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.     

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.     

Sorption of Cd(II) onto carbon-based materials—a comparative study

The sorption behaviour of Cd(II) on three carbon-based materials including activated carbon (AC), carbon nanotubes (CNTs) and carbon-encapsulated magnetic nanoparticles (CEMNPs) which were prepared under similar conditions by nitric acid treatment were investigated. Generally, sorption of cadmium on these materials increased with the increase of pH. For AC and CNTs very similar results were obtained, while CEMNPs exhibits much higher affinity for Cd(II) despite of almost the same surface acidity. Thus, cadmium retention on tested sorbents was more dependent on the concentration of specific active sites than the total surface area available. The equilibrium sorption data were better fitted to Langmuir isotherm. The theoretical saturation capacity of the monolayer derived from this model at pH 8.0 for AC, CNTs and CEMNPs are 9.91 mg g^?1, 20.37 mg g^?1 and 91.0 mg g^?1, respectively. The kinetic of Cd(II) sorption is fitted for pseudo-second order equation and could be described as a combination of film diffusion and intra-particle diffusion, whereby the last one dominates. The experimental parameters for preconcentration of cadmium on a microcolumn packed with CEMNPs prior to its determination by flame atomic absorption spectrometry have been investigated. Cadmium can be quantitatively retained at pH 8 from sample volumes up to 150 mL and then eluted completely with 3 mL of 0.5 mol L^?1 HNO₃.     

Multi‐Walled Carbon Nanotubes as Sorbent for Flow Injection On‐Line Microcolumn Preconcentration Coupled with Flame Atomic Absorption Spectrometry for Determination of Cadmium and Copper

Abstract

Multi‐walled carbon nanotubes (MWNTs) were used as sorbent for flow injection (FI) on‐line microcolumn preconcentration coupled with flame atomic absorption spectrometry (FAAS) for determination of trace cadmium and copper in environmental and biological samples. Effective preconcentration of trace cadmium and copper was achieved in a pH range of 4.5–6.5 and 5.0–7.5, respectively. The retained cadmium and copper were efficiently eluted with 0.5 mol L^?1 HCl for on‐line FAAS determination. The MWNTs packed microcolumn exhibited fairly fast kinetics for the adsorption of cadmium and copper, permitting the use of high sample flow rates up to at least 7.8 mL min^?1 for the FI on‐line microcolumn preconcentration system without loss of the retention efficiency. With a preconcentration time of 60 sec at a sample loading flow rate of 4.3 mL min^?1, the enhancement factor was 24 for cadmium and 25 for copper at a sample throughput of 45 h^?1. The detection limits (3σ) were 0.30 and 0.11 µg L^?1 for Cd and Cu, respectively. The precision (RSD) for 11 replicate measurements was 2.1% at the 10‐µg L^?1 Cd level and 2.4% at the 10‐µg L^?1 Cu level. The developed method was successfully applied to the determination of trace Cd and Cu in a variety of environmental and biological samples.     

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.     

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.     

Dispersive liquid–liquid microextraction combined with flow injection inductively coupled plasma mass spectrometry for simultaneous determination of cadmium, lead and bismuth in water samples

Dispersive liquid–liquid microextraction (DLLME) was combined with flow injection inductively coupled plasma mass spectrometry for simultaneous determination of cadmium, lead and bismuth in water samples. The metal elements were complexed with sodium diethyldithiocarbamate, and then the complexes were extracted into carbon tetrachloride by using DLLME. Under the optimized conditions, the enrichment factors for Cd, Pb and Bi are 460, 900 and 645 in 5 mL of a spiked water sample, respectively. The calibration graphs for the three metals are linear in the range of concentrations from <10 ng L^?1 to 1,000 ng L^?1. The detection limits are 0.5 ng L^?1, 1.6 ng L^?1 and 4.7 ng L^?1, respectively. The relative standard deviations for ten replicate measurements of 50 ng L^?1 cadmium, lead and bismuth are 2.6%, 6.7%, and 4.9%, respectively, and the relative recoveries in various water samples at a spiking level of 50 ng L^?1 range from 83.6% to 107.0%.     

Co-microprecipitation/flotation of trace amounts of cadmium from environmental samples through its complexation with iodide and neutralization with cetyltrimethylammonium bromide in the presence of perchlorate ions

