Search

The present work focuses on the investigation of protective coatings produced on zinc from chitosan (Chit) and an anionic dye, namely cresol red. Cresol red (CR) fulfills the basic requirements to be used as a corrosion inhibitor because it possesses a relatively high molecular weight and includes in its structure oxygen and sulfur atoms as well as aromatic rings. Moreover, it is an anionic compound that can interact with positively charged chitosan to produce reinforced coatings for zinc anti-corrosion protection. The influence of cresol red as a possible corrosion inhibitor for zinc substrates was investigated either in solution or incorporated in Chit coatings. Two preparation methods for the coatings were used: (i) Chit coating impregnation by immersion in the CR solution after Chit deposition on Zn, and (ii) chitosan mixing with the CR solution before applying the dip-coating technique. Potentiodynamic polarization curves were used to determine the kinetic parameters of the corrosion process. Long-term measurements were carried out in wet/dry cyclic conditions by using electrochemical impedance spectroscopy. EIS measurements recorded in 0.2 g/L Na2SO4 at pH = 7 show an important increase in the impedance of the coatings occurring from the first until the fifty-fifth day in a row, in dry–wet cycles. This increase is due to the beneficial effect of CR incorporated in Chitosan and could be, at least partially, related to a consolidation of the Chit coating structure in the presence of CR by crosslinking between Chit and CR molecules. The structure of the coatings was studied, and the interactions between chitosan and cresol red were put into evidence by using FT-IR spectroscopy. Adhesion and wettability measurements were also carried out. The adhesion of Chit incorporating CR on Zn was better than that on glass substrates and reached ~99.99%, suggesting a better affinity of the chitosan coating towards the Zn substrate due to the existence of ZnO on the substrate surface. All the results show that CR could be used on zinc as a corrosion inhibitor incorporated in chitosan at basic pHs, but without taking advantage of its pH-indicating properties, which are lost due to the interactions occurring between the positively charged biopolymer and the negatively charged dye molecule. The preparation method of Chit coating impregnation with CR by immersion in the solution after deposition on Zn led to poorer results than the method in which chitosan was previously mixed with CR before applying the dip-coating technique. [ABSTRACT FROM AUTHOR]

Since SARS-CoV-2 is a highly transmissible virus, a rapid and accurate diagnostic method is necessary to prevent virus spread. We aimed to develop and evaluate a new rapid colorimetric reverse transcription loop--mediated isothermal amplification (RT-LAMP) assay for SARS-CoV-2 detection in a single closed tube. Nasopharyngeal and throat swabs collected from at-risk individuals testing for SARS-CoV-2 were used to assess the sensitivity and specificity of a new RT-LAMP assay against a commercial qRT-PCR assay. Total RNA extracts were submitted to the RT-LAMP reaction under optimal conditions and amplified at 65 °C for 30 min using three sets of specific primers targeting the nucleocapsid gene. The reaction was detected using two different indicator dyes, hydroxynaphthol blue (HNB) and cresol red. A total of 82 samples were used for detection with HNB and 94 samples with cresol red, and results were compared with the qRT-PCR assay. The sensitivity of the RT-LAMP-based HNB assay was 92.1% and the specificity was 93.2%. The sensitivity of the RT-LAMP-based cresol red assay was 80.3%, and the specificity was 97%. This colorimetric feature makes this assay highly accessible, low-cost, and user-friendly, which can be deployed for massive scale-up and rapid diagnosis of SARS-CoV-2 infection, particularly in low-resource settings. [ABSTRACT FROM AUTHOR]

In this work, flower-like β-Ni(OH)2 nanoarchitectonic particles were successfully synthesized via a simple homogeneous precipitation method. The crystal structure and morphology were detected by x-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The influence of the dosage of β-Ni(OH)2 and potassium persulfate (PS) on adsorption and degradation of cresol red dye was studied. The results indicate that when the dosage of β-Ni(OH)2 was larger than 5 g/L, the major reason for cresol red dye removal was adsorption due to its large specific surface area of 45 m2/g. However, when the dosage of β-Ni(OH)2 was 0.5–0.7 g/L, the adsorption effect on cresol red dye was not obvious, but the degradation effect became significant after adding 0.3–0.5 mmol/L PS, benefiting from the strong activation of PS to generate ·SO4−, ·OH− and S2O8− radicals by β-Ni(OH)2. The degradation efficiency of 0.1 mmol/L cresol red dye reached over 98% in a neutral or alkaline medium. In particular, at pH = 9, the initial degradation efficiency was 99.9% and remained 99.25% after eight cycles. Thus, the high activity and stability make β-Ni(OH)2 a promising catalyst for activating persulfate to degrade organic pollutants. [ABSTRACT FROM AUTHOR]

