Sequential Injection Chemiluminescence Methodology for Ozone Evaluation

A sequential injection methodology with chemiluminescence detection for the evaluation of residual ozone in waters is presented. The procedure is based on the reaction between luminol and ozone without catalysts.

Linear calibration plots were obtained for ozone concentrations between 0.05 and 2.0 mg L^?1, with a detection limit of 0.04 mg L^?1.

The developed methodology was applied to the determination of residual ozone in ozonized waters and the results complied with those furnished by the spectrophotometric reference procedure (relative deviations < 6.3%). The method exhibited good precision (RSD < 3.5%) and the sampling rate was about 140 determinations per hour.     

An Automated Multi-Pumping Pulsed Flow System with Spectrophotometric Detection for the Determination of Phosphate in Natural Waters

In this work, an automated multipumping pulsed flow system was implemented for the determination of phosphate in natural waters. The developed flow approach was based on the spectrophotometric determination of phosphate by using the vanadomolybdate reaction. The exploitation of a very simple manifold configuration relying on the utilization of just two active components, in this case two solenoid actuated micropumps that were accountable for sample and reagent insertion and commutation, reaction zone formation, and solutions propelling, provided a great operational and optimization simplicity, low reagent consumption, and waste minimization.

Linear calibration plots for phosphate concentrations of up to 20 mg L^?1 (R² = 0.999, n = 6) were obtained, with a detection limit of 0.2 mg L^?1. The sampling rate was about 60 samples per hour. The system was applied to the monitoring of phosphate in local streams at specific sampling stations.     

Determination of Trenbolone Acetate in Cattle Feeds by a Flow Injection Chemiluminescence Method

A flow injection chemiluminescence (CL) method is described for the determination of trenbolone acetate based on the CL generated during its reaction with KMnO₄ in acidic medium. The CL intensity is greatly enhanced by alizarin yellow R. The CL intensity is linear with trenbolone acetate concentration in the range 0.1–100.0 mg L^?1 with a detection limit of 0.05 mg L^?1. The sample throughout is about 90 h^?1 and the relative standard deviation for 2.0 mg L^?1 trenbolone acetate solution is 1.5% (n = 11). The proposed method was applied to the determination of trenbolone acetate in cattle feeds.     

Ciprofloxacin and Norfloxacin Spectrophotometric Determination in a Fully Automated Multi-Pumping Flow System

A flow-based methodology for the spectrophotometric determination of ciprofloxacin and norfloxacin, based on the oxidation with N-bromosuccinimide in acidic medium, was developed. The proposed procedure was implemented in a multi-pumping flow system, which provided excellent mixing conditions due to the pulsed flow produced by solenoid micro-pumps actuation, resulting on a sensitive, simple, fast, and versatile analytical method. Linear calibration plots were obtained for ciprofloxacin and norfloxacin concentrations ranging from 5 to 70 mg L^?1 with an R.S.D < 2.2% (n = 10). Detection limits (3σ) were 0.27 mg L^?1 and 0.99 mg L^?1 for norfloxacin and ciprofloxacin, respectively.     

Determination of Silicon in Lubricant Oil by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry Using Least-Square Background Correction and Internal Standardization

The least-squares background correction (LSBC) and internal standardization procedures were combined to eliminate spectral interferences caused by the CS molecular band (251.602 nm) and transport effects for determining Si in sulfuric acid digests of lubricant oil by high-resolution continuum source flame atomic absorption spectrometry. Aluminum, Ba, Ti, V, and W were tested as internal standard (IS) candidates, and W provided the best results. For absorbance measurements of solutions containing 0.5–5.0 mg L^?1 Si in the presence of 25 mg L^?1 W (at the wavelength integrated absorbance equivalent to 3 pixels), the correlation coefficient for the ratio of absorbance of Si to absorbance of W vs. analyte concentration was 0.9978. Fluctuations in analytical signals due to variations in sulfuric acid concentrations or acetylene/nitrous oxide flow-rate ratios were corrected by using this calibration plot. Relative standard deviations varied from 1.9 to 7.2% and 2.1 to 5.4% (n = 12) with and without LSBC/IS, respectively. Recoveries for samples spiked with 2.0 mg L^?1 Si in 5.0% (v/v) sulfuric acid were within the 72.5–82.5% and 94.0–99.0% ranges without correction and by LSBC associated with internal standardization procedure, respectively. Accuracy of the proposed method was checked for the determination of Si in commercial lubricant oils and results obtained with internal standardization were better than those without correction.     

