FAAS slurry analysis of lead and copper ions preconcentrated on titanium dioxide nanoparticles coated with a silver shell and modified with cysteamine

We report on the separation and preconcentration of lead(II) and copper(II) ions using silver-coated titanium dioxide nanoparticles modified with cysteamine, and their determination by slurry analysis via flame atomic absorption spectrometry. The ions were adsorbed via a conventional batch technique, and the ion-loaded slurry was separated and directly introduced into the spectrometer, thereby eliminating a number of drawbacks. The effects of pH, amount of sorbent, slurry volume, sample volume and other ions on the recovery were investigated. Under optimized experimental conditions, copper and lead can be recovered within the 95% confidence level in certificated waste water, but also in spiked sea water samples. The technique is fast, simple, and leads to complete elution. The limit of detection (3δ, at n?=?10) was 0.37 μg L^?1 for Cu(II), and 0.38 μg L^?1 for Pb(II).

Preconcentration and in-situ photoreduction of trace selenium using TiO2 nanoparticles, followed by its determination by slurry photochemical vapor generation atomic fluorescence spectrometry

We have developed a method for the determination of trace levels of total selenium in water samples. It integrates preconcentration, in-situ photoreduction and slurry photochemical vapor generation using TiO₂ nanoparticles, and the determination of total selenium by AFS. The Se(IV) and Se(VI) species were adsorbed on a slurry of TiO₂ nanoparticles which then were exposed to UV irradiation in the presence of formic acid to form volatile selenium species. The detection limits were improved 17-fold compared to hydride generation and 56-fold compared to photochemical vapor generation, both without any preconcentration. No significant difference was found in the limits of detection (LODs) for Se(IV) and Se(VI). The LOD is as low as 0.8 ng L^?1, the precision is better than 4.5 % (at a level of 0.1 μg L^?1 of selenium). The method gave good recoveries when applied to the determination of total selenium in a certified tissue reference material (DORM-3) and in spiked drinking water and wastewater samples containing high concentrations of transition and noble metal ions. It also excels by very low LODs, a significant enhancement of sample throughput, reduced reagent consumption and sample loss, and minimal interference by transition and noble metal ions.

Emulsification based dispersive liquid microextraction prior to flame atomic absorption spectrometry for the sensitive determination of Cd(II) in water samples

We report on the application of emulsification-based dispersive liquid microextraction (EB-DLME) to the preconcentration of Cd(II). This procedure not only possesses all the advantages of routine DLLME, but also results in a more stable cloudy state which is particularly useful when coupling it to FAAS. In EB-DLME, appropriate amounts of the extraction solvent (a solution of dithizone in chloroform) and an aqueous solution of sodium dodecyl sulfate (SDS; acting as a disperser) are injected into the samples. A stable cloudy microemulsion is formed and Cd(II) ion is extracted by chelation. After phase separation, the sedimented phase is subjected to FAAS. Under optimized conditions, the calibration curve for Cd(II) is linear in the range from 0.1 to 25 μg L^?1, the limit of detection (at S/N?=?3) is 30 pg L^?1, the relative standard deviations for seven replicate analyses (at 0.56 μg L^?1 of Cd(II)) is 4.6 %, and the enrichment factor is 151. EB-DLME in our opinion is a simple, efficient and rapid method for the preconcentration of Cd(II) (and most likely of many other ions) prior to FAAS determination.

Preconcentration of trace amounts of formaldehyde from water, biological and food samples using an efficient nanosized solid phase, and its determination by a novel kinetic method

This work presents a sensitive method for the determination of formaldehyde. It is based on the use of modified alumina nanoparticles for its preconcentration, this followed by a new and simple catalytic kinetic method for its determination. Alumina nanoparticles were chemically modified by immobilization of 2,4-dinitrophenylhydrazine via sodium dodecyl sulfate as a surfactant. The formaldehyde retained on the modified adsorbent was then desorbed and determined via its catalytic effect on the oxidation of thionine by bromate ion. Factors affecting the preconcentration and determination of formaldehyde have been investigated. Formaldehyde can be detected in the range from 0.05 to 38.75 μg L^?1, and no serious interferences have been observed. The method has been successfully applied to the quantitation of formaldehyde in water, food, and certain biological samples.

