Precipitation Titration Research Articles

Solubility product and total solubility in water of copper(II) nicotinate

A method for determining the solubility product of sparingly soluble copper (II) salts based on the data of precipitation potentiometric titration with a copper indicator electrode is proposed and substantiated. For the first time, a systematic study of the solubility in aqueous media of copper (II) nicotinate (pyridine-3-carboxylate, CuNic2) has been carried out. The solubility product KSP(CuNic2) was determined from the precipitation titration curves of Cu(NO3)2 solution with sodium nicotinate. The value of log10KSP(CuNic2) = –14.10 ± 0.31 was obtained, and it does not depend on temperature in the range of 14–45 °C. The total solubility of CuNic2 was estimated by atomic absorption spectroscopy; in aqueous solutions with pH 6.3–6.5 containing ∼ 0.07 mol kg−1 NaNic and ∼ 0.04 mol kg−1 NaNO3, it is equal to (1.63 ± 0.12) × 10–5 mol kg−1 at a temperature of 20–25 °C. The cumulative stability constant of the CuNic2(aq) complex was estimated from the values of the solubility product and total solubility: log10β2 = 9.31 ± 0.31 (20–25 °C).

User-friendly diameter-based measurement paper sensor for chloride detection in water

Chloride (Cl−) is an anion widely distributed in nature. It is also an essential parameter to consider when assessing the water quality for ensuring drinking water safety, preventing infrastructure damage, mitigating environmental impact, identifying groundwater contamination. This work presents the first development of a diameter-based measurement paper sensor for chloride analysis using the reaction based on a Mohr's precipitation titration. The paper sensor that has a circular shape with 3-cm diameter was pre-coated with AgNO3 and CrO42− forming brown precipitates of the Ag2CrO4. The sensor was sealed using lamination films with 3-mm diameter hole-punched inlets on the top of the lamination film for sample delivery. To detect chloride, the sensor was simply immersed into the sample. The chloride solution flows into the central sample inlet and spreads radially to undergo the displacement reaction with Ag2CrO4 precipitate, forming AgCl white precipitate whose diameter proportional to the chloride that can be observed within 3 min. Concentration of AgNO3 used was found to impact the analytical figures of merit. The lower AgNO3 concentration yields lower limit of detection, narrower linear range but higher sensitivity. The sensor was applied for chloride analysis in tap water, drinking water and industrial water and the chloride concentration obtained from the developed sensors are not significant differences from those obtained from the standard titration method at 95% confidence interval (two tailed P = 0.08) indicating that the developed sensor provides accurate analysis of chloride in water samples from various sources. The developed sensor was used by the untrained staffs for on-site of analysis chloride in tap water collected at 26 locations in SaenSuk Municipality area, Chonburi, Thailand. The results showed that the chloride level in all samples is in range of 52.2–84.7 mg L−1 which is far below the acceptable range set by the Provincial Waterwork Authority of Thailand (< 250 mg L−1) indicating that the tap water used in this area is safe for consumers.

A comparative study of thermodynamic modeling and experimental measurement of precipitation titration curves for single- and multi-component sulfate systems

The current study is focused on the thermodynamic modeling and experimental measurement of metal hydroxide precipitation titration curves for the single- and multi-component sulfate systems. The systematic analytical model is developed based on Bromley-Zemaitis's theory and H. E. Wirth's theory to accurately predict the precipitation behavior of sulfate systems under different operating conditions and to simulate the precipitation titration curve. The titration curves established using the analytical model are compared with the curves built using the numerical mixed-solvent electrolyte model provided in OLI software along with the experimental measurement. The results demonstrate a good agreement between the analytical model, numerical model, and experimental approach while unveiling the limitations of the developed analytical model such as the disregard of multi-species ions, constant solution density, and constant water activity. The effect of three key operating parameters, namely initial solution pH, initial metal ion concentration, and reaction temperature, on the precipitation behaviors is investigated with emphasis on the ion interaction, precipitation pH, the amount of precipitant required, and species equilibrium.