ABSTRACT

A fast, cost-effective and reliable method is presented for separation and preconcentration of trace amounts of cadmium based on co-precipitation and flotation prior to its flame atomic absorption (AAS) spectrometric determination. Cadmium (II) was complexed with iodide and neutralized with cetyltrimethylammonium bromide (CTAB) in the presence of perchlorate ions. This resulted in the formation of a bulky precipitate containing the ternary complex of CdI₄(CTA)₂, floating on the top of the solution. The aqueous layer was then simply drained out, the floated layer was dissolved in 1.0 mL of acetonitrile, and its Cd content was determined by flame atomic absorption spectrometry. The parameters affecting the designed separation method such as KI, CTAB, and ClO₄^? concentration, pH, ionic strength, volumes of sample and dissolving solvent, and extraction time were studied and optimized. For preconcentration of 200 mL of the sample, the calibration graph was linear in the range of 1–30 μg L^?1 of cadmium with a correlation coefficient of 0.9997, enhancement factor of 194 and a limit of detection of 0.18 μg L^?1. The relative standard deviation for seven replicate determinations at 20 μg L^?1 levels of cadmium was found to be 2.1%. The effect of the presence of different common cations and anions on the separation and determination of Cd(II) by the developed method was studied. The method was successfully applied to the determination of trace amounts of Cd(II) ions in different types of real samples including tap water, polluted industrial wastewater, dust, and soil with the recoveries in the range of 95.3 to 103.4.     

Characterization of River Natural Organic Matter by High-Performance Size Exclusion Chromatography

The molecular weight of natural organic matter from the Yeongsan and Seomjin Rivers and the discharge from the wastewater treatment plants were analyzed for seasonal characteristics by high-performance size exclusion chromatography. The distribution of molecular weights demonstrated relationships with microbial activity and seasonal variations with temperature. Dissolved organic carbon and total organic carbon for the Seomjin River were from 1.6 to 3.1 mg L^?1; for the Yeongsan River system, these parameters were between 2.0 and 8.0 mg L^?1. There were no significant differences between upstream and downstream organic matter. The biochemical oxygen demand (0.8–2.5 mg L^?1) for the Seomjin River was less than the chemical oxygen demand (2.9–5.0 mg L^?1). Similarly, the biochemical oxygen demand (0.9–4.6 mg L^?1) for the Yeongsan River was lower than the chemical oxygen demand (3.8–10.6 mg L^?1). The molecular weight of aromatic compounds increased as the water temperature decreased in October, whereas the molecular weights of proteins decreased as the water temperature increased. These results suggest that as microbial activity increased, natural organic matter with a smaller molecular weight may be employed as an energy source by microorganisms. As a result, seasonal variation of the water temperature may influence the distribution of organic matter in the rivers based on molecular weight and microbial activity such that the smaller natural organic matter was more readily degraded by microorganisms.     

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.     

International comparison of the determination of the mass fraction of cadmium, chromium, mercury and lead in polypropylene: the Comité Consultatif pour la Quantité de Matière pilot study CCQM-P106

The CCQM-P106 pilot study was organized by the inorganic working group of the Comité Consultatif pour la Quantité de Matière (CCQM) as a feasibility comparison to study the applicability of different analysis methods to the polypropylene sample and test the abilities of the participants for measuring the Cd, Cr, Hg and Pb in polypropylene. National Institute of Metrology P.R. China (NIM) acted as the coordinating laboratory of this pilot study. There were 21 laboratories that submitted the final results. The median values of the mass fraction of Cd, Cr, Hg and Pb were 36.12 mg kg^?1 (the median absolute deviation about the median (MADe) = 0.46 mg kg^?1), 252.5 mg kg^?1 (MADe = 3.4 mg kg^?1), 387.0 mg kg^?1 (MADe = 10.1 mg kg^?1) and 466.2 mg kg^?1 (MADe = 8.9 mg kg^?1), respectively. Isotope dilution mass spectrometry (IDMS), inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-optical emission spectrometry (ICP-OES), atomic absorption spectrometry (AAS), instrumental neutron activation analysis (INAA) and X-ray fluorescence (XRF) measurement methods were used, and microwave digestion was used by the most of the participants. In general, very good agreement of the results was observed. Moreover, compared to the results of other methods, the results of IDMS still showed less spread amongst laboratories and had a smaller uncertainty. In addition, the results of some analytes used by XRF and INAA also got satisfactory agreement with the median value.     

In-Capillary Derivatization and Preconcentration for CE of Metal Ions as Their Phenanthroline Complexes

A simple and automated method involving in-capillary derivatization and in-capillary preconcentration was developed for the simultaneous determination of metal ions by capillary zone electrophoresis. Fe(II), Zn(II), Cu(II) and Cd(II) were derivatized using 1,10-phenanthroline as the derivatizing agent. The in-capillary derivatization and in-capillary preconcentration via large volume injection were performed sequentially as follows: 60 mmol L^?1 1,10-phenanthroline was first hydrodynamically injected (0.2 psi) for 2 s; metal ions were introduced by hydrodynamic injection (0.5 psi) for 60 s; 0.2 mol L^?1 acetate pH 5.5 containing 20 % methanol was used as the running buffer. Four metal ions can be determined within 8 min using 16 kV. The resulting preconcentration factors were in the range 12–21. Good linearity was obtained for concentrations of 0.1–8.0 mg L^?1 (r ² > 0.990). The mean recoveries of the metal ions evaluated by fortification of wine samples were in the range 90–102 %. The limits of detection ranged from 0.05 to 0.2 mg L^?1. The proposed method can be applied for directly determining metal ions in wine samples.     

