Colorimetric Reagent Research Articles

Bedside colorimetric reagent dipstick in the diagnosis of meningitis in low- and middle-income countries: A prospective, international blinded comparison with laboratory analysis.

BackgroundColorimetric reagent dipstick (CRD) for leukocyte esterase (LE) has shown potential for diagnosing and ruling out bacterial meningitis. Potential advantages over traditional cerebrospinal fluid (CSF) analysis include the small quantity of CSF required, rapid results, and easy interpretation. Our study aimed to determine whether clinicians in LMICs could accurately diagnose bacterial meningitis using CRD at the bedside.MethodsA convenience sample of 143 patients requiring lumbar puncture for possible meningitis were enrolled from 1 October 2018 to 31 December 2019 at three hospitals, one each in rural Burundi, the Democratic Republic of Congo, and Kenya. CSF was analyzed using CRD followed by traditional laboratory-based analysis by technicians blinded to bedside results. Results were analyzed for concordance rates, sensitivity/specificity, positive and negative predictive values and impact on clinical decision-making.ResultsOne hundred and one patients were included in the analysis. The prevalence of bacterial meningitis in the convenience sample was 35% (35/101) as defined by microscopy or positive Gram stain. Using a threshold of “any positivity” for LE on the CRD, bedside testing correctly identified 33/35 cases (sensitivity 94.3%) and had a NPV of 92%. When only a clearly positive (≥ “+” for LE) CRD criterion was used, sensitivity and NPV were 77.1% and 86.2%, respectively.ConclusionDespite considerable promise, in our study, color reagent dipstick analysis of CSF did not perform well enough to rule out meningitis or screen samples for the need for microscopy. The development of a CSF-specific dipstick should be considered.

Correction for Oshiki et al., "Determination of 15N/14N of Ammonium, Nitrite, Nitrate, Hydroxylamine, and Hydrazine Using Colorimetric Reagents and Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF MS)".

Correction for Oshiki et al., "Determination of 15N/14N of Ammonium, Nitrite, Nitrate, Hydroxylamine, and Hydrazine Using Colorimetric Reagents and Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF MS)".

A Continuous Flow Injection/Indirect Photometric Method for the Detection of Fosetyl Aluminum in Commercial Pesticide Formulations

AbstractBecause of their Physico‐chemical characteristics and its composition, the development of new specific analytical methodologies to determine some highly polar pesticides are required. The reported methods demand long analysis time, expensive instruments and prior extraction of pesticide for detection. The current work presents a new flow injection analysis method combined with indirect photometric detection for the determination of Fosetyl‐Aluminum (Fosetyl‐Al) in commercial formulations, with rapid and highly accurate determination involving only construction of manifold system combined with photometric detector without need some of the pre‐treatments to the sample before the analysis such as extraction or separation. The proposed method is based on the reaction between the Fosetyl‐Al with the colorimetric reagent (Aluminon dye) in an aqueous medium of sodium nitrite resulting in the formation of a red complex and its absorbance is measured using the photometric detector. The proposed method included optimization of several parameters such as sodium nitrite concentration, flow rate, sample volume, Aluminon dye concentration, mixing coil and light intensity. The linear range of the detector response was in the range of 0.005–1.8 mmol/L for the sample with r (coefficient of determination) 0.9909, R2 (correlation coefficient) 0.9954 at 95 % and 0.0041 mmol/L as a limit of detection. The relative standard deviation was less than 1.5 % for 0.005 mmol/L of the analyte (n=11). The proposed method was validated and applied successfully for the determination of Fosetyl‐Al in commercial formulations and can be used as an alternative method for quality control assessment.

