pH indicator

Research assessing the biological impacts of global ocean change often requires a burdensome characterization of seawater carbonate chemistry. For laboratory-based ocean acidification research, this impedes the scope of experimental design. Honeywell Durafet® III pH electrodes provide precise and continuous seawater pH measurements. In addition to use in oceanographic sensor packages, Durafets can also be used in the laboratory to track and control seawater treatments via Honeywell Universal Dual Analyzers (UDA). Here we provide performance data, instructions, and step-by-step recommendations for use of multiple UDA-Durafets. Durafet pH measurements were within ± 0.005 units pHT of spectrophotometric measurements and agreement among eight Durafets was better than ± 0.005 units pHT. These results indicate equal performance to Durafets in oceanographic sensor packages, but methods for calibration and quality control differ. Use of UDA-Durafets vastly improves time-course documentation...

In this work, we describe the synthesis of a novel 9-aminoacridine derivative that presents surprisingly different colors when exposed to neutral, acidic or basic mediums with potential application as pH indicator in organic solvents. Furthermore, pKa and molar absorptivity values were determined and theoretical studies supported by density functional theory (DFT) calculations were performed to elucidate the different structures of this compound.

Using both the proton selective vibrating electrode to probe the extracellular currents and ratiometric wide-field fluorescence microscopy with the indicator 2 Ј ,7 Ј -bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran to image the intracellular pH, we have examined the distribution and activity of protons (H ϩ ) associated with pollen tube growth. The intracellular images reveal that lily pollen tubes possess a constitutive alkaline band at the base of the clear zone and an acidic domain at the extreme apex. The extracellular observations, in close agreement, show a proton influx at the extreme apex of the pollen tube and an efflux in the region that corresponds to the position of the alkaline band. The ability to detect the intracellular pH gradient is strongly dependent on the concentration of exogenous buffers in the cytoplasm. Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 M or greater, will dissipate the gradient, possibly through shuttle buffering. The apical acidic domain correlates closely with the process of growth, and thus may play a direct role, possibly in facilitating vesicle movement and exocytosis. The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins. These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.

A new optical pH sensor based on polysulfone (PSU) and polyaniline (PANI) was developed. A transparent and flexible PSU membrane was employed as a support. The electrically conductive and pH-responsive PANI was deposited onto the membrane surface by in situ chemical oxidative polymerization (COP). The absorption spectra of the PANI-coated PSU membranes exhibited sensitivity to pH changes in the range of 4-12, which allowed for designing a dual wavelength pH optical sensor. The performance of the membranes was assessed by measuring their response starting from high pH and going down to low pH, and vice versa. It was found that it is necessary to precondition the sensor layers before each measurement due to the slight hysteresis observed during forward and backward pH titrations. PSU membranes with polyaniline coating thicknesses in the range of «100-200 nm exhibited fast response times of <4 s, which are attributed to the porous, rough and nanofibrillar morphology of the polyaniline coating. The fabricated pH sensor was characterized by a sigmoidal response (R 2 = 0.997) which allows for pH determination over a wide dynamic range. All membranes were stable for a period of more than six months when stored in 1 M HCl solution. The reproducibility of the fabricated optical pH sensors was found to be <0.02 absorption units after one month storage in 1 M HCl solution. The performance of the optical pH sensor was tested and the obtained pH values were compared with the results obtained using a pH meter device.

Recibido el 22 de marzo del 2004; aceptado el 27 de agosto del 2004 Resumen. Se preparó un sensor de respuesta óptica para medir acidez ambiental, a partir de la mezcla de cuatro moléculas orgánicas, pdimetilaminoazobenceno (amarillo de dimetilo), (acido o-[[p-(dimetila-mino)fenil]azo]benzoico) (rojo de metilo), α,α Bis (6 bromo 5 hidroxicarvacril) a hidroxi -o-tolueno g sulfona (azul de bromotimol), y ácido α-hidroxi-α,α-bis (5 hidroxicarvacril)-p-toluensulfonico (azul de timol), incorporadas a una matriz vítrea, obtenida vía sol-gel utilizando como precursores tetraetóxido de silicio (TEOS) y metiltrietóxido de silicio (ME 3 S); el intervalo de pH varía entre 1 y 10. La caracterización óptica de las películas depositadas en pequeñas láminas de vidrio de silicato sódico potásico, se llevó a cabo por espectrometría de absorción con un equipo Perkin Elmer 11. Los ensayos de fotoestabilidad se realizaron mediante exposiciones con una lámpara ultravioleta de 10 w. La adherencia y la resistencia química se llevaron a cabo sometiendo las películas a diferentes ambientes acuosos y alcalinos (NaOH 0.5M, Na 2 CO 3 0,1M). El sensor obtenido es sensible a las variaciones de pH, tanto en líquidos como en gases húmedos, además es reversible y estable a los cambios químicos.

