Greener analytical method for the determination of copper(II) in wastewater by micro flow system with optical sensor

Greener analytical method using micro flow system for the determination of Cu(II) in wastewater samples was designed and investigated. The micro flow system consisted of a planar glass chip with poly(dimethylsiloxane) (PDMS) top plate and fixed with fiber optic probe as optical sensor for monitoring of Cu(II) that reacted with 2-carboxy-2′-hydroxy-5′-sulfoformazyl benzene (zincon) on the chip at 605 nm. This design gave a satisfied sensitivity with a linear calibration graph over the range of 0.1-3.0 μg mL⁻¹ of Cu(II) and correlation coefficient 0.9991. The percentage relative standard deviation was 2.5 for 10-replicate measurements and the limit of detection (LOD) was 0.1 μg mL⁻¹. This system has been successfully applied to the determination of Cu(II) in wastewaters from electroplating industry with less reagents and samples consumption and diminutive waste generation.     

Exploiting green analytical procedures for acidity and iron assays employing flow analysis with simple natural reagent extracts

Green analytical methods employing flow analysis with simple natural reagent extracts have been exploited. Various formats of flow based analysis systems including a single line FIA, a simple lab on chip with webcam camera detector, and a newly developed simple lab on chip system with reflective absorption detection and the simple extracts from some available local plants including butterfly pea flower, orchid flower, and beet root were investigated and shown to be useful as alternative self indicator reagents for acidity assay. Various tea drinks were explored to be used for chromogenic reagents in iron determination. The benefit of a flow based system, which allows standards and samples to go through the analysis process in exactly the same conditions, makes it possible to employ simple natural extracts with minimal or no pretreatment or purification. The combinations of non-synthetic natural reagents with minimal processed extracts and the low volume requirement flow based systems create some unique green chemical analyses.     

A green analytical procedure for sensitive and selective determination of iron in water samples by flow-injection solid-phase spectrophotometry

A greener analytical procedure based on flow-injection solid-phase spectrophotometry is proposed for iron determination. Iron(II) is reversibly retained on 1-(2-thiazolylazo)-2-naphthol immobilized on C18-bonded silica, yielding a brown complex. The metal ion is eluted as iron(II) with a small volume of a diluted acid solution without removing the immobilized reagent, which can be used for at least 100 determinations. Other chemicals (buffer and reducing agent) were carefully selected taking into account the analytical performance and toxicity. The developed procedure is 10-fold more sensitive in comparison to the analogous procedure based on measurements in solution, being suitable for the determination of iron in water samples with good accuracy and precision. The detection limit (99.7% confidence level), sampling rate and coefficient of variation (n = 10) were estimated as 15 μg L⁻¹, 25 measurements per hour and 4.0%, respectively. The proposed procedure involves a reduced effluent generation (3.6 mL per determination) and consumes micro amounts of reagents.     

Development of a green chromatographic method for determination of colorants in food samples

A green chromatographic analytical method for determination of Tartrazine, Brilliant Blue and Sunset Yellow in food samples is proposed. The method is based on the modification of a C18 column with a 0.25% (v/v) Triton X-100 aqueous solution at pH 7 and in the usage of the same surfactant solution as mobile phase without the presence of any organic solvent modifier. After the separation process on the chromatographic column, the colorants are detected at 430, 630 and 480 nm, respectively. The chromatographic procedure yielded precise results and is able to run one sample in only 8 min, consuming 15.0 mg of Triton X-100 and 38.8 mg of phosphate. When the flow rate of the mobile phase is 1 ml min⁻¹ the retention times are 2.1, 3.6 and 7.0 min for Tartrazine, Brilliant Blue and Sunset Yellow, respectively; and all peak resolutions are ca. 2. The analytical curves present the following linear equations: area = 7.44 10⁵ + 2.71 10⁵ [Tartrazine] (R = 0.998, n = 7); area = 1.09 10⁵ + 3.75 10⁵ [Brilliant] (R = 0.9995, n = 7) and area = −7.34 10⁴ + 2.33 10⁵ [Sunset] (R = 0.998), n = 7) and, the limits of detection for Tartrazine, Brilliant Blue and Sunset Yellow were estimated as 0.125, 0.080 and 0.143 mg l⁻¹. When the proposed method is applied to food samples analysis, precise results are obtained (R.S.D. < 5%, n = 3) and in agreement with those obtained by using the classical spectrophotometric method. The traditional usage of organic solvent as mobile phase in HPLC is not used here, which permits to classify the present method as green.     

