Determination of lead and manganese in biological samples and sediment using slurry sampling and flame atomic absorption spectrometry

A procedure was developed for the determination of lead (Pb) and manganese (Mn) using slurry sampling. The two elements were detected using flame atomic absorption spectrometry with a slotted tube atom trap. Slurries were prepared by adding nitric acid solution (0.30%, w/v) to a powdered sample (0.10 g). After homogenization by ultrasonic bath for 15 min, the slurries were introduced directly into the detection equipment. Some conditions of the procedure were evaluated, such as acid concentration, presence of surfactants, and sonication time. Under optimized conditions, the LODs and LOQs achieved were 0.8 and 2.6 microg/g for Pb and 0.5 and 1.6 microg/g for Mn, respectively. The precision obtained varied between 3.1 and 5.8% (Mn), and 2.6 and 5.4% (Pb) for slurries of shrimp and sediment. The analytical curves were established using aqueous standards in nitric acid solutions. The accuracy of the method was assessed through the determination of Pb and Mn in the following certified reference materials: ERM-CE 278 (mussel tissue), CRM 397 (human hair), and SRM 1646a (estuarine sediment). The proposed procedure was successfully applied to the determination of Pb and Mn in six samples of shrimp powder, seasoning, and river sediment. The levels of Mn detected varied from 2.2 to 71.3 microg/g; Pb was detected in only one sediment sample (4.3 microg/g).     

Solid-phase Microextraction of Volatile Polar Compounds in Water

A method was developed for the analysis of volatile polar compounds in a water matrix using open cap vials Solid Phase Micro-Extraction (SPME) and Capillary Gas Chromatography (CGC). Both SPME techniques – direct sampling and headspace – were tested. Optimization of experimental conditions – exposure time, desorption time, with headspace SPME in addition the influence of the temperature and ionic strength of the sample solution on compound sorption, and finally GC response – were investigated. The analytes were extracted by directly immersing the 85 μm polyacrylate fiber in the aqueous sample or in the headspace. The linear range of the preconcentration process and the precision were examined. The amount of polar analytes sorbed on the fiber was determined and was found to be concentration dependent; it amounted to 0.014–0.64% in the concentration range of 0.00425–425 ppm studied in aqueous solution for direct sampling SPME and to 0.011–2.76% for solutions of concentration 0.0425–255 ppm for headspace SPME. The limits of determination were ascertained. Headspace SPME was applied to the analysis of real-life samples.     

Determination of lead in fish samples by slurry sampling electrothermal atomic absorption spectrometry

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry (USS-ETAAS) was been applied to the determination of lead in several fish samples. The influences of instrument operating conditions and slurry preparation on the signal were examined. Palladium and ammonium nitrate were used as the modifier to improve the signal. Since the sensitivity to lead in various fish slurries and aqueous solutions was different, the standard additions method was used for the determination of lead in these fish samples. The method was applied to the determination of lead in dogfish muscle reference material (DORM-2) and a swordfish muscle sample purchased from the local market. The analysis results agreed with the reference value. The accuracy was better than 6%. The precision between sample replicates was better than 16% with the USS-ETAAS method. The detection limit of lead estimated from standard additions curve was about 0.053-0.058 microgram g-1 in different samples.     

Improvement of extraction capability of magnetic molecularly imprinted polymer beads in aqueous media via dual-phase solvent system

In this study, a novel and simple dual-phase solvent system for the improvement of extraction capability of magnetic molecularly imprinted polymer (MIP) beads in aqueous sample was proposed. The method integrated MIP extraction and micro-liquid-liquid extraction (micro-LLE) into only one step. A magnetic MIP beads using atrazine as template was synthesized, and was applied to aqueous media by adding micro-volume of n-hexane to form a co-extraction system. The magnetic MIP beads preferred to suspend in the organic phase, which shielded them from the disturbance of water molecule. The target analytes in the water sample was extracted into the organic phase by micro-LLE and then further bound to the solid-phase of magnetic MIP beads. The beads specificity was significantly improved with the imprinting efficiency of template increasing from 0.5 to 4.4, as compared with that in pure aqueous media. The extraction capacity, equilibration process and cross-selectivity of the MIP dual-phase solvent extraction system were investigated.The proposed method coupled with high-performance liquid chromatography was applied to the analysis of atrazine, simazine, propazine, simetryn, prometryne, ametryn and terbutryn in complicated sample such as tomato, strawberry juice and milk. The method is selective, sensitive and low organic solvent-consuming, and has potential to broaden the range of MIP application in biological and environmental sample.     