A recent analysis of full water column hydrographic data revealed a pH-dependent discrepancy between spectrophotometrically measured pH using purified meta-cresol purple and pH calculated from dissolved inorganic carbon (DIC) and total alkalinity (TA). The discrepancy (pH spec -pH TA,DIC ) is approximately -0.018 and 0.014 at pH 7.4 and 8.2, respectively. This discrepancy has a wide range of implications for marine inorganic carbon measurements, such as establishing robust calibration protocols for pH sensors operating on profiling floats. Here, we conducted a series of lab based experiments to assess the magnitude of pH-dependent errors for spectrophotometric pH measurements in seawater by directly comparing its performance to pH measured by an Ion Sensitive Field Effect Transistor (ISFET) pH sensor known to have Nernstian behavior. Natural seawater was titrated with high CO 2 seawater while simultaneously measuring pH using spectrophotometry and an ISFET sensor over a large range in pH (7-8.5) and temperature (5-30 °C). The two pH measurements were consistent to better than ± 0.003 (range) at all temperatures except at 5 and 10 °C and very low and high pH, where discrepancies were as large as ± 0.005. These results demonstrate that pH-dependent errors in spectrophotometric pH measurements can be rejected as the cause of the pH-dependent discrepancy between pH spec and pH TA,DIC . The cause of this discrepancy is thus likely due to our incomplete understanding of the marine inorganic carbon model that could include errors in thermodynamic constants, concentrations of major ions in seawater, systematic biases in measurements of TA or DIC, or contributions of organic compounds that are not accounted for in the definition of total alkalinity. This should be a research priority for the inorganic carbon community.

Recibido el 22 de marzo del 2004; aceptado el 27 de agosto del 2004 Resumen. Se preparó un sensor de respuesta óptica para medir acidez ambiental, a partir de la mezcla de cuatro moléculas orgánicas, pdimetilaminoazobenceno (amarillo de dimetilo), (acido o-[[p-(dimetila-mino)fenil]azo]benzoico) (rojo de metilo), α,α Bis (6 bromo 5 hidroxicarvacril) a hidroxi -o-tolueno g sulfona (azul de bromotimol), y ácido α-hidroxi-α,α-bis (5 hidroxicarvacril)-p-toluensulfonico (azul de timol), incorporadas a una matriz vítrea, obtenida vía sol-gel utilizando como precursores tetraetóxido de silicio (TEOS) y metiltrietóxido de silicio (ME 3 S); el intervalo de pH varía entre 1 y 10. La caracterización óptica de las películas depositadas en pequeñas láminas de vidrio de silicato sódico potásico, se llevó a cabo por espectrometría de absorción con un equipo Perkin Elmer 11. Los ensayos de fotoestabilidad se realizaron mediante exposiciones con una lámpara ultravioleta de 10 w. La adherencia y la resistencia química se llevaron a cabo sometiendo las películas a diferentes ambientes acuosos y alcalinos (NaOH 0.5M, Na 2 CO 3 0,1M). El sensor obtenido es sensible a las variaciones de pH, tanto en líquidos como en gases húmedos, además es reversible y estable a los cambios químicos.

The mechanism of proton transfer from the bulk into the membrane protein interior was studied. The light-induced reduction of a bound ubiquinone molecule Q B by the photosynthetic reaction center is accompanied by proton trapping. We used kinetic spectroscopy to measure ( i ) the electron transfer to Q B (at 450 nm), ( ii ) the electrogenic proton delivery from the surface to the Q B site (by electrochromic carotenoid response at 524 nm), and ( iii ) the disappearance of protons from the bulk solution (by pH indicators). The electron transfer to Q B − and the proton-related electrogenesis proceeded with the same time constant of ≈100 μs (at pH 6.2), whereas the alkalinization in the bulk was distinctly delayed (τ ≈ 400 μs). We investigated the latter reaction as a function of the pH indicator concentration, the added pH buffers, and the temperature. The results led us to the following conclusions: ( i ) proton transfer from the surface-located acidic groups into the Q B site followe...

2‐Phenyl‐5‐p‐tolyl‐1‐salicylideneamino‐1,3,4‐triazole (PTST) was studied among 2,5‐diaryl‐1‐salicylidene amino‐1,3,4‐triazole derivatives as a novel potential pH indicator. In terms of absorption intensity coming from the acid‐base reactions, PTST showed strong yellow‐green colour with high extinction coefficient in the pH range 7.0–9.5. In addition, the corresponding colour development at the transition point can be attributed to the resonance structures of PTST, which were caused by the hydrogen ion dissociation from the acidic form of the compound in the presence of alkali. The full geometric optimization and achievement of the electronic structure of the molecule were performed by an AM1 semiempirical method. The triazole compound was compared with phenolphthalein (PT), which is widely used as an acid‐base indicator in titrimetry, for accuracy test.