A simple flow injection spectrophotometric determination method for iron(III) based on O-acetylsalicylhydroxamic acid complexation

A simple and rapid flow-injection spectrophotometric method for the determination of iron(III) and total iron is proposed. The method is based on the reaction between iron(III) and O-acetylsalicylhydroxamic acid (AcSHA) in a 2 % methanol solution resulting in an intense violet complex with strong absorption at 475 nm. Optimum conditions for the determination of iron(III) and the interfering ions were tested. The relative standard deviation for the determination of 5 μg L⁻¹ iron(III) was 0.85 % (n = 10), and the limit of detection (blank signal plus three times the standard deviation of the blank) was 0.5 μg L⁻¹, both based on the injection volumes of 20 μL. The method was successfully applied in the determination of iron(III) and total iron in water and ore samples. The method was verified by analysing a certified reference material Zn/Al/Cu 43XZ3F and also by the AAS method.     

A green analytical procedure for flow-injection determination of nitrate in natural waters

Nitrate determination in waters is generally carried out with cadmium filings and carcinogenic reagents or by reaction with phenolic compounds in highly concentrated sulfuric acid medium. In this work, it was developed a green analytical procedure for nitrate determination in natural waters based on direct spectrophotometric measurements in ultraviolet, using a flow-injection system with an anion-exchange column for separation of nitrate from interfering species. The proposed method employs only one reagent (HClO₄) in a minimum amount (equivalent to 18 μL concentrated acid per determination), and allowed nitrate determination within 0.50-25.0 mg L⁻¹, without interference of up to 200.0 mg L⁻¹ humic acid; 1.0 mg L⁻¹ NO₂⁻; 200.0 mg L⁻¹ PO₄³⁻; 75.0 mg L⁻¹ Cl⁻; 50.0 mg L⁻¹ SO₄²⁻ and 15.0 mg L⁻¹ Fe³⁺. The detection limit (99.7% confidence level) and the coefficient of variation (n = 20) were estimated as 0.1 mg L⁻¹ and 0.7%, respectively. The results obtained for natural water samples were in agreement with those achieved by the reference method based on nitrate reduction with copperized cadmium at the 95% confidence level.     

Multisyringe flow injection analysis hyphenated with liquid core waveguides for the development of cleaner spectroscopic analytical methods: improved determination of chloride in waters

In this work, the hyphenation of the multisyringe flow injection analysis technique with a 100-cm-long pathlength liquid core waveguide has been accomplished. The Cl⁻/Hg(SCN)₂/Fe³⁺ reaction system for the spectrophotometric determination of chloride (Cl⁻) in waters was used as chemical model. As a result, this classic analytical methodology has been improved, minimizing dramatically the consumption of reagents, in particular, that of the highly biotoxic chemical Hg(SCN)₂. The proposed method features a linear dynamic range composed of two steps between (1) 0.2–2 and (2) 2–8 mg Cl⁻ L⁻¹, thus extended applicability due to on-line sample dilution (up to 400 mg Cl⁻ L⁻¹). It also presents improved limits of detection and quantification of 0.06 and 0.20 mg Cl⁻ L⁻¹, respectively. The coefficient of variation and the injection throughput were 1.3% (n = 10, 2 mg Cl⁻ L⁻¹) and 21 h⁻¹. Furthermore, a very low consumption of reagents per Cl⁻ determination of 0.2 μg Hg(II) and 28 μg Fe³⁺ has been achieved. The method was successfully applied to the determination of Cl⁻ in different types of water samples. Finally, the proposed system is critically compared from a green analytical chemistry point of view against other flow systems for the same purpose.     

