Flow Injection Preconcentration Research Articles

Spectrophotometric Determination of Fe(II) and Fe(III) Using 5-(4-Ethylphenyl azo ) 2-Hydroxybenzaldehyde Oxime Reagent

Spectrophotometric Determination of Fe(II) and Fe(III) Using 5-(4-Ethylphenyl azo ) 2-Hydroxybenzaldehyde Oxime Reagent

Separation of nickel and cadmium from aqueous solutions by flow injection preconcentration onto cadion functionalized polyurethane foam

A simultaneous spectrophotometric method was developed for the rapid determination of the binary elements nickel and cadmium. Two polyurethane foam sorbents, cadion functionalized foam and untreated foam, were separately packed in two minicolumns and used for on-line preconcentration/separation. The two elements were separated/preconcentrated on the cadion- foam minicolumn, and then they were eluted by hydrochloric acid and mixed with a thiocyante stream before entering the untreated foam minicolumn. Nickel passed out to react with 4-(2-pyridylazo)-resorcinol reagent and measured spectrophotometrically at 498 nm. The adsorbed cadmium-thiocyanate on the untreated foam was further eluted by sodium hydroxide and identically detected. At a preconcentration time of 60 sec (100 µg L−1), the detection limit was 4.6 and 3.3 µg L−1 and the quantification limit was 15.3 and 11.0 µg L−1 for cadmium and nickel, respectively. The preconcentration factor was 5.0 and 11.0, respectively, and sampling frequency was 12 and 20 h−1. The accuracy was assessed using the BCR397R human hair and NIST 1577b bovine liver certified reference materials with a recovery of 92.0–94.2% (Relative standard deviation = 5.3–8.2%). The analysis of human urine and tap water samples demonstrated the applicability of the method and showed a relative recovery of 89.6 to106% (Relative standard deviation ≤ 9.4%).

Performance of Avocado Seed Activated Carbon as Adsorbent for Highly Sensitive Determination of Cd Using a Flow Injection System Online Coupled to TS-FF-AAS

A flow-injection preconcentration system using detection by the thermospray flame furnace atomic absorption spectrometry (FIA-TS-FF-AAS) is proposed. Cd2+ are adsorbed on avocado seed activated carbon (ASAC) packed into a cylindrical mini-column and eluted using HCl solutions for the detection system. A 25–1 fractional factorial and Doehlert matrix design were employed to determine the optimum conditions for cadmium preconcentration (pH 7.68, buffer concentration (Tris/Tris-HCl) of 0.023 mol L-1, eluent concentration (HCl) of 2.0 mol L-1, the adsorbent mass of 100.0 mg and preconcentration flow rate of 4.8 mL min-1). The preconcentration method presents linearity within the range of 0.41-15.00 µg L-1, limits of quantification and detection of 0.41 and 0.12 µg L-1, respectively, preconcentration factor of 10.7, consumption of index of 0.93 mL and sample throughput of 26 h-1. The precision assessed as the relative standard deviation (RSD) were found to be 0.48, 0.90 and 2.30% for inter-day precision (n = 2), and 0.30, 0.44 and 2.48% for intra-day precision (n = 6) for respective cadmium concentration of 0.50, 5.00 and 15.00 µg L-1. The proposed method was applied satisfactorily in samples of cigarette (62.84 ± 11.28 µg kg-1), human hair (69.61 ± 2.38 µg kg-1) and water samples [lake (0.65 ± 0.01 µg L-1), tap and mineral].