The structures and functions of the cellular acidic compartments are strongly dependent on the pH gradients across vesicular membranes. Measurement and imaging of the vesicular pH require fluorophores with appropriate pK a values. In this report, we characterized the pH-dependent lifetime responses of a family of acidotropic probes, LysoSensors, to evaluate their usefulness to low-pH lifetime imaging. LysoSensors are cell-permeable weak bases that selectively accumulate in acidic vesicles after being protonated. They have higher quantum yields at lower pH ranges to allow visualization of the lysosomes. For LysoSensors DND-167, DND-189, and DND-153, raising the buffer pH increased the quenching effects of their basic side chains and substantially reduced their steady-state fluorescence and lifetimes. The apparent pK a values determined from their lifetime responses were shifted to near neutral values because of the dominant intensity contribution from their protonated species. One unique property of LysoSensor DND-189 is its non-monotonic lifetime responses of the maxima occurring between pH 4 and 5. LysoSensor DND-192 did not show significant lifetime changes over a wide pH range. LysoSensor DND-160, which was the only excitation and emission ratiometric probe, showed significant pH-dependent lifetime changes as well as its spectral shifts. Its apparent pK a values determined from the lifetime responses were comparable to the lysosomal pH because of its bright basic form. Because of the pH-dependent absorption spectra, the apparent pK a values could be manipulated between 3 and 5 by changing the excitation and/or emission wavelengths. These results indicate that LysoSensor DND-160 is a promising probe for lifetime imaging to determine lysosomal pH. Keywords lifetime-based sensing; lifetime imaging; pH probes; fluorescence Endocytic vesicles are intracellular acidic compartments in the cytoplasm which perform transportation and biodegradation functions in cells. From their ultrastructural differences and subcellular distributions, endocytic vesicles can be classified as early endosomes, recycling endosomes, multivesicular endosomes, and late endosomes. The vesicles participate in processing and sorting of antigens, recycling and down-regulation of membrane receptors, and delivery and degradation of foreign materials internalized by the 3

Indicator is a chemical agent which is used to recognize the attainment of end point in titration. After the reaction between the chemical and the standard solution is complete, the indicator should give a color change. A pH indicator is a chemical which changes the color of solution with change in pH in response to a chemical change. An acid-base indicator changes its color depending on pH change. Redox indicators are also commonly used (eg. - methylene blue). Synthetic indicators are frequently used in acid-base titrations. As synthetic indicators have certain drawback like unavailability, expensive. An experiment has been made to recognize the indicator property of various natural pigments. The main goal of this attempt is to replace the synthetic indicators. Natural indicators are inexpensive as compare to synthetic indicators. Ethanolic extract of Withania somnifera (Ashwagandha) and Curcuma longa (Turmeric) were evaluated and sample extract gives sharp and intense color change...

Synthetic acid-base indicators possess some disadvantages. Therefore, it is necessary to develop a natural acid-base indicator made from a mixture of plant extracts, which has a strip form, is safe, eco-friendly, has a wide pH range, and has clear color changing. This research aims to determine the pH range, make a pH indicator in the strip form, and produce a biodegradable acid-base indicator made from a mixture of Melastoma malabathricum flower, Dioscorea alata rhizome, Syzygium paniculatum leaves, Garcinia fruit peel, Eleutherine bulbosa rhizome extracts. Plant extracts were obtained using the maceration method. pH range was evaluated using the visual method by sensing the color changing in the pH range from 1 to 14. pH indicator strip was made by applying filter paper in the strip form into the extract mixture for 2 hours. The biodegradable property of acid-base indicator strips was established by measuring indicator strip degradation after planting it in the ground for 20 days at room temperature. The results showed that the acid-base indicator strip made from a mixture of plant extracts was able to give a color change from pink to light green in the pH range of 3-8 and can be decomposed completely after planting it in the ground for 20 days. Thus, it indicated that a natural pH indicator strip based on West Kalimantan plants has the potential to be developed as a safe and effective acid-base indicator to substitute synthetic acid-base indicators.

Synthetic acid-base indicators possess some disadvantages. Therefore, it is necessary to develop a natural acid-base indicator made from a mixture of plant extracts, which has a strip form, is safe, eco-friendly, has a wide pH range, and has clear color changing. This research aims to determine the pH range, make a pH indicator in the strip form, and produce a biodegradable acid-base indicator made from a mixture of Melastoma malabathricum flower, Dioscorea alata rhizome, Syzygium paniculatum leaves, Garcinia fruit peel, Eleutherine bulbosa rhizome extracts. Plant extracts were obtained using the maceration method. pH range was evaluated using the visual method by sensing the color changing in the pH range from 1 to 14. pH indicator strip was made by applying filter paper in the strip form into the extract mixture for 2 hours. The biodegradable property of acid-base indicator strips was established by measuring indicator strip degradation after planting it in the ground for 20 days at room temperature. The results showed that the acid-base indicator strip made from a mixture of plant extracts was able to give a color change from pink to light green in the pH range of 3-8 and can be decomposed completely after planting it in the ground for 20 days. Thus, it indicated that a natural pH indicator strip based on West Kalimantan plants has the potential to be developed as a safe and effective acid-base indicator to substitute synthetic acid-base indicators.

каф. акушерства и гинекологии № 2, каф. онкологии и специализированных хирургических дисциплин ИДПО, каф. биохимии; 2 ФГБОУ ВО ВГУ , каф. материаловедения и индустрии наносистем Резюме. Задача коррекции нарушений влагалищной микробиоты достаточно сложна для решения. Несмотря на разнообразие современных диагностических возможностей идентификация возбудителя влагалищного заболевания достаточно трудна, поэтому лечение зачастую назначается симптоматически. Статья посвящена возможности использования индикатора бромтимолового синего для ранней диагностики нарушения биоценоза влагалища с целью оптимизации подбора фармакотерапии. Обсуждены различные методы приготовления раствора индикаторы и предложена методика приготовления раствора для нанесения на гигиеническую прокладку для динамического контроля рН влагалищных выделений. Показано, что бромтимоловый синий является в целом походящим индикатором для динамического контроля за изменением рН влагалищных выделений, так как индикатор обладает высокой чувствительностью к рН>6 и несколько меньшей, но достаточной чувствительностью в интервале рН от 4 до 5. Определена целесообразность использования раствора бромтимолового синего в глицерине в качестве экспресс-диагностикума. Ключевые слова: фармакотерапия, влагалищная микробиота, бромтимоловый синий, рН.