Environmentally friendly method for determination of ammonia nitrogen in fertilisers and wastewaters based on flow injection-spectrophotometric detection using natural reagent from orchid flower

Crude aqueous extract from the orchid ‘Dendrobium Sonia earsakul’ was utilised as a natural product reagent in flow injection analysis (FIA) incorporating a gas diffusion unit (GD) for the determination of ammonia nitrogen. Sample solution was injected into a NaOH donor stream to generate ammonia gas (NH₃). In the GD unit, NH₃ diffused across a PTFE gas-permeable membrane into the acceptor stream of the orchid extract. As the result, the aqueous orchid reagent became more alkaline and its colour changed from purple to green. The change in the colour of orchid acceptor correlated with the concentration of ammonia nitrogen in the sample and its absorbance monitored by a spectrophotometer at 600 nm. Ammonia nitrogen in chemical fertiliser samples and wastewater samples from agricultural fields were determined and reported as %N (w/w) and mg N L^?1, respectively. For chemical fertilisers which contained high content of ammonia nitrogen, a flow rate of 1.0 mL min^?1 and injection volume of 100 µL were used with a linear range of 5–40 mmol L^?1 and detection limit of 2.12 mmol L^?1. However, a higher sensitivity was required for wastewater samples having low ammonia nitrogen content. The flow rate was reduced to 0.3 mL min^?1 and the injection volume increased to 1000 µL. As a result, detection limit of 0.76 mmol L^?1 was achieved with linear range of 1–5 mmol L^?1. The results of our method agreed well with that using the OPA method employing fluorescence detection.     

An environmental friendly method for the automatic determination of hypochlorite in commercial products using multisyringe flow injection analysis

A multisyringe flow injection analysis system was used for the determination of hypochlorite in cleaning agents, by measurement of the native absorbance of hypochlorite at 292 nm. The methodology was based on the selective decomposition of hypochlorite by a cobalt oxide catalyst giving chloride and oxygen. The difference of the absorbance of the sample before and after its pass through a cobalt oxide column was selected as analytical signal. As no further reagent was required this work can be considered as a contribution to environmental friendly analytical chemistry. The entire analytical procedure, including in-line sample dilution in three steps was automated by first, dilution in a stirred miniature vessel, second by dispersion and third by in-line addition of water using multisyringe flow injection technique. The dynamic concentration range was 0.04-0.78 g L⁻¹ (relative standard deviation lower than 3%), where the extension of the hypochlorite decomposition was of 90 ± 4%. The proposed method was successfully applied to the analysis of commercial cleaning products. The accuracy of the method was established by iodometric titration.     

A green flow-based procedure for fluorimetric determination of acid-dissociable cyanide in natural waters exploiting multicommutation

A flow system designed with solenoid valves is proposed for determination of weak acid dissociable cyanide, based on the reaction with o-phthalaldehyde (OPA) and glycine yielding a highly fluorescent isoindole derivative. The proposed procedure minimizes the main drawbacks related to the reference batch procedure, based on reaction with barbituric acid and pyridine followed by spectrophotometric detection, i.e., use of toxic reagents, high reagent consumption and waste generation, low sampling rate, and poor sensitivity. Retention of the sample zone was exploited to increase the conversion rate of the analyte with minimized sample dispersion. Linear response (r = 0.999) was observed for cyanide concentrations in the range 1–200 μg L⁻¹, with a detection limit (99.7% confidence level) of 0.5 μg L⁻¹ (19 nmol L⁻¹). The sampling rate and coefficient of variation (n = 10) were estimated as 22 measurements per hour and 1.4%, respectively. The results of determination of weak acid dissociable cyanide in natural water samples were in agreement with those achieved by the batch reference procedure at the 95% confidence level. Additionally to the improvement in the analytical features in comparison with those of the flow system with continuous reagent addition (sensitivity and sampling rate 90 and 83% higher, respectively), the consumption of OPA was 230-fold lower.     