Optical properties of a synthetic dye cresol red (CR) were investigated at its absorption band maxima (λ max) using double beam scanning UV/VIS spectrophotometer for the sample solutions having initial optimized dye-concentration. Urbach Edge method was utilized for the investigations of absorption edge ( A E = 2.35 eV) while Mott and Davis model was utilized for the investigations of band gap energy for direct ( E g , direct = 2.45 eV) and indirect ( E g , indirect = 2.23 eV) allowed transitions. The spectrophotometric-evaluations assisted most-sensitive working pH of sample solutions was optimized for a long spectrum of pH values from 1 to 12 for further investigations. Some spectrophotometric and comercial parameters e.g., molar extinction coefficient ε , stability, reproducibility and fading were figured out. The response efficacy was also observed to enhanc the sensitivity and stability of the CR solutions by incorporating a selected amount (by %vol) of a polar additive ethanol. The invariant aborbance related isosbestic wavelength for both acidic and alkaline samples remained unaffected from pH and firmly stood at 475 nm. The improved and reasonable pH values were found to be pH 4 and pH 9 and hence were opted for CR solutions and may further be applicable to the radiation-induced degradation phenomenon based on radiolytic bleaching. [ABSTRACT FROM AUTHOR]

The present work focuses on the investigation of protective coatings produced on zinc from chitosan (Chit) and an anionic dye, namely cresol red. Cresol red (CR) fulfills the basic requirements to be used as a corrosion inhibitor because it possesses a relatively high molecular weight and includes in its structure oxygen and sulfur atoms as well as aromatic rings. Moreover, it is an anionic compound that can interact with positively charged chitosan to produce reinforced coatings for zinc anti-corrosion protection. The influence of cresol red as a possible corrosion inhibitor for zinc substrates was investigated either in solution or incorporated in Chit coatings. Two preparation methods for the coatings were used: (i) Chit coating impregnation by immersion in the CR solution after Chit deposition on Zn, and (ii) chitosan mixing with the CR solution before applying the dip-coating technique. Potentiodynamic polarization curves were used to determine the kinetic parameters of the corrosion process. Long-term measurements were carried out in wet/dry cyclic conditions by using electrochemical impedance spectroscopy. EIS measurements recorded in 0.2 g/L Na2SO4 at pH = 7 show an important increase in the impedance of the coatings occurring from the first until the fifty-fifth day in a row, in dry–wet cycles. This increase is due to the beneficial effect of CR incorporated in Chitosan and could be, at least partially, related to a consolidation of the Chit coating structure in the presence of CR by crosslinking between Chit and CR molecules. The structure of the coatings was studied, and the interactions between chitosan and cresol red were put into evidence by using FT-IR spectroscopy. Adhesion and wettability measurements were also carried out. The adhesion of Chit incorporating CR on Zn was better than that on glass substrates and reached ~99.99%, suggesting a better affinity of the chitosan coating towards the Zn substrate due to the existence of ZnO on the substrate surface. All the results show that CR could be used on zinc as a corrosion inhibitor incorporated in chitosan at basic pHs, but without taking advantage of its pH-indicating properties, which are lost due to the interactions occurring between the positively charged biopolymer and the negatively charged dye molecule. The preparation method of Chit coating impregnation with CR by immersion in the solution after deposition on Zn led to poorer results than the method in which chitosan was previously mixed with CR before applying the dip-coating technique.