Nitrogen-Doped Graphene Quantum Dots as “Off–On” Fluorescent Probes in Paper-Based Test Kits for Selective Monitoring of Cyanide in Food

We successfully developed a fluorometric paper-based test kit for the selective and sensitive determination of cyanide using nitrogen-doped graphene quantum dots (N-GQDs) as the fluorescent probe. Citric acid and tris(hydroxymethyl)aminomethane were precursors for the one-step synthesis of N-GQDs via in situ hydrothermal methods, providing a high quantum yield of 57.9%. The proposed mechanism uses a fluorescence turn-on approach. Specifically, the fluorescence of N-GQDs is quenched by the incorporation of Ag+ via a photoinduced electron transfer (PET). During the detection step, sulfuric acid converts cyanide (CN–) into hydrogen cyanide (HCN). The Ag+ species on the N-GQD surface then react with the evolved HCN via a coordination bond to form a silver cyanide complex, resulting in the fluorescence emission of the N-GQDs being turned back on. As a result, the fluorescence emission intensity of N-GQDs linearly increased with increasing CN– concentrations in the range of 0.5–25 mg L–1, with a limit of detection (LOD) of 0.08 mg L–1. Notably, the developed sensor has advantages in terms of simplicity, rapidity, low cost, and high selectivity toward CN–. The analytical performance of the test kit was also validated the performance of the test kit against a conventional precipitation titration method.

Potentiometric Titration Based on the Reference Electrode Equipped with Ionic Liquid Salt Bridge — 1. Precipitation Titration of Chloride with Silver Ions in Water

Potentiometric Titration Based on the Reference Electrode Equipped with Ionic Liquid Salt Bridge — 1. Precipitation Titration of Chloride with Silver Ions in Water

Ag3PO4/Ag nanocomposite for selective and sensitive cyanide determination in food samples through catalytical colorimetry using a paper-based test kit

A paper-based test kit for selective and sensitive determination of cyanide was successfully developed using a Ag3PO4/Ag nanocomposite for catalytic colorimetry. The Ag3PO4/Ag nanocomposite synthesized via a one-step chemical bath method could instantly oxidize the chromogenic substrate ABTS for the color development under acidic conditions without the requirement of H2O2. During the detection step, cyanide in the sample was converted into gaseous hydrogen cyanide (HCN) using sulfuric acid. The HCN species then reacted with the generated Ag+ species via coordinate covalent bonding to form silver cyanide complex ions [Ag (CN2)]-. The amount of Ag+ species used for oxidizing ABTS subsequently decreased and so did the color intensity on the paper-based test kit. Specifically, the color intensity decreased with increasing cyanide concentrations in the range of 2.50–20.0 mg L−1. The limit of detection (LOD) and limit of quantification (LOQ) were 0.48 mg L−1 and 1.59 mg L−1, respectively. The developed test kit showed relatively high selectivity towards cyanide and high tolerance towards other cations and anions present in real samples. When applied to real samples including fruit juices and food products, the performance of the rapid and low-cost test kit was well validated by a conventional precipitation titration method.

Supporting students’ inquiry in accurate precipitation titration conditions with a virtual laboratory tool as learning scaffold

This work uses a virtual laboratory (VL) as a learning scaffold for students to explore the conditions for accurate titration. A simulation program for precipitation titration and a simulation-based exploration exercise were developed. The exercise consists of three questions/tasks related to conditions for accurate titration, in which students independently design solutions, conduct virtual experiments, analyze the results, and draw conclusions based on the guided questions. After using the program, 22 chemistry education students who do not often use the app found the program to be easy to use, practical, and effective, and achieved a scoring rate of 79.4% in the exercise.