A simple colorimetric FIA method for the determination of pyrite oxidation rates

A method for the rapid determination of the oxidation rate of naturally occurring pyrite (FeS₂) samples is presented. The progress of the oxidation reaction was followed by measurement of the concentration of total dissolved iron using flow injection analysis. Iron was determined using UV-vis detection after reaction with the colorimetric reagent 5-sulfosalicylic acid in the presence of ammonia. The calibration function was linear between 5 and 150 mg L⁻¹, and the detection limit was 0.46 mg L⁻¹. The relative standard deviation was typically less than 1% (n = 10) and the measurement frequency was 60/h. The method was used to quantify the oxidation rate of 10 ground and cleaned pyrite samples (53 μm < x < 106 μm) from various international locations that were subjected to accelerate oxidation in acidic hydrogen peroxide. Results of these experiments showed that there was almost an order of magnitude of difference in oxidation rates of the pyrite samples.     

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min^?1 providing a sample throughput of more than 15 samples h^?1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.     

Downscaling a multicommuted flow injection analysis system for the photometric determination of iodate in table salt

In this work a downscaled multicommuted flow injection analysis setup for photometric determination is described. The setup consists of a flow system module and a LED based photometer, with a total internal volume of about 170 μL. The system was tested by developing an analytical procedure for the photometric determination of iodate in table salt using N,N-diethyl-henylenediamine (DPD) as the chromogenic reagent. Accuracy was accessed by applying the paired t-test between results obtained using the proposed procedure and a reference method, and no significant difference at the 95% confidence level was observed. Other profitable features, such as a low reagent consumption of 7.3 μg DPD per determination; a linear response ranging from 0.1 up to 3.0 m IO₃⁻, a relative standard deviation of 0.9% (n = 11) for samples containing 0.5 m IO₃⁻, a detection limit of 17 μg L⁻¹ IO₃⁻, a sampling throughput of 117 determination per hour, and a waste generation 600 μL per determination, were also achieved.     

Optical fibre reflectance sensor for the determination and speciation analysis of iron in fresh and seawater samples coupled to a multisyringe flow injection system

A novel optical fibre reflectance sensor coupled to a multisyringe flow injection system (MSFIA) for the determination and speciation analysis of iron at trace level using chelating disks (iminodiacetic groups) is proposed. Once iron(III) has been retained onto a chelating disk, an ammonium thiocyanate stream is injected in order to form the iron(III)-thiocyanate complex which is spectrophotometrically detected at 480 nm. Iron(III) is eluted with 2 M hydrochloric acid so that the chelating disk is regenerated for subsequent experiments. The determination of total iron is achieved by the on-line oxidation of iron(II) to iron(III) with a suitable hydrogen peroxide stream.A mass calibration was feasible in the range from 0.001 to 0.25 μg. The detection limit (3s_b/S) was 0.001 μg. The repeatability (RSD), calculated from nine replicates using 1 ml injections of a 0.1 mg/l concentration, was 2.2%. The repeatability between five chelating disks was 3.6%. The applicability of the proposed methodology in fresh and seawater samples has been proved.The proposed technique has been validated by replicate analysis (n = 4) of certified reference materials of water with satisfactory results.     

Improved method for shipboard determination of iron in seawater by flow injection analysis

A flow injection analysis (FIA) catalytic spectrophotometric method for the determination of dissolved iron in seawater was further developed to yield a more sensitive assay with a low detection limit. The method employs an initial sample acidification step followed by an iron pre-concentration step involving an in-line 8-hydroxy-quinoline (8-HQ) metal-chelating resin column. The copper capacity and elution efficiency, as well as the iron FIA performance of three trace-metal clean resins were compared, resulting in the selection of a clean silica gel support for the 8-HQ ligand. The concentrated sample is eluted from the resin with an acidic carrier and mixed with reagents, initiating an iron-catalyzed, color-forming reaction. Increasing the reaction temperature from 18 to 30 °C doubled the sensitivity; reaction temperature control was necessary to obtain good reproducibility in the field. Reagent blanks were as low as 0.05 nM and a detection limit of 0.016 nM was obtained from three times the S.D. of a 0.06 nM seawater sample repeated six times. A 0.06 nM detection limit was calculated from shipboard experiments where total dissolved iron was determined for 10 different samples from the same station. The instrumental sensitivity and precision evolved to the point where the blank associated with the technique is the major factor influencing its detection limit.     

