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In this work, an innovative fiber-optic sensor for measuring total acidity (TA: expressed as the % w/v of acetic acid) in beverages was developed. For this purpose, we relied on the kinetic principles of heterogeneous solid-phase reactions (slow reactions due to diffusion processes) to develop a novel pH-sensitive fluorescent membrane calibration method for the quantification of TA. In the proposed calibration method, a linear relationship between TA and the protonation rate of a pH-sensitive fluorescent membrane with a pKa ≥ 9 (Paper-FM) is established. Paper-FM was synthesized by the covalent immobilization of the pH-probe Nile Blue on a porous paper membrane. In addition, a 3D-printed interface was designed to implement Paper-FM into a 0.5 mm diameter optical fiber. The fiber-optic sensor developed in this work was tested by analyzing 21 vinegar samples of different origins, and the results were successfully validated with a reference titration method. The results presented in this work show that our fiber-optic sensor allows a direct, simple, and fast (15 s response time) quantification of TA in vinegar samples. In addition, it is environmentally friendly, because, unlike titration methods, it does not generate toxic waste, is reversible, and is extremely stable (a 0.9 mm diameter circle of Paper-FM allows at least 50 consecutive measurements). [Display omitted] • A pH-fluorescent membrane was designed and implemented into a fiber-optic device. • A novel calibration strategy of a fluorescent pH-membrane was developed. • The total acidity of real food samples was successfully determined. • The fiber-optic sensor is reversible and reusable. • The fiber-optic sensor is environmentally friendly as it does not generate waste. [ABSTRACT FROM AUTHOR]

An accurate and nondestructive prediction method of lime acidity was established based on near infrared (NIR) spectroscopy and ensemble learning strategy. Dual-band spectra were obtained nondestructively with a single scan using a desk-top Fourier transform spectrometer and a grating portable spectrometer. Spectral preprocessing methods were used to eliminate the interferences in the spectra. The quantification models of available acidity (pH and 10−pH) and total acidity (TA) were developed with the ensemble learning strategy compared with partial least squares (PLS) and variable selection methods. The results indicated that due to the high-energy light source, the models of the grating portable spectrometer were much better than those of the Fourier transform spectrometer. Short-wave NIR (SWNIR) was more suitable for quantitative analysis of available acidity, while long-wave NIR (LWNIR) was more effective for quantitative analysis of TA. Besides, the models of available acidity were ahead of those of TA. Compared with PLS and variables selection methods, the ensemble learning strategy can produce models with higher prediction accuracy and better robustness. In the optimized models, the correlation coefficients of pH, 10−pH and TA for the prediction set were 0.84, 0.82 and 0.66, respectively. The experiment results show that accurate and nondestructive prediction of lime acidity can be achieved with the grating portable NIR spectrometer and ensemble learning strategy. [Display omitted] • Simultaneous and nondestructive detection of pH and TA in lime was achieved. • Dual-band spectra were obtained with a single scan using two spectrometers. • Models of the grating portable spectrometer can satisfy practical application. • Ensemble learning strategy can produce models with higher prediction accuracy. • SWNIR was more suitable for pH, while LWNIR was more effective for TA. [ABSTRACT FROM AUTHOR]