Since SARS-CoV-2 is a highly transmissible virus, a rapid and accurate diagnostic method is necessary to prevent virus spread. We aimed to develop and evaluate a new rapid colorimetric reverse transcription loop--mediated isothermal amplification (RT-LAMP) assay for SARS-CoV-2 detection in a single closed tube. Nasopharyngeal and throat swabs collected from at-risk individuals testing for SARS-CoV-2 were used to assess the sensitivity and specificity of a new RT-LAMP assay against a commercial qRT-PCR assay. Total RNA extracts were submitted to the RT-LAMP reaction under optimal conditions and amplified at 65 °C for 30 min using three sets of specific primers targeting the nucleocapsid gene. The reaction was detected using two different indicator dyes, hydroxynaphthol blue (HNB) and cresol red. A total of 82 samples were used for detection with HNB and 94 samples with cresol red, and results were compared with the qRT-PCR assay. The sensitivity of the RT-LAMP-based HNB assay was 92.1% and the specificity was 93.2%. The sensitivity of the RT-LAMP-based cresol red assay was 80.3%, and the specificity was 97%. This colorimetric feature makes this assay highly accessible, low-cost, and user-friendly, which can be deployed for massive scale-up and rapid diagnosis of SARS-CoV-2 infection, particularly in low-resource settings.

Existing optical carbon dioxide sensors using ion pair materials with pH indicators need moisture to function. To sense dry carbon dioxide gas, hydrophobic films were prepared using an amine polymer (branched-polyethyleneimine) instead of water, along with an ion pair dye and an aromatic polymer. The color of the ion pair formed between cresol red sodium salt and tetra-n-octylammonium bromide was yellow when the pH was below neutral. After adding branched polyethyleneimine, the color changed to violet as the pH became basic. On exposure to carbon dioxide, the amine groups on the branched-polyethyleneimine were converted to alkyl carbamate anions and ammonium cations via reaction with the carbon dioxide. When the ion pair reacted with the resulting ammonium cations, the film changed color from violet to yellow. It was determined that the degree of color change was dependent on the carbon dioxide exposure times and the amount of branched-polyethyleneimine added to the film. [ABSTRACT FROM AUTHOR]

This study investigates the effect of mediating plant extract on the photocatalytic activities of four eco-friendly synthesized magnetite (Fe 3 O 4) nanoparticles (NPs) against the photodegradation of cresol red (CR). For this purpose, the adsorption of CR has been carried out in dark ambient conditions at first to eliminate the impact of adsorption, followed by the recovery of Fe 3 O 4 NPs by a centrifuge. Second, photocatalytic reactions of CR have been conducted on recovered magnetite NPs, under UV-Vis irradiation (365 nm) in ambient conditions. This study presents a novel investigation of the effect of mediating plant extract on the densities of surfacic photoactivated Brönsted and Lewis acid sites on Fe 3 O 4 NPs against photocatalytic reactions of CR. To do so, free auxochromes and chromophores that are not reacted with photoactivated Brönsted and Lewis acid sites have been analyzed using FTIR spectroscopy. This analysis provides insights into the densities of photoactivated Brönsted and Lewis acid sites during CR photodegradation reactions on the four Fe 3 O 4 surfaces and permits their comparison. Found results showed that, during CR photodegradation, the band gap energy is not the single parameter responsible herein for the photoactivation of acid sites and hence photocatalytic activity, but also mediating plant extract plays a crucial role. Where, a decrease in plant extract's acidity guides to more photoactivate Lewis acid sites, and an increase in the acidity guides to more photoactivate Brönsted acid sites. Because most functional groups of CR are auxochromes that favor reacting with photoactivated Lewis acid sites, the Fe 3 O 4 synthesized using less acidic plant extract showed the highest photocatalytic activity. These results are in accord with the calculated photodegradation capacities, yields, and kinetic rates. [Display omitted] • Study of photocatalytic activity of four F e 3 O 4 NPs samples via CR photodegradation. • Effect of mediating plant extract on photoactivated acid sites has been investigated. • An increase in plant extract acidity leads to more photoactivate Brönsted acid sites. • A decrease in plant extract acidity leads more photoactivate Lewis's acid sites. • Less acidic plant extract increases better F e 3 O 4 NPs' photocatalytic activity on CR. [ABSTRACT FROM AUTHOR]