Simple biodegradable plastic screen-printing for microfluidic paper-based analytical devices

Abstract The goal of using microfluidic paper-based analytical devices (μPADs) in remote areas has prompted the development of uncomplicated, affordable, and environmentally-friendly fabrication methods. Here, screen-printed biodegradable polycaprolactone (PCL) as a simple, low-cost, and non-toxic alternative approach to create μPADs was introduced. No need for a heating step contributed to low PCL dispersion resulting in high resolution hydrophobic barriers. The proposed method achieved a narrowest hydrophilic channel and hydrophobic edge of 510 ± 40 μm and 490 ± 30 μm, respectively. The method was used to generate several designs for Cr3+ and Cl− detections. For Cr3+ analysis, silver nanoparticles were used as the colorimetric probe to selectively measure Cr3+ using a spot format that achieved a limit of detection (LOD) of 15.0 μg L-1 and a linear working range of 50.0–1000.0 μg L-1. For Cl- determination, the distance-based pattern using traditional precipitation titration was utilized to resolve the coffee ring effect from colorimetric detection. The method gave an LOD and a linear range for Cl- detection of 10.0 mg L-1 and 10.0–500.0 mg L -1, respectively. Finally, the μPADs were applied for Cl- analysis in instant noodle seasonings and the results significantly agreed with those using the traditional titration at 95 % confidence.

Determining the Endpoint of Sediment Titrations by Smartphones

In this research work, we have used the image processing technique for determining the end of sodiumsulphate with standard barium chloride in precipitation titration. The white precipitate of barium sulphateproduced by the reaction of barium chloride and sodium sulphate was dispersed in deionized water bymagnetic stirrer and its images were taken by mobile phone camera. The resulting pictures were analyzed byPhotoshop Software which shows that the intensity of magenta colour has maximum sensitivity by changingthe mass of barium sulphate. Therefore; magenta colour was selected as the optimum colour. Also, to depictthe calibration curve of sulphate anion, different concentrations of sulphate were prepared in bufferedsolutions and by addition of barium chloride to them, the intensity of magenta colour was calculated. Theresults show that the calibration curve was linear in the range of 5-75 mg.L-1 of sulpahte with a correlationcoefficient of 0.973. Finally, by titration of different real samples such as Tap, river and mineral waterscontaining sulphate anion with standard barium chloride, the variation of magenta colour was recorded andthe concentration of sulpahte anion was determined.

Endometrial cancer patients have high affinity antibodies for estrogen metabolite-receptor aggregate: A potential biomarker for EC.

Elevated levels of 16α-hydroxyestrone (16α-OHE1 ) have been described in endometrial cancer (EC) and estrogen receptors (ER) expressed in endometrial tissue, but research on their combined role is lacking. We aimed to investigate the affinity and binding specificity of EC antibodies against the 16α-OHE1 -ERα aggregate in the serum of EC patients. Specificities of EC antibodies were also evaluated according to various clinical characteristics found in these cancer patients. The binding specificity and affinity of EC antibodies against 16α-OHE1 -ERα in the serum of 120 EC patients were evaluated by direct binding and competition ELISA and quantitative precipitation titration. Binding of EC antibodies was also determined according to various clinical characteristics in EC patients through competition ELISA. Antibodies from EC patients demonstrated high recognition of 16α-OHE1 -ERα compared to ERα (P < 0.05) or 16α-OHE1 (P < 0.001). The relative affinity of EC IgG was 1.49 × 10-7 M, 1.34 × 10-6 M and 1.13 × 10-6 M for 16α-OHE1 -ERα, ERα and 16α-OHE1 , respectively. Several factors, such as obesity, postmenopausal status, use of hormonal therapy, ER and progesterone receptor (PR) status, low 2-OHE1 /16α-OHE1 ratio, chemotherapy and hypertension, augment the production of antibodies against 16α-OHE1 -ERα in EC patients. 16α-OHE1 -ERα is a high-affinity antigen for EC antibodies in the serum of EC patients and might function as a biomarker for this disease. Furthermore, several factors enhanced the production of antibodies against 16α-OHE1 -ERα in the sera of these EC patients.

Indicator-Free Argentometric Titration for Distance-Based Detection of Chloride Using Microfluidic Paper-Based Analytical Devices.

