully applied for sulphate determination in automotive fuel alcohol and the results agreed with the reference volumetric method. In the optimized condition the SIA system carried out 27 samples per hour.     

Optimisation of a flow injection system with electrochemical detection using the desirability function: Application to the determination of hydroquinone in cosmetics

A procedure is proposed in which the determination of hydroquinone using a flow injection system with electrochemical detection is described. Size and coefficient of variation of the signal are optimised by a desirability function and a central composite design. The robustness of the optimum reached in the optimisation step is evaluated by means a Plackett-Burman design. The optimised FIA system is able to determine hydroquinone with a minimum detectable net concentration of 10 μg l⁻¹ with a false positive probability of 0.05 and a false negative probability less than 0.05. In samples of bleaching cream, the proposed procedure has a recovery of 102.2% with standard deviation of 4.4% and a relative error of 6.2%.     

Optimization and characterization of UV-curable adhesives for optical communications by response surface methodology

Novel organic UV-curable material (UCM) containing fluorine and methoxy-silane has been specifically developed for the fabrication of optical-communications systems devices. Response surface methodology (RSM) was used to evaluate the effect of UCM and colloidal silica content in UV-curable adhesive formulations on the refractive index, curing, adhesion strength (dry and wet) and coefficient of thermal expansion (CTE). A central composite design for two variables at five levels was chosen as the experimental design. UCM for all six responses was highly significant and colloidal silica was significant for conversion and adhesion strength (dry and wet). UCM and colloidal silica had significant interactive effects on adhesion strength and CTE. Based on the fitted model, in order to get the optimal conditions for the application of optical adhesives in high-performance optical components, UCM should be set over 20 wt% and colloidal silica be set below 10 wt%.     

Determination of total and oxidized glutathione in human whole blood with a sequential injection analysis system

This work reports the development of a simple, robust, automated sequential injection analysis (SIA) system for the enzymatic determination of total (tGSH) and oxidized (GSSG) glutathione in human whole blood. The reduced (GSH) glutathione concentration is then obtained as the difference between the tGSH and GSSG concentrations. The determination was based on the DTNB–GSSG reductase recycling assay, which couples the specificity of the GSSG reductase (GR) with an amplification of the response to glutathione, followed by spectrophotometric detection of the 2-nitro-5-thiobenzoic acid (TNB) formed (λ = 412 nm). The implementation of this reaction in a SIA flow system with an in-line dilution strategy permitted the necessary distinct application ranges for tGSH and for GSSG. It also guaranteed the exact timing of fluidic manipulations and precise control of the reaction conditions.

The influence of parameters such as reagents concentration, temperature, pH, flow rate of the carrier buffer solution, as well as reaction coil length, etc., on the sensitivity and performance of the SIA system were studied and the optimum reaction conditions subsequently selected. Linear calibration plots were obtained for GSH and GSSG concentrations up to 3.00 and 1.50 μM, with detection limits of 0.031 and 0.014 μM, respectively. The developed methodology showed good precision, with a relative standard deviation (R.S.D.) < 5.0% (n = 10) for determination of both glutathione forms. Statistical evaluation showed good compliance, for a 95% confidence level, between the results obtained with the SIA system and those furnished by the comparison batch procedure.     

A multisyringe sequential injection method for monitoring water in the energy cogeneration system of a municipal waste incinerator

Leading-edge urban solid waste ashing plants use burning heat energy to obtain electrical power. Water fed to their boilers for conversion into steam should be highly pure in order to minimize corrosion, scaling and similar phenomena, which can lead to malfunctioning and a reduced useful life but can be avoided by proper management and control of the water supply. In this work, we developed a multiparameter monitor based on multisyringe sequential injection for the sequential determination of up to eight important parameters, namely: pH, specific and acid conductivity, hydrazine, ammonium, phosphate, silicate and total iron.Acid conductivity was determined by passing the sample through a cation-exchange resin in order to retain ammonium ion and release protons. This parameter was deemed the most accurate indicator of dissolved solids in boiler water. Chemical parameters were determined spectrophotometrically: hydrazine by reaction with p-dimethylaminobenzaldehyde, ammonium by the modified Berthelot reaction, iron with o-phenanthroline, and phosphate and silica by formation of a molybdoheteropoly blue dye in the presence of ascorbic acid as reductant. Use of the optimum chemical and physical operating conditions provided 3s_blank detection limits of 0.01 mg l⁻¹ N₂H₄, 0.13 mg l⁻¹ NH₄⁺, 0.04 mg l⁻¹ Fe, 0.03 mg l⁻¹ SiO₂ and 0.05 mg l⁻¹ PO₄³⁻, and relative standard deviations not greater than 2.5%. The methods integrated in the proposed monitor were successfully applied to real samples from the water-steam cycle at the Son Reus ashing plant in Palma de Mallorca (Spain).     