Rapid on-line solid phase enrichment using polytetrafluoroethylene beads for chromium speciation in contaminated real water samples

Due to unchecked disposal of industrial wastes into surrounding areas, the pollution of water bodies with heavy metal toxicants has become an environmental menace. The toxicity of chromium species depends on its oxidation states, and thus regular monitoring of environmental water sources vulnerable to pollution is a must. In this regard, an on-line method for chromium speciation and determination using FAAS has been proposed. The flow-injection preconcentration mini-column containing polytetrafluoroethylene beads was used as the solid phase extractant, and chromium speciation was done by complexing Cr(III) and Cr(VI) with thiosemicarbazide chelating agent. The figures of merit for Cr(III) and Cr(VI) obtained were 61 and 56 (preconcentration factors); 0.13 and 0.14 µg L−1 (detection limits); 1.6 and 1.3% (R.S.D.). The optimized method for chromium speciation was successfully applied to industrial and Yamuna River water samples. The method validation was carried out using SRM 1640a (Trace Elements in Natural Water, NIST), and recovery > 95% was obtained.

Chromium Speciation Using Flow-injection Preconcentration on Xylenol Orange Functionalized Amberlite XAD-16 and Determination in Industrial Water Samples by Flame Atomic Absorption Spectrometry.

A speciation method for Cr(III) and Cr(VI) by on-line solid-phase extraction using a flow-injection system with FAAS has been proposed. The Cr(III) was selectively retained at pH 5 on the AXAD16-XO chelating resin and was eluted using 0.5 mol L(-1) HNO3. The preconcentration factor and the detection limit (3σ) of 73 and 0.11 μg L(-1), respectively, were obtained for a 120-s preconcentration time. The precision (%RSD) at the 100 μg L(-1) level was 1.08%. The linearity for Cr(III) measurements was up to 600 μg L(-1). The total chromium was determined by reducing Cr(VI) to Cr(III) using hydroxylamine hydrochloride, and the Cr(VI) concentration was obtained by subtraction from the total chromium concentration. The effect of interfering ions was examined towards the selectivity of the proposed system for Cr(III). Spike recovery studies in industrial water samples were carried out using standard Cr(III) and Cr(VI) solutions traceable to NIST. The proposed method was validated using SRM 1643e (Trace Elements in Water) supplied by NIST, USA.

Determination of Cadmium by Magnetic Multiwalled Carbon Nanotube Flow Injection Preconcentration and Graphite Furnace Atomic Absorption Spectrometry

ABSTRACTMagnetic multiwalled carbon nanotubes were incorporated on iron oxide nanoparticles and used for the magnetic solid-phase extraction of cadmium prior to quantification by graphite furnace atomic absorption spectrometry with flow injection analysis. Cadmium was retained in a microcolumn filled with the magnetic multiwalled carbon nanotubes and quantitatively eluted with nitric acid. The major parameters affecting the extraction efficiency were investigated, including the sample pH, sample flow rate, sorbent amount, sample volume, eluent concentration, and eluent volume. The optimum conditions were pH 7.0, a flow rate of 16 µL s−1, 10 mg of magnetic nanoparticles, a sample volume of 10 mL, an eluent concentration of 0.1 mol L−1, and an eluent volume of 1 mL. The linear dynamic range was from 0.01 to 10 µg L−1, with a relative standard deviation of 2.3% at 1.0 µg L−1. The limit of detection was 1.2 ng L−1 and the preconcentration factor was approximately 160. The accuracy of the method was evaluated by the analysis of urine, water, and certified reference materials.

Flow Injection Solid Phase Extraction for Trace Metal Determination Using a Chelating Resin and Flame Atomic Absorption Spectrometry Detection

ABSTRACTThe development of a simple and sensitive on-line flow injection preconcentration system is reported using a polyamino-polycarboxylic acid chelating resin for the automated determination of cadmium(II), chromium(III), copper(II), and lead(II) in natural waters and urine by flame atomic absorption spectrometry (FAAS). The adsorbent showed a high sorption affinity for the metal ions at pH values from 5.0 to 6.0. The retained analytes were efficiently eluted by 1.5 mol/L HNO3. The effect of chemical and hydrodynamic parameters such as pH, selection of eluent (type, volume and concentration), and sample/eluent flow rates were studied, providing optimum conditions for the analysis of real samples. For a preconcentration time of 120 sec, the sampling frequency was 22/h and the enhancement factors were 105, 49, 106, and 98 for cadmium(II), chromium(III), copper(II), and lead(II), respectively. The detection limits were between 0.1 and 1.6 mg/L, while the precision was less than 3.3% as the relative standard deviation for all metal ions. The accuracy of the method was evaluated by the analysis of certified reference materials and fortified environmental and biological samples.