Atomic and molecular spectra of vapors evolved in a graphite furnace. Part 5: gallium,indium and thallium nitrates and chlorides

The vaporization behavior and vapor spectra of Ga, In and Tl nitrates and chlorides in the tube furnace was investigated using an UV spectrometer with CCD detector. Fifty spectra in the wavelength range of 200–475 nm were collected in each experiment during the vaporization step, with temperature increase from 473 to 2673 K. The vaporization patterns were compared for the pyrocoated, non-pyrocoated graphite tubes, and Ta-lined tubes. Nitrate and chloride aqueous solutions and chloride slurries in chloroform were used to distinguish the impact of hydrolysis on the vaporization behavior of these chlorides. The spectra of oxygen and chlorine containing molecules, presumably of suboxides, chlorides and dichlorides were identified upon variation of the experimental conditions. The release of suboxide vapors due to the reduction of oxides by carbon was promoted after the decomposition of nitrates. The presence of other elements on the vaporization surface, or the isolation of the sample from the graphite surface by Ta-lining, impeded the vapor release and reduced the intensity of molecular bands. Adsorption of chlorine onto graphite caused a decrease of chloride and dichloride bands. The suboxide bands were observed in the spectra of Ga and In chlorides introduced in the tube as aqueous solutions, due to partial hydrolysis.     

Low-temperature migration of lead,thallium, and selenium onto a palladium modifier during the analysis of solutions and slurries by electrothermal atomic absorption spectrometry

A palladium/magnesium modifier, when premixed with solutions or slurries, stabilizes many analytes to higher pyrolysis and atomization temperatures. Similar behavior was seen when analyte and modifier were physically separated by pipetting them onto opposite sides of a L'vov platform. During the pyrolysis stage of the furnace heating cycle, lead, thallium, and selenium migrated from the platform surface and interacted with the modifier on the opposite side. This behavior explains the consistent stabilization by palladium of analytes in slurry samples. Under conventional operating conditions the modifier is premixed with the slurry, and on drying in the furnace, the analyte and modifier may not make close contact. However, this is unimportant since the analyte will migrate to the palladium on heating. Then the rate-limiting step leading to atomization is the release of analyte from palladium, and it is the same for solutions and slurries. Therefore, aqueous standards can be used for slurry analysis.     

One-step synthesis of agarose coated magnetic nanoparticles and their application in the solid phase extraction of Pd(II) using a new magnetic field agitation device

A magnetic solid phase extraction method based on agarose coated magnetic nanoparticles)ACMNPs(coupled to a new magnetic field agitation (MFA) device was developed and investigated for the separation, preconcentration and determination of Pd(II) in aqueous solutions. For the first time, the formation of the nanoparticles and their encapsulation in agarose micro-flakes was conducted in a single step. For this purpose, preparation of the magnetic iron oxide nanoparticles was performed in an alkaline agarose solution. The sizes of Fe₃O₄ nanoparticles and agarose micro-flakes were 10–14 nm and 90–130 μm, respectively. The nanomagnetic agarose particles were functionalized by iminodiacetic acid and subjected to magnetic field agitation in the MFA device. The influence of different analytical parameters such as pH, ionic strength, type and volume of desorption solvent and amount of the adsorbent on the preconcentration of Pd(II) were investigated. Eight replicated analysis at the optimized conditions, resulted in a recovery of 94.1% with an RSD of 5.2% for Pd(II). The detection limit of the method (3σ) was 47 ng L⁻¹ for the analyte. The method was successfully applied to the determination of Pd(II) in natural water samples.     