Bacteriorhodopsin-containing vesicles that were able to alkalize the extravesicular medium by > 1.5 pH units under illumination, Le., inside-out vesicles, were reconstituted by reverse-phase evaporation with Halobacterium halobium polar lipids or exogenous phospholipids. Acid titration of a dark-adapted sample was accompanied by a color change from purple to blue (pKa = 2.5-4.5 in 0.15 M K2S04), and alkali titration resulted in the formation of a red species absorbing maximally a t 480 nm (pKa = 7 to >9), the pKa values and the extents of these color changes being dependent on the nature of lipid. When a vesicle suspension a t neutral or weakly acidic pH was irradiated by continuous light so that a large pH gradient was generated across the membrane, either a purple-to-blue or a purple-to-red transition took place. The light-induced purple-to-red transition was significant in an unbuffered vesicle suspension and correlated with the pH change in the extravesicular medium. The result suggests that the purple-to-red transition is driven from the extravesicular side, i.e., from the C-terminal membrane surface. In the presence of buffer molecules outside, the dominant color change induced in the light was the purple-to-blue transition, which seemed to be due to a large decrease in the intravesicular pH. But an apparently inconsistent result was obtained when the extravesicular medium was acidified by a HCl pulse, which was accompanied by a rapid color change to blue. W e arrived a t the following explanation: The two bR isomers, one containing all-trans-retinal and the other 1 34s-retinal, respond differently to p H changes in the extravesicular and the intravesicular medium. In this relation, full light adaptation was not achieved when the light-induced purple-to-blue transition was significant; i.e., only the 13-cis isomer is likely to respond to a p H change at the N-terminal membrane surface.

Indonesia kaya dengan sediaan bahan alam yang beraneka warna, dengan kandungan bahan aktif yang sangat beragam. Salah satu yang dapat dimanfaatkan adalah pigmen warna yang terdapat dalam tanaman. Pigmen ini dapat dimanfaatkan sebagai indikator asam basa karena dapat memberikan warna yang berbeda pada nilai pH tertentu. Salah satu tanaman yang dilaporkan potensial sebagai indikator asam basa adalah buah naga merah (Hylocereus polyrhizus). Warna merah menandakan adanya senyawa antosianin yang dapat memberikan warna yang berbeda pada pH asam dan basa. Penggunaan indikator asam basa, salah satunya adalah untuk menentukan terjadinya titik ekivalen pada titrasi. Melalui penelitian ini diharapkan dapat mengetahui potensi ekstak etanol kulit buah naga merah sebagai alternatif indikator pada titrasi asam basa. Penelitian ini merupakan penelitian eksperimental. Penelitian diawali dengan melakukan ekstraksi kulit buah naga menggunakan pelarut etanol. Selanjutnya dilakukan pengukuran absorbansi ekstrak untuk mengetahui panjan gelombang maksimumnya. Ekstrak ini kemudian digunakan sebagai indikator pada titrasi penentuan konsentrasi HCl. Hasil pengujian dibandingkan dengan penentuan konsentrasi larutan menggunakan indikator pp. Ekstrak yang diperoleh berwarna merah dengan panjang gelombang maksimum 539 nm. Konsentrasi HCl yang diperoleh untuk titrasi menggunakan indikator pp sebesar 0,0909 M dan dengan indikator ekstrak sebesar 0,1011 M. Ekstrak ini dapat digunakan pada titrasi asam basa dengan perubahan warna dari merah muda menjadi peach pada titik akhir titrasi.

Recently, interest in smart packaging, which can show the color change of the packaging film according to the state of the food and evaluate the quality or freshness of the packaged food in real-time, is increasing. As a color indicator, a natural colorant, anthocyanin, drew a lot of attention due to their various colors as well as useful functions properties such as antioxidant activity and anti-carcinogenic and anti-inflammatory effects, prevention of cardiovascular disease, obesity, and diabetes. In particular, the pH-responsive color-changing function of anthocyanins is useful for making color indicator smart packaging films. This review addressed the latest information on the use of natural pigment anthocyanins for intelligent and active food packaging applications. Recent studies on eco-friendly biodegradable polymer-based color indicator films incorporated with anthocyanins have been addressed. Also, studies on the use of smart packaging films to monitor the freshness of foods such as milk, meat, and fish were reviewed. This review highlights the potential and challenges for the use of anthocyanins as pH-responsive color-changing films for intelligent food packaging applications, which may be beneficial for further development of smart color indicator films for practical use.