Flow-injection solid phase extraction using Dowex Optipore L493 loaded with dithizone for preconcentration of chromium species from industrial waters and determination by FAAS

An online flow injection preconcentration system for speciation of Cr(iii) and Cr(vi) based on the combination of solid phase extraction (SPE) and flame atomic absorption spectrometry (FAAS) has been described.

On-Line Flow Injection Preconcentration of Palladium in Environmental Waters Using a Microcolumn Packed with Silica Nanoparticles Modified by γ-Aminopropyltriethoxisilane and Determination by Flame Atomic Absorption Spectrometry

A novel solid phase sorbent with silica nanoparticles modified by γ-aminopropyltriethoxysilane (modified nanometer SiO2-γ-APS) was employed for the separation and preconcentration of palladium(II) before determination by flame atomic absorption spectrometry. The analytical conditions including pH, the eluent, and flow rates were optimized. Trace palladium(II) was quantitatively absorbed on a microcolumn of the sorbent at pH 5.0. The enrichment factor and sampling frequency were 45 and 12 h−1, respectively. Palladium(II) adsorbed on microcolumn was eluted quantitatively with 9% KSCN solution; the eluent solution was introduced into a flame atomic absorption spectrophotometer. The detection limit for palladium was 2.48 µ gL−1 and the relative standard deviation (RSD) was 1.8% (n = 11) at the 0.1 mg L−1 palladium level. The recoveries of palladium were 95.0% to 100.3%. The proposed method was successfully applied to the determination of palladium in pond and river water samples.

Preconcentration and Determination of Trace Silver Ion Using Benzothiazole Calix[4]arene Modified Silica by Flow Injection Flame Atomic Absorption Spectrometry

The silica gel modified with benzothiazole calix[4]arene (APS-L1) via Schiff's base reaction was applied as a sorbent in an online system for preconcentration and determination of silver ion by flame atomic absorption spectrometry (FAAS). APS-L1 was used as an effective sorbent for solid phase extraction (SPE) of silver(I) ion in both batch and column methods. The optimum experimental parameters such as pH, eluent type, sample flow rate, eluent volume and eluent flow rate including the effect of interfering ions were investigated. Silver(I) ion was determined at pH 6-7. The capacity of APS-L1 sorbent was found to be 12.2 mg/g of sorbent. The high affinity was obtained without interference from the interfering ions. The optimum conditions of the online flow injection preconcentration coupled with the FAAS (FI-FAAS system) were evaluated. The sample flow rate was 3.0 mL min(-1) using sample volume of 5-10 mL. Elution was performed with 250 μL of 0.1 mol L(-1) thiosulfate at the flow rate of 1.5 mL min(-1). The analytical characteristics and performance of the FI-FAAS system were studied under optimum conditions using a solution spiked with standard silver(I) ion at 20 and 50 μg L(-1). The detection limit of 0.44 μg L(-1) was obtained. The accuracy of the proposed method was evaluated and percentages of recovery at 20 and 50 μg L(-1) were 100.2 and 99.5%, respectively. The percent relative standard deviations (%RSD) at 20 and 50 μg L(-1) were 6.1 and 3.3%, respectively. The developed method was successfully applied to determine trace silver(I) ion in drinking and tap water samples.