A novel open-tubular capillary electrochromatography with magnetic nanoparticle coating as stationary phase

A novel open‐tubular capillary electrochromatography (OT‐CEC) with modified core/shell magnetic nanoparticles coating as stationary phase was introduced using external magnetic force to fix magnetic nanoparticles. The magnetic nanoparticles coating inside the capillary columns could be easily regenerated by removing and re‐applying the external magnetic field. Magnetic field intensity, concentration and flow rate of nanoparticles suspension were investigated to achieve simple and stable preparation. Mixture of five organic acids was used as the marker sample to evaluate the OT‐CEC system, and the relative column efficiency of anthranilic acid reaches 220 000 plates/m. The excellent within‐column and between‐column repeatability has been testified with the RSDs of retention time of less than 1.51 and 5.29%, respectively. The aqueous extract of rhizoma gastrodiae was analyzed by the OT‐CEC system, and 23 peaks were eluted in 30 min. Compared with conventional open‐tubular capillary column, this new system shows faster separation speed and higher column efficiency from the larger surface area of nanoparticles. It has great potential in the method development for the analysis of complex samples, since magnetic coating can effectively prolong the column life by expediently replacing stationary phase to eliminate the pollution or irreversible adsorption.     

Affinity-based mass spectrometry using magnetic iron oxide particles as the matrix and concentrating probes for SALDI MS analysis of peptides and proteins

Silane-immobilized magnetic iron oxide particles were used as the assisting material in surface-assisted laser desorption/ionization (SALDI) mass spectrometric analysis. This approach can be used to analyze small proteins and peptides. The upper detectable mass range is approximately 16 kDa. The detection limit for peptides is about 20 fmol. Silanized iron oxide particles with negatively charged functionalities can also be used as the affinity probes to selectively trap oppositely charged species from sample solutions by adjusting the pH of the solution. A tryptic digest product of cytochrome C at a concentration as low as 10 nM can be enriched by the particles and directly analyzed by iron oxide SALDI MS without the need for elution steps. Affinity-based mass spectrometry using the bifunctional silanized magnetic iron oxide particles as the SALDI matrix and concentrating probe is demonstrated in this study.     

Injection of large volumes of aqueous solutions in capillary supercritical fluid chromatography and sample preconcentration by multiple injections

The possibility of using water or aqueous solutions as the solvent in capillary supercritical fluid chromatography was successfully demonstrated. Large volumes (up to 1 μl) of aqueous sample solutions were injected. Sample preconcentration was performed by means of multiple injections of aqueous sample solutions. The solutes were trapped at the beginning of the column at low density (high temperature and low pressure) and eluted using a density programme. The method can be applied to trace analysis. It proved to be linear in the range examined. Flame ionization detection was used for the studies. As this technique is not sensitive to water, no solvent peak appears, which may be an advantage for certain applications. The influence of water injections on the column performance and the reproducibility of injection was investigated.     

Magnetic molecularly imprinted composite for the selective solid‐phase extraction of p‐aminosalicylic acid followed by high‐performance liquid chromatography with ultraviolet detection

A new method for the selective extraction of p‐aminosalicylic acid from aqueous and urine samples has been developed using magnetic molecularly imprinted polymer nanoparticles before determination by high‐performance liquid chromatography. The Fe₃O₄ nanoparticles were first prepared through the chemical coprecipitation of Fe²⁺ and Fe³⁺ and then coated with a vinyl shell. Subsequently, a layer of molecularly imprinted polymers was grafted onto the vinyl‐modified magnetic nanoparticles by precipitation polymerization. FTIR spectroscopy, scanning electron microscopy, vibrating sample magnetometry, and thermogravimetric analysis were applied to characterize the sorbent properties. Moreover, the predominant parameters affecting the magnetic solid phase extraction such as sample pH, sorption and elution times, the amount of sorbent, and composition and volume of eluent were investigated thoroughly. The maximum sorption capacity of the imprinted polymer toward p‐aminosalicylic acid was 70.9 mg/g, which is 4.5 times higher than that of the magnetic nonimprinted polymer. The magnetic molecularly imprinted polymer nanoparticles were applied for the selective extraction of p‐aminosalicylic acid from aqueous and urine samples and satisfactory results were achieved. The results illustrate that magnetic molecularly imprinted polymer nanoparticles have a great potential in the extraction of p‐aminosalicylic acid from environmental and biological matrices.     

