A Novel Polymer Inclusion Membrane-Based Green Optical Sensor for Selective Determination of Iron: Design, Characterization, and Analytical Applications.

The design, characterization, and analytical application of a green optical sensor for the selective determination of Fe(II) ions is proposed. The sensor is based on the immobilization of the chromogenic reagent picolinaldehyde salicyloylhydrazone (SHPA) within a polymer inclusion membrane. To reduce solvent usage, the reagent was synthesized using a green mechanochemical procedure. The components for sensor preparation were optimized with a sequential simplex method and the optimal composition was found to be 0.59 g cellulose triacetate (base polymer), 0.04 g SHPA (chemosensor reagent), 4.9 mL dibutyl phthalate (plasticizer), and 38 mL dichloromethane (solvent). The conditions of iron analysis were also optimized resulting in pH 6 for aqueous solution, 90 min exposure time and 10 min short-term stability. The optical sensor showed a linear range from the limit of detection (0.48 µmol L-1) to 54 µmol L-1 Fe(II). The precision of the method was found to be 1.44% and 1.19% for 17.9 and 45 µmol L-1 Fe(II), respectively. The characteristics of the sensor allowed the design of a Fe(II)/Fe(III) speciation scheme. The methodology was successfully applied to the determination of iron in food preservatives, food additives, and dietary supplement. Additionally, the Fe speciation scheme was successfully applied to an agricultural fertilizer.

Ultrasound-Assisted One-Pot Cloud Point Extraction for Iron Determination Using Natural Chelating Ligands from Dipterocarpus intricatus Dyer Fruit.

An ultrasound-assisted, one-pot cloud point extraction was developed for the determination of iron in vegetable samples by UV-Visible spectrophotometry. This method was based on the complexation of iron with an environmentally-friendly natural chelating agent extracted from Dipterocarpus intricatus Dyer fruit at pH 5.5 in the presence of Triton X-114. Reagent extraction, complexation, and preconcentration were performed simultaneously using ultrasound-assisted extraction at 45 °C. The surfactant-rich phase was diluted with ethanol and loaded through a syringe barrel packed with cotton that acted as a filter to trap the reagent powder. Analyte-entrapped on cotton was eluted using 0.1 mol·L-1 nitric acid solution. Filtrate and eluate solutions were measured absorbance of the dark-blue product at 575 nm. Influential parameters for the procedure were investigated. Under the optimum experimental conditions, the calibration curve was linear, ranging from 0.1 to 1.0 mg·L-1 with r2 = 0.997. Limits of detection and quantification were 0.03 and 0.09 mg·L-1, respectively while precision values of intra-day and inter-day were less than 5%. Recovery at 0.5 mg·L-1 ranged from 89.0 to 99.8%, while iron content in vegetable samples ranged from 2.45 to 13.36 mg/100 g. This method was cost-effective, reliable, eco-friendly, and convenient as a green analytical approach to determining iron content.

Simple, fast, and instrumentless fabrication of paper analytical devices by novel contact stamping method based on acrylic varnish and 3D printing.

A new contact stamping method for fabrication of paper-based analytical devices (PADs) is reported. It uses an all-purpose acrylic varnish and 3D-printed stamps to pattern hydrophobic structures on paper substrates. The use of 3D printing allows quickly prototyping the desired stamp shape without resorting to third-party services, which are often expensive and time consuming. To the best of our knowledge, this is the first report regarding the use of this material for creation of hydrophobic barriers in paper substrates, as well as this 3D printing-based stamping method. The acrylic varnish was characterized and the features of the stamping method were studied. The PADs developed here presented better compatibility with organic solvents and surfactants compared with similar protocols. Furthermore, the use of this contact stamping method for fabrication of paper electrochemical devices was also possible, as well as multiplexed microfluidic devices for lateral flow testing. The analytical applicability of the varnish-based PADs was demonstrated through the image-based colorimetric quantification of iron in pharmaceutical samples. A limit of detection of 0.61 mg L-1 was achieved. The results were compared with spectrophotometry for validation and presented great concordance (relative error was < 5% and recoveries were between 104 and 108%). Thus, taking into account the performance of the devices explored here, we believe this novel contact stamping method is a very interesting alternative for production of PADs, exhibiting great potentiality. In addition, this work brings a new application of 3D printing in analytical sciences.