Microscale assessment of iodate fortificant in food-grade salt using the potassium iodide/polyvinyl alcohol colorimetric reagent

A rapid and straightforward spectrophotometric measurement of iodate in food-grade sodium chloride was developed based on the formation of a purple-red polyvinyl alcohol-iodine complex monitored at 490 nm. The conditions that influence the colorimetric reactions were optimized using a univariate approach. The method exhibited optimum results using 2% polyvinyl alcohol, 10 mM KI, and 0.5 M phosphoric acid. A matrix-matched calibration curve was prepared to eliminate interference due to the presence of NaCl and to provide a direct reading of iodate concentration in salt from the absorbance reading. Under optimum conditions, a linear calibration plot was observed from 5 to 140 mg iodate per kilogram (r = 0.9931). The method exhibited a sensitivity of 6.8 × 10−3 (mg iodate per kg of salt)−1 with a detection limit of 0.61 mg kg−1. The method was applied in actual samples, and the results agreed well with the titration method at a 95% confidence level using a paired t-test. The method supports the green analytical method as evaluated using Green Analytical Procedure Index (GAPI) and Analytical Eco-scale.

Determination of 15N/14N of Ammonium, Nitrite, Nitrate, Hydroxylamine, and Hydrazine Using Colorimetric Reagents and Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF MS).

In the nitrogen (N) cycle, nitrogenous compounds are chemically and biologically converted to various aqueous and gaseous N species. The 15N-labeling approach is a powerful culture-dependent technique to obtain insights into the complex nitrogen transformation reactions that occur in cultures. In the 15N-labeling approach, the fates of supplemented 15N- and/or unlabeled gaseous and aqueous compounds are tracked by mass spectrometry (MS) analysis, whereas MS analysis of aqueous N species requires laborious sample preparation steps and is performed using isotope-ratio mass spectrometry, which requires an expensive mass spectrometer. We developed a simple and high-throughput MS method for determining the 15N atoms percent of NH4+, NO2-, NO3-, NH2OH, and N2H4, where liquid samples (<0.5 mL) were mixed with colorimetric reagents (naphthylethylenediamine for NO2-, indophenol for NH4+, and p-aminobenzaldehyde for N2H4), and the mass spectra of the formed N complex dyes were obtained by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) MS. NH2OH and NO3- were chemically converted to NO2- by iodine oxidation and copper/hydrazine reduction reaction, respectively, prior to the above colorimetric reaction. The intensity of the isotope peak (M + 1 or M + 2) increased when the N complex dye was formed by coupling with a 15N-labeled compound, and a linear relationship was found between the determined 15N/14N peak ratio and 15N atom% for the tested N species. The developed method was applied to bacterial cultures to examine their N-transformation reactions, enabling us to observe the occurrence of NO2- oxidation and NO3- reduction in a hypoxic Nitrobacter winogradskyi culture. IMPORTANCE15N/14N analysis for aqueous N species is a powerful tool for obtaining insights into the global N cycle, but the procedure is cumbersome and laborious. The combined use of colorimetric reagents and MALDI-TOF MS, designated color MALDI-TOF MS, enabled us to determine the 15N atom% of common aqueous N species without laborious sample preparation and chromatographic separation steps; for instance, the 15N atom% of NO2- can be determined from >1,000 liquid samples daily at <$1 (U.S.) per 384 samples for routine analysis. This convenient MS method is a powerful tool that will advance our ability to explore the N-transformation reactions that occur in various environments and biological samples.

Effects of FOLFIRINOX Components on Pancreatic Adenocarcinoma Cells

Pancreatic adenocarcinoma is one of the lethal types of cancer worldwide. This study aimed to evaluate the cytotoxic effects of FOLFIRINOX compounds [oxaliplatin (OXA), irinotecan (IRI), fluorouracil (5FU), and leucovorin (LEU)] on a pancreatic adenocarcinoma cell line (PANC-1), both individually and collectively. Cell viability was determined using the colorimetric MTT reagent and apoptosis was assessed using the propidium iodide – Hoechst 33342 staining assay. Based on cell viability data, 5FU and FOLFIRINOX treatments were more potent against PANC-1 than the other test groups. The apoptotic trend, nevertheless, was not different between them and the control group. Moreover, OXA, LEU, and IRI significantly increase apoptotic cell death. Our findings indicate that 5FU and FOLFIRINOX are comparably effective in reducing the PANC-1 cell viability. In the future, 5FU and FOLFIRINOX may be adapted to local pancreatic adenocarcinoma treatments, but the development of these localized drug release platforms requires further attention as the microenvironment of pancreatic adenocarcinoma inherently contains many unknowns.