[Display omitted] • XGaO y /meso-HZSM-5 catalysts with different GaO y loading (X, wt%) were prepared. • BTX was produced by coaromatization of methane and propane. • Total acidity showed a volcano-shaped trend with respect to gallium oxide loading. • BTX yield showed a volcano-shaped trend with respect to gallium oxide loading. • BTX yield increased with increasing total acidity of the catalysts. 2 wt% GaO y catalysts supported on mesoporous HZSM-5 and microporous HZSM-5 (denoted as 2GaO y /meso-HZSM-5 and 2GaO y /micro-HZSM-5, respectively) were prepared for use in the BTX (benzene, toluene, and xylene) production by coaromatization of methane and propane. It was revealed that 2GaO y /meso-HZSM-5 catalyst showed higher reactant conversion and initial BTX yield than 2GaO y /micro-HZSM-5 catalyst due to the enhanced mass transfer through 2GaO y /meso-HZSM-5 catalyst. On the basis of this result, a series of XGaO y /meso-HZSM-5 (X = 0.5, 1, 2, 4, and 6) catalysts with different gallium oxide loading (X, wt%) were prepared for BTX production by coaromatization of methane and propane. The effect of gallium oxide loading on the acid properties and catalytic activities of XGaO y /meso-HZSM-5 catalysts was investigated. It was found that total acidity of the catalysts served as a crucial factor determining the catalytic performance in the BTX production. Conversion of reactants and initial BTX yield increased with increasing total acidity of the catalysts. Among the catalysts tested, 2GaO y /meso-HZSM-5 catalyst with the largest total acidity showed the best catalytic performance in the BTX production. Thus, an optimal gallium oxide loading of XGaO y /meso-HZSM-5 catalysts was required for maximum production of BTX by coaromatization of methane and propane. [ABSTRACT FROM AUTHOR]

A novel method for correction of unknown unspecific (additive) interferences was developed in sequential injection analysis (SIA) using a Lab on Valve module (LOV) with spectrophotometric detection. The method implements a novel idea to calibrate by the standard addition method in several different chemical conditions created in such a way to measure different signal for an analyte and unchanged signal for interferents causing additive effect. This approach, being an enhancement of the H-point standard addition method (HPSAM), enables to quantify unbiased concentration of an analyte in the presence of unknown interferences. The method was tested on the example of the determination of ascorbic acid in soft drinks and juices basing on reduction of Fe(III) to Fe(II) and reaction of the latter with o-phenanthroline to the ferroin complex absorbing at 512.0 nm. The analytical utility of the method has been verified and confirmed by the spectrophotometric determination of total acidity in rose and red wines in the presence of bromothymol blue absorbing at 616.0 nm. Calibration solutions were prepared automatically in the designed flow system. Ascorbic acid was determined with LOD of 1.4 mg L −1 and LOQ of 4.2 mg L −1 within linear working range up to 80 mg L −1 , while in case of the determination of total acidity the values of 4.2, 11.8 and 100, respectively, were obtained. A sample was consumed in volumes of 400 and 1000 µL in both cases. The analyses are simple, “green”, and non-expensive. The developed method is readily applicable to analysis of real samples of complex unknown matrices and adaptable to different analytical methods. [ABSTRACT FROM AUTHOR]

The inability of refineries in some nations globally to produce kerosene locally as an aviation fuel is due to its acidity. In this study the viability of selected alkaline rich ash materials (e.g. cocoa husk, cassava peels, etc.) readily obtainable in tropical nations were examined for their ability to remove the acids. Fresh acidic kerosene samples were equilibrated with different ashes in predetermined ratios, filtered and characterized alongside with non-treated reference samples. Results revealed that the physicochemical properties of non-treated and treated kerosene remained the same except for conductivity, total acidity and micro-separation. The total acidity was reduced to a lowest limit than 0.015 mg KOH/g required. Treatment studies with specific masses of ashes and kerosene reduced acidity to approximately 0.00 mg KOH/g. Overall these alkaline source materials should be seen as a promising and alternative option in the systematic reduction of acidity in kerosene for aviation use. [ABSTRACT FROM AUTHOR]

Highlights: [•] NIR approach was assessed in order to determine the SSC and TA. [•] Three fruits with different internal structures were utiliszed. [•] Good results were obtained for the apricot. [•] Unsatisfactory results were obtained for the tomato and passion fruit. [•] Fruits physical features are limitations to NIR approach and should be considered. [ABSTRACT FROM AUTHOR]