Two accurate spectrophotometric methods described for the estimation of carbamazepine (CBZ) in both pharmaceutical and pure form. These methodologies are attached to the bromination of CBZ by bromine formed in instantly from the bromate-bromide reaction. The general procedure includes the additional of a known amount of bromate-bromide reagent in an acidic mediocre to CBZ. After the reaction is integrated, the unreacted bromine was reacted with a steady amount of methylene blue, and the absorbance was measured at 665 nm (method A) or, cresol red could be used for the reaction and the absorbance moderated at 517 nm (method B). Beer’s law was submitted from 0.45 to 15.00 µg/mL CBZ with a molar absorptivity of 4.93 × 103 L/mol.cm for method A and from 0.50 to 12.00 µg/mL CBZ with a molar absorptivity of 1.37 × 104 L/mol.cm for method B. The proposed methods were effective for the determination of CBZ in tablets with great precision and accuracy.

In 2016, a novel porcine circovirus (PCV), PCV3, was identified in USA. Subsequently, it was proved to be also epidemic in China, Poland, and Korea. To analyze and control the epidemic situation of PCV3, it is necessary to establish accurate and high-throughput detection methods. In this study, the colorimetric isothermal multiple-self-matching-initiated amplification (IMSA) using cresol red was developed to detect PCV3 for the first time. The reaction can be easily performed by incubating the tube at 63°C for 60 min. By the addition of pH-sensitive indicator dye cresol red, the initial color of the reaction mixture is red. When PCV3 capsid gene DNA was positive in the sample, the color of the reaction mixture changed from red to yellow after the isothermal incubation at 63°C, while the negative control maintained the red color. The colorimetric IMSA displayed good specificity in detecting PCV3, PCV2, and PCV1 and 4 porcine DNA pathogens. Moreover, it has a low and repeatable detection limit of 10 copies, which is consistent with TaqMan-based qPCR, but 10 times more sensitive than PCR. In diagnosing 128 clinical specimens, it not only showed 100% agreement with qPCR but also detected 15 positive results more than PCR. The colorimetric IMSA we offered might be a good choice for PCV3 epidemiological investigation and point-of-care testing.

Abstract The purpose of this study was to investigate the feasibility of simultaneous optimization and removal of dyes, Malachite green (MG), Rhodamine B (RhB) and Cresol Red (CR) from aqueous solutions by using Sistan sand as an extremely low cost adsorbent. Factors affecting adsorption of the analytes on the sorbent were investigated experimentally and by using Taguchi and Plackett–Burman experimental design methods. In most cases, the results of these two models were in agreement with each other and with experimental data obtained. Taguchi method was capable to predict results with accuracies better than 97.89%, 95.43%, and 97.79% for MG, RhB, and CR, respectively. Under the optimum conditions, the sorbent could remove simultaneously more than 83% of the dyes with the amount of adsorbed dyes of 0.132, 0.109, and 0.120 mg g−1 for MG, RhB and CR on sand, respectively. Kinetic studies showed that pseudo second order is the best model of adsorption for all analytes. Thermodynamic parameters revealed that this process is spontaneous and endothermic.

Fabrication of pH sensor based on fiber optic coated bromophenol blue and cresol red has been done. Briefly, jacket in the middle part of the fiber optic was removed for 5 cm. Then the core of each of fiber optics was washed in ethanol. Nitric acid, demineralized water, and ethanol again consecutively. Then the cleaned core was coated using active material using sol-gel immobilization technique. Tetraehyl orthosilicate was used as a binder in the immobilization of active materials. Bromophenol blue will start change the color to yellow at below pH 3.00±0.01 and blue at above pH 4.60±0.01, while the cresol red will start change the color to yellow at below pH 7.20±0.01 and violet at above pH 8.80±0.01. The pH sensors which have been made show the sigmoidal response over pH from 1.00±0.01 to 11.00±0.01. The sensor has a better performance in comparation with the other sensor. [ABSTRACT FROM AUTHOR]