Heat-based procedure for detectability enhancement of colorimetric paper-based spot tests

Colorimetry is an analytical procedure in which a colored compound is formed or degraded from a selective reaction between the analyte and a chromophore followed by color intensity measurement for quantification purposes. The employment of paper-based analytical devices as a solid substrate to perform chemical reactions enabled the miniaturization of the analytical system, thus requiring a minimum volume of sample (e.g., µL) and resulting in low cost, disposability, and ease of use. On the other hand, the detectability of such devices is usually not suitable for a variety of practical applications where the analyte concentration is present in either low parts-per-million or high parts-per-billion concentration range. In this study, we describe a simple procedure for analyte preconcentration (i.e., enrichment) based on a multiple and automated sample delivery of 15 µL per time on a heated paper surface. In this procedure, an aliquot of the sample solution diffuses through the center of the paper to form a circular spot, followed by quick solvent vaporization prior to the next volume injection. After the enrichment procedure,15 µL of the reagent is added to perform the colorimetric reaction. The applicability of the proposed procedure was demonstrated for the determination of nickel (II) in natural waters and iron (III) in ethanol fuel using dimethylglyoxime and 1,10 phenanthroline as colorimetric reagents, respectively. By relating the color intensity of the products formed to the concentration, the limits of detection were as low as 0.1 mg L−1 for nickel (II) and iron (III) using 20 and 10 aliquots of 15 µL of each metal ion solution. Under these conditions, the enrichment factors were 180- and 20-fold higher for Ni2+ and Fe3+, respectively, with a total time of analysis inferior to 10 min. We anticipate that the proposed procedure can be tailored for a wide range of analytical problems using colorimetric determinations in spot tests with low concentration detectability and ease of operation.

Printed Ultrastable Bioplasmonic Microarrays for Point-of-Need Biosensing.

Paper-based point-of-need (PON) biosensors are attractive for various applications, including food safety, agriculture, disease diagnosis, and drug screening, owing to their low cost and ease of use. However, existing paper-based biosensors mainly rely on biolabels, colorimetric reagents, and biorecognition elements and exhibit limited stability under harsh environments. Here, we report a label-free paper-based biosensor composed of bioplasmonic microarrays for sensitive detection and quantification of protein targets in small volumes of biofluids. Bioplasmonic microarrays were printed using an ultrastable bioplasmonic ink, rendering the PON sensors excellent thermal, chemical, and biological stability for their reliable performance in resource-limited settings. We fabricated silicone hydrophobic barriers and bioplasmonic microarrays with direct writing and droplet jetting approaches on a three-dimensional (3D) nanoporous paper. Direct writing hydrophobic barriers can define hydrophilic channels less than 100 μm wide. High-resolution patterning of hydrophilic test domains enables the handling and analysis of small fluid volumes. We show that the plasmonic sensors based on a vertical flow assay provide similar sensitivity and low limit of detection with a 60 μL sample volume compared to those with 500 μL samples based on an immersion approach and can shorten assay time from 90 to 20 min.

Application of flow injection analysis-solid phase extraction based on ion-pair formation for selective preconcentration of trace amount of anti-HIV drug