The use of a voltammetric electronic tongue as a tool to monitor grape ripeness is proposed herein. The electronic tongue consists of eight metallic electrodes housed inside a stainless steel cylinder. The study was carried out over a period of ca. 1month (August 2012) on different grape varieties (Macabeo, Chardonnay, Pinot Noir, Cabernet Sauvignon, Shyrah, Merlot and Bobal) from various vineyards near Requena and Utiel (Valencia, Spain). Apart from the electrochemical studies, the physico-chemical parameters, such as, Total Acidity, pH and °Brix, were also determined in grapes. The PCA models, obtained using the physico-chemical or electrochemical data, showed variation of ripeness with time. Moreover the study was completed by using partial least squares (PLS) regression in an attempt to establish a correlation between the data collected from the electronic tongue and Total Acidity, pH and °Brix values. A good predictive model was obtained for the prediction of Total Acidity and °Brix. These results suggest the possibility of employing electronic tongues to monitor grape ripeness and of, therefore, evaluating the right time for harvesting. [ABSTRACT FROM AUTHOR]

Abstract: This work proposes the use of digital image-based method for determination of total acidity in red wines by means of acid–base titration without using an external indicator or any pre-treatment of the sample. Digital images present the colour of the emergent radiation which is complementary to the radiation absorbed by anthocyanines present in wines. Anthocyanines change colour depending on the pH of the medium, and from the variation of colour in the images obtained during titration, the end point can be localized with accuracy and precision. RGB-based values were employed to build titration curves, and end points were localized by second derivative curves. The official method recommends potentiometric titration with a NaOH standard solution, and sample dilution until the pH reaches 8.2–8.4. In order to illustrate the feasibility of the proposed method, titrations of ten red wines were carried out. Results were compared with the reference method, and no statistically significant difference was observed between the results by applying the paired t-test at the 95% confidence level. The proposed method yielded more precise results than the official method. This is due to the trivariate nature of the measurements (RGB), associated with digital images. [Copyright &y& Elsevier]

Abstract: The square wave voltammetric response of the reduction of acids of different strength namely, hydrochloric acid, phosphoric acid, lactic acid, acetic acid and sodium dihydrogenophosphate at a platinum microdisk electrode are presented. The voltammograms of HCl and display a single peak which height increased linearly with concentration. The acids of intermediary strength exhibit voltammograms resulting from the overlapping of two peaks that are assigned to the reduction of hydrogen ions (H+) and of the undissociated acid form (HA). Peaks separation depends on the acid strength and concentration. A numerical deconvolution of voltammograms was performed based on Gaussian peaks fitting. The deconvoluted peak current data for H+ were validated towards calibration curves of HCl. The validation of the current data of HA was performed using buffer solutions. The methodology present herein allows to assess simultaneously the concentration of each acid form from a single square wave voltammogram. [ABSTRACT FROM AUTHOR]

Abstract: On 35 unheated honeys coming from an area with typical Continental climate, we studied the evolution of pH, free acid, lactones and total acidity throughout 30 months, as well as the influence of induced granulation on acidity evolution. All samples were stored at room temperature and analyzed, in duplicate, each 5 months. We observed that storage had an effect on pH and free acid values. On the contrary, induced granulation did not show any influence on these parameters. In the end of the study, pH average had decreased down to 5%. After 20 months from harvesting, the vast majority of honeys showed a constant increase of free acid, although until 30 months, none sample exceeded the limit of 50meq/kg. A direct relationship was found between pH and free acid within each time of analysis. Both storage and induced granulation had an effect on honey lactones, parameter that steadily decreased after 20 months, and oscillated less markedly in samples subjected to induced granulation. For honeys from continental climates, taking free acid and lactones into account, 20 months could be proposed as best before period “once opened”. Neither storage nor induced granulation had an effect on total acidity, which hardly varied within 30 months storage. We found significant relationships between initial values of free acid and lactones and the values of these parameters at each time of analysis, meaning that aging of these honeys due to acidity could be predicted. [Copyright &y& Elsevier]