Photometric Determination of Iron in Pharmaceutical Formulations Using Double-Beam Direct Injection Flow Detector.

In this work, an innovative, flow-through, double-beam, photometric detector with direct injection of the reagents (double-DID) was used for the first time for the determination of iron in pharmaceuticals. For stable measurement of the absorbance, double paired emission-detection LED diodes and a log ratio precision amplifier have been applied. The detector was integrated with the system of solenoid micro-pumps. The micro-pumps helped to reduce the number of reagents used and are responsible for precise solution dispensing and propelling. The flow system is characterized by a high level of automation. The total iron was determined as a Fe(II) with photometric detection using 1,10-phenanthroline as a complexing agent. The optimum conditions of the propose analytical procedure were established and the method was validated. The calibration graph was linear in the range of 1 to 30 mg L-1. The limit of detection (LOD) was 0.5 mg L-1. The throughput of the method was 90 samples/hour. The repeatability of the method expressed as the relative standard deviation (R.S.D.) was 2% (n = 10). The method was characterized by very low consumption of reagents and samples (20 µL each) and a small amount of waste produced (about 540 µL per analysis). The proposed flow method was successfully applied for determination of iron in pharmaceutical products. The results were in good agreement with those obtained using the manual UV-Vis spectrophotometry and with values claimed by the manufacturers. The flow system worked very stably and was insensitive to bubbles appearing in the system.

Use of an ether-derived 3-hydroxy-4-pyridinone chelator as a new chromogenic reagent in the development of a microfluidic paper-based analytical device for Fe(III) determination in natural waters.

This article reports on the development and validation of a disposable microfluidic paper-based analytical device (µPAD) for on-hand, in-situ, and cheap Fe(III) determination in natural waters complying with World Health Organization guidelines. The developed µPAD used 3-hydroxy-4-pyridinone (3,4-HPO) as a colour reagent due to its considerably lower toxicity than traditionally used iron analytical reagents. It was selected among a group of hydrophilic 3,4-HPO chelators containing ether-derived chains in their structure which were prepared using green methods. The relatively high water solubility of these chelators improved the detection limit and applicability as µPAD reagents. Under optimal conditions, the µPAD is characterised by a quantification range between 0.25 and 2.0 mg/L, a detection limit of 55 µg/L and 15 min of analysis time. The signal stability extends up to 4 h and the device is stable for at least one month. The reagent consumption is below 0.2 mg per analysis and the µPAD method was validated by analysis certified reference materials and by comparison with atomic absorption results (RD < 10%). The newly developed µPAD was successfully applied to the determination of iron in river, well and tap waters with no need of any prior sample pre-treatment.

Usage of thiocyanate-based ionic liquid as new optical sensor reagent: Absorption and emission based selective determination of Fe (III) ions.

In this work, the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) was evaluated for the first time for its probable usage as new optical sensor reagent for the determination of several metal ions. The ionic liquid exhibited a selective and sensitive response to iron ions in acidic aqueous solutions among all of the tested metal ions. The ([BMIM][SCN]) was encapsulated in ethyl cellulose (EC) matrix in the form of continuous thin films. The effect of [BMIM][SCN] concentration and pH to iron response, the fluorescence quantum yield, the absorption, emission and excitation based characteristics of the ionic liquid in presence of Fe3+ and Fe2+ ions were investigated in both EC and [BMIM][SCN]/aqueous buffer solution mixtures. As a result, the highly sensitive, selective and rapid responding optical sensor reagent which does not need any time-consuming extraction, oxidation and reduction procedures was presented for the distinguishing determination of Fe3+ and Fe2+ in both aqueous solutions and solid thin film matrix. The ionic liquid exhibited a better emission and absorption based response for Fe3+ ions when compared with the Fe2+ ions. The molar absorptivity constant in presence of ionic liquid-based SCN- was enhanced 10 times to 1.21 × 104 L mol-1 cm-1 for Fe3+ ions in the solution phase. Linear absorption and emission-based calibration graphs were obtained for a wide concentration range of 8.0 × 10-8-6.2 × 10-4 M and 8.0 × 10-8-6.2 × 10-5 M for Fe3+, respectively. Limit of detection (LOD) values for absorption and emission-based methods were 2.48 × 10-5 and 2.4 × 10-8, respectively. The reaction is instantaneous and absorbance remains stable for over 4 months.