Evaluation of poly(vinylpyridine)-supported protoporphyrin resin for the sampling/separation of manganese(ii) using a hyphenated FIA-FAAS system

The present study describes the development of a preconcentration method for manganese determination by FAAS using poly(protoporphyrin-co-vinylpyridine) as a sorbent. To synthesize this material, 4-vinylpyridine and protoporphyrin were copolymerized in the presence of ethylene glycol dimethacrylate as a cross-linker and 2,2-azobisisobutyronitrile as an initiator. The factors affecting the flow injection preconcentration system were optimized by employing 25 fractional factorial and Doehlert matrix designs. The proposed on-line preconcentration method was performed by percolating 18.0 mL aliquots of Mn(II) solutions (pH 8.3) at a flow rate of 6.0 mL min−1 through a mini-column, packed with 100 mg of poly(protoporphyrin-co-vinylpyridine); the Mn(II) ions were then on-line eluted with 1.5 mol L−1 HNO3 into the FAAS nebulizer. Under these conditions, it was possible to yield a linear curve in the concentration range of 0.0–120.0 μg L−1, with a correlation coefficient of 0.997. Besides, the following system parameters were obtained: sampling frequency of 15 h−1, preconcentration factor of 53, consumptive index of 0.34 mL, concentration efficiency of 17.6 min−1, detection limit of 0.34 μg L−1, and quantification limit of 1.13 μg L−1. The method precision (repeatability) estimated for ten measurements of 1.0 and 50.0 μg L−1 Mn(II) standard solutions was found to be 5.2 and 4.9%, respectively. Moreover, the protoporphyrin incorporation into the poly(vinylpyridine) network caused a remarkable 323% increase in the method's sensitivity. Finally, the proposed procedure was not affected by potentially interfering ions. Thus, it was successfully applied to the Mn(II) determination in water, food and sediment samples.

Determination of total iron in food samples after flow injection preconcentration on polyurethane foam functionalized with N,N-bis(salicylidene)-1,3-propanediamine

A highly selective flow injection sorption system was developed for the fast determination of total iron in food samples. Iron (III) was reduced to iron (II) by ascorbic acid and preconcentrated on a mini-column packed with polyurethane foam (PUF) functionalized with N,N-bis(salicylidene)-1,3-propanediamine (SPDA). The retained Fe (II) was eluted with hydrochloric acid and subsequently reacted to 2,4,6-tri(2′-pyridyl)-1,3,5-triazine (TPTZ) then measured at 593nm. The procedure has resulted preconcentration factor 36, sample frequency 20h−1 and detection limit 18μgL−1. The precision (RSD) was found to be 5.7% and 3.1% at concentration levels 0.1 and 5.0μgmL−1 iron (II), respectively. Finally, the method was successfully applied to determination of total iron in reference material and food samples.

Cationic polyelectrolyte copolymer modified polyurethane foam for flow injection preconcentration and separation of trace amounts of β-lactam antibiotics

A more sensitive flow injection preconcentration method has been developed for the determination of four β-lactam antibiotics (BLAs) namely cefaclor, cefotaxime, amoxicillin and ampicillin in urine, pharmaceuticals and milk. A mini-column packed with PUF functionalized with the cationic polyelectrolyte, poly(N-chloranil N,N,N′,N′-tetramethylethylene diammonium dichloride) PCTDD, was utilized for selective preconcentration. The detection limits with this method were 3.3, 3.8, 5.1 and 7.0ngmL−1 and enrichment factors were 38, 21, 39, and 36 for cefaclor, cefotaxime, amoxicillin and ampicillin, respectively with a sample throughput of 12h−1 for all BLAs. Moreover, the BLAs were successfully separated by isocratic elution using a micellar mobile phase. Application of the method developed has resulted in recovery values in the range 95%–109% (RSD≤8.7), 83%–99% (RSD≤9.7) and 91%–103% (RSD≤4.0) for urine, pharmaceuticals and milk samples, respectively.