A magnetic metal-organic framework as a new sorbent for solid-phase extraction of copper(II), and its determination by electrothermal AAS

We report on the synthesis of Fe₃O₄-functionalized metal-organic framework (m-MOF) composite from Zn(II) and 2-aminoterephthalic acid by a hydrothermal reaction. The magnetic composite is iso-reticular and was characterized by FTIR, X-ray diffraction, SEM, magnetization, and TGA. The m-MOF was then applied as a sorbent for the solid-phase extraction of trace levels of copper ions with subsequent quantification by electrothermal AAS. The amount of sorbent applied, the pH of the sample solution, extraction time, eluent concentration and volume, and desorption time were optimized. Under the optimum conditions, the enrichment factor is 50, and the sorption capacity of the material is 2.4 mg g^?1. The calibration plot is linear over the 0.1 to 10 μg L^?1 Cu(II) concentration range, the relative standard deviation is 0.4 % at a level of 0.1 μg L^?1 (for n?=?10), and the detection limit is as low as 73 ng L^?1. We consider this magnetic MOF composite to be a promising and highly efficient material for the preconcentration of metal ions.

Polythiophene-coated Fe3O4 nanoparticles as a selective adsorbent for magnetic solid-phase extraction of silver(I), gold(III), copper(II) and palladium(II)

We have developed a fast method for sensitive extraction and determination of the metal ions silver(I), gold(III), copper(II) and palladium(II). Fe₃O₄ magnetic nanoparticles were modified with polythiophene and used for extraction the metal ions without a chelating agent. Following extraction, the ions were determined by flow injection inductively coupled plasma optical emission spectrometry. The influence of sample pH, type and volume of eluent, amount of adsorbent, sample volume and time of adsorption and desorption were optimized. Under the optimum conditions, the calibration plots are linear in the 0.75 to 100 μg L^?1 concentration range (R²?>?0.998), limits of detection in the range from 0.2 to 2.0 μg L^?1, and enhancement factors in the range from 70 to 129. Precisions, expressed as relative standard deviations, are lower than 4.2 %. The applicability of the method was demonstrated by the successful analysis of tap water, mineral water, and river water.

Solid-phase preconcentration of cadmium(II) using amino-functionalized magnetic-core silica-shell nanoparticles, and its determination by hydride generation atomic fluorescence spectrometry

We report on the synthesis and evaluation of aminated-CoFe₂O₄/SiO₂ nanoparticles that can serve as a selective solid-phase sorbent for the extraction of cadmium ion. The nanoparticles consist of a magnetic CoFe₂O₄ core and an amino-modified silica shell. They can efficiently extract cadmium(II) ion and then can be isolated from the sample solution due to the magnetic nature of the core. The effects of the experimental conditions on the extraction process were optimized. Cadmium was then quantified by hydride generation atomic fluorescence spectrometry. The resulting calibration curve is linear in the concentration range of 0.01–10 μg?L^?1, the instrumental detection limits (3σ) is 3.15 ng?L^?1 and the relative standard deviation is 4.9 % at the 1.0 μg?L^?1 level (for n?=?11). The enrichment factor is 50 (for 50 mL samples), and the adsorbent can be used for at least 45 cycles of preconcentration and elution. The method was applied to the determination of cadmium in environmental water samples, and successfully validated by analyzing two certified reference materials.

Ligandless temperature-controlled ionic liquid-phase microextraction of lead(II) ion prior to its determination by FAAS

We describe the application of temperature-controlled ionic liquid based microextraction (TC-IL-ME) of lead(II) ion. The method does not require the use of an organic solvent or a ligand. Rather, the IL is directly added to the aqueous sample containing Pb(II) in a centrifuge tube, and the mixture is heated to 80 °C for 4 min. After cooling at 0 °C, the solution turns cludy due to the formation of fine droplets of the IL containing Pb(II). The IL is separated by centrifugation, acidified, and directly submitted to FAAS by microinjection. The effects of pH value, volume of IL, extraction time, temperature, sample volume and matrix were optimized to result in a preconcentration factor of 30, a detection limit of 5.8 μg L^?1, and a limit of quantification of 19.3 μg L^?1. The method was validated by analyzing a certified reference material (NCSZC81002B; hair). A recovery test performed with spiked samples gave values between 102 % and 105 %. The method was also used to determine Pb(II) in hair samples.

