A green-PAD array combined with chemometrics for pH measurements

Seven increasing levels of water salinity from 0.029 to 0.600 M (as NaCl) were used to investigate the dependence of pH measurement, performed using colorimetric sensor arrays (CSAs), on ionic strength. The CSAs were arrays of sensing spots prepared in the form of sol–gel-embedding Bromothymol Blue (BB) and Bromocresol Green (BCG) in a porous nitrocellulose support. The support was impregnated over the entire thickness (≈100 µm), allowing for the signal (Hue) acquisition on the opposite side to the contact with the sample solution. Three CSAs were prepared, M1, M2, and M3. M1 contained a free cationic surfactant, hexadecyltrimethylammonium p-toluenesulfonate (CTApTs), for modulating the pKa of the indicators. In M2, the surfactant dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DTSACl) was covalently bonded to the sol–gel. M3 was prepared like M2 but using a larger amount of ethanol as the solvent for the synthesis. The modulation of the CTApTs or the DTSACl concentration enabled the tuning of the pKa. In general, the pKa modulation ability decreased with the increase in salinity. The presence of a surfactant covalently linked to the backbone partially reduced the competitiveness of the anionic species, improving the results. Nevertheless, the salt effect was still present, and a correction algorithm was required. Between pH 5.00 and 12.00, this correction could be made automatically by using spots taken as references to produce sensors independent of salinity. As the salt effect is virtually absent above 0.160 M, M2 and M3 can be used for future applications in seawater.

Section: Introductionmentioning

confidence: 99%

Positively Charged Organosilanes Covalently Linked to the Silica Network as Modulating Tools for the Salinity Correction of pH Values Obtained with Colorimetric Sensor Arrays (CSAs)

Pastore,

Badocco,

Cappellin

et al. 2024

“…Moving to the main features of these sensors and limiting the investigation to the most recent papers, different pH-sensitive molecules have been proposed, among which the most common are commercial pH indicators [ 1 , 4 , 5 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], novel pH-sensitive compounds [ 1 , 4 , 5 , 17 , 18 ], natural dyes [ 1 , 4 , 19 , 20 , 21 , 22 , 23 ], and luminescent probes [ 1 , 3 , 4 , 24 , 25 , 26 , 27 ]. On the other hand, unlike pH papers, these sensors can exploit different solid substrates and, consequently, anchor mechanisms such as physical entrapment, [ 1 , 3 , 4 , 5 , 11 , 19 , 20 , 23 ] sol–gel synthesis [ 1 , 4 , 10 , 12 , 13 , 14 , 15 , 16 , 24 ] or covalent immobilization [ 1 , 4 , 5 ], hence offering a fully tunable device depending on the final application. Moving forward, the target pH range represents a crucial aspect that must be considered when developing a novel optical pH sens...…”

Section: Introductionmentioning

confidence: 99%

“…Last but not least, as we hinted before, the lack of reversibility and accuracy represents one of the main drawbacks of traditional pH papers; regarding the first feature, unfortunately, reversibility also still remains the Achilles heel for optical pH sensors since only a few of them are actually fully reversible, while most of them ensure reversibility only in typical conditions or they are theoretically reversible but cannot operate reversibly [ 3 ]. As for the latter aspect, nowadays, several strategies have been proposed to overcome the simple coloration comparison typical of pH papers, mainly relying on complex data manipulation, linearization, and other univariate analysis on color indices [ 1 , 3 , 4 , 5 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 20 , 22 , 23 , 24 ] or seldom exploiting simple and reliable multivariate approaches [ 1 , 4 , 5 , 19 ].…”

Section: Introductionmentioning

confidence: 99%

Chemometric-Assisted Litmus Test: One Single Sensing Platform Adapted from 1–13 to Narrow pH Ranges

Magnaghi

Alberti

Zanoni

et al. 2023

Self Cite

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.

“…These devices have several advantages: they are sensitive, practical, and adapt to inexperienced users. Among them, Paper-based Analytical Devices (PADs) were widely used for environmental analyses, food controls and clinical trials due to their easy preparation and quick response pros [34][35][36].…”

Section: Introductionmentioning

confidence: 99%

“…The capillary properties of paper provided by the cellulosic fiber network eliminate the necessity of pumping methods instead ofconventional microfluidic devices. In addition, the paper's ample availability, biodegradability, low price, and ease of surface functionalization make it an attractive substrate in sensors' development [36][37][38].…”

Section: Introductionmentioning

confidence: 99%

Colorimetric Paper-Based Analytical Devices (PADs) Backed by Chemometrics for Pd(II) Detection

Alberti,

Magnaghi,

Iurato

et al. 2023

Self Cite

This paper presents the development of cheap and selective Paper-based Analytical Devices (PADs) for selective Pd(II) determination from very acidic aqueous solutions. The PADs were obtained by impregnating two cm-side squares of filter paper with an azoic ligand, (2-(tetrazolylazo)-1,8 dihydroxy naphthalene-3,6,-disulphonic acid), termed TazoC. The so-obtained orange TazoC-PADs interact quickly with Pd(II) in aqueous solutions by forming a complex purple-blue-colored already at pH lower than 2. The dye complexes no other metal ions at such an acidic media, making TazoC-PADs highly selective to Pd(II) detection. Besides, at higher pH values, other cations, for example, Cu(II) and Ni(II), can interact with TazoC through the formation of stable and pink-magenta-colored complexes; however, it is possible to quantify Pd(II) in the presence of other cations using a multivariate approach. To this end, UV-vis spectra of the TazoC-PADs after equilibration with the metal ions solutions were registered in the 300–800 nm wavelength range. By applying Partial Least Square regression (PLS), the whole UV-vis spectra of the TazoC-PADs were related to the Pd(II) concentrations both when present alone in solution and also in the presence of Cu(II) and Ni(II). Tailored PLS models obtained with matrix-matched standard solutions correctly predicted Pd(II) concentrations in unknown samples and tap water spiked with the metal cation, making the method promising for quick and economical sensing of Pd(II).