Novel analytical applications of porphyrin to HPLC post-column flow injection system for determination of the lanthanides

A novel indirect substitution spectrophotometric methodology using porphyrin is developed for the determination of some metals that do not react with porphyrin directly. The methodology is concerned with a multistep reaction system, which consists of 3 complexation reactions that occur in a sequence of EDTA with metal, EDTA with Cu(II) and porphyrin with Cu(II). The complexation reaction of Cu(II) with a cationic porphyrin, meso-tetrakis (4-N-trimethylaminophenyl)-porphine (ttmapp), which has a high molar absorptivity about 5 × 10⁵ l mol⁻¹ cm⁻¹, serves for spectrophotometric detection. This methodology was verified through individual determinations of 14 species of lanthanides following a batchwise procedure, which was further developed to an automatic procedure on a HPLC post-column flow injection system for simultaneous analysis of the lanthanides. Compared with the conventional post-column derivatization method using 4-(2-pyridylazo) resorcinol (PAR), the analytical sensitivity was greatly improved in this method and the results also showed good linearity.     

A simple and green analytical method for determination of glyphosate in commercial formulations and water by diffuse reflectance spectroscopy

This article describes a simple, inexpensive, and environmentally friendly method for the monitoring of glyphosate using diffuse reflectance spectroscopy. The proposed method is based on reflectance measurements of the colored compound produced from the spot test reaction between glyphosate and p-dimethylaminocinnamaldehyde (p-DAC) in acid medium, using a filter paper as solid support. Experimental designs were used to optimize the analytical conditions. All reflectance measurements were carried out at 495 nm. Under optimal conditions, the glyphosate calibration graphs obtained by plotting the optical density of the reflectance signal (AR) against the concentration were linear in the range 50-500 μg mL(-1), with a correlation coefficient of 0.9987. The limit of detection (LOD) for glyphosate was 7.28 μg mL(-1). The technique was successfully applied to the direct determination of glyphosate in commercial formulations, as well as in water samples (river water, pure water and mineral drinking water) after a previous clean-up or pre-concentration step. Recoveries were in the ranges 93.2-102.6% and 91.3-102.9% for the commercial formulations and water samples, respectively.     

An improved flow system for phenols determination exploiting multicommutation and long pathlength spectrophotometry

A greener and sensitive procedure for spectrophotometric determination of phenols based on a multicommuted flow system with a 100 cm optical path flow cell is presented. The method exploited the oxidative coupling of phenolic compounds with 4-aminoantipyrine in alkaline medium containing potassium hexacyanoferrate(III). Sensitivity was 80-fold higher than that achieved with a 1 cm flow cell, making feasible the determination of phenols in the 10-100 μg l⁻¹ range with a detection limit estimated as 1 μg l⁻¹ phenol. The sampling rate and the coefficient of variation were estimated as 90 determinations per hour and 0.6% (n=10), respectively. The multicommutation approach allowed a 200-fold reduction of the reagent consumption in comparison with the reference batch method. Moreover, the chloroform extraction for analyte concentration is unnecessary in view of the increase in sensitivity. Recoveries within 93.3 and 106% were achieved for determination of phenol in natural and wastewater samples. Results agreed with the obtained by a reference method at the 95% confidence level.     

A clean analytical method for the spectrophotometric determination of formetanate incorporating an on-line microwave assisted hydrolysis step

A fast and completely automated procedure is proposed for the spectrophotometric determination of formetanate in waters by means of its reaction with p-aminophenol (PAP). The method involves the on-line alkaline hydrolysis of formetanate to m-aminophenol (MAP) and its reaction, in the presence of KIO₄ as oxidant agent, with the quinoneimine form of PAP, to form a blue indophenol dye which absorbs at 576 nm. The on-line hydrolysis can be carried out in a 6 m reaction coil located inside the cavity of a domestic microwave oven operated at 650 W, or in a 4 m reaction coil located inside the cavity of a Microdigest 301 microwave system operated at 60 W and allows us, in both cases, a complete hydrolysis of formetanate thus improving the complete automation of the analytical procedure. After the measurement step, the analytical waste is merged with a TiO₂ slurry and then detoxified by on-line UV-irradiation.