A new method for the estimation of steady-state ApH, and the rate of acidification, by H+-ATPases (and other proton transporters) in inverted membrane vesicles is described. The method is based on a combination of two widely used fluorescent ApH probes, 9-aminoacridine and 9-amino-6-chloro-2-methoxyacridine. It is demonstrated that 9-amino-6-chloro-2-methoxyacridine fluorescence quenching, which is very sensitive to small pH gradients, is not sensitive to the magnitude of large pH gradient, while 9-aminoacridine, which does not sense small gradients, is very sensitive to large pH gradients. A proper mixture of the two probes provides a method which is equally sensitive to pH gradients from very small values up to 3.5 pH units. The probe response was evaluated by titrations of the fluorescence signal with nigericin and adjusted by changing the concentration ratio and the emission wavelength. In liposomes, submitochondrial particles and bacterial vesicles an almost linear dependence of quenching on ApH over the entire range can be obtained with this method. It is demonstrated that the new method can be used to obtain more reliable estimates of the rate of acidification as well as the magnitude of ApH, whereas each of these and similar probes, by themselves are not as reliable. A determination of the ratio AGp/AIx H over a wide range of values reveal that this ratio is not constant but decreases with AGp. This finding should be taken into consideration when attempting to estimate the H+/ATP ratio form the measurement of AGp/A/~ H.

Often encountered in laboratory settings, conventional pH level indicators are crucial tools that come in various forms, determining a substance's pH. However, synthetic indicators have some drawbacks, including high cost, limited availability, and chemical pollution. This study aims to investigate the effectiveness and accuracy of red cabbage as a pH level indicator as an alternative. Using a quantitative quasi-experimental design, the researchers employed a purposive sampling technique to select the survey respondents. In total, the number of respondents for this research were 32. The researchers created the pH jellies using environmentally friendly materials such as red cabbage, unflavored gelatin, and distilled water. The statistical treatment used was the weighted mean, with results interpreted as highly effective for each indicator. The researchers found that the pH jellies were highly acceptable in terms of portability and accuracy. Based on the trials the pH jellies can only be used up to pH-12. Despite the positive results, the researchers suggest further investigation on the effectiveness of the indicator particularly in modifying its pH range up to pH-14 and extending its shelter life.

Anthocyanin pigment profiles, colours and pH values of Agapanthus praecox were investigated. The anthocyanin pigments from the blue flower petals were solvent extracted with 70% acetone, and the pH of the extracts was varied (pH 1, 2?5, 4?5 and 7). The colour of the pigment solution changed with pH, where it became pinkish purple at pH 1, dark red at pH 2?5, light purple at pH 4?5, dark turquoise at pH 7, dark green at pH 9?5, light green at pH 11?5 and yellow at pH 14. The extracts were also subjected to ultraviolet-visible spectrophotometric analysis, where a distinct peak at 544 nm was observed for both pH 1 and 2?5, while multiple peaks at 535, 571?5 and 627 nm were observed for pH 4?5 and at 535, 574 and 620 nm for pH 7. The anthocyanin extract with the most stable pH (at pH 1) was mixed with 20% poly(methyl methacrylate) and coated onto glass slides, which was then subjected to weathering tests to determine its durability.

In this work, we describe the synthesis of a novel 9-aminoacridine derivative that presents surprisingly different colors when exposed to neutral, acidic or basic mediums with potential application as pH indicator in organic solvents. Furthermore, pKa and molar absorptivity values were determined and theoretical studies supported by density functional theory (DFT) calculations were performed to elucidate the different structures of this compound.

Acidity is an outstanding parameter that affect the correct preservation of most part of materials engaged in artworks and heritage objects. In spite of the new generation of advanced analytical devices, the conservation/heritage management sector claims for some kind of simple, robust and low-cost device to monitor environmental acidity wherever necessary. The purpose of this paper is to offer a suitable alternative for the estimation of environmental acidity by means of detectors to be used without electrodes, solutions, pH meters, wires or batteries. Doped sol-gel thin coatings have been used as transductors for producing pH detectors. The coatings consist of a partially densified polysiloxane network and an organic dye sensitive to pH changes. The siloxane network behaves as a host for immobilisation of the dye molecules, in such a way that chemical-optical properties of the dye are preserved as far as possible. The transductors were applied on common glass substrates by dipping. Further heat-treatment allows the coating partial densification. The optical response of the detectors was analysed by VIS absorption spectroscopy, since a change of colour took place when the detectors were submitted to different pH buffered solutions. With the aim to investigate their optical behaviour as a function of pH, several experimental measurements were undertaken: absorption intensity; maximum spectral wavelength; colour coordinates; colour purity percentages. Time response and memory effect were also studied. The detector operation conditions for monitoring environmental acidity both indoor and outdoor are discussed.

In this study, the possible use of anthocyanins of black carrot (ABC) as a chemo-responsive dye to fabricate a colorimetric pH indicator in a cellulose-chitosan matrix was investigated in order to the monitoring of spoilage in pasteurized milk. Cellulose paper was impregnated with a chitosan solution prepared by a sol-gel method containing ABC (total anthocyanins content of 10 mg/100 mL) and characterized. The swelling and water solubility increased by incorporation of ABC into the chitosan-cellulose film. The colorimetric pH indicator showed an obvious color variation from pink to khaki at different pH values (pH 2-11). Stability tests revealed that the indicator had acceptable color stability during one-month storage at 20 °C. The results also confirmed the immobilization of ABC into the matrix of the polymeric indicator with no significant effect on the chemical and super-molecular structure of the samples. In food trial, fresh pasteurized milk was entirely discerned through a perceptible color change from blue to violet rose color after 48 hr storage at 20 °C, which was comfortably observable by the naked eye. The results proved that the fabricated indicator could be used as food grade biomaterials to monitor freshness/spoilage of milk.