Determination of impurities in magnesium niobate by slurry introduction axially viewed inductively coupled plasma optical emission spectrometry

A simple preparation scheme is described for the quantitative analysis of a magnesium niobate sample using slurry introduction axially viewed inductively coupled plasma optical emission spectrometry. Relationships between the stability of slurries and the conditions, such as particle size, pH, dispersant and amount of dispersant, were investigated experimentally. The MgNb₂O₆ slurry sample was prepared by adding the dispersant sodium polyacrylate and agitation in an ultrasonic bath to ensure good dispersion. Under optimization of pH and amount of dispersant, an analysis of minor and trace impurities (Ba, Ca, Cr, Cu, Fe, Mn, Ni, Pb) in magnesium niobate was accomplished. Applying a paired t test, we showed that the results were in agreement at a 95% confidence level with the reference values obtained by a fusion method for a magnesium niobate sample, which verified that the calibration curves could be established by aqueous standards. Analytical results demonstrate that the factors that affected the accuracy of determination for MgNb₂O₆ are mainly the particle size of the sample and the stability of slurry.     

Analysis of cement slurries by inductively coupled plasma optical emission spectrometry with axial viewing

The feasibility of Portland cement analysis by introduction of slurries in an inductively coupled plasma optical emission spectrometer (ICP-OES) with axial viewing has been evaluated. After a fast manual grinding of the cement samples, owing to the pulverized state of this material, 0.1% m/v slurries were prepared in 1% v/v HCl. The calibration was performed adopting two strategies: one based on slurries prepared from different masses (50, 75, 100 and 125 mg) of a Portland cement standard reference material (NIST SRM 1881), and the other one based on aqueous reference solutions. A complete analysis of cement for major (Al, Ca, Fe, Mg and Si), minor and trace elements (Mn, P, S, Sr and Ti) was accomplished. Both strategies led to accurate results for commercial Portland cement samples, except for Si and Ti, for which the calibration with aqueous reference solutions resulted in low values. Applying a paired t-test it was shown that most results were in agreement at a 95% confidence level with a conventional fusion decomposition procedure. The ICP-OES with axial viewing and end-on gas configuration for removal of the recombination plasma zone was effective for cement slurry analysis without any undesirable particle deposition in the pre-optics interface and without severe spectral interferences.     

Rapid slurry analysis of solid coal and fly ash samples

Coal and coal fly ash samples were analyzed as solid slurries. These preliminary experiments used fast sampling STPF procedures which omitted the pyrolysis step and the matrix modifier. The experiments also used an ultrasonic mixing device that automatically stirred the suspension just before the autosampler probe withdrew the aliquot which it would dispense onto the platform. The combination of these techniques made it possible to reduce the analytical time to less than 1 min per sample. Simple aqueous standards were used for calibration. The NIST SRM 1633a Coal Fly Ash was successfully analyzed for As, Pb and Tl, with results for Se in this material that suggested that more work was required to gain confidence in the determination. The SRM 1632a Coal was successfully analyzed for As and Pb. The methods were the same for both materials. A few mg of the dry solid powder was weighed directly into the autosampler cup followed by a weighed amount (about 1.5 ml) of suspending diluent The characteristic mass was calculated from several aliquots of simple aqueous standards and this value was used to calculate the amount of analyte delivered to the furnace. In the work reported here the detection limits for the elements determined were about 0.5–1 μg/g in the solid sample. With further experience these limits may be improved. The precision for replicates of slurries from the same cup varied from 2 to 10% depending upon the amount of solid sample delivered to the furnace.     

Synthesis and characterization of CoFe2O4@SiO2-polyethyleneimine magnetic nanoparticle and its application for ultrasonic-assisted removal of disulfine blue dye from aqueous solution