In this study, a flow injection analysis (FIA) system combined with solid phase extraction (SPE) was designed for preconcentration and selective extraction of an HIV anti-virus drug (i.e. Nevirapine (NVP)). Molecularly imprinted polymer (MIP) nanostructures were used as the selective adsorbent in the extraction column. The synthesis of MIP was carried out, using methacrylic acid (MAA) as the functional monomer, ethyleneglycoldimetacrylate (EGDMA) as the cross-linking agent in methanol/acetonitrile as porogen solvent. Scanning electron microscopy (SEM) and differential thermal analysis (DTA) were used for the characterization of the as-synthesized NVP-MIP. In the SPE-FIA procedure, after analyte loading, the eluted NVP drug was treated with fast green (FCF) as a colorimetric reagent. After the formation of colored ion-pair between NVP and FCF in an acidic media, the quantitative determination was performed spectrophotometrically at 620 nm. The influence of experimental parameters on the NVP extraction, including adsorption and desorption flow rate, MIP amount, sampling time, and elution condition were studied and optimized. For the present method, two linear concentration ranges (0.0010–0.10 mg L-1 and 0.10–80 mg L-1), a low detection limit of 0.0005 mg L-1, and an acceptable preconcentration factor of 100 was obtained in optimum conditions. Meanwhile, a selective binding affinity of NVP toward MIP sorbent was observed against other drugs, in the selectivity study. Moreover, the applicability of the designed method was confirmed by successfully uptaking NVP from human urine real samples and artificial aqueous samples.

Application of electrocolorimetric extraction for the determination of Ni(II) ions in chocolate samples: A green methodology for food analysis

This study developed an electrocolorimetric extraction technique as a simple, rapid, and green method for the simultaneous preconcentration and determination of Ni(II) in chocolate samples. The system was designed using an agarose gel (3% w/v) solution containing 10% v/v 80 mM dimethylglyoxime (DMG) and 10% v/v 0.03 M ammonia as colorimetric reagents to determine Ni(II) ions. When voltage was applied to the system, Ni(II) ions were extracted from the donor solution into the gel and formed Ni-DMG complexes with a pink color. Under the optimal conditions, a good linear range was obtained from 30 to 750 µg L−1 (R2 > 0.998) with a detection limit of 1 µg L−1. Inter- and intra-assay results showing relative standard deviations were less than 2.6% and 1.9%, respectively. Our developed method was applied to determine Ni(II) in chocolate samples. The results were in agreement with those obtained using ICP–OES.

Phytochemical prospection, total flavonoids and total phenolic and antioxidant activity of the mushroom extract Scleroderma verrucosum (Bull.) Pers

Scleroderma verrucosum is a species of mushroom belonging to the family Sclerodermataceae found in the Americas and Europe. This study aimed to evaluate the 70% ethanol extract of the vegetative part of the mushroom S. verrucosum for qualitative phytochemical constituents and total content of flavonoids and phenolics, and the DPPH free radical reduction activity. Mushroom extract was prepared in 70% ethanol solution. Qualitative phytochemical assay was performed for different groups using colorimetric reagents. The contents of total flavonoids and phenolics, and antioxidant activity in reducing the DPPH free radical were quantitatively determined. The positive presence of alkaloids, flavonoids, phenolics, triterpenoids, steroids, tannins, organic acids, reducing sugars, aromatic compounds and carboxylic acids were observed. The extract exhibited total flavonoid content = 60.14 QE 100 g-1, for total phenolics = 309.14 GAE 100 g-1 and free radical reduction of = 5.97 µg mL-1. Mushroom extract Scleroderma verrucosum demonstrated the presence of several medicinal important phytochemical groups as well as total flavonoid and phenolic content that exhibit the potential for antioxidant activity.

Fully integrated colorimetric sensor based on transparency substrate for salbutamol determination

A facile colorimetric method based on a typical redox reaction was first developed for the determination of salbutamol (SAL) using a low-cost and portable transparency-based analytical device (TAD). The TAD was simply fabricated by wax-printing onto a transparent polymer-based substrate to create the hydrophobic barriers and the colorimetric reaction zones where the color changes could be easily observed with the naked eye. Potassium permanganate (KMnO4), a common oxidizing agent, was deliberately used as a colorimetric reagent for SAL. Once SAL reacted with KMnO4 in the acidified system, it could undergo oxidation and the color of KMnO4 subsequently changed from light pink to orange. The color change corresponding to the SAL concentration could be clearly observed at the TAD sensor. In addition, the reaction color could be recorded using a digital camera and then analyzed by ImageJ for quantitative analysis. Under the optimized conditions, the developed method together with the TAD sensor exhibited high efficiency for SAL determination with linearity ranging from 0.5 to 40 mg·L−1 and a limit of detection (LOD) of 0.05 mg·L−1.•This proposed TAD-based colorimetric method using permanganate as color reagent showed excellent performance in SAL detection with good accuracy and high precision.