Obtaining information from the brain in a non-invasive way: determination of iron in nasal exudate to differentiate hemorrhagic and ischemic strokes.

Background Differentiation between hemorrhagic and ischemic stroke is currently made by brain imaging or analyzing blood and cerebrospinal fluid (CSF) samples. After describing a new drainage route from brain to nasal mucosa, nasal exudate samples can be considered a new and promising source of biomarkers. Saliva can also be evaluated. Methods We determined iron in nasal exudate and saliva samples from patients of acute stroke during the first 48 h from onset. A simple, non-invasive sampling procedure was employed to obtain information from the brain. Samples were taken with a pre-weighed swab, solved in a 2% nitric acid solution and iron was measured by inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS). Results A significant difference in the dispersion of results of iron concentration for both stroke subtypes was observed in nasal exudate samples. The interquartile range was 0.608 nmol mg-1 of iron for hemorrhagic strokes and only 0.044 nmol mg-1 for ischemic strokes. In saliva samples, however, the values were 0.236 vs. 0.157 nmol mg-1. A cut-off limit of 0.102 nmol of iron per mg of nasal exudate provides a methodology with a 90% of sensitivity and a 90% of specificity. The value of the area under (AUC) the receiver operating characteristic curve (ROC) for nasal exudate samples is 0.960, considered as very good in which regards to its predictive value. Conclusions Non-invasive samples of nasal secretion have allowed obtaining, for the first time, information from the brain. Determination of iron in nasal exudate by ICP-MS allowed differentiation between ischemic and hemorrhagic strokes.

Graphite Furnace Atomic Absorption Spectrometric Evaluation of Iron Excretion in Mouse Urine Caused by Whole-Body Gamma Irradiation.

A procedure for the determination of iron in mice urine using graphite furnace atomic absorption spectrometry was developed. The mice urinary samples contain many organic compounds in the matrix, whose concentrations are approximately 20%, and the value is 30-fold higher compared to those found in human urine. Moreover, only 0.2 mL or less of urine was obtained as a sample volume per urination event. It was difficult to decompose the organic materials in the samples by wet digestion using mineral acids and oxidising agents, because of the tiny volumes. In this experiment, raw urinary samples were placed directly into the graphite tube furnace for analysis. The organic contents were simply ashed during the preheating stages. To facilitate ashing in the furnace, air was invaded from the surroundings by interrupting the stream of argon gas. Atomic absorption was measured at 248.3270 nm (wavelength for atomic absorption), with the background monitored at 247.0658 nm (wavelength for background correction). The optimised instrument operating conditions precluded the use of chemical modification technique. The analytical procedures used are quite simple, i.e. an aliquot of raw urine sample was injected directly into the graphite tube furnace and was followed by a suitable heating programme with no chemical modifier. Therefore, this method is useful for scientists who are not familiar with delicate chemical experiments. The proposed analytical method was applied as a kind of biomarker by determining iron concentrations in urinary samples of mice, which were irradiated with 4 Gy of gamma irradiation to their whole body. The time dependence of the iron concentration was determined, and the iron concentrations increased within 1 day of irradiation exposure, then decreased to ordinal values after several days.

Development of spectrophotometric method for iron determination in fortified wheat and maize flours.