In the present work, a simple synthesis approach was applied for the fabrication of CoFe₂O₄@SiO₂-polyethyleneimine magnetic nanoparticles as an effective sorbent for ultrasonic-assisted removal of disulfine blue dye from an aqueous solution. For identification and characterization of prepared sorbent, different analysis including Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), Vibrating sample magnetometer (VSM), Energy dispersive X-ray analysis (EDX) and Transmission electron microscopy (TEM) were applied. The effect of effective parameters on the removal of disulfine blue such as pH, sorbent mass, ultrasonic time and disulfine blue concentration were also assessed. The optimum values for investigated parameters were achieved to be as follows: pH of 5.0, sorbent mass of 0.015 g, ultrasonic time of 5.0 min and disulfine blue concentration of 10.0 mg L⁻¹. Different isotherm and kinetic models were used for the evaluation of isotherm and kinetic of adsorption. Results showed that the Langmuir isotherm model was better than other isotherm models as well as the second-order equation model was selected as a kinetic model. The maximum adsorption capacity of the proposed magnetic sorbent was achieved to be 110.0 mg g⁻¹ which shows the applicability of proposed sorbent for removal of disulfine blue dye from aqueous solution.     

Potential of capillary-column-switching liquid chromatography-tandem mass spectrometry for the quantitative trace analysis of small molecules. Application to the on-line screening of drugs in water

We have investigated the potential of capillary-column-switching liquid chromatography coupled to tandem mass spectrometry (cLC-MS-MS) for the quantitative on-line trace analysis of target compounds in aqueous solutions. The technical design of the nano-scale cLC system developed at our Institute for peptide and protein identification has been tested and evaluated for the direct trace analysis of drugs in water samples. Sulphametoxazole, bezafibrate, metoprolol, carbamazepine and bisoprolol occurring frequently in Dutch waters, were selected as test compounds. Adequate conditions for trapping, elution and MS-MS detection were investigated by employing laboratory made 200 microm i.d. capillary columns packed with 5 microm aqua C18 material. In the final cLC-MS-MS conditions, a 1 cm length trapping column and a 4 cm length analytical column were selected. Under these conditions, the target compounds could be directly determined in water down to a level of around 50 ng/l employing only 25 microl of water sample. Validation was done by recovery experiments in ground-, surface- and drinking-water matrices as well as by the analysis of water samples with incurred residues and previously analyzed with a conventional procedure involving off-line solid-phase extraction and narrow-bore LC with MS-MS detection. The new methodology provided recoveries (50-500 ng/l level) between 50 and 114% with RSDs (n = 3, each level) below 20% for most of the compounds. Despite the somewhat less analytical performance in comparison to the conventional procedure, the on-line approach of the new methodology is very suitable for screening of drugs in aqueous samples.     

Fast and sensitive trace metal analysis in aqueous solutions by laser-induced breakdown spectroscopy using wood slice substrates

To perform fast and sensitive trace metal analysis in aqueous solutions by laser-induced breakdown spectroscopy (LIBS) based on only one single-pulse laser system, a wood slice has been used as a liquid absorber to transform liquid sample analysis to solid sample analysis using LIBS. High detection sensitivity and good reproducibility can be achieved with this approach. Calibration curves for five metal elements, Cr, Mn, Cu, Cd, and Pb under trace concentrations, have been obtained, and the limits of their detection were determined to be in the range of 0.029–0.59 mg L^− 1, 2–3 orders better than those obtained by directly analyzing liquid samples where the laser was focused on a liquid surface. The wood slice was very easy to handle and thus, the whole analysis process took only 4–5 min for each sample. This approach provides a more practical approach for fast and sensitive metal element analysis in aqueous solutions using LIBS, which is especially useful for monitoring toxic heavy metals in water.     

Feasibility of employing permanent chemical modifiers for the determination of cadmium in coal using slurry sampling electrothermal atomic absorption spectrometry

Iridium and ruthenium, alone and in combination with tungsten, thermally deposited on the platform of a transversely heated graphite tube, were investigated for their suitability as permanent chemical modifiers for the determination of cadmium in coal slurries by electrothermal atomic absorption spectrometry (ET AAS). The conventional mixed palladium and magnesium nitrates (Pd–Mg) modifiers, added in solution, were also investigated for comparison. The latter one showed the best performance for aqueous solutions, and the mixed W–Ir and W–Ru permanent modifiers had the lowest stabilizing power. All of the investigated modifiers lost some of their stabilizing power when coal slurries were investigated. The Pd–Mg modifier, pure Ir and Ru, and a mixture of 300 μg W + 200 μg Ir could stabilize Cd at least to a pyrolysis temperature of 600 °C, whereas all the other combinations already failed at temperatures above 500–550 °C. Additional investigations of the supernatant liquid of the slurries supported the assumption that the high acid concentration of the slurries and/or a concomitant leaching out of the coal might be responsible for the reduced stabilizing power of the modifiers. The maximum applicable pyrolysis temperature of 600 °C was not sufficient to reduce the background absorption to a manageable level in the majority of the coal samples. High-resolution continuum source ET AAS revealed that the continuous background absorption was exceeding values of A = 2, and was overlapping with the analyte signal. Although the latter technique could correct for this background absorption, some analyte was apparently lost with the rapidly vaporizing matrix so that the method could not be considered to be rugged. A characteristic mass of 1.0 pg and a detection limit of 0.6 ng g^− 1 could be obtained under these conditions.     