Determination of Silver with On-Line Preconcentration Using Dithiozone Chelate and Carbon Nanotubes for Preconcentration with Detection by Flame Atomic Absorption Spectrometry

A novel flow injection system incorporating a micro-column packed with carbon nanotubes (CNTs) as an adsorbent has been applied to the on-line preconcentration of trace silver with detection by flame atomic absorption spectrometry. Silver is first chelated by dithizone (H₂Dz), then retained on the CNTs surface and afterward quantitatively eluted by methanol. Influencing parameters, including the concentration of reaction reagent, enrichment variables, and elution variables were investigated. The adsorption mechanisms of Ag-H₂Dz chelate retained onto the CNTs surface have also been studied. By loading 6.9 mL sample solution, a linear calibration graph is obtained within the range of 3–120 µg L^?1 with R of 0.9996, and a detection limit (3σ) of 0.8 µg L^?1 is achieved, along with a precision of 1.6% R.S.D. at the 30 µg L^?1 level (n = 7). The dynamic sorption capacity of CNTs for silver is 122 mg g^?1. The procedure is demonstrated by measurement of spike recovery in a series of water samples, giving rise to spike recoveries in the range of 96.8–99.7%.     

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.     

Electromagnetic induction-assisted heating as a new method for on-line cloud point extraction of cadmium from water samples

We report on a novel method for on-line cloud point extraction (CPE) for preconcentration of cadmium ions. It is based on electromagnetic induction-assisted heating (EMIH) of iron particles in a packed bed contained in a quartz tube that acts as an on-line CPE enrichment column. The cadmium complex of 1-(2-pyridylazo)-2-naphthol is quantitatively retained by the column under the cloud point temperature with the help of EMIH. The column was then eluted with alcoholic borax buffer at room temperature and on-line coupled to FAAS. Under optimum conditions, the limit of detection (3 s_b/b) and limit of quantification (10 s_b/b) are 0.21 μg?L^?1 and 0.70 μg?L^?1 of Cd(II), respectively, and the relative standard deviation is 3.8 % (for n?=?8; at 20 ng?mL^?1). An enhancement factor of 76 is typically achieved. The correlation coefficient of the calibration graph using the present method was 0.9986. The method was successfully applied to determine Cd(II) in water samples

Cadmium Distribution in a Timberline Forest in the Hengduan Mountains in the Eastern Tibetan Plateau

In order to study the regional distribution, characterization, and possible source of Cadmium in the eastern Tibetan Plateau, samples of leaves, xylem, twigs, bark, and roots of timberline forest trees (fir or spruce) and soils at depths from 0 to 40 cm were collected in eight sites in Hengduan Mountains. According to Cd contents, organs and tissues were divided into three groups: the highest-level organ (roots: 0.237 mg · kg^?1), the high-level organ/tissue (bark: 0.183 mg · kg^?1 and twigs: 0.159 mg · kg^?1), and the low-level organ/tissue (xylem: 0.054 mg · kg^?1and leaves: 0.048 mg · kg^?1). Cd contents in Transect A were a little higher than Transect B. Sites near pollutant sources and high-levels are more sensitive to Cd pollution and accumulated more Cd, while Cd contents in sites far away from pollutant sources and low-level organ/tissue were relatively low. It is suggested that the eastern Tibetan Plateau has already been polluted by the influence of general circulation to some extent. Nevertheless, low Cd contents in some sites prove that high mountains may barricade Cd pollutants from monsoon.     

Simultaneous determination of Ponceau-4R and Allura Red in soft drinks based on the ionic liquid modified expanded graphite paste electrode

A convenient and sensitive method was developed for the simultaneous determination of Ponceau-4R and Allura Red using an ionic liquid modified expanded graphite paste electrode (IL-EGPE). The IL-EGPE was prepared by mixing ionic liquid-expanded graphite (IL-EG) composites with solid paraffin. Based on the advantageous functions of IL and EG, IL-EGPE showed enhanced electrocatalytic activity towards the simultaneous oxidation of Ponceau-4R and Allura Red. Under optimal experimental conditions, the IL-EGPE exhibited wide linear responses to Ponceau-4R and Allura Red ranging from 6.0 to 7.5 mg L^?1 and 5.0 to 0.5 mg L^?1, respectively. The detection limits for Ponceau-4R and Allura Red were 1.15 and 0.89 μg L^?1 at a signal-to-noise ratio of 3, respectively. The designed electrode showed good reproducibility, stability and reusability. The proposed method was successfully applied in the simultaneous determination of Ponceau-4R and Allura Red in soft drinks. This method presented a simple, rapid and sensitive platform for simultaneous determination of Ponceau-4R and Allura Red and would become a versatile and powerful tool for food safety.     

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.     

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.     

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%.