Natural indicators using anthocyanin compounds can be an alternative to synthetic indicators on acid-base titration because anthocyanin is an organic compound that is unstable with changes in pH. The extraction was carried out with ethanol because the compounds of anthocyanin were polar. This study was to ensure an ethanol extract of some plants could be used as an acid-base indicator that had a pH range of color change and the value of the equality parameter was not significantly different from the phenolphthalein indicator. The research method is to collect research journals on making natural indicators from ethanol extracts of various plants compared to phenolphthalein indicators so that secondary data from these journals can be processed statistically. Research results and conclusions: Based on the results of statistical data processing using the t-test there was no difference in the average pH of the phenolphthalein indicator with the average pH of ethanol extracts of adam air ...

Objectives. Herein, the effects of cationic polyelectrolytes on the properties of solid substrate immobilized acid–base indicators are investigated to predict shifts in their spectral patterns and characteristics. Methods. The properties of the silica gel immobilized indicator dye in a solution of the cationic polyelectrolyte were studied using automatic photometric titration in the visible region and spectrophotometry using a specialized computerized setup. Results. The measured pKa value of the immobilized dye, which had shifted by three units to the acidic region, was very similar to the pKa value observed for the indicator in the modifying polymer solution. The observed change in pKa of the immobilized dye and the influence of the solution’s ionic strength were attributed to the local electric potential of the polymer globule. In contrast to the processes associated with covalent immobilization, the effect exerted by the solution’s ionic strength on the indicator reaction dimini...

A novel 3 × 4 colorimetric sensing platform, named the chemometric-assisted litmus test (CLT), has been developed by covalently anchoring commercial pH indicators to ethylene vinyl alcohol (EVOH). The proposed device can be exploited for pH determinations in a wide range from 1 to 13 and in specific narrow ranges, achieving sufficient accuracy and errors below 0.5 pH units. The experimental procedure is simple, quick and reliable; equilibration is reached in less than 2 h, CLT pictures are acquired by a camera, and data treatment is performed applying chemometric techniques such as principal component analysis (PCA) and partial least square regression (PLS) to RGB indices.

A novel 3 × 4 colorimetric sensing platform, named the chemometric-assisted litmus test (CLT), has been developed by covalently anchoring commercial pH indicators to ethylene vinyl alcohol (EVOH). The proposed device can be exploited for pH determinations in a wide range from 1 to 13 and in specific narrow ranges, achieving sufficient accuracy and errors below 0.5 pH units. The experimental procedure is simple, quick and reliable; equilibration is reached in less than 2 h, CLT pictures are acquired by a camera, and data treatment is performed applying chemometric techniques such as principal component analysis (PCA) and partial least square regression (PLS) to RGB indices.

Experiment on natural acid-base indicators is usually done by extracting the natural sources with certain solvent, testing the extract with acid, base and neutral solutions, observing the color changes, making conclusion and discharging the remaining extract at the end of the experiment. Production of long-lasting natural acid-base indicator is needed to reduce the discharged of chemicals excessively. This research was carried out to produce natural acid-base indicator from extract of shoot leaves of &lt;em&gt;Syzygium oleana&lt;/em&gt; (SLS). The extraction was done by maceration technique using ethanol 95% for 13 h. The extract of SLS (SLS indicator solution) is then used to produce SLS indicator paper by soaking the filter paper in SLS indicator solution and followed by drying under shade. Both of the solution and paper indicators were tested for their color changes in pH solutions range of 1-13. Durability and performance of the indicator was investigated for 6 d. Absorbance of ...

Acidity is an outstanding parameter that affect the correct preservation of most part of materials engaged in artworks and heritage objects. In spite of the new generation of advanced analytical devices, the conservation/heritage management sector claims for some kind of simple, robust and low-cost device to monitor environmental acidity wherever necessary. The purpose of this paper is to offer a suitable alternative for the estimation of environmental acidity by means of detectors to be used without electrodes, solutions, pH meters, wires or batteries. Doped sol-gel thin coatings have been used as transductors for producing pH detectors. The coatings consist of a partially densified polysiloxane network and an organic dye sensitive to pH changes. The siloxane network behaves as a host for immobilisation of the dye molecules, in such a way that chemical-optical properties of the dye are preserved as far as possible. The transductors were applied on common glass substrates by dipping. Further heat-treatment allows the coating partial densification. The optical response of the detectors was analysed by VIS absorption spectroscopy, since a change of colour took place when the detectors were submitted to different pH buffered solutions. With the aim to investigate their optical behaviour as a function of pH, several experimental measurements were undertaken: absorption intensity; maximum spectral wavelength; colour coordinates; colour purity percentages. Time response and memory effect were also studied. The detector operation conditions for monitoring environmental acidity both indoor and outdoor are discussed.

