1,721,018 research outputs found
Determination of the relevant equilibrium constants working in pH Colorimetric Sensor Arrays (CSAs)
No full textThe rationalization of the behavior of pH Colorimetric Sensor Arrays, based on Bromophenol Blue embedded in tetraethyl orthosilicates-based matrices, was accomplished by calculating the thermodynamic constants of the reactions involved. The constants were determined in four matrices upon variation of the concentration of surfactant, indicator, and anionic species present in buffers and samples. Based on the values found, it was demonstrated that the variation of the surfactant concentration widened the working interval up to 1.80 and 5.30 pH units in the solution and one of the tested polymers, respectively. The competitive reaction between anionic species and cationic head-groups of the surfactant shifted the position of the calibration profile up to 1.50 pH units in solution. For the CSA, the shift was 0.35 pH units for a large concentration of surfactant (0.1 M) and negligible at low concentrations (<0.01 M). The proposed mechanism allowed for a very good curve fitting in all conditions
Kinetic response of pH colorimetric sensors: Role of the cationic surfactant concentration and amount and type of solvent used in the preparation of the sensing spot
No full textA pH colorimetric sensor array (CSA) with a kinetic response comparable to those of the pH-meter was prepared. The signal comes from the Hue coordinate (H) and RGB profiles of some pH indicators such as Bromothymol Blue (BB) and Nitrazine Yellow (NY) in polyvinylidene fluoride (PVDF)-supported organically modified silicate (OrMoSil) spots. The t95 is of the order of 50–150 s for RGB coordinates but is lowered of one order of magnitude employing the H coordinate as the detection signal. The addition of the Hexadecyltrimethylammonium p-toluenesulfonate (CTApTs) additive in the interval 0.10 0.19 gCTApTs/gprecursors, the transition from the basic to the acid form was hindered by the cationic interface due to the surfactant. The CTApTs concentrations, leading to a t95 lower than one minute, were in the interval 0.10 < R < 0.37 gCTApTs/gprecursors for NY and 0.10 < R < 0.28 gCTApTs/gprecursors for BB, comparable to the response time of the potentiometric measurements. Indeed, the kinetic profiles did not change with the amount and type of solvent
High accuracy OrMoSil (Polyvinylidene Fluoride)-supported colorimetric sensor: Novel approach for the calculation of the pH prediction error
No full textpH 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, spHjavax.xml.bind.JAXBElement@315a8962 = 0.03 in both environments; for TBB, spHjavax.xml.bind.JAXBElement@4f058030 = 0.02 in the sensing spot and 0.05 in solution; for CR, spHjavax.xml.bind.JAXBElement@4ee5bdc0 = 0.11 in the sensing spot and 0.04 in solution; for BY, spHjavax.xml.bind.JAXBElement@36932dcd = 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)
Reversible and high accuracy pH colorimetric sensor array based on a single acid-base indicator working in a wide pH interval
No full textA pH colorimetric sensor array (CSA) with fast response time (<1 min) using only one acid-base indicator, Bromothymol Blue (BB), was prepared and characterized by modulating the amount, C, of the surfactant Hexadecyltrimethylammonium p-toluenesulfonate between 0 and 0.3725 gCTApTs/gprecursor with a constant amount of the OrMoSil precursors. The effect of the C increase is a continuous acidic shift of the calibration position, i.e. a huge variation of the pKa value of BB in the pH range 5.80-13.50. The precision error decreased with increasing C from 0.096 pH units (lower C values) to 0.023 pH units (larger C values). This result led to the development of a model to determine the number of spots with suitable C values required for having a similar value of precision in the entire working interval of the CSA. By selecting only 4 spots the precision error is < 0.100 pH units in the pH range 5.80–13.50. With 256 spots (diameter of each spot ≈ 3 mm), the model predicted an error almost constant (≈0.010) in the entire pH range
Influence of surfactant chain length, counterion and OrMoSil precursors on reversibility and working interval of pH colorimetric sensors
No full textAn in-depth study was conducted to determine the influence of some important parameters to produce a pH colorimetric sensor characterized by long-term stability, lack of leaching, high reversibility, repeatability and extended working range. Bromothymol Blue (BB) was used as pH sensitive molecule. Its performance was monitored while tailoring the concentration of some added cationic surfactants, together with the organic fraction of the sol-gel composition to avoid leaching phenomena, low homogeneity and to increase reversibility. Five cationic surfactants with different linear alkyl chain length (from C8 to C18) were added to a sol-gel containing BB. The C16 was chosen as optimal. The effect of the surfactant counterion was also investigated. The C16 surfactant had a pH working interval of 3 pH unit by using chloride, 1.5 with bromide and 1 pH unit with p-toluenesulfonate as counterions, respectively. Chloride was characterized by a larger inhomogeneity while p-toluenesulfonate gave homogeneity and high repeatability. The hexadecyltrimethylammonium p-toluenesulfonate was therefore chosen as the best surfactant. Leaching in alkaline medium was avoided by using the dodecyl moiety among three organic groups linked to the OrMoSil matrix (dodecyl, phenyl and methyl). Colorimetric sensor arrays made with these specifications remained stable and reversible for months
Behavior of Sulfonephthalein and Azo dyes as effective pH sensors in hybrid materials