Photochemical decoration of silver nanoparticles on magnetic microspheres as substrates for the detection of adenine by surface-enhanced Raman scattering

In this work, silver nanoparticles (AgNPs) decorated magnetic microspheres (MMs) are prepared as surface-enhanced Raman scattering (SERS) substrate for the analysis of adenine in aqueous solutions. To prepare these substrates, magnetic particles were first synthesized by coprecipitation of Fe(II) and Fe(III) with ammonium hydroxide. A thin layer of cross-linked polymer was formed on these magnetic particles by polymerization through suspension of magnetic particles into a solution of divinyl benzene/methyl methacrylate. The resulted polymer protected magnetic particles are round in shape with a size of 80 μm in diameter. To form AgNPs on these MMs, photochemical reduction method was employed and the factors in photochemical reduction method were studied and optimized for the preparation of highly sensitive and stable AgNPs on MMs substrates (abbreviated as AgMMs substrates). By dispersing the AgMMs in aqueous samples, cylindrical magnet was used to attract the AgMMs for SERS detections. The observed enhancement factor of AgMMs reached 7 orders in magnitude for detection of adenine with a detection limit approaching to few hundreds of nanomolar.     

Sequential injection chemiluminescence immunoassay for nonionic surfactants by using magnetic microbeads

A rapid and sensitive immunoassay based on a sequential injection analysis (SIA) using magnetic microbeads for the determination of alkylphenol polyethoxylates (APnEOs) is described. An SIA system was constructed from a syringe pump, a switching valve, a flow-through type immunoreaction cell equipped with a photon counting unit and a neodymium magnet. Magnetic beads, to which an anti-APnEOs monoclonal antibody was immobilized, were used as a solid support in an immunoassay. The introduction, trapping and release of the magnetic beads in and from the immunoreaction cell were controlled by means of a neodymium magnet and adjusting the flow of a carrier solution. The immunoassay was based on an indirect competitive immunoreaction of an anti-APnEOs monoclonal antibody immobilized on the magnetic beads with a sample APnEOs and a horseradish peroxidase (HRP)-labeled APnEOs in the same sample solution, and was based on the subsequent chemiluminscence reaction of HRP on the magnetic microbeads with a luminol solution containing hydrogen peroxide and p-iodophenol. The anti-APnEOs antibody was immobilized on the magnetic microbeads by coupling the antibody with the magnetic beads after activation of a carboxylate moiety on the surface of the magnetic beads that had been coated with a polylactic acid film. The antibody immobilized magnetic beads were introduced in the immunoreaction cell and trapped in it by the neodymium magnet, which was equipped beneath the immunoreaction cell. An APnEOs sample solution containing the HRP-labeled APnEOs at a constant concentration, and a luminol solution containing hydrogen peroxide and p-iodophenol were sequentially introduced into the immunoreaction cell, according to an SIA programmed sequence. Chemiluminescence emission was monitored by means of a photon counting unit located at the upper side of the immunoreaction cell by collecting the emitted light with a lens. A typical sigmoidal calibration curve was obtained, when the logarithm of the concentration of APnEOs was plotted against the chemiluminescence intensity as the number of photons in 100 ms using standard APnEOs sample solutions at various concentrations (0–1000 ppb) under optimum conditions. The lower detection limit defined as IC₈₀ is ca 10 ppb. The time required for analysis is less than 15 min per a sample. The present method was successfully applied to the determination of APnEOs in river water.