Rapid automated assay of anti-oxidation/radical-scavenging activity of natural substances by sequential injection technique (SIA) using spectrophotometric detection

A PC-controlled sequential injection analysis (SIA) system equipped with a spectrophotometric diode-array detector is used for rapid monitoring and evaluation of antioxidation/radical scavenging activity of biological samples. The automated method is based on the known reaction of stable 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) with antioxidants in organic or aqueous-organic media resulting in bleaching of DPPH due to its quenching by the interaction with the analytes. The decrease of the absorbance of DPPH (compared to blank experiment carried out with water–ethanol 1:1 instead of the test solution) measured at 525 nm is related to concentration of an antioxidant in the test solution. With the optimised SIA procedure it is possible to detect down to micromolar concentrations of model antioxidants such as ascorbic acid, caffeic acid, (+)-catechin, (–)-epicatechin and rutin and to evaluate the concentration of these antioxidants in the micromolar to millimolar range. The sample throughput is 45 h^–1. Thanks to its rapidity and sensitivity, the proposed SIA method is suitable for performing routine screening tests for the presence of various antioxidants in large series of lyophilised herbal or mushroom extracts (the amount of sample needed for the analysis is several milligrams).     

Determination of paracetamol in pharmaceutical formulations using a sequential injection system

A simple method for the rapid determination of paracetamol in pharmaceutical formulations is described. The method involves oxidation of paracetamol by potassium hexacyanoferrate(III) and a subsequent reaction with phenol in the presence of ammonia. The blue complex formed is measured at 630 nm. The system has a sample frequency of 27 samples per h with a detection limit of 0.2 mg l⁻¹. The calibration curve is linear up to 60 mg l⁻¹ with a relative standard deviation of 1.2% (n=10).     

Optimization of methylene blue removal from aqueous solutions using activated carbon derived from coffee ground pyrolysis: A response surface methodology (RSM) approach for natural and cost-effective adsorption

This study aimed to examine the impact of operational factors on the adsorption capacity of methylene blue (MB) using a natural and cost-effective adsorbent, activated carbon from coffee grounds (CAP). The three-factor Box-Behnken design of the response surface methodology (RSM) was employed to optimize this economically viable process with maximum efficiency. Through extensive experiments, the factors influencing the adsorption process were identified, their interactions were measured, and a mathematical model was developed. The experiment evaluated the quantity of MB adsorbed by CAP based on pH (2.5–10), initial MB concentration (10–100 mg/L), and CAP adsorbent amount (0.05–0.1 g/L). The results revealed that both concentration and mass significantly influenced the decoloration enhancement. Optimal conditions for achieving a 91 % degradation efficiency were determined as 0.05 g/L adsorbent weight, 100 mg/L dye concentration, and pH 2.5, with a desirability score of approximately 0.986, aligning closely with the predictions of the BBD model. In conclusion, this research addresses a research gap by demonstrating the high effectiveness of the CAP adsorbent in removing dyes from textiles.     

Purity determination of yunaconitine reference standard using HPLC with experimental design and response surface optimization

Experimental design and response surface methodology have been used for the development of the stability‐indicating HPLC method for the purity determination of yunaconitine reference standard. Significant factors including the contents of ACN, perchloric acid, triethylamine (TEA), and column temperature were optimized using a Box–Behnken design. A mixture of crude yunaconitine extract and degradation solutions of yunaconitine under stress conditions was chromatogramed. The normalized peak area of total impurities, the retention time of yunaconitine, and the resolutions between yunaconitine and its adjacent peaks were selected as optimization criteria. Derringer desirability function of the multicriteria and the tested factors were used to establish 3‐D response surfaces. The optimal condition was achieved with a mobile phase of ACN/water (30:70, containing 0.125% perchloric acid and 1.0% TEA) at a column temperature of 37.5°C. The method was validated and shown comparable to that of phase solubility analysis. As a result, the newly developed method can be used to determine the chromatographic purity and stability of the yunaconitine reference standard.     

Optimization of solid-phase microextraction of volatile phenols in water by a polyaniline-coated Pt-fiber using experimental design

Solid-phase microextraction (SPME) coupled to gas chromatography (GC) was applied to the extraction of phenol and some of its volatile derivatives in water samples. The SPME fiber consisted of a thin layer of polyaniline, which was electrochemically coated on a fine Pt wire. The stability of the coating was such that it could be used at temperatures as high as 325 °C, without any deterioration. The effects of various parameters affecting the extraction efficiency were studied, simultaneously. From these, optimization of the extraction temperature, extraction time, coating thickness, sample pH, salt concentration and desorption time was carried out by means of a (2^6-2) fractional factorial design. It was found that the effects and interactions of five out of six factors were significant. However, the coating thickness showed a large main effect but an insignificant interaction effect, so it was kept constant. Also, the effect of desorption time was insignificant if sufficient time was allowed for desorption to take place. Therefore, a central composite design (CCD) with four remaining factors, i.e., sample pH, salt concentration, extraction time and sample temperature was performed and a response surface equation was derived. The statistical parameters of the derived model were r = 0.97 and F = 25.3. The optimum conditions were obtained using a grid method. Using the optimum conditions, the method was analytically evaluated. The detection limit, relative standard deviation, linear range and recovery were 1.3-12.8 ng mL⁻¹, 2.2-5.3%, 0.01-5.0 μg mL⁻¹, and 88-103%, respectively. The results showed the suitability of polyaniline-coated fiber in analyzing volatile phenolic compounds in water samples.     