Advanced graphene oxide-based paper sensor for colorimetric detection of miRNA.

MicroRNAs (miRNAs), found in blood and body fluids, have emerged as potential non-invasive biomarkers for disease and injury. miRNAs are quantitatively evaluated using typical RNA analysis methods such as the quantitative reverse transcription polymerase chain reaction, microarrays, and Northern blot, all of which require complex procedures and expensive reagents. To utilize miRNAs as practical biomarkers, it will be helpful to develop simple and user-friendly sensors. In this study, a paper-based miRNA sensor was developed by combining two methods: (1) target-recycled DNAzyme (Dz) amplification and (2) graphene oxide-assisted Dz blotting on paper. The Dz spots on paper caused amiRNA-dependent color change in presence of colorimetric reagents and facilitated the quantification of absolute amount of the target miRNA, irrespective of the volume, with high reproducibility. This approach is technologically straightforward and enables quantification of as low as 7.75 fmol miRNA using a portable smartphone.

DEVELOPMENT OF PAPER-BASED ANALYTICAL DEVICE FOR DETECTING DIAZEPAM IN URINE

Objective: The aim of this study was to develop Paper-based Analytical Devices (PADs) with colorimetric method as a presumptive test for detecting diazepam in urine&#x0D; Methods: Colorimetric method was used as a principle of this study. PADs were fabricated with wax-printing methods. Chosen colorimetric reagent was tested for selectivity with hydromorphone and codeine; and sensitivity by measuring the absorbance with UV-Vis spectrophotometer. PADs were tested for its sensitivity and stability. The intensity of color developed on PADs are measured with ImageJ. The ability of PADs to detect diazepam in urine was simulated with testing spiked urine sample to the PADs&#x0D; Results: Zimmermann gave the most obvious prominent color change from colorless to purple-red color out of the four reagents. PAD is selective to diazepam when tested with hydromorphone and codeine. PAD is sensitive with a cut-off concentration at 100 ppm. PAD can detect diazepam in urine with the highest recovery percent at 92.8%±4,6&#x0D; Conclusion: It can be concluded that PAD is quite selective and sensitive to detect diazepam in urine and can be done easily and fast for onsite analysis

Colorimetric and fluorometric determination of boron using β-diketone–BF2 compounds containing catechol moiety

In this study, we attempted to develop a new boron quantification reagent using β-diketones, because β-diketones often exhibit strong absorption and luminescence and react with boric acid. The luminescence intensity remarkably varied with the addition of boric acid to a solution of β-diketone containing 4-methoxyphenyl groups. However, luminescence intensity gradually decreased with time because of the tautomerization of the enol form of β-diketone to its keto form. Therefore, in this study, we synthesized novel β-diketone–BF2 compounds in which the β-diketone site was cross-linked with BF2 to avoid changes in the luminescence intensity owing to the keto-enol tautomerization. We introduced a catechol moiety as a reaction site with boron and examined their effectiveness in quantifying boron using absorption and emission spectroscopy. Furthermore, the synthesized β-diketone–BF2 compounds (1–9) that contained 4-dimethylaminophenyl (4-NMe2Ph) or 4-methoxyphenyl (4-MeOPh) group and catechol or salicylic acid moiety as the reaction site, were characterized using various analytical methods. No correlation was observed between the pKa values of β-diketone–BF2 compounds and the formation constants for the reactions with boric acid (log K1). Additionally, quantification limit estimation carried out using absorption and emission spectroscopy suggested that β-diketone–BF2 compounds 3 and 7, which contain 4-NMe2Ph group and catechol moiety, can be used to determine boric acid concentrations > ca. 2 × 10–4 M. This study demonstrated the usefulness of the β-diketone-BF2 compound as a colorimetric and fluorescence quantifying reagent for boric acid.