The interaction of mono-alkylamines with ETS-10 was studied by means of thermogravimetry, infrared spectroscopy and elemental analysis. Thermal effects from the adsorption of methyl, ethyl, propyl, butyl and pentylamine on ETS-10 suggest that the sites are saturated by 8.0 mmol of amine l−1 g−1 of solid. Elemental analysis indicate that no alkylamine is decomposed on adsorption and that an increased number of moles are adsorbed as the number of carbon atoms per molecule is increased. The derivative thermal analysis shows that a higher number of discrete mass losses are seen when the amine molecule is larger. Infrared spectroscopy of ETS samples where the alkylamines were adsorbed shows that the larger amines are more effective at giving clear bands for Lewis and Bro¨nsted acid sites, probably because they are adsorbed to a larger extent. [Copyright &y& Elsevier]

A potentiometric SI titration system for the determination of total acidity in soft drinks is proposed. The concept is based on the aspiration of the acid soft drink sample between two base zones into a holding coil with the volume of the first base zone twice to that of the second one and channelled by flow reversal through a reaction coil to a potentiometric sensor. A solution of 0.1 mol l−1 sodium chloride is used as ionic strength adjustment buffer in the carrier stream. The system has been applied to the analysis of some South African soft drinks having a total acidity level of about 0.2–0.3% (w/v). The method has a sample frequency of 45 samples per h with a linear range of 0.1 and 0.6% (w/v). It is easy to use, fully computerised, and gives the results that are comparable to both automated batch titration and manual titration. [Copyright &y& Elsevier]

• The total acidity in lactic acid is quantified by a direct potentiometric titration. • The novel method's procedure is simpler than the traditional back titration. • Reducing sugars do not interfere with measurements. • Oligomers of lactic acid in aqueous solutions (<30 wt%) can be fully hydrolyzed. • Monomeric lactic acid is stable in aqueous dilute solutions at room temperature. In aqueous solutions of concentrated lactic acid (>30 wt%), oligomers of lactic acid can produce via the intermolecular esterification of lactic acid, and thus the amount of titratable acidity is often less than that of total acidity. In this paper, the hydrolysis of oligomers of lactic acid was investigated at different temperatures in detail. The experimental results showed that when the content of total acidity is lower than 30 wt% in aqueous lactic acid solutions, the oligomers of lactic acid can been completely hydrolyzed to give monomeric lactic acid and the monomeric lactic acid is stable at temperatures of 8–33 °C, thus the total acidity is equivalent to the titratable acidity and can be determined quantitatively by a direct potentiometric titration. The results for determining total acidities were in good agreement with those obtained from a back titration by a two tailed t -test. Compared with the back titration, the novel method's procedure is simpler and reducing sugars do not interfere with measurements. The relative standard deviation (RSD) was less than 0.7% and 1.1% for the direct potentiometric and back titrations, respectively, which indicated that the direct potentiometric titration has a higher precision. [ABSTRACT FROM AUTHOR]

Abstract: The soluble solids content (SSC) and total acidity (TA) are the major characteristics for assessing quality and maturity of Nanfeng mandarin fruits. The feasibility of charge coupled device near infrared spectroscopy (CCD-NIRS) combining with effective wavelengths selection algorithm used to measure SSC and TA nondestructively was investigated. The effective wavelengths to SSC and TA were chosen by interval partial least squares (iPLS) in the wavelength range of 600–980nm. The predictive ability of SSC model used PLS regression was improved with r of 0.92 and RMSEP of 0.65°Brix using effective wavelengths of 681.36–740.51nm, 798.60–836.19nm and 945.52–962.75nm. The TA model was simplified with r of 0.64 and RMSEP of 0.09% using effective wavelengths of 817.57–836.19nm, 909.85–927.60nm and 945.52–962.75nm. The experimental results demonstrated that the CCD-NIRS technique combining with iPLS algorithm was a feasible method to measure SSC and TA of Nanfeng mandarin fruits nondestructively. [Copyright &y& Elsevier]