This work was carried out in the field of water treatment using advanced oxidation processes (AOPs), especially photolysis of carboxylic acid that leads to the formation in situ of hydroxyl radical (·OH). Cresol red (CR) degradation induced by organic acids/UV system was investigated in aqueous solution. The preliminary study of CR-organic acid mixture in the dark and at room temperature allowed confirming the absence of interaction under our experimental conditions. However, upon irradiation at 365 nm, the proportion of elimination of CR was 89% after 5 h of irradiation. Indeed, the CR degradation efficiency depends on the acid concentration and the pH of the medium. The concentration of acid is optimized to the 5 × 10−3 M. pH 2.39 was the optimal one when C2HO−4 was the most important species at this pH. The use of i-PrOH as ·OH confirmed the involvement of ·OH in photodegradation of CR induced by Ox. The addition of metal ions including Zn2+ and Cu2+ to the CR-organic acid mixture slowed the CR degradation unlike Fe2+, hence an improvement of its disappearance was observed. The results showed a faster degradation of the pollutant under excitation by sunlight. This environmentally friendly method appears to be very effective in the treatment of wastewater. [ABSTRACT FROM AUTHOR]

l -asparaginase is a pharmaceutically and industrially important enzyme as it has potential to treat different cancers and inhibit acrylamide formation in fried and baked food products. In the present study, an attempt was made to screen for new and novel l -asparaginase producers using a widely applied phenol red and bromothymol blue (BTB) 1 1 BTB, bromothymol blue. dye-based plate assay. Screening of four different soil samples for l -asparaginase producers resulted in the isolation of three new potential l -asparaginase producing bacteria. These three strains identified (by 16S rRNA sequencing) as a Pseudomonas resinovorans strain IGS-131, a Bacillus safensis strain IGS-81, and a Glutamicibacter arilaitensis strain ICS-13 with enzyme activities of 10.91 IU/ml, 6.65 IU/ml, and 1.47 IU/ml, respectively. These three strains of bacteria have not been reported as l -asparaginase producers previously. Also, we developed a new pH indicator dye-based plate assay for the screening of l -asparaginase producers after testing eight different pH indicator dyes. This cresol red dye-based method gave a better differentiable zone of hydrolysis and consistent results as compared to previously reported phenol red and BTB-based plate assay. It was also found to be efficient in comparison to all other dyes studied. It produced a bright yellow color at acidic pH (5.5) and turned into a dark red or maroon color when pH was increased (above 7.5). This finding is expected to make screening of all kinds of l -asparaginases more comfortable, rapid, and efficient. [ABSTRACT FROM AUTHOR]

In this study, removal of Cresol Red (CR), a cationic triphenylmethane dye, by 300 kHz ultrasound was investigated. The effect of additive such as potassium monopersulfate (oxone) was studied. Additionally, sonolytic degradation of CR was investigated at varying power and initial pH. RC can be readily eliminated by the ultrasound process. The obtained results showed that. Sonochemical degradation of CR was strongly affected by ultrasonic power and pH. The degradation rate of the dye increased substantially with increasing ultrasonic power in the range of 20–80 W. This improvement could be explained by the increase in the number of active cavitation bubbles. The significant degradation was achieved in acidic conditions (pH = 2) where the color removal was 99% higher than those observed in higher pH aqueous solutions. The ultrasonic degradation of dye was enhanced by potassium monopersulfate (oxone) addition. It was found that the degradation of the dye was accelerated with increased concentrations of oxone for a reaction time of 75 min. [ABSTRACT FROM AUTHOR]

Cresol Red, a commercial dye that used widely to color nylon, wool, cotton, and polyacrylonitrile-modified nylon in the massive textile manufacture is toxic recalcitrant. Absidia spinosa M15, a novel fungal strain isolated from a tropical rain forest, was found to decolorize Cresol Red 65% within 30 d under agitation condition. UV–Vis spectroscopy, TLC analysis and mass spectra of samples after decolorization process in culture medium confirmed final decolorization of Cresol Red. Two metabolites were identified in the treated medium: benzeneacetic acid (t R 9.6 min and m/z 136) and benzoic acid (t R 5.7 min and m/z 122). Laccase showed the significant activity (133.8 U/L) in biomass obtained at the end of experiment demonstrates role of the enzyme in the decolorization process. [ABSTRACT FROM AUTHOR]