Butterfly pea is a perennial leguminous twiner that lives within the tropical belt and certain warm areas. Butterfly pea contains anthocyanin that are highly sensitive towards any change of pH, making them suitable to be used as pH indicator. The mechanism of the pH sensing capabilities of anthocyanin from butterfly pea involves four reversible structure of anthocyanin that are present in different range of pH: flavylium cation, hemiketal, quinonoid base and chalcone. Colorimetric indicator is a tool that are used in an intelligent food packaging. Its purpose in intelligent food packaging is to provide information of the food contained inside through colour changes that are visible to naked eyes. This colorimetric indicator utilizes pH indicator to assess the freshness of the food by measuring the change of pH that the product undergoes. Anthocyanin from butterfly pea provides an option of natural and organic pH indicator as opposes to synthetic pH indicators that can cause health issues. Anthocyanin from butterfly pea is capable to react towards any change of pH both acidic and basic, stable at least up to 60 days and are organic, perfect to be used in intelligent food packaging and other food related purposes.

Butterfly pea is a perennial leguminous twiner that lives within the tropical belt and certain warm areas. Butterfly pea contains anthocyanin that are highly sensitive towards any change of pH, making them suitable to be used as pH indicator. The mechanism of the pH sensing capabilities of anthocyanin from butterfly pea involves four reversible structure of anthocyanin that are present in different range of pH: flavylium cation, hemiketal, quinonoid base and chalcone. Colorimetric indicator is a tool that are used in an intelligent food packaging. Its purpose in intelligent food packaging is to provide information of the food contained inside through colour changes that are visible to naked eyes. This colorimetric indicator utilizes pH indicator to assess the freshness of the food by measuring the change of pH that the product undergoes. Anthocyanin from butterfly pea provides an option of natural and organic pH indicator as opposes to synthetic pH indicators that can cause health i...

Natural colorimetric indicators have been fabricated using annatto and pomegranate extract powder and compared with chemical colorimetric indicator fabricated using bromophenol blue (BPB) to monitor the freshness of ready‐to‐cook (RTC) idli batter. The fabricated colorimetric indicator labels work on increasing headspace carbon dioxide (CO2) concentration and decreasing pH of stored batter, where indicators showed visible color change from lightest to darkest for spoiled samples. The headspace CO2 concentration of RTC idli batter increased from 0.15 ± 0.05 to 18.07 ± 0.21% (v/v) and pH decreased from 6.7 ± 0.06 to 4.5 ± 0.06 at optimum storage condition (35 ± 1°C) up to 24 h. The percent titratable acidity (% TA) increased from 0.44 ± 0.02 to 0.90 ± 0.02% up to 24 h. The viable lactic acid bacteria count (LABC) and total bacterial count (TBC) increased while yeast and mold count (YMC) was decreased with increasing fermentation time up to 24 h for batter stored at optimum condition. ...

The first paper-based polyion-sensitive optodes are reported. Dinonylnaphthalene sulfonic acid (a cation exchanger) and chromoionophore I (a lipophilic optical pH indicator) are printed on filter paper in the absence of any plasticizer and/or additional hydrophobic polymeric phase. The resulting optodes exhibit sensitive colorimetric response to polycations such as protamine but not to small inorganic cations because only polycations are able to form cooperative ion pairs with dinonylnaphthalene sulfonate adsorbed to the cellulose paper. The color change of the optode is recorded via an iPhone camera and analyzed by an iPhone App. The protamine sensing optode platform is used to indirectly detect protease activity (trypsin) based on proteolytic digestion of protamine, and polyanions (pentosan polysulfate and heparin) based on the strong binding reaction of polyanions with protamine. The indirect sensing system is further simplified on a multilayer membrane device that consists of an optode paper site modified with buffer to prevent optode dependence on sample pH, and an underlying cellulose acetate filter membrane coated with protamine to eliminate addition of the indicator polycation into the sample. The detection of pentosan polysulfate concentrations in an undiluted urine sample is successfully demonstrated via this approach. Lastly, it is shown that plasticizer-free polyanion-sensitive optodes based on an adsorbed layer of quaternary ammonium type anion exchanger and a phenolic azo type proton chromoionophore can also be fabricated directly on cellulose paper strips.

In medicine knowledge of pH values can provide us with information not only about the patients' status but also about physiological processes in the patient's body. Measurements of pH in small-sample volumes and online pH monitoring in vivo can be employed to obtain such information. For such measurements we have developed and investigated U-shaped fiber-optic probes with immobilized pH indicators in this paper. U-shaped probes with a diameter of about 2 mm were prepared. Three different pH indicators, methyl red, methyl orange, and bromothymol blue, were immobilized in two types of matrices, namely, porous silica (PS) and ethylcellulose (EC), and applied on the U-shaped probes. Changes in spectra of transmitted power were measured and calibration curves were determined from these spectra. It has been found that a working pH range of prepared probes was from 3.1 to 7.6. The maximum sensitivity was about 0.1 1/pH unit. Effects of structural relaxations of detection layers and indicator leaching observed in experiments are discussed.