Enzymes Immobilized on a Tubular Reactor for Fast Amperometric Determination of Glucose in Brazilian Honey

Abstract

Glucose present in honey was rapidly determined by the differential amperometric method using two tubular reactors containing glucose oxidase and peroxidase. The linear dynamic range extends from 5 × 10^?5 to 2 × 10^?4mol L^?1, at pH 7.0. At flow rate of 1.5 mL min^?1 and injecting 150-µL sample volumes, a sampling frequency of the 33 determinations per hour is afforded. The reproducibility of the methods showed a relative standard deviation (RSD) < 4%. The detection limit of this method is 1.7 × 10^?5 mol L^?1. The samples analyses were compared with the parallel spectrophotometric determination.     

Multivariate Optimization and Validation of a CZE Method for the Analysis of Pridinol Mesylate and Meloxicam in Tablets

A capillary zone electrophoresis method for the simultaneous determination of pridinol mesylate (PRI) and meloxicam (MEL) employing epinastine hydrochloride and piroxicam as internal standards, was developed and optimized employing experimental design and response surface methodologies. The separation was optimally achieved in less than 2 min at 30 kV in an uncoated fused-silica capillary (41.4 cm × 75 ??m I.D.), employing an 18 mmol L^?1 sodium phosphate buffer solution (pH 5.90) at 25 °C. Samples were injected in hydrodynamic mode (50 mbar, 5 s) and the analytes were spectrophotometrically detected at 200 nm. Method robustness was demonstrated by ANOVA of determinations performed under conditions slightly different from the optimum. The method was validated regarding separation selectivity (peak purity factors > 0.99), linearity and range (PRI = 17.6?C31.4 mg L^?1; MEL = 66.5?C122.5 mg L^?1), accuracy (PRI = 100.2?C101.9%; MEL = 98.9?C100.7%) and precision. The RSD values obtained were ??1.3% for injection repeatability and ??1.9% for intra-day precision. The limits of detection (1.0 and 0.9 mg L^?1) and quantification (3.3 and 16.5 mg L^?1) of PRI and MEL, respectively, were also determined. The method was successfully applied to the determination of both drugs in three brands of tablet formulations. No statistically significant differences were observed when these results were compared with those of a RP-HPLC method.     

A Flow-Based Analytical Procedure for Salbutamol Determination Exploiting Chemiluminescence in a Liquid-Core Waveguide

Abstract

Salbutamol is a bronchodilator whose use is restricted due to its anabolic effects. A flow-based procedure for salbutamol determination based on the inhibition of chemiluminescence of the luminol/hypochlorite system was developed. A flow cell constructed with a liquid-core waveguide was employed to constrain the emitted radiation, minimizing losses during transport to detector. Linear response was observed within 2.5 × 10^?6 and 1.0 × 10^?5 mol L^?1 with a detection limit estimated as 1 × 10^?7 mol L^?1 at the 99.7% confidence level. The coefficient of variation (n = 20), sampling rate, and luminol consumption per determination were estimated as 2.8%, 164 determinations h^?1, and 50 µg, respectively. Results for pharmaceutical samples were in agreement with those obtained by reference procedures at the 95% confidence level.     

Graphite-Polyurethane Composite Electrode as an Amperometric Flow Detector in the Determination of Atenolol

Abstract

A bare graphite-polyurethane composite was evaluated as an amperometric detector in the flow injection determination of atenolol in pharmaceutical formulations. Using a flow injection analysis (FIA) procedure, a linear analytical curve was observed in the 0.2–3.0 mmol L^?1 range with a minimum detectable net concentration limit of detection (LOD = 18.1 µmol L^?1 and 90 determinations h^?1. Interferences from propranolol and furosemide were observed but not from the other components of the tablet. Thus, it was possible to determine atenolol in tablets without interference and with results that agreed with high performance liquid chromatography (HPLC) procedure with a 95% confidence level in a fast and accurate procedure.     