No full textThe behavior of pH indicators belonging to two different families, Sulfonephthalein and Azo in the Organically modified silicates (OrMoSil) polymer matrix, was investigated. The fraction and the dimension of the OrMoSil organic moiety were co-modulated with the cationic surfactant Hexadecyltrimethylammonium p-toluenesulfonate concentration. Two matrices were tested: the former based on Tetraethyl orthosilicate/ Trimethoxyphenylsilane (TEOS/FTMS), the latter, more lipophilic, based on TEOS/Dodecyl-TEOS. The working interval of Bromothymol Blue (BB) and Nitrazine Yellow (NY), with the co-variation of cationic surfactant amount, C, was wider for the matrix based on TEOS/Dodecyl-TEOS. The overall working interval of BB was between pH 5.80 and 12.50 and between 6.00 and 11.30 for NY. Among the pH indicators characterized by transitions between non-complementary colors, the most important results could be achieved with Methyl Red (MR). With the addition of Tetrabromophenol Blue (TBB), the sensitivity gradually rises with a linear hue profile between pH = 4.20 and pH = 11.90 with a small amount of dye for only one spot. In correspondence of the molar ratio nTBB/nMR = 0.233, there is the inversion point characterizing a spot working as an “on-off” sensor centered at pH = 4.15 suitable for pH measurement of acidic soils
Enhancement of the pH measurement of a PVDF-supported colorimetric sensor by tailoring hue changes with the addition of a second dye
No full textA pH colorimetric sensor was prepared and characterized by combining two acid-base indicators, Tetrabromophenol blue (TBB) and Phenol Red (PR) with molar ratios ranging from 0 to 0.47. Indicators were embedded in Organically Modified Silicate (OrMoSil) spots supported in Polyvinylidene fluoride (PVDF) together with a suitable cationic surfactant. The deposition procedure was very repeatable allowing a single calibration for all membranes built in the same preparation lot. The signal was based on the Hue profile (H) vs. pH. The CIE-xy color space contains an achromatic point that is the key point of the colorimetric sensor behavior as it causes the inversion of the slope of the H calibration curve at a specific inversion point. For this reason, the identification of the effective conditions of the improvement of the PR analytical performances are not trivial, 0.186 < nTBB/nPR < 0.324 with prediction error in the range 0.01–0.16 pH unit. The proposed adjustment allowed the construction of pH colorimetric sensors with prediction error comparable to that of potentiometric measurements. The obtained results indicated the route to widen the availability even to those acid-base indicators lacking of suitable color transitions but having suitable pKa values
Ph colorimetric sensor arrays: Role of the color space adopted for the calculation of the prediction error
Full text linkA pH colorimetric sensor array was prepared and characterized by combining tetrabromophenol blue (TBB) and bromothymol blue (BB) embedded in organically modified silicate (OrMoSil) spots polyvinylidene fluoride (PVDF)-supported. The signal was based on the Hue profile (H). The individual calibrations of TBB and BB showed precisions with minimum values of 0.012 pH units at pH = 2.196 for TBB and 0.018 at pH = 6.692 for BB. The overall precision of 10 spots of the mixture TBB/BB increased in the pH range of 1.000–8.000 from a minimum value of pH precision of 0.009 at pH = 2.196 to 0.012 at pH = 6.692, with the worst value of 0.279 pH units at pH = 4.101. The possibility to produce an array with much more than 10 spots allows for improving precision. The H analytical performance was compared to those of other color spaces such as RGB, Lab, and XYZ. H was the best one, with prediction error in the range of 0.016 to 0.021 pH units, at least three times lower than the second-best (x coordinate), with 0.064 pH units. These results were also confirmed by the calculation of the main experimental contributions to the pH prediction error, demonstrating the consistency of the proposed calculation approach
Cannabis potency in North-East Italy: A ten-year study (2010–2019)
No full textThis paper presents data about potency of herbal and resin cannabis products seized during 2010–2019 in north-east Italy. More than 12,000 cannabis samples were analyzed and concentrations of THC, CBD and CBN were collected. The results of our study provided clear evidence for an increase in the potency of cannabis products across the study period, which is consistent with other studies. Globally, the median THC concentrations increased from about 6%–11%, but differences were found between herbal and resin materials. THC potency in resin materials increased more consistently across the study period with a dramatic raise during 2018–2019, with median THC contents around 17%. CBD concentrations were found to decrease constantly over the study period, especially in herbal materials, which had a mean CBD concentration of 0.3%. In particular, about 75% of the analyzed herbal samples had a CBD concentration which was less than 3% of the corresponding THC concentration. In contrast, more than 50% of the analyzed resin materials had a CBD concentration which was about 30% of the corresponding THC concentration. This is consistent with the increase in prevalence of high-potency seedless female herbal products observed in the same period and indicates that herbal and resin materials were produced from different varieties of cannabis plants. However, resin materials derived from high THC/low CBD cannabis plants were recently found. Different routes (e.g. northern Europe) or different modalities of distribution were assumed for these products. CBN concentrations were also considered and found to be very low and consistent across the study period indicating reliability of THC values used in statistical analysis. In conclusion, this study provided an accurate picture of cannabis products seized over a decade over a definite geographical area which can be extremely helpful for comparative purposes and for national and international statistical analyses on cannabis products
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