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pH colorimetric sensors with prediction error comparable to the potentiometric measurements in the working range of the indicator employed, were prepared. Bromothymol Blue (BB), Tetrabromophenol Blue (TBB), Cresol Red (CR) and Brilliant Yellow (BY) in PVDF (Polyvinylidene Fluoride)-supported OrMoSil (organically modified silicate) matrix, were used. Sensor preparation was reproducible. Signal was based on a suitably modified Hue coordinate from HSV (Hue, Saturation, Value) color space, H. Although H profile was not influenced by the indicator concentrations, the prediction error depended on the product of saturation and luminance, Δ. By using H, the response of every spot was less affected by shape and optical inhomogeneity. The H calibration held for all the spots of the same lot and remained identical in time giving an advantage with respect to a glass electrode requiring calibration before each set of measurements. The prediction errors both in solution and in the OrMoSil matrix were similar: for BB, s p H i = 0.03 in both environments; for TBB, s p H i = 0.02 in the sensing spot and 0.05 in solution; for CR, s p H i = 0.11 in the sensing spot and 0.04 in solution; for BY, s p H i = 0.17 in the sensing spot and 0.07 in solution. Indeed, H values of TBB and BB increased their variances near the inflection point where Δ has the minimum value (heteroscedastic behavior).

This article demonstrates an example of a wearable chemical sensor based on a fingernail platform. Fingernails represent an attractive wearable platform, merging beauty products with chemical sensing, to enable monitoring of our surrounding environment. The new colorimetric pH fingernail sensor relies on coating artificial nails with a recognition layer consisted of pH indicators entrapped in a polyvinyl chloride (PVC) matrix. Such color changing fingernails offer fast and reversible response to pH changes, repeated use, and intense color change detected easily with naked eye. The PVC matrix prevents leaching out of the indicator molecules from the fingernail sensor toward such repeated use. The limited narrow working pH range of a single pH indicator has been addressed by multiplexing three different pH indicators: bromothymol blue (pH 6.0-7.6), bromocresol green (pH 3.8-5.4), and cresol red (pH 7.2-8.8), as demonstrated for analyses of real-life samples of acidic, neutral, and basic character. The new concept of an optical wearable chemical sensor on fingernail platforms can be expanded towards diverse analytes for various applications in connection to the judicious design of the recognition layer.

A simple, rapid and reliable gas-diffusion flow injection (GD-FI) method for ammonium determination in building materials has been developed. It is based on leaching ammonium from a ground solid sample into an alkaline solution with subsequent ammonia gas generation. Ammonia is then transported in a nitrogen stream to the GD cell of the FI system where it is absorbed into its acceptor solution containing a mixture of the acid-base indicators cresol red and thymol blue. The maximum increase in the absorbance of the acceptor solution at 580 nm is related to the ammonium concentration in the solid sample. The proposed method is characterized by a linear concentration range of 0.1-5.0 mg NH4(+) kg(-1), a limit of detection of 8 μg NH4(+) kg(-1) and a sample throughput of 10h(-1). A successful application of this method for the determination of ammonium in building materials such as concrete, cement and sand is reported.

An extraction method based on the butanol—water system is used in an improved spectrophotometric determination of Xylenol Orange (XO), Semi-Xylenol Orange (SXO) and Cresol Red (CR) in mixtures. Small amounts of SXO in the presence of much greater amounts of XO, and small amounts of XO in the presence of large amounts of SXO can be determined with good accuracy after extractive separation of the compound to be determined, from the bulk of the other components of the mixture.

A mixture of Xylenol Orange (XO) and Semi-Xylenol Orange (SXO) was chromatographed on a cellulose column and ion-exchanged with Diaion SK-1 resin. XO and SXO in the acidic forms were titrated with sodium hydroxide to determine the basicities and the acid formation constants. The absorption spectra of XO and SXO were measured over a wide pH range, and were used for the calculation of acid formation constants, molar absorptivities, and the effect of ionic strength on the activity of XO. The purity of a commercial XO was measured by absorption spectroscopy, and it was found that the sample contained 36.3% of XO and 17.2% of SXO. Pure XO and SXO form a 1:2 and a 1:1 complex respectively with Zn(II). On the basis of these data the ionic structure of XO and SXO have been compared with those of Cresol Red and iminodiacetic acid, and discussed.

Several sulphone-phthalein indicators have been examined to test their possible application as redox indicators in titrations with hypochlorite, bromate, iodate and chloramine-T. It was confirmed that Cerana's indicator, Bromothymol Blue, is an excellent reversible indicator for titrations with hypochlorite. Bromocresol Purple is possibly slightly better. Cresol Red, Xylenol Orange, Thymol Blue and Methyl Thymol Blue are also suitable, but there is little point in using them, because the first two are converted to Bromocresol Purple and the last two to Bromothymol Blue. In the remaining systems the indicators were inferior to or no better than conventional indicators.

By Mannich condensation of o -Cresol Red, iminodiacetic acid and formaldehyde, Semi-Xylenol Orange (SXO) has been prepared in a 10-hr batch-procedure with a yield of about 30%. From the crude product SXO has been isolated by reversed-phase HPLC with perchloric acid-acetone mixtures as the mobile phase and C 18 -bonded silica as the stationary phase. The SXO fraction was freed from accompanying perchloric acid by a second separation on the same column, with water as eluent. After elution with acetone, the SXO was crystallized by evaporation.

A pH-scale in ethylene glycol is defined, based on potentiometric measurements for a cell without liquid junction: glass electrode || 0.1M (HCl + KCl), ethylene glycol | AgCl:Ag; and a potentiometric-spectrophotometric method for the determination of pK-value of acid-base indicators in ethylene glycol on the basis of this pH scale is proposed, in which the pH scale is established and the pK-value determined in a single titration at constant ionic strength. The following pK-values of indicators are reported: Cresol Red-3.00, Thymol Blue-3.39, Bromophenol Blue-6.49, Bromocresol Green-7.38, Bromocresol Purple- 9.00 and Cresol Red (2nd change)-11.07. A linear relationship was found between the pK-values of four sulphonphthalein indicators in ethylene glycol and in water according to the following equation (pK(HI)(c))(EG) = 2.3 + 1.1 (pK(HI)(c))(W). An attempt is made to explain this dependence, based on the idea of solute-solvent interaction of species of the same charge type.