We described an indicator-free argentometric titration strategy using a microfluidic paper-based analytical device. This strategy was based on the formation of insoluble silver salts by reactions occurring between analytes and titrant (Ag+) on a paper channel. After the insoluble silver salts were formed and precipitated on the channel, the paper substrate modified with the surplus titrant on the channel turned reddish-brown by exposure of the devices to a simple and cheap UV light source for 5 min, generating a colored band on the channel. Distance-based detection of chloride was achieved by measuring the length of the colored band with a detection limit of 1.7 mg L–1 Cl–. This method was used to detect chlorides in tap water, with an analytical result (10.1 ± 1.2 mg L–1) agreeing well with that obtained by a classical conventional precipitation titration (9.8 mg L–1), which was based on the measurement of the consumed volume of titrant. This paper-based precipitation titration method is free of skilled personnel and has advantages of low reagent/sample consumption, disposability, portability, and simple operation over the conventional precipitation titration. More importantly, being free of any indicator, this method may be used to detect more species than the conventional precipitation titrations, which are limited by the indicator, for example, CO32– and SO42–, which could form insoluble silver salts in aqueous liquids. Additionally, comparing with most of those paper-based titrimetry reported previously, this presented precipitation titration is free of any indicator or ion selective electrode to detect the end point of titration.

Semi-quantitative analysis by spot counting on origami paper-based device for endpoint detection in titrimetric analysis

Use of spot counting on an origami paper-based device (SC-PAD) was proposed for end point detection in titrimetric analysis. The multi-folded device allows sample solution to flow from the top layer to the bottom layer. Each layer contains a circular reaction zone by which its hydrophobic barrier was made by wax printing. Reagents used for titration (titrant and indicator) were added onto the circular pattern of the origami PAD. The sample solution was added onto the top layer of the origami PAD. During the solution flow, the analyte then reacted with the pre-deposited reagents on the circular reaction zone of each paper layer. After the reaction was completed, the folded paper was then unfolded for counting the numbers of circular spot that exhibited the color change. This SC-PAD was applied for end point detection for determination of various analytes in water samples by various types of titrimetric analysis. These included the determination of alkalinity by acid-base titration, water hardness by complexometric titration, chloride by precipitation titration, and thiosulfate by redox titration. This SC-PAD could be used for on site test of water quality for the determination of alkalinity in the range of 25 – 400 mg CaCO3 L−1, water hardness in the range of 50 – 425 mg CaCO3 L−1, chloride in the range of 75 – 2500 mg L−1, and thiosulfate in the range of 10 – 200 mg L−1. The SC-PAD was applied to determine hardness and chloride in drinking water and natural water samples. The results obtained by SC-PAD were in good agreement with those from conventional titration in the laboratory. Not only that the SC-PAD platform minimizes the use of chemicals, it enables visual quantitative readout without the use of any instrument.

A Selective Membrane Electrode for Iodide Ion based on New Ionophore and its Application to Pharmaceutical Samples

Background and Objectives: On the basis of newly synthesized i.e. imidazolidine-2tion (IMT), highly selective poly vinyl chloride (PVC) membrane electrode was utilized as a carrier for iodide selective electrode via the incorporation of membrane ingredients within the graphite electrode surface. Method: The impact of different factors consisting of the pH, membrane arrangement and likely intervening anions were examined on the electrode’s response characteristics. The created sensor displayed Nernstian responses to iodide across a concentration of 1× 10-6 to 0.1 M with slopes of 57.8± 0.7 mV per iodide concentration decade and 7 × 10-7M detection limit, across a pH range of 3.0-10.5. Results: The sensor response time was 6 seconds and may be used for a minimum of 2 months with no significant divergence at potential responses. Conclusion: The electrode was implemented with success to determine iodide within synthetic pharmaceutical samples as well as using as an indicator electrode for precipitation titration.