Optimization of hydroxyl radical formation using TiO2 as photocatalyst by response surface methodology

The determination of the optimum parameters for hydroxyl radicals (OH) formation by a TiO₂ solution has been investigated by measuring the emitted fluorescence after the reaction with terephthalic acid has occurred. After UV irradiation, the terephthalic acid was transformed into 2-hydroxyterephthalic acid whose fluorescence is directly proportional to the generated OH. Optimization of hydroxyl radicals’ formation using TiO₂ as catalyst was carried out by studying the effects of irradiation time, TiO₂ concentration and terephthalic acid concentration on the production of the fluorescent HTA with an experimental design. The aim of our research was to apply response surface methodology as a chemometric method for the optimization of the reaction conditions. The combination of irradiation time, TiO₂ concentration and terephthalic acid concentration was varied at designed points of a central composite rotatable design. The three factors were found to have a significant effect upon the reaction. The optimum conditions for the reaction achievement were estimated to be 10 min for the irradiation time, 25 μg mL⁻¹ TiO₂ concentration and 0.1 mmol L⁻¹ terephthalic acid concentration. Afterwards, using these parameters the method was applied for the determination of the ability of several plant extract samples to scavenge the formed OH.     

Optimization of tensile properties of injection molded α-nucleated polypropylene using response surface methodology

Tensile properties are among the significant properties of isotactic polypropylene (iPP). The mechanical properties including the tensile properties are fairly dependent on the overall crystallinity and crystallite size and their distribution in molded product, type of crystal structure and testing conditions. In presence of α-nucleating agents, the crystallization rate and onset temperature of isotactic PP increase. In this paper, the role of externally added commercial α-nucleating agent HPN-20E (Milliken Inc.) on tensile properties was investigated with respect to tensile properties of pure iPP. The experimental part includes the use of design of experiment (DoE) - response surface methodology (RSM) with central composite design (CCD) having three factors namely mold temperature, melt temperature and injection rate. Two levels of each factor with six centre points and five numbers of replicates were selected. The nucleating agent, HPN-20E, was added 1.0% by wt. in iPP (mfr 11.0 g/10min) using a lab scale co-rotating twin screw extruder. The compounded pellets were dried at 85 °C in a circulating hot air oven for 24 h. The tensile samples (ASTM-638D, type-I) were molded on a micro-injection molding machine (make BabyPlast, Italy). The samples were tested for tensile properties on a universal testing machine (make Lloyds, USA). The measured responses were tensile strength (MPa), Young's modulus (MPa) and work to break (N.mm). The same experimental procedure was also followed for pure iPP and same responses were measured to set the baseline of experiment. The analysis of variance (ANOVA) tests unearth that mold and melt temperatures are highly interacting in nature. That is why previous attempts based on traditional way of varying one parameter at a time were not so successful to relate tensile properties with injection molding variables. The RSM tests resulted into useful quantitative relationship between the tensile properties and injection molding process variables.     

响应曲面法用于高效液相色谱优化分离磺胺的研究

通过响应曲面法对高效液相色谱分离磺胺的优化过程进行了研究,分别考察了分离的3个主要因素(柱温、流动相配比、流速)对最小分离度与分离时间的影响,建立了3个因素与最小分离度和最大保留时间的目标函数,从响应曲面图可优化预测因素水平范围内的最佳分离条件.在选定优化条件下:柱温为20℃,乙腈的体积分数19%,流速1.5 mL/min,8种磺胺组分可在8 min内达到基线分离.     

Determination of boron as boric acid in eye lotions using a sequential injection system

A simple and reliable sequential injection analysis (SIA) system is described for the determination of boron as boric acid in eye lotions. This method is based on the complexation reaction between d-sorbitol and boric acid followed by the acid-base reaction with methyl orange (MO). The colour change reaction is monitored at 520 nm. The system is able to monitor boron at a frequency of 30 samples per h with a relative standard deviation of less than 0.6%. The calibration graph is linear up to 12-mg l(-1). The system has a detection limit of 0.06-mg l(-1). No significant differences (at 95% probability level) were found between the proposed SIA method and the reference method.