A simple paper-based biosensor for on-site visual detection of organophosphate residues

In general, the laboratory method of analyzing pesticides in vegetables is complicated due to the high cost of equipment and chemicals. The process of analyzing pesticide residues generally requires expertise as well as a significant period of time. In this study, a paper-based biosensor was developed for the detection of acetylcholinesterase (AChE) inhibitors, particularly organophosphate pesticides. The paperbased biosensor was constructed based on the Ellman colorimetric assay by immobilizing AChE on cellulose paper with 2% alginate gel, 0.25% glutaraldehyde and the colorimetric reagent 5,5-dithio-bis-(2-nitrobenzoic acid) (DTNB) in phosphate buffer (pH 8.0). As a substrate, acetylthiocholine chloride (ATChCl) was used. The results showed that the developed paperbased biosensor has been stable for 2 weeks with a detection limit of 0.03 mM of chlorpyrifos. The paper-based biosensor was applied to detect organophosphate pesticides in vegetables from the farmers’ market, Ratchaburi Province. It was found that the test results of the paper-based biosensor were similar to the commercial GT-test kit. The paper-based biosensor was 10 times faster than the GT-test kit in terms of testing time and the results were easy to identify due to the color-based indicator. As a result, a paper-based biosensor is rapid, portable and easy to use by the general population.

Profile and correlates of colorimetric reagent kit use among people who use ecstasy/MDMA and other illegal stimulants in Australia.

Colorimetric reagent kits can provide information about the compounds present in drug samples. This study aimed to identify patterns and correlates of colorimetric reagent kit use, as well as behavioural outcomes of testing, amongst people who use illegal stimulants in a context that lacks permanent government-sanctioned drug checking services. Australians residing in capital cities who reported regularly using ecstasy/MDMA and/or other illegal stimulants ≥monthly in the past six months were recruited via social media and word-of-mouth from April-July 2019 (N=792). Participants were asked about testing the contents and/or purity of illegal drugs, and features of last colorimetric reagent kit use. Logistic regression identified correlates of last using a kit (referent: no use of drug checking technology to test drug contents/purity in the past year). Over one-third (36%) reported testing drug contents and/or purity; of this group, 86% had last used a colorimetric reagent kit. On the last occasion, 52% reported someone else had conducted testing; 58% said testing occurred <24h before planned drug use; and 24% reported testing for quantity of a substance. Correlates of drug checking comprised: being younger, male, past six-month use of new psychoactive substances, accessing community-based health services for alcohol or other drug reasons, selling drugs for cash profit, obtaining information from peers who had tried the drug, and searching online for reports of the drug by stamp/appearance. The majority (84%) tested a substance they had been sold and/or given as MDMA; of these, 87% detected MDMA. Of those who expected and detected MDMA, 29% and 11% reported results to their peers and dealer, respectively. People who use ecstasy/MDMA and/or other illegal stimulants seek out objective information about substance contents. In countries that lack permanent government-sanctioned drug checking services, it is important to acknowledge that people already engage in drug checking but with suboptimal technologies and without tailored specialist advice and education.

Efficient comparative evaluation of spectrophotometrically determined phosphate in synthetic and in actual human embryos' culture medium

The determination of phosphate in human embryos' culture medium is the main target of this manuscript using novel mixed reagents. This research also aimed to perform comparative evaluation of spectrophotometrically determined phosphate in synthetic and in actual human embryos' culture medium. It depents on the reaction of phosphate with mixed colorimetric reagents. The molybdenum blue formed attained a λmax of 825 nm and molar absorptivity of 2.190 x 103 L mol-1 cm-1. The product of the reaction in case of adding potassium hydrogen tartrate to the reagent showed a λmax at 830 nm and the molar absorptivity of molybdenum blue was 2.833 x 104 L mol-1 cm-1. So, antimony potassium tartrate was added to the reagent to increase the reaction rate in order to be able to make determination at the maximum absorbance of the product and subsequently increase the sensitivity of the method. This reduced the time of reaction to 5−10 min and wavelength at the maximum absorbance was shifted to be 896 nm with molar absorptivity 1.797 x 104 L mol-1 cm-1. Tracing the reaction between sodium dihydrogen phosphate and ammonium molybdate under the optimum conditions led to the construction of a calibration curve. The concentration range of the calibration graph was found to be 3.183−17.5 µg mL-1 and correlation coefficient of the data obtained was 0.999. The method was applied to a synthetic mixture containing some components of the human embryos’ culture medium without interference. This leads to the successful application of the suggested procedures to the spectrophotometric micro-determination of phosphate content in actual human embryos’ culture medium; which was in a good matching with the data of determining phosphate in the same media in literature.