Preconcentration of Trace Cadmium (II) and Copper (II) in Environmental Water Using a Column Packed with Modified Silica Gel-Chitosan Prior to Flame Atomic Absorption Spectrometry Determination

A new column loaded with modified silica gel-chitosan is proposed as a preconcentration system for adsorption of trace cadmium (II) and copper (II). The optimization steps were performed under dynamic conditions, involving pH, sample flow rate, eluent selection, concentration, volume, and flow rate. Trace Cd(II) and Cu(II) were quantitatively adsorbed by the modified silica gel-chitosan. The metal ions adsorbed on the separation column were eluted with 0.1 M HNO₃ and determined by flame atomic absorption spectrometry. Under the optimum conditions, this method allowed the determination of cadmium and copper with limits of detection (LOD) of 20 ng L^?1 and 38 ng L^?1, respectively. The relative standard deviation values (RSDs) for 1.0 mg L^?1 of cadmium and 1.0 mg L^?1 of copper were 2.62% and 2.85%, respectively.     

Automated Derivatization of Pharmaceutically Active Thiols Under Flow Conditions Using an o-Phthalaldehyde/Glycine Fluorogenic System and Sequential Injection Analysis

The present study reports a new automated, generic analytical method for the determination of the pharmaceutically active thiols captopril (CAP), N-acetylcysteine (NAC), and D-Penicillamine (PEN). The proposed sequential injection (SI) method is based on the on-line reaction of the selected thiols with o-phthalaldehyde/glycine in alkaline medium (pH = 9.5) to form highly fluorescent iso -indole derivatives. The effect of all major flow and reaction variables was investigated, while validation was carried out in terms of linearity/range (2.5–7.5 mg L^?1), limits of detection (1.6–2.3 µ g L^?1), quantification (5.3–7.7 µ g L^?1), precision (0.9–1.2% for repeatability and 3.5–4.9% for intermediate precision), selectivity, and accuracy (98.3–102.8%). The developed method was applied to the assay and dosage uniformity tests of various pharmaceutical formulations at a sampling rate of 73 h^?1.     

Hydrothermal synthesis of nitrogen-doped carbon dots as a sensitive fluorescent probe for the rapid,selective determination of Hg2+

In the present work, a green synthetic method for producing nitrogen-doped carbon dots (NCDs) by using ammonium citrate and urea is introduced. The obtained NCDs were characterised by transmission electron microscopy, Fourier transform infrared spectra, UV–vis absorption and fluorescence spectra. The results showed that the prepared NCDs were spherical with a size of about 3.5 nm, emitting strong and stable blue fluorescence when excited at 352 nm. It was noting that the NCDs enable sensitive and selective determination of Hg²⁺ in tap water with a linear range of 0.01–5 mg L^?1 based on a possible charge transfer process. The detection limit was 9.4 µg L^?1.     

Determination of Vitamins A and E Exploiting Cloud Point Extraction and Micellar Liquid Chromatography

Cloud point extraction and micellar chromatographic methods were developed for determination of vitamins A and E. The stationary phase was C18 and the mobile phase was 3.00% (w/v) SDS, 15.0% (v/v) butyl alcohol and 0.02 mol L^?1 phosphate buffer solution at pH 7.0. The retention times for vitamins A and E were 9.6 and 13.0, respectively. The extraction solution was 100 mmol L^?1 Triton X-100, 650 mg NaCl and 1.0% ascorbic acid at 70°C for 30 min. The method is precise (r.s.d. < 7%), the linear range was from 5.0 up to 360.0 mg L^?1 for both vitamins. Recovery test showed recuperation between 90.2 and 99.2%, and LOD and LOQ of 0.234 and 0.108 mg L^?1, 0.780 and 0.360 mg L^?1 to vitamins A and E were found.     