Cresol Red belongs to the triphenylmethane (TPM) class of dyes which are potentially carcinogenic or mutagenic. However, very few studies on biodegradation of Cresol Red were investigated as compared to other type dyes such as azo and anthraquinone dye. The aim of this work is to evaluate triphenylmethane dye Cresol Red degradation by fungal strain isolated from the decayed wood in Johor Bahru, Malaysia. Detailed taxonomic studies identified the organisms as Trichoderma species and designated as strain Trichoderma harzianum M06. In this study, Cresol Red was decolorized up to 88 % within 30 days under agitation condition by Trichoderma harzianum M06. Data analysis revealed that a pH value of 3 yielded a highest degradation rate among pH concentrations (73 %), salinity concentrations of 100 g/L (73 %), and a volume of 0.1 mL of Tween 80 (79 %). Induction in the enzyme activities of manganese peroxidase, lignin peroxidase, laccase, 1,2- and 2,3-dioxygenase indicates their involvement in Cresol Red removal. Various analytical studies such as Thin-Layer Chromatography (TLC), UV-Vis spectrophotometer, and Gas chromatography mass spectrometry (GC-MS) confirmed the biotransformation of Cresol Red by the fungus. Two metabolites were identified in the treated medium: 2,4-dihydroxybenzoic acid ( t 7.3 min and m/z 355) and 2-hydroxybenzoic acid ( t 8.6 min and m/z 267). Based on these products, a probable pathway has been proposed for the degradation of Cresol Red by Trichoderma harzianum M06. [ABSTRACT FROM AUTHOR]

Abstract: Interaction of anionic dye, cresol red (CR), with cationic surfactants, dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB), in aqueous solution in the submicellar and micellar concentration ranges has been investigated by using thermodynamic and spectroscopic methods. The equilibrium model has been used to calculate the standard free energy (∆G m o), enthalpy (∆H m o), and entropy (∆S m o) of micelle formation. The increase in the critical micelle concentration (cmc) with rise in temperature is attributed to the disruption of the structured water surrounding the hydrophobic groups of the surfactants. A marked decrease in the cmc is observed as the number of carbon atoms in the hydrophobic group increases from DTAB to CTAB. Higher values of the degree of ionization (α) of the micelles of DTAB and CTAB are obtained in the presence of CR than in its absence. Negative values of ∆G m o and ∆H m o for the surfactants in aqueous and in aqueous CR solutions show that the process of micellization is thermodynamically spontaneous and exothermic. The values of −T∆S m o are much higher than the ∆H m o values, indicating that the micellization process is governed primarily by the entropy gain associated with it. The heat capacity of micellization (ΔC p,m ο ) is negative which is mainly due to the change in the exposure of the hydrophobic groups to the water molecules. UV–visible spectra suggest interaction between dye and surfactant monomers forming ion-pair complex in the pre-micellar region whereas above the cmc solubilization of dye in the micelle dominates over ion-pair formation. [Copyright &y& Elsevier]

Dissolved CO 2 originating from underground structures at high concentrations may pose a threat to public and environmental health. Therefore, a convenient monitoring technique that allows fast detection of dissolved CO 2 needs to be developed. In this study, a low-cost colorimetric CO 2 sensor was applied for monitoring dissolved CO 2. The sensor is composed of an acrylic reactor, cresol red pH indicator solution, and a gas-permeable membrane, and the performance of the sensor was tested for the detection of dissolved CO 2 at the range of 2–800 mg CO 2 L−1. Color change of the detection solution within the sensor was mainly dependent on CO 2 dissolved in the water sample. This was analyzed using an RGB program that extracts the red, green, and blue intensity of a target color on a scale of 0–255. Δ GB , an index of CO 2 concentration corresponding to the change in intensity of green (G) and blue (B) extracted by the RGB program, exhibited a linear relationship with dissolved CO 2 concentrations (r 2 > 0.95, p < 0.005). In the field, the sensor was able to measure dissolved CO 2 between 10 and 411 mg CO 2 L−1 within 1 min. Overall, our CO 2 sensor has high potential to be used in detection of dissolved CO 2 in groundwater and surface waters. [Display omitted] • An optical sensor based on a pH indicator was applied in measuring dissolved CO 2. • RGB program was used for the quantification of dissolved CO 2. • Dissolved CO 2 at 2–800 mg L−1 was measured in spring and sea water. • The sensor performed successfully in the laboratory and field. • Dissolved CO 2 in natural waters can be monitored using this cost-efficient sensor. [ABSTRACT FROM AUTHOR]