The determination of iron in fortified foods is mandatory by many global regulatory agencies. However, the spectroscopic techniques require elevated investments limiting their applicability especially in developing countries. Therefore, simple, viable and analytical methods with sufficient sensitivity can become an alternative. In this work, a sensitive, simple and viable spectrophotometry method to determine iron in wheat and maize flours was developed following a cloud point extraction (CPE) procedure. The analyte was first complexed with 2-(5-Bromine-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) in the presence of the surfactant octylphenoxypolyethoxyethanol (Triton X-114). For the CPE optimization the variables: pH of the medium, stoichiometry of the complex, surfactant, and salt concentrations were evaluated. Linearity in the analytical blank was obtained by using the square root of absorbance (Abs) in order to adjust the residues of the curve. The precision was lower than 5% and the accuracy ranged from 97 to 101%. The limits of detection and quantification were 0.004µgmL-1 and 0.01µgmL-1, respectively. The method was applied to investigate the content of iron in 14 brands of fortified flours. The concentrations of iron varied from 0.435 to 3.62mg/100g and 0.570 to 3.15mg/100g in wheat and maize flour, respectively. The content of iron in all brands investigated in this study was approximately 10-fold lower than the value required by (ANVISA). The amount of iron in fortified foods was satisfactorily determined by using a simple, sensitive, and low cost spectrophotometric method.

3D printed device including disk-based solid-phase extraction for the automated speciation of iron using the multisyringe flow injection analysis technique.

The development of advanced manufacturing techniques is crucial for the design of novel analytical tools with unprecedented features. Advanced manufacturing, also known as 3D printing, has been explored for the first time to fabricate modular devices with integrated features for disk-based automated solid-phase extraction (SPE). A modular device integrating analyte oxidation, disk-based SPE and analyte complexation has been fabricated using stereolithographic 3D printing. The 3D printed device is directly connected to flow-based analytical instrumentation, replacing typical flow networks based on discrete elements. As proof of concept, the 3D printed device was implemented in a multisyringe flow injection analysis (MSFIA) system, and applied to the fully automated speciation, SPE and spectrophotometric quantification of Fe in water samples. The obtained limit of detection for total Fe determination was 7ng, with a dynamic linear range from 22ng to 2400ng Fe (3mL sample). An intra-day RSD of 4% (n = 12) and an inter-day RSD of 4.3% (n = 5, 3mL sample, different day with a different disk), were obtained. Incorporation of integrated 3D printed devices with automated flow-based techniques showed improved sensitivity (85% increase on the measured peak height for the determination of total Fe) in comparison with analogous flow manifolds built from conventional tubing and connectors. Our work represents a step forward towards the improved reproducibility in the fabrication of manifolds for flow-based automated methods of analysis, which is especially relevant in the implementation of interlaboratory analysis.

Optoelectronic iron detectors for pharmaceutical flow analysis.

Compact flow-through optoelectronic detectors fabricated by pairing of light emitting diodes have been applied for development of economic flow analysis systems dedicated for iron ions determination. Three analytical methods with different chromogens selectively recognizing iron ions have been compared. Ferrozine and ferene S based methods offer higher sensitivity and slightly lower detection limits than method with 1,10-phenantroline, but narrower ranges of linear response. Each system allows detection of iron in micromolar range of concentration with comparable sample throughput (20 injections per hour). The developed flow analysis systems have been successfully applied for determination of iron in diet supplements. The utility of developed analytical systems for iron release studies from drug formulations has also been demonstrated.

A Simple Spectrofluorimetric Method for Iron Determination with a Chalcone-Based Schiff Base.

A chalcone-based Schiff base (5), capable of detecting iron (III) in partially aqueous media, has been designed, then synthesized by the condensation of 3-formyl-2-hydroxyquinoline and acetophenone. To determine iron (III) ion, a simple spectrofluorimetric method was developed by using the synthesized Schiff base. The developed method was validated by analyzing the certified reference material (CRM-SA-C Sandy Soil C). During the process of the determination of iron in food samples, satisfactory accuracy was obtained for spinach and rocket. Nitric acid and hydrogen fluoride were used for the digestion of the certified reference material whereas only nitric acid was used for food samples, in a closed microwave system. Measurements were carried out by using the modified standard addition method. The standard addition graph was linear until 5.0 mg/L. in determination of iron (III). Detection and quantification limits were 0.06 and 0.20 mg/L., respectively. The presented method is simple, time-saving, cost-effective and suitable for determination of iron content of soil and foods.

Large volume preconcentration and determination of nanomolar concentrations of iron in seawater using a renewable cellulose 8-hydroquinoline sorbent microcolumn and universal approach of post-column eluate utilization in a Lab-on-Valve system.