Speciation of Cr(III) and Cr(VI) ions using a β-cyclodextrin-crosslinked polymer micro-column and graphite furnace atomic absorption spectrometry

A sensitive and selective method for the speciation of Cr(III) and Cr(VI) in water samples was developed. It is based on the selective binding of the complex formed between Cr(III) and 4-(2-pyridylazo)resorcinol adsorbed on a cross-linked polymer modified with β-cyclodextrin and placed in a micro-column. Graphite furnace atomic absorption spectrometry (GFAAS) was used to quantify chromium. Cr(VI) ion is not adsorbed but remains in the aqueous sample phase. Thus, an in-situ separation of Cr(VI) and Cr(III) is accomplished. The concentration of Cr (VI) was calculated by subtracting the value for Cr(III) from that for total chromium. Under optimum conditions, the limit of detection of Cr(III) is 0.056 μg L^?1, and the linear range is from 2.0 to 160.0 μg L^?1. The relative standard deviation is 2.5% (n?=?3, at 30.0 μg L^?1). The preconcentration factor is 25. The method was applied to the speciation of chromium in water samples, and recoveries in spiked real samples range from 101.9% to 104.5%. A reference water sample (GBW(E)080642) also was analyzed, and the results were in good agreement with the certified values.

Highly sensitive SERS probe for mercury(II) using cyclodextrin-protected silver nanoparticles functionalized with methimazole

We have developed a surface-enhanced Raman scattering (SERS) probe for the determination of mercury(II) using methimazole-functionalized and cyclodextrin-coated silver nanoparticles (AgNPs). These AgNPs in pH 10 solution containing sodium chloride exhibit strong SERS at 502 cm^?1. Its intensity strongly decreases in the presence of Hg(II). This effect serves as the basis for a new method for the rapid, fast and selective determination of trace Hg(II). The analytical range is from 0.50 μg L^?1 to 150 μg L^?1, and the limit of detection is 0.10 μg L^?1. The influence of 11 metal ions commonly encountered in environmental water samples was found to be quite small. The method was applied to the determination of Hg(II) in spiked water samples and gave recoveries ranging from 98.5 to 105.2 % and with relative standard deviations of <3.5 % (n?=?5). The total analysis time is <10 min for a single sample.

Comparison of the performance of different modified graphene oxide nanosheets for the extraction of Pb(II) and Cd(II) from natural samples

Graphene nanosheets were modified with amino groups and the resulting material was used as a sorbent for the extraction of cadmium and lead ions. The nanosheets were characterized by IR spectroscopy, transmission electron microscopy, thermal gravimetric analysis and elemental analysis. The effects of sample pH, eluent parameters (type, concentration and volume of eluent), flow rates (of both sample and eluent), and of a variety of other ions on the efficiency of the extraction of Cd(II) and Pb(II) were optimized. Following solid phase extraction, the elements were determined by FAAS. The limits of detection are <0.9 μg L^?1 for Pb(II) and <5 ng L^?1 for Cd(II). The relative standard deviations are <2.2 %. The method was validated by analyzing several certified reference materials and was then used for Pb(II) and Cd(II) determination in natural waters and vegetables.

Rapid determination of melamine in milk and milk powder by surface-enhanced Raman spectroscopy and using cyclodextrin-decorated silver nanoparticles

We have synthesized silver nanoparticles (AgNPs) decorated with α-cyclodextrin (CD) by using the traditional silver mirror reaction in the presence of CD. The CD-AgNPs were used as substrate in surface-enhanced Raman spectroscopy (SERS) for determining melamine. The intensity of the Raman band of melamine at 704 cm^?1 was used to determine melamine in milk and milk powder. The use of CD-AgNPs as the SERS substrate rather than classical silver nanoparticles makes the method more sensitive in giving an enhancement by a factor of up to?~?10⁶ in scattering efficiency. The effects of the volume of solutions (of CD-AgNPs, NaCl, NaOH, melamine) and of mixing time were optimized. The standard addition method was employed for quantitative analysis. The correlation coefficient of the calibration plot is 0.9995, and the limit of detection is 3.0 μg L^?1. The method was successfully applied to the determination of melamine in milk and milk powder, with relative standard deviations of <10 % and recoveries between 89 and 104 %.