Abstract: The MicroResp™ method allows soil respiration and microbial community physiological profiles to be determined colorimetrically in microplates. This method, however, neglects CO2 storage in the agar gel carrying the colorimetric indicator, and calcite dissolution associated with CO2-induced change in soil solution pH. Our objective was to improve the method by taking into account CO2 in the gel in the calculation of microbial respiration, describing the effect of microbial CO2 on the pH of the soil solution and calcite dissolution, and checking whether CO2 distribution among calcite, soil solution, air and gel is near equilibrium after incubation. We propose a thermodynamic equilibrium model describing (a) distribution of CO2 among calcite, soil solution, gel and air, (b) dissociations of water, carbonic acid, cresol red, and substrates in the gel and soil solution, (c) exchange of adsorbed cations with H3O+ in the gel, and (d) calcite dissolution in soil. In-gel experiments were designed to calibrate the model, quantify the rate of CO2 exchange with air, and compare conservation procedures. On-soil experiments were designed to check whether calcite dissolution is near equilibrium and whether the model predicts the effect of CO2 on the pH of the solution. In-microplate experiments were designed to assess the effects of incubation period and soil quantity on estimated microbial respiration. The model can describe the distribution and speciation of CO2 in the gel, the soil solution and the air space of each microplate well. Initial properties of the gel vary with storage: soda lime partly extracts CO2 supplied as NaHCO3, and dries out the gel, which can skew the calibration. When incubation is over, the proportion of microbial CO2 in the gel is higher at lower microbial respiration. Incubations shorter than 4h underestimate microbial respiration due to the slow diffusion of CO2 in the gel. CO2 in the soil solution cannot be overlooked; it decreases the soil pH and may promote calcite dissolution in calcareous soil. It is important to precisely estimate initial CO2 air fraction and to control temperature, which affects both thermodynamic constants and microorganisms. [Copyright &y& Elsevier]

Abstract: The use of impure cresol red in spectrophotometric seawater pH measurements can introduce systematic inaccuracies greater than 0.1. Cresol red has been purified on a bulk scale to address this problem, but a characterization of the dye's physical–chemical properties has not been provided to date. This work reports the physical–chemical characteristics of purified cresol red for use in spectrophotometric seawater pH measurements over a range of temperatures and salinities. Seawater pH is expressed on the total hydrogen ion concentration scale (pHT) in terms of the ratio (R) of cresol red absorbances (A) at 433 and 573nm (R CR = 573 A/433 A): where −log(K 2 T e 2)= a + b/T + c ln T − dT and cresol red molar absorptivity ratios are expressed as: for 278.15≤ T ≤308.15K and 20≤ S ≤40. We recommend using cresol red to measure the acidity of seawater that has (at 298.15K) a pHT of 6.8–7.8. This range might be encountered in ocean areas such as oxygen minimum zones or, hydrothermal vent fields, or it might be imposed in controlled laboratory studies. Ocean acidification will make cresol red an increasingly important indicator in coming decades as waters within ever larger ocean areas shift into its optimal indicating range. [Copyright &y& Elsevier]

Abstract: Impurities in sulphonephthalein indicator salts can result in significant errors in seawater pH determinations. To ensure suitable measurement accuracy and intercomparability on a global basis, impurities must be removed from all indicators used for oceanographic CO2 system analyses. Previous work has described an effective HPLC (high-performance liquid chromatography) procedure for purification of meta-cresol purple, but the technique is labor-intensive, with each HPLC run producing only a small batch of purified indicator. This work describes the use of flash chromatography to more efficiently produce large batches of purified meta-cresol purple (mCP) and cresol red (CR), the preferred indicators for direct water column determinations of seawater pH. Several batches of unrefined mCP and CR of independent origin were prepared by flash chromatography. Indicator purity was then assessed in two ways: by (a) HPLC verification and (b) pH measurements of highly buffered solutions. HPLC chromatograms of the various flash-prepared mCPs indicated that the process did not always result in a completely pure product. In terms of performance, however – i.e., pH measurements of highly buffered solutions – no differences were observed between an HPLC-purified reference mCP and the flash-purified mCPs. HPLC examination of the flash-purified CRs indicated that every product was free of detectable impurities. No differences were seen in comparative pH measurements made with the purified CRs. The flash chromatography procedures outlined in this work are suitable for producing bulk quantities of mCP and CR for use in high-precision spectrophotometric pH measurements in seawater. [Copyright &y& Elsevier]