In medicine knowledge of pH values can provide us with information not only about the patients’ status but also about physiological processes in the patient’s body. Measurements of pH in small-sample volumes and online pH monitoring in vivo can be employed to obtain such information. For such measurements we have developed and investigated U-shaped fiber-optic probes with immobilized pH indicators in this paper. U-shaped probes with a diameter of about 2 mm were prepared. Three different pH indicators, methyl red, methyl orange, and bromothymol blue, were immobilized in two types of matrices, namely, porous silica (PS) and ethylcellulose (EC), and applied on the U-shaped probes. Changes in spectra of transmitted power were measured and calibration curves were determined from these spectra. It has been found that a working pH range of prepared probes was from 3.1 to 7.6. The maximum sensitivity was about 0.1 1/pH unit. Effects of structural relaxations of detection layers and indicat...

A significant challenge concerning the development of fluorescence lifetime (FL) based pH sensors is the paucity of fluorophores with sufficiently large FL variation with pH. Acridine is amongst the indicators with highest fluoresce lifetime responses to pH, with a change in lifetime of about 13 ns within a pH range of 5-8. Here we examine the two acridine derivatives, 9acridinemethanamine (9-AMA) and acridine-9-carbaldehyde (9-ACA) in terms of their FL pH sensitivity and pH sensing range. Both indicators are characterized when dissolved in buffer solutions, as well as when immobilized in support materials. 9-AMA has a change in FL of 11 ns between pH 2-5, both when dissolved in solution and when immobilized in surfactant-filled mesoporous silica. The FL of 9-ACA is not sensitive to pH when dissolved in buffer solutions; however, when covalently bound to amine-modified silica, its FL changes 15 ns between pH 3-6. 9-AMA and 9-ACA represent promising FL in the pH range of pH 2-6, and could potentially form the basis of new FL pH sensors.

Surfactant filled mesoporous silica is applied as a matrix for immobilizing the fluorescence lifetime pHindicator acridine. We demonstrate that this type of encapsulation provides a stable and uniform chemical environment for the indicator and has good proton transport properties leading to rapid pH response times. Furthermore, the immobilising medium effectively prevents leaching of the indicator, facilitates high long-term stability and does not influence the pH sensing-range of the indicator.

A general drawback for optical based pH sensors is that their response is typically limited to within 2-3 pH units centered around the pK a of the indicator. Fluorescence lifetime (FL) is a particularly compelling basis for highly stable pH sensors since this is an intrinsic property of the indicator molecule. Here we demonstrate that it is possible to broaden the sensing range of FL based sensors significantly by placing the indicator in a support material where the indicator's chemical environment itself changes with pH. For acridine immobilized in amine-modified porous silica, a total FL change of 20 ns in the pH range 2-12 is achieved. A linear pH vs FL relationship is observed with three break points occurring at pH 4, 6 and 9 that are related to the pK a values of the indicator and the silica material. This proves the concept that tuning the fluorophore's chemical environment can broaden the FL pH sensing range, where currently available fluorophores do not cover the full pH range.

The apparent dissociation constants of five sulfonephthalein indicators (thymol blue, bromophenol blue, bromocresol green, bromocresol purple and phenol red) were determined in 35%o seawater at 25 ° C. Measurements of seawater pH were made using the ratio of the optical absorbance of the acidic and basic components of a particular indicator and the apparent dissociation constant of the indicator. The suite of indicators allows quantitative determination of seawater pH over the pH range 1.5-8.5. For seven seawater samples ranging from pH 1.5 to 8.0 the average difference between pH measurements made with indicators and conventional electrodes was + 0.005. Measurements of seawater pH with indicators is not limited to single indicator solutions. Simultaneous addition of phenol red and bromocresol green allows pH determinations from 3.0 to 8.2, which are suitable for All~Minity titrations. The pK.' values of the indicators were determined independently of potentiometric pH measurements. The pH indicators provide an absolute free hydrogen ion molality scale independent of the problems of electrode drift and liquid junction errors associated with potentiometric pH measurements.

A pH optical sensor was developed based on the use of a mixture of Malachite Green Oxalate and Bromocresol Green indicators immobilized in a triacetylcellulose membrane, which had been previously hydrolyzed. Requirements of the pH indicators were investigated, including the effects of the coupling pH, indicator ratio, and concentrations of the indicators. The pH sensor performed with a very fast response (10 s) and long term stability with no significant leaching of the dyes. The sensor had a linear response over a range of 6.6 pH units in the pH range between 0.4 and 7.0. A relative standard deviation of pH equal to 1.59% was obtained for 7 replicated pH measurements. The procedure for preparation of this optical sensor is simple, inexpensive, and rapid.

Based on the color change of an indicator due to the release of hydrogen ion from a nitrilase-catalyzed reaction, a rapid colorimetric method was established for the enantioselective screening of nitrilase-producing microorganisms. The formation of acids due to the nitrilase-mediated hydrolysis of nitriles causes a drop in the pH, which in turn results in a change of color of the solution (containing indicator) that can be observed visually. The buffer (0.01 M phosphate, pH 7.2) and indicator (Bromothymol blue, 0.01%) were selected in such a way that both have the same affinity for the released protons. The enantioselectivity of nitrilases was estimated by comparing the hydrolysis of ( R)-mandelonitrile with that of racemate under the same conditions. The method was used to screen a library of nitrilase-producing microorganisms, isolated in the authors&#39; laboratory for their ability to enantioselectively hydrolyze mandelonitrile to mandelic acid, an important chiral building bloc...