THE IMPORTANCE OF TEACHING TITRATION CURVES IN ANALYTICAL CHEMISTRY

Titration curves are an essential subject of an Analytical Chemistry course. The main objective of calculating titration curves is the selection of an indicator for such titrations. The calculation of titration errors is imperative because they establish if a given indicator can be used for a given titration. This study reviews the available literature on titration curves and calculating their errors. Its purpose is to draw attention to the importance of undergraduate chemistry students having competencies to determine the titration errors rather than skills to build titration curves as the ultimate purpose of these curves is to determine the failure committed when using a given indicator to assess their endpoints. It is shown that the pH and potential calculation at the equivalence point in acid-base and redox titrations, respectively, are not required to choose the titration indicator, one that yields an acceptable error according to the type of application needed. Methods to calculate these errors in the four main types of titrations are presented; those for complexometric and precipitation titrations are simpler than in the literature. Here, it is also demonstrated that calculating points immediately after and before the curve inflection are more critical for this selection in these two types of titrations. Also, it is deducted that complexometric and precipitation curves are not required to select indicators for these titrations. These demonstrations are essential because analytical chemistry teachers may disregard teaching important topics by spending time calculating unnecessary titration curves (complexometric and precipitation titrations) or additional points of titration curves (redox and acid-base titrations) when the calculation of titration errors of these reactions is more critical. Most analytical chemistry textbooks neglect this topic. Undergraduate chemistry programs should focus more on calculating titration errors than on the construction of titration curves.

Carbon thick sheet potentiometric sensor for selective determination of silver ions in X-ray photographic film

Innovative screen-printed electrode (SPE) based on Alizarin Red S (ARS) for Ag (I) ion determination was developed. The ionophore content was varied and optimized which indicated that the ink incorporating 30 mg of Alizarin Red S reflects the best experimental performance exhibiting monovalent Nernstian slope value of 59.95 mV decade−1 over a considerable spacious concentration range from 5.0 × 10−7 to 1.0 × 10−2 mol L − 1 with a lower detection limit value of 5.0 × 10−7 mol L − 1. Additionally, the developed sensor stable for more than 112 days without any significant drift in potential exhibited a fast response time (7 s). The interaction between Ag (I) ions and ARS ionophore at the electrode surface was investigated and elucidated using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and FTIR spectra measurement. The proposed sensor achieved constant potentiometric response in pH range of 4–8 and thermally stable to 50 ͦ C. The developed sensor indicates discriminating capability toward Ag (I) ions with regard to most common transition metal ions. The new developed sensor used for determination of Ag (I) ion in x-ray photographic film and can be applied as indicator electrode in precipitation titrations. Furthermore, the method was validated according to IUPAC recommendation parameters.

Metal removal from aqueous solutions: insights from modeling precipitation titration curves

To provide a good reference for many metal ion removal processes, we developed an analytical model (AM) and used the PHREEQC computer program to numerically model (NM) arbitrary metal hydroxide precipitation titration curves (PTCs). For validation, these models were compared to slow titration experiments of ZnCl2 with NaOH to precipitate Zn(OH)2. The AM effectively demonstrates how initial pH, metal ion concentration and - valence and metal hydroxide equilibrium constant affect the shape of the PTCs. Comparison of AM and NM exposed AM limitations that include the effect of NaCl concentration, activity coefficients, and multi-species ions, on the shape of the PTCs. The experimental results agree well with either model for different concentrations of ZnCl2 at slow titration rates. However, the models and experiments deviated at higher titration rates. These deviations were attributed to inhomogeneities in the solution concentration, which caused precipitation at a bulk pH below the theoretical precipitation pH (i.e., pre-precipitation).

Instrument-free argentometric determination of chloride via trapezoidal distance-based microfluidic paper devices

Chloride (Cl−) is an inorganic anion present in a broad range of samples (e.g. biological, environmental, food, water, etc.), the determination of which is of widespread significance. In this work, we translate the well-established traditional argentometric method (Mohr's precipitation titration) into a small, simple, portable, and low-cost paper-based microfluidic diagnostic device, which provides rapid and quantitative analysis. The developed device enables the determination of chloride sample volumes as small as 5 μL. A distance-based detection method is implemented providing fully instrument-free quantitation. The beneficial effects of channel geometry (variable widths with constant heights) on analytical parameters were investigated. Trapezoidal channels (channel width changes linearly with height) were used to create a gradient of paper surface (titrant) available for the reaction, compared to the typical uniform rectangular channels (constant channel width). The trapezoid with increasing width offered higher sensitivity and lower detection limits (i.e. 0.05 mM vs 0.1 mM from the rectangular channel) for chloride determination across the concentration range of 0.05–25 mM. In addition, the effect of concentration of the deposited reagent on the obtained distance signals was investigated using varying concentrations of titrant (AgNO3), which allowed determination of chloride across a wider dynamic range (up to 200 mM). The utility of the paper devices was demonstrated by determination of chloride in a variety of matrices including body fluids (sweat, serum, and urine) and water samples (drinking, mineral, river water).