Temperature-assisted ionic liquid-based dispersive liquid–liquid microextraction with following back-extraction for HPLC/UV–Vis determination of 3-indole acetic acid in pea plants

In this work, the ionic liquid (IL)[C₆mim][PF₆] was used as IL-based extractant for dispersive liquid–liquid microextraction, followed by back-extraction and HPLC/UV–Vis determination of 3-indole acetic acid (IAA) in pea plant. The effects of some crucial factors such as chemical structure and volume of IL, pH adjustment, dissolution temperature, extraction time, centrifugation time, and ionic strength of aqueous sample were studied. The linear range of the HPLC method for IAA quantification was 17.5 × 10^?2–36.8 mg L^?1. LOD, LOQ, method recovery, and preconcentration factor values were 0.170 mg L^?1, 0.175 mg L^?1, 98.3, and 40 %, respectively. The RSD for the suggested method was calculated as 0.93 % at 35.04 mg L^?1 of IAA and each IL phase was able to be reused for at least four DLLME/back-extraction cycles. To evaluate the applicability of the suggested method, IAA was determined in pea plant samples.     

Spectrophotometric Multicommutated Flow System for the Determination of Hypochlorite in Bleaching Products

Abstract

A multicommutation flow system for the spectrophotometric determination of hypochlorite in bleaching products is proposed. In this system, N,N-diethyl-p-phenylenediamine (DPD) reacts with hypochlorite, and the product was monitored at 515 nm. The analytical curve for hypochlorite was linear in the concentration range from 2.68 × 10^?5 to 1.88 × 10^?4 mol L^?1 (2–14 mg L^?1) with a detection limit of 6.84 × 10^?6 mol L^?1 (0.51 mg L^?1). The sampling rate was 45 h^?1, and a relative standard deviation of 1.4% (n = 10) was obtained. The recovery of this analyte ranged from 97.2% to 102.5%, and the results found using the proposed spectrophotometric multicommutated flow system agreed with the data obtained using a reference method (iodometric titration) at the 95% confidence level.     

Determination of Sb(III) and Total Sb in Antileishmanial Drugs by Spectrophotometric Flow‐Injection Hydride Generation

Abstract

A spectrophotometric procedure based on hydride generation and flow analysis is proposed for determination of antimony (III) [Sb(III)] and total antimony (Sb) in pharmaceutical samples. Firstly, Sb(III) reacts with hydrogen species generated in the system, forming antimony hydride. The reaction leads to a decrease in the permanganate concentration and, hence, in the intensity of the color of this specie, which is spectrophotometrically measured at 528 nm. Total Sb is determined as Sb(III) after Sb(V) reduction using 0.02% (m/v) KI. Some parameters, such as the number of channels of the gas phase separator, injection volume, coil length, and KBH₄ concentration, are investigated. The system presents a frequency of ca. 100 h^?1 and precision <3.0% [expressed as relative standard deviation (RSD) of 30 measurements using a 3.0 mg L^?1 Sb(III) solution]. The analytical curve ranging from 0.5 mg L^?1 to 5.0 mg L^?1 (r>0.998; n=5) permits limit of detection (LOD) and limit of quantification (LOQ) of 83 and 250 µg L^?1. For total Sb, the accuracy is checked by atomic absorption spectrometry applying the t test and the results are in accordance at the 95% confidence level. Recovery tests are used to check the accuracy for Sb(III) determination, and the recoveries are between 95% and 105%.     

Fast Determination of Phenolic Compounds in Brazilian Wines from Vale do São Francisco Region by CE

Six phenolic compounds were separated and determined by capillary zone electrophoresis in red wine from Brazil’s region Vale do São Francisco with total analysis time of 12 min. The limit of detections varied from 1.59 to 2.24 mg L^?1. The relative standard deviations (for n = 6) varied from 0.28 to 3.50 %. The red wine samples analyzed were bought in the local market and the phenolic compound recoveries were in the range of 98–101 %. The concentrations of gallic acid in the samples of wines varied from 16.0 to 42.0 mg L^?1, caffeic acid (3.16–5.18 mg L^?1), syringic acid (5.73–13.0 mg L^?1), kaempferol (2.32–4.33 mg L^?1), quercetin (1.68–4.03 mg L^?1), myricetin (7.52–25.1 mg L^?1). The concentrations found agree with data reported in the literature.     