Flow-Injection Flame Atomic Absorption Determination of Hexavalent Chromium with On-Line Preconcentration on an Anion Imprinted Polymer

A flow injection preconcentration system for the flame atomic absorption spectrometric determination of hexavalent chromium has been developed. The method employs on-line preconcentration of Cr(VI) on a minicolumn packed with Cr(VI)-imprinted poly(4-vinyl pyridineco-2-hydroxyethyl methacrylate) placed into a flow injection system. Hexava-lent chromium was eluted with a small volume of diluted hydrochloric acid into the nebulizer-burner system of a flame atomic absorption spectrometer. An enrichment factor of 550 and a 3σ detection limit of 0.04 μg·L-1 along a sampling frequency of 4 h-1 at a sample flow rate of 3.5 mL·min-1. The relative standard deviation is 2.9% for 1 μg·L-1 Cr(VI) (n = 11). The flow injection system proposed has the advantage of being simpler because the use of expensive and sophisticated instruments is avoided. Ease of use, continuous process and selectivity make this method suitable for Cr(VI) determination in different environmental samples such as sea and river waters, soils and sediments.

Chromium fractionation and speciation in natural waters

It is common for leather industries to dump chromium-contaminated effluent into rivers and other bodies of water. Thus, it is crucial to know the impacts caused by this practice to the environment. A study on chromium partitioning and speciation, with determination at trace levels, was carried out in a potentially contaminated creek. Chromium fractionation and speciation was performed using a flow-injection preconcentration system and detection by flame atomic absorption spectrometry. High levels of this element were found in the particulate material (449-9320 mg kg(-1)), which indicates its compatibility with this fraction. The concentration of Cr(iii) in the water samples collected ranged from 5.2-105.2 μg L(-1). Cr(vi) was always below of the DL (0.3 μg L(-1)). Chromium accumulation observed in the sediment (873-1691 mg kg(-1)) may confirm contamination due to the long term release of contaminated effluents in the creek.

Microwave plasma torch-atomic emission spectrometry for the on-line determination of rare earth elements based on flow injection preconcentration by TiO2–graphene composite

In this work, we synthesized TiO2–graphene composite as a novel preconcentration material. It was enclosed in a microcolumn in the on-line flow injection system to adsorb trace light (La), medium (Tb), and heavy (Ho) rare earth elements (REEs) prior to their determinations by microwave plasma torch-atomic emission spectrometry (MPT-AES). Various experimental parameters, such as sample loading time, sample flow rate, sample pH, eluent flow rate, eluent concentration, and interfering ions, were investigated systematically. Under the optimum conditions, the detection limits (three times of standard deviations of blank by 7 reiterations) of La, Tb, and Ho were found to be 2.2, 1.6, and 2.8μgL−1, with enrichment factors of 17.1, 11.1, and 10.2, respectively. Relative standard deviations for the determination of the target REEs were 3.6%, 1.3%, and 1.4%, respectively (n=7). The developed method was validated by the analysis of La, Tb, and Ho in certified reference material (GBW07313, marine sediment) and high purity REE oxide samples.

A new flow injection preconcentration method based on multiwalled carbon nanotubes for the ETA-AAS determination of Cd in urine

A new flow injection (FIA) procedure for the preconcentration of cadmium in urine using multiwalled carbon nanotubes (MWCNT) as sorbent and posterior electrothermal atomization atomic absorption spectrometry (ETA-AAS) Cd determination has been developed. Cadmium was retained in a column filled with previously oxidized MWCNTs and it was quantitatively eluted with a nitric acid solution. The parameters influencing the adsorption–elution process such as pH of the sample solution, amount of sorbent and flow rates of sample as well as eluent solutions have been studied. Cd concentration in the eluent was measured by ETA-AAS under the optimized conditions obtained. The results indicated the elimination of urine matrix effect as a consequence of the preconcentration process performed. Total recovery of cadmium from urine at pH 7.2 using a column with 45mg of MWCNTs as sorbent and employing a HNO3 0.5molL−1 solution for elution was attained. The detection limit obtained was 0.010μgL−1 and the preconcentration factor achieved was 3.4. The method showed adequate precision (RSD: 3.4–9.8%) and accuracy (mean recovery: 97.4–100%). The developed method was applied for the determination of cadmium in real urine samples from healthy people (in the range of 0.14–2.94μgL−1) with satisfactory results.