The effect of synthesis conditions and tunable hydrophilicity on the drug encapsulation capability of PLA and PLGA nanoparticles.

Three drugs with different hydrophilicity are encapsulated in poly-lactide (PLA) and Poly(lactide-co-glycolide) (PLGA) drug delivery systems prepared by ring-opening polymerization (ROP). Formation of well-defined core-shell type nanoparticles (NPs) is observed for α-tocopherol (TP) and by systematically altering the hydrophilicity of the drug carrier NPs the entrapment efficiency (EE (%)) can be remarkably controlled. The highest (90%) of EE (%) is obtained for the most lipophilic TP from the applied three drugs in the 75% lactide-containing PLGA75 NPs, which is ca. 69% for PLA NPs. Subsequent to drug loading the detailed characterization of the polymers and the formed NPs was carried out. Precipitation titrations reveal that our PLGAs have narrower weight distribution than the commercially available polymer enabling favorable properties to obtain NPs with better size distribution. It is pointed out that during the synthesis the applied solvent and stabilizing agent play a decisive role in the size distribution and stability of the drug carrier NPs. The Pluronic F127-stabilized NPs have the smallest diameter (ca. 190 nm) with less polydispersity among the applied stabilizing agent in nanoprecipitation.

16 α-Hydroxyestrone induced adduct generate high affinity autoantibodies in SLE

PurposeIncreased 16 α-hydroxyestrone (16 α-OHE1) and autoantibodies against histone H1 (H1) have been well described in systemic lupus erythematosus (SLE), but the combination effects of 16 α-OHE1 and H1 remains unclear. Here, we tried to assess the affinity and binding specificity of SLE autoantibodies against the 16 α-OHE1-H1 adduct. IgG was induced against this adduct and was also used as immunochemical probe for the estimation of 16 α-OHE1 in the serum of SLE patients. Materials and methodsThe affinity and binding specificities of SLE autoantibodies against 16 α-OHE1-H1 were determined by direct binding and inhibition ELISA as well as quantitative precipitation titration in 60 patients and 30 control subjects. ResultsPurified SLE autoantibodies showed greater recognition to 16 α-OHE1-H1 over H1 (p < 0.05) or 16 α-OHE1 (p < 0.001). The relative affinity of SLE autoantibodies for 16 α-OHE1-H1, H1 and 16 α-OHE1 was 1.41 × 10−7, 1.31 × 10−6, and 1.03 × 10−6, respectively. The concentration of 16 α-OHE1 in the sera of SLE patients was significantly higher than controls (p < 0.05) as estimated by anti-16 α-OHE1-H1 antibodies. ConclusionsHigh affinity of 16 α-OHE1-H1 with SLE autoantibodies might suggest an antigenic role of this adduct in the production of these autoantibodies. The anti-16 α-OHE1-H1 antibody is a good immunochemical probe to measure 16 α-OHE1 in different SLE sera.

A portable eight-channel titrator based on high-throughput capacitively coupled contactless conductivity measurements

Analytical chemists require multichannel and automatic tools for batch measurements. Herein, an eight-channel electronic titrator (8-CET) system was constructed to facilitate high-throughput titrations. In this system, multichannel piston pumps were used for delivery, and an 8-channel capacitively coupled contactless conductivity detector (8-C4D) was used to monitor the conductivity of the titration solutions in arrays of disposable reaction cells. The delivery and the monitoring were both fully software-controlled allowing a simultaneous formation of eight titration curves. Its capacity for classical acid-base and precipitation titration was characterized with satisfactory results. It was also used to measure the content of CH3COOH in batched vinegar samples. The RSD between each reaction cell was 1.9%. There are two outstanding features of this new system: 1) Up to eight samples can be measured simultaneously; and 2) simple operation is realized by avoiding electrode switching and cleaning after each measurement. Therefore, it is reasonable to believe that this 8-CET system is a prospective alternative for developing more automatic and efficient titration platforms.