Sensitive and simple colorimetric methods for visual detection and quantitative determination of semicarbazide in flour products using colorimetric reagents

After baking the flour, azodicarbonamide, an approved food additive, can be converted into carcinogenic semicarbazide hydrochloride (SEM) and biurea in flour products. Thus, determine SEM in commercial bread products is become mandatory and need to be performed. Therefore, two accurate, precision, simple and economics colorimetric methods have been developed for the visual detection and quantitative determination of SEM in commercial flour products. The 1st method is based on the formation of a blue-coloured product with λmax at 690 nm as a result of a reaction between the SEM and potassium ferrocyanide in an acidic medium (pH 6.0). In the 2nd method, a brownish-green colored product is formed due to the reaction between the SEM and phosphomolybdic acid (PMA) in a basic medium (pH 9.0). The resulting product absorbs light at λmax 750 nm. The colorimetric methods can be used either as sensors to detect the SEM by bare eye observation as little as 10 ppm and 2.0 ppm within 4−2 min or by spectrophotometry as the determination methods with linearity ranges 8.0−180 ppm and 0.5−30 ppm for the 1st and 2nd methods respectively. The developed methods were successfully applied to determine the SEM in the commercial bread products with a relative standard deviation (RSD) <3 %, <2 % and recovery of 94–103 %, 96–101 % for methods (1st and 2nd) respectively. The visual detection limits of the sensors can be used as a platform for SEM field-portable detection due to their lower limitations than the reported SEM in flour products, which opens the doors for on-site detection of SEM with instrument free.

Electrocolorimetric gel-based sensing approach for simultaneous extraction, preconcentration, and detection of iodide and chromium (VI) ions

A total integrated electrocolorimetric sensing approach consisting of gel-based electromembrane extraction and colorimetric detection in a one-step process was developed. This system was designed using colorimetric reagents preadded to the agarose gel for the determination of the following two model analytes: iodide and hexavalent chromium [Cr(VI)]. In this system, when a voltage was applied, the analytes were extracted and transferred from the sample solution (donor phase) to the gel (acceptor phase). The analytes then simultaneously reacted with the colorimetric reagents inside the gel, yielding blue and violet colors for iodide and Cr(VI), respectively. These colors were then analyzed using a portable spectrometer and could also be distinguished with the naked eye. Parameters affecting the extraction efficiency were studied and optimized for both analytes. The gel composition for iodide detection was 4% (w/v) agarose, 5% (v/v) H2O2, and 1% (w/v) starch in 2 mM HCl. The gel composition for Cr(VI) detection was 2% (w/v) agarose and 1% (w/v) DPC in 0.5 mM HNO3. Both analytes were extracted at an applied potential of 50 V, an extraction time of 15 min and a stirring rate of 600 rpm. Under the optimized conditions, the developed systems provided linear responses within 15 min for iodide concentrations ranging from 50 to 250 μg L−1 with a detection limit of 18 μg L−1 and for Cr(VI) concentrations ranging from 30 to 125 μg L−1 with a detection limit of 5 μg L−1. Finally, these systems were successfully applied to the determination of iodide in iodide food supplement samples and Cr(VI) in drinking water samples, showing a negligible matrix effect. This integration could also be extended to other analytes and detection systems to develop sensitive, on-site, and environmentally friendly sensing approaches.