We report on a Lab-On-Valve (LOV) configuration for analyte preconcentration from milliliter sample volumes using confluent mixing in the holding coil for in-line addition of loading buffer. The system was applied to the spectrophotometric determination of iron(II) in acidified seawater using 1,10-phenanthroline as color reagent. A cellulose-based chelating sorbent containing 8-hydroxyquinoline was used for the first time in LOV and excellent retention behavior and loading capacity were found. The flow system employs a syringe pump for handling all solutions (sorbent suspension, loading buffer, water, eluent, and color reagent) and a peristaltic pump for sample propulsion and includes a fit-for-purpose 14 cm long detection glass flow cell and a bubble trap for in-line carrier degasification. Advantage was taken of the LOV flow-through port to keep the eluted analytes for re-aspiration for subsequent chromogenic reaction. In effect, a universal analyzer configuration and preconcentration procedure was developed, which is combinable with other analytes, sorbents, and reagents. Among the studied parameters were the compositions, pH, volumes, and flow rates of loading buffer, eluent, and color reagent, as well as the microcolumn size, repeatability, and system stability. Reproducibility of 4.1% RSD over the entire working range, a LOD of down to 5 nmol L(-1), sampling frequency of 12h(-1), and linearity up to 1 µmol L(-1) for 3.3 mL of sample were obtained and applicability to real samples was demonstrated. It was proven that both Fe(III) and Fe(II) were retained and yielded similar recovery and sensitivity values. The method was applied to coastal seawater samples and spiking experiments yielded recovery values close to 100%.

Simple time-saving method for iron determination based on fluorescence quenching of an azaflavanon-3-ol compound.

A simple and time-saving spectrofluorometric method developed using an azaflavanon-3-ol compound was used for the determination of iron in various food samples. Nitric acid and hydrogen peroxide were used for digestion of samples in a closed microwave system. The method was validated by analyzing two certified reference materials (CRM-SA-C Sandy Soil C and Mixed Polish Herbs INCT-MPH-2). Measurements were carried out using a modified standard addition method. The standard addition graph was linear until 21.6 mg/L in the determination of iron(III). Detection and quantification limits were 0.81 and 2.4 mg/L, respectively. Satisfactory accuracy was obtained for spinach, dill, mint, purslane, rocket, red lentils, dry beans, and two iron medicinal tablets. High recoveries were found for streamwater samples fortified at three different concentrations. The method is simple, time-saving, cost-effective, and suitable for the determination of the iron content of foods.

Spectrophotometric determination of iron in environmental and food samples using solid phase extraction.

A simple, selective and highly sensitive extraction method has been developed for the determination of iron(II) spectrophotometrically after solid phase extraction. The absorbance is measured at λmax 644 nm. Beer's law was obeyed up to 450 ng mL(-1) of iron. The molar absorptivity, Sandell's sensitivity, detection and quantification limits were calculated and found to be 1.09×10(5) L mol(-1) cm(-1), 0.51 ng cm(-2), 1.98 and 6.0 ng mL(-1), respectively and compared with parameters obtained without using solid phase extraction method. After reduction of Fe(III) by addition of 2.0 mL of 10% hydroxylamine HCl, the system was applied to the total iron. The interference of various ions has been studied in detail and the statistical evaluation of the experimental results is reported. The proposed methods have been successfully applied for the determination of trace amount of iron in environment water, soil and botanical reference materials with recovery range (98.71-101.51%).

The use of flow-injection analysis with chemiluminescence detection of aqueous ferrous iron in waters containing high concentrations of organic compounds.

An evaluation of flow-injection analysis with chemiluminescence detection (FIA-CL) to quantify Fe(2+) ((aq)) in freshwaters was performed. Iron-coordinating and/or iron-reducing compounds, dissolved organic matter (DOM), and samples from two natural water systems were used to amend standard solutions of Fe(2+) ((aq)). Slopes of the response curves from ferrous iron standards (1 - 100 nM) were compared to the response curves of iron standards containing the amendments. Results suggest that FIA-CL is not suitable for systems containing ascorbate, hydroxylamine, cysteine or DOM. Little or no change in sensitivity occurred in solutions of oxalate and glycine or in natural waters with little organic matter.