Flow-Batch Method with a Sequential Injection System for Spectrophotometric Determination of Selenium(IV) in Selenium-Enriched Yeast Using o-Phenylenediamine

A precise, accurate, and reliable flow-batch spectrophotometric method for the determination of selenium (IV) was developed using o-phenylenediamine as a reagent with a sequential injection monosegmented flow system incorporating a simple heating unit. The reaction zones of selenium(IV) and o-phenylenediamine were mixed and heated in a chamber at 62°C for 5 minutes. The piaselanol complexes were then detected at a maximum absorption wavelength of 335 nm. In-line single standard calibration and standard addition procedures were developed employing the monosegmented flow technique. Under the optimized conditions, a linear calibration graph in a range of 0.1–4.0 mg L^?1 selenium (IV) was obtained with limits of detection and quantitation of 0.01 and 0.1 mg L^?1, respectively. Relative standard deviations were 2% [for both 0.1 and 0.5 mg L^?1 selenium (IV) (n = 11)]. A sample throughput of 2 h^?1 using four standard addition levels was achieved. The developed system was successfully applied to raw selenium-enriched yeast samples. The analyses performed by the developed method agreed well with those obtained from a standard inductively coupled plasma mass spectrometry method.     

Removal of Lead (II) Ions by Poly(2‐octadecyl butanedioic acid): Isothermal and Kinetic Studies

Poly(2‐octadecyl‐butanedioic acid), prepared from polyanhydride PA‐18, possesses novel heavy metal adsorption characteristics. The adsorption capacity of this water insoluble polymer for lead (II) was substantially higher than other heterogeneous adsorbants and is equivalent to those obtained with homogeneous sorbants. The polymer exhibited pseudo‐second‐order kinetics and nearly complete adsorption of lead occurred in 15 min with initial lead (II) concentrations greater than 100 mg · L^?1. Adsorptive behavior was accurately predicted by the Dubinin‐Radushkevich isotherm model. The mean free energy of adsorption of lead (II) onto poly(2‐octadecyl‐butanedioic acid) was determined to be 31.6 kJ · mol^?1, suggesting an ion exchange component to the adsorption mechanism. Gibb's free energy values for this process indicate that it is spontaneous. Adsorption was relatively independent of pH in the range of 3–5, due to the utilization of the sodium carboxylate form of the chelating groups, and was not influenced by high Na⁺ concentration and moderate concentrations (up to 200 mg · L^?1) of Ca⁺². Lead (II) solutions containing 2000 mg · L^?1 Ca⁺² did reduce the adsorption of 2000 mg · L^?1 lead (II) by 28%.     

High-Throughput Determination of Quinine in Beverages and Soft Drinks Based on Zone-Fluidics Coupled to Monolithic Liquid Chromatography

In the present study we propose a new automated analytical scheme for the determination of quinine in soft drinks and beverages by coupling zone-fluidics (ZF) to liquid chromatography (LC). Certain pretreatment tasks involving precise liquid handling, such as sample dilution and addition of the internal standard (ISTD) were automated by ZF. After on-line filling of the loop of the LC injection valve, separation was carried out in less than 2.5 min by using a reversed phase monolithic column (100 × 4.6 mm i.d.) at a flow rate of 2 mL min^?1. The ZF and LC parts of the setup operated independently: during LC separation the next sample was treated by ZF allowing a high throughput of 24 h^?1. The proposed assay was thoroughly validated in terms of linearity (up to 150 mg L^?1), LOD (0.25 mg L^?1), LOQ (0.8 mg L^?1), precision, accuracy, and ruggedness. The ZF-LC method was successfully applied for the determination of quinine in beverages and soft-drinks.