Cresol Red (CR) pH indicator was encapsulated into silica network using the sol-gel process. Transparent monolithic disks of entrapped CR were obtained in the presence of cetyl trimethyl ammonium bromide (CTAB) or dodecyl dimethyl amino oxide (Genaminox LA,GLA) alkyl hydroxyethyl dimethyl ammonium chloride (HY, R = 12-14) and TX-100 surfactants. UV/VIS spectra showed that the encapsulated CR retains its structure in terms of its response to pH. At the neutral conditions it is found that the HY surfactant is considered as proton donor as favor the cationic form of the indicator, while CTAB surfactant favor the neutral, however GLA surfactant, the anionic form of CR is more favored because GLA has a zwitterionic head. The surfactant GLA with TEOS has shifted the equilibrium to the ionized form of CR due to the electrostatic interaction between the surfactant and the CR anion. Therefore their pH range is dependent on the nature of a surfactant used. It is found that the HY surfactant is more efficient as far as loading of CR is concern and it widened the working pH range. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic Fe3O4/C core–shell nanoparticles have been synthesized by a simple strategy and used as adsorbents for removal of organic dyes from aqueous solution. The resulting products are characterized by scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectra and Fourier transform infrared spectra (FTIR). Adsorption performances of the nanomaterial adsorbents are tested with removal of methylene blue (MB) and cresol red (CR) from aqueous solution. The effects of solution pH value, adsorption time and capacity of the nanocomposites have been fully investigated. The results reveal that the nanospheres can be easily manipulated by an external magnetic field with high separation efficiency. In addition, the process is clean and safe for purifying water pollution. The prepared Fe3O4/C complex nanomaterials could thus be used as promising adsorbents for the remove organic dyes, especially, cationic dye, from polluted water. [Copyright &y& Elsevier]

The tendency of anions of sulfophthaleine dyes to heteroassociation was studied in aqueous solutions of phenol red, cresol red, thymol blue, and non-substituted phenol red. It was spectrophotometrically determined that single (HAn) and doubly charged anions (An) of sulfophthaleines can form stable heteroassociates of the composition Ct · HAn and (Ct) · An with cations (Ct) of polymethine dyes, pinacyanol, and quinaldine red. The values of enthalpy formation of ions of dyes and heteroassociates were calculated semi-empirically and compared with experimentally determined values of the equilibrium association constants. [ABSTRACT FROM AUTHOR]

Abstract: An optical biosensing scheme based on urease encapsulated calcium alginate microspheres which are coated with polyelectrolyte nanofilms predominantly composed of cresol red (CR) dye is demonstrated in this paper. The dye molecules within the nanofilms are deposited via the layer-by-layer (LbL) self-assembly technique on the microspheres and used as the optical transducer. A flow through cell constructed using a cuvette attached to a fiber optic spectrometer was used to determine the response of the biosensor to standard urea solutions of different concentrations. The change in pH and the absorbance ratio was monitored with time and these results were used for measurements of urea concentrations in the spent dialysate fluid. The biological parameters controlling hemodialysis such as dialyzer clearance or Kt/V and percent removed urea (PRU) have also been reported. The results demonstrate that the urea biosensor is pH reversible with a sensitivity of 0.09 pH units/min and is able to detect a change of 0.005 ratio units in urea concentration ranging 0.1–60mgdL−1. The response time of the sensor was calculated as 8min while the detection range of urea covered the levels that are present in the spent dialysate fluid. The results obtained in the analysis of biological samples were in good agreement with those obtained by a reference method, showing no significant differences at a confidence level of 95%. [ABSTRACT FROM AUTHOR]