Preconcentration of ultra-trace amounts of iron and antimony using ion pair solid phase extraction with modified multi-walled carbon nanotubes

Ion pair solid phase extraction was applied to the simultaneous preconcentration of iron and antimony. The ion pairs consisting of FeCl₄ ^? or SbCl₄ ^? anions and the benzyldimethyltetradecyl ammonium cation were formed on the surface of multi-walled carbon nanotubes, then eluted with nitric acid, and the elements finally quantified by ETAAS. The adsorption capacities of the impregnated MWCNTs are 9.2 mg g^?1 for iron and 27.5 mg g^?1 for antimony. The following analytical figures of merit were determined for iron and antimony, respectively: Enrichment factors of 210 and 230, assay precisions of ±5.3 % and ±4.8 %, linear calibration plots from 0.7 to 9.4 and 13.0 to 190 ng L^?1, and detection limits of 0.17 and 3.5 ng L^?1. The method was applied to the determination of iron and antimony in human hair, synthetic sample, and to the certified reference materials gold ore (MA-1b) and trace elements in water (SRM 1643d).

Determination of Se(IV) using solidified floating organic drop microextraction coupled to ultrasound-assisted back-extraction and hydride generation atomic fluorescence spectrometry

A method is presented for matrix separation, preconcentration and determination by hydride generation atomic fluorescence spectrometry of trace amounts of Se(IV). It is based on solidified floating drops of 1-undecanol that are capable of extracting the target analyte after chelation with a water soluble ligand and subsequent ultrasound-assisted back-extraction into a aqueous solution. Hydride generation was then accomplished by reaction with a solution of sodium borohydride. Under optimized conditions, an enrichment factor of 15 and a linear calibration plot in the range from 0.01 to 5.0 μg L^?1 were achieved using a 10.0 mL sample. The detection limit (3σ) is 7.0 ng L^?1, and the relative standard deviation (RSD) is 2.1% at 1.0 μg L^?1 (n?=?11). The method was applied to determination of Se(IV) in different real water samples through recovery experiments and subsequently validated against two certified reference materials.

Electrochemically controlled solid-phase micro-extraction of proline using a nanostructured film of polypyrrole, and its determination by ion mobility spectrometry

We report on a fast, simple and accurate method for the determination of proline in urine samples by employing a nanostructured film of conducting polypyrrole for electrochemically controlled solid-phase microextraction, and ion mobility spectrometry (IMS) for detection. This method has the advantages of simple sample preparation and a sensitivity of IMS to proline that is higher than that for other amino acids. The calibration curve is linear in the range of 0.5–60 μg L^?1 (4–521 nmol L^?1), and the detection limit is 0.2 μg L^?1. The electrochemical potentials for uptake and release were optimized. The method was successfully applied to the clean-up and quantitation of trace amounts of proline in urine samples.

Determination of chlorobenzenes in water samples based on fully automated microextraction by packed sorbent coupled with programmed temperature vaporization–gas chromatography–mass spectrometry

A fully automated method consisting of microextraction by packed sorbent (MEPS) coupled directly to programmed temperature vaporizer–gas chromatography–mass spectrometry (PTV–GC–MS) has been developed to determine the 12 chlorobenzene congeners (chlorobenzene; 1,2-, 1,3-, and 1,4-dichlorobenzene; 1,2,3-, 1,2,4-, and 1,3,5-trichlorobenzene; 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-tetrachlorobenzene; pentachlorobenzene; and hexachlorobenzene) in water samples. The effects of the variables on MEPS extraction, using a C18 sorbent, and the instrumental PTV conditions were studied. The internal standard 1,4-dichlorobenzene d4 was used as a surrogate. The proposed method afforded good reproducibility, with relative standard deviations (RSD %) lower than 12 %. The limits of detection varied between 0.0003 μg L^?1 for 1,2,3,4-tetrachlorobenzene and 0.07 μg L^?1 for 1,3- and 1,4-dichlorobenzene, while those of quantification varied between 0.001 μg L^?1 and 0.2 μg L^?1 for the same compounds. Accuracy of the proposed method was confirmed by applying it to the determination of chlorobenzenes in different spiked water samples, including river, reservoir, and effluent wastewater.