Cellulose microfiber functionalized with N,N′-bis (2-aminoethyl)-1,2-ethanediamine as a solid sorbent for the fast preconcentration of Cd(II) in flow system analysis

The present paper describes the synthesis of a new chemically modified cellulose microfiber through oxidation with sodium periodate and functionalization with N,N′-bis (2-aminoethyl)-1,2-ethanediamine for the fast and selective preconcentration of Cd(II) ions in flow system analysis. The new sorbentsorbent was characterized by FTIR, SEM, and surface area values. The uptake behavior of Cd(II) ions onto this sorbent was evaluated from kinetic data, pseudo-first-order and pseudo-second-order models, as well as from Langmuir, Freundlich and Langmuir–Freundlich adsorption isotherms. The maximum sorption capacity of 4.59mgg−1 was estimated by the Langmuir–Freundlich model with fast kinetics for the sorption of Cd(II) described by the pseudo-second-order kinetic model. After characterization, the sorbent was packed in a mini-column, and a fast flow injection preconcentration system for Cd(II) determination by FAAS was developed. The best Cd(II) preconcentration condition, obtained by means of factorial design and response surface methodology, was achieved at pH 9.36 and a flow rate of 10mLmin−1 followed by elution with 1.0molL−1 nitric acid. By using 78s preconcentration time, fast and highly sensitive determination of Cd(II) ions could be achieved with a limit of quantification of 0.20μgL−1, preconcentration factor of 26, consumption index of 0.5mL, concentration efficiency of 20min−1, and sample throughput of 39h−1. The repeatability for 10 replicate determinations was found to be 7.8 and 2.5% for Cd(II) ion concentrations of 5.0 and 100.0μgL−1, respectively. The new sorbent efficiency for the interference-free preconcentration of Cd(II) ions was assessed by analysis of tap, mineral and lake waters, as well as synthetic seawater and normal saline waters. Furthermore, complex samples, such as biological samples, could be analysed by the proposed method in accordance with the accuracy attested by analysis of certified reference materials, TORT-2 (lobster hepatopancreas), and DOLT-4 (dogfish liver).

DETERMINATION OF TRACE CADMIUM BY FLOW INJECTION ON-LINE MICROCOLUMN PRECONCENTRATION COUPLED WITH FLAME ATOMIC ABSORPTION SPECTROMETRY USING HUMAN HAIR AS A SORBENT

A novel method using a cone-shaped pipette tip packed with human hair as an adsorption material has been developed for the on-line flow injection preconcentration of trace Cd(II) ions based on its complex formation with the ammonium pyrrolidine dithiocarbamate (APDC) prior to flame atomic absorption spectrometric (FAAS) determination. Cd-PDC complex sorbed on the human hair was eluted by 4.0 mol L−1 HNO3. The enhancement factor is 19, and the detection limit (3σ) is 0.77 μg L−1. The proposed method was successfully applied to the determination of trace cadmium in drinking water, beverage samples, and the certified reference materials.

Flow-Injection Preconcentration of Chloramphenicol Using Molecularly Imprinted Polymer for HPLC Determination in Environmental Samples

The residue of antibiotic chloramphenicol (CAP) is important issue for food quality control and also for the environmental monitoring. It is banned for use in food-producing animals and has very limited use in human medicine, because of its severe impact on human health. Determination of trace level of CAP in environmental samples requires a very sensitive analytical method and efficient preconcentration procedure. CAP can be efficiently preconcentrated in flow-injection system using flow-through reactor packed with molecularly imprinted polymer (MIP), but determination of CAP in eluate from MIP requires the application of chromatographic separation, which was made in reversed-phase HPLC system with UV detection. In optimized conditions the limit of detection for 100 mL sample in HPLC with offline preconcentration on MIP was evaluated as 0.66 mg/L. In hyphenated FIA-HPLC system with zone sampling the LOD for developed method was evaluated as 15 ng/L, which indicates the possibility of using it for analysis of environmental samples.