Ultra-sensitive spectrophotometric determination of nickel after complexation and membrane filtration

We report on a simple, sensitive and selective method for the spectrophotometric determination of Ni²⁺ in water samples. The analyte ions were collected on a membrane filter in the form of their red complex with 1-(2-pyridylazo)-2-naphthol (PAN), and the absorption spectra of the colored membrane filters were acquired. Effects of pH value, sample volume, and amount of PAN were examined in order to optimize sensitivity. The interference by common other ions was eliminated using appropriate masking agents. The absorbance is linearly related to the concentration of Ni²⁺ in the ranges from 0.3 to 1.5 μg L^?1, and from 2 to 10 μg L^?1, respectively, the correlation coefficients (R²) being 0.9871 and 0.9954. Under the optimal conditions, the detection limit is 0.1 μg L^?1. The recoveries in case of spiked samples are between 95.0% and 101.5%, and the relative standard deviations range from 2.8% to 4.1%.

Sensitive detection of trace hemoglobin using fluorescence method based on functionalized quantum dots

The fluorescence quenching of quantum dots by hemoglobin has been demonstrated to depend on surface functionalization, and this property has been utilized to construct a novel fluorescent method for rapid, sensitive, and selective detection of trace hemoglobin in urine at microgram level. This method shows low interference and high selectivity for hemoglobin with a limit of detection of 4.3 μg L^?1 in water and 66.1 μg L^?1 in urine, which are lower than those of currently used methods in labs and clinics. Spike and recovery tests in raw, acidified, and alkalized urine samples exhibit good recovery rates for the spiked concentrations close to the limit of detection.

Preconcentration of trace lead via formation of the bis(2,2-bipyridyl) complex and its adsorption on oxidized multiwalled carbon nanotubes

A solid phase extraction method is presented for the preconcentration of trace lead ions on oxidized multiwalled carbon nanotubes (ox-MWCNTs). In the first step, the cationic Pb(II) complex of 2,2-bipyridyl is formed which, in a second step, is adsorbed on ox-MWCNTs mainly due to electrostatic and van der Waals interactions. The Pb(II) ions were then eluted with dilute nitric acid and quantified by FAAS. The effects of pH value, mass of sorbent, concentration of 2,2-bipyridyl, stirring time, of type, concentration and volume of eluent, of eluent flow rate and sample volume were examined. Most other ions do not affect the recovery of Pb(II). The limits of detection are 240 and 60 ng L^?1 for sample volumes of 100 and 400 mL, respectively. The recovery and relative standard deviation are >95 % and 2.4 %, respectively. Other figures of merit include a preconcentration factor of 160 and a maximum adsorption capacity of 165 mg g^?1. The method was successfully applied to the determination of Pb(II) in spiked tap water samples. The accuracy of the method was verified by correctly analyzing a certified reference material (NCS ZC85006; lead in tomatoes).

A highly sensitive caffeine immunoassay based on a monoclonal antibody

A new immunoassay has been developed based on a commercially available anti-caffeine monoclonal antibody and a de novo synthesized tracer, using horseradish peroxidase and UV–visible detection. Caffeine, which is frequently found in surface waters, can be quantified with a relative error lower than 20% for concentrations above 0.025 μg L^?1 (limit of quantitation, direct analysis). The limit of detection is 0.001 μg L^?1 and can be reduced by solid-phase extraction (SPE). Moreover, with minor adaptations, the assay can be used to quantify caffeine in several beverages, shampoo, and caffeine tablets. The results obtained by ELISA correlate well with those from liquid chromatography–tandem mass spectrometry (LC–MS–MS) for the tested matrices. Several surface waters from Berlin were analysed and all tested positive for caffeine, with concentrations higher than 0.030 μg L^?1. In one run 66 samples can be analysed within 2 h.