High Percentage Of Recovery Research Articles

Development of membrane selective electrode for determination of the antipsychotic sulpiride in pharmaceuticals and urine.

The construction and electrochemical response characteristics of a poly(vinyl chloride) (PVC) membrane selective electrode for the determination of sulpiride (SPD) are described. The sensing membrane comprised an ion-exchanger formed between the protonated drug and tetraphenylborate (TPB-) in a plasticized PVC matrix. The influence of membrane composition on the electrode response was studied. The electrode showed a fast, stable and Nernstian response over a sulpiride concentration range (1 × 10-4 – 1 × 10-2 M) with a mean slope of 58.4 ± 0.9 mV dec-1 of concentration, a mean detection limit of 4.2 × 10-5 ± 1.2 × 10-5 M, a wide working pH range (2 – 8) and a fast response time (< 15 s). The electrode showed good selectivity towards sulpiride with respect to some inorganic and organic compounds. When the electrode was applied to the determination of sulpiride in pharmaceuticals and human urine, a high percentage of recovery was attained with no need for sample pretreatment procedures because of the lack of interfering matrix effects.

Summary of United States Human Proteome Organisation (HUPO) Symposium Entitled “Standardized Clinical Proteomics Platforms”

Summary of United States Human Proteome Organisation (HUPO) Symposium Entitled “Standardized Clinical Proteomics Platforms”

Production of vanillin from wheat bran hydrolyzates via microbial bioconversion

AbstractBACKGROUND: Wheat bran contains a large amount of ferulic acid, which can be released through enzymatic hydrolysis and bioconverted into vanillin. A previous study has shown that ferulic acid purification from bran carbohydrates with the Amberlite® IRA 95 resin allowed an increased vanillin molar yield. In this work, alternative ferulic acid recovery methods were proposed and the possibility of exploiting the residual carbohydrate‐rich water phase was explored.RESULTS: Ferulic acid was recovered from crude wheat bran hydrolyzate by: (i) a hydrophobic sorbent cartridge (ISOLUTE ENV+®): (ii) ethyl acetate extraction; and (iii) the resin previously employed. The highest recovery percentage (95%) was obtained with ISOLUTE ENV+®, which also allowed an interesting vanillin molar yield from ferulic acid bioconversion (75% from 0.5 mmol L−1 ferulic acid). The residual water phase was a good growth substrate for the microorganism operating the bioconversion. Cells grown on this matrix could efficiently bioconvert the recovered ferulic acid to vanillinCONCLUSION: The possibility of efficiently recovering ferulic acid from wheat bran hydrolyzates, bioconverting it into vanillin, and valorizing the sugar‐rich exhausted water fraction was demonstrated in this work. The approach allowed the production of a value‐added fine‐chemical from a food‐industry by‐product. Copyright © 2009 Society of Chemical Industry

The novel G10680A mutation is associated with complete penetrance of the LHON/T14484C family

We report the clinical and genetic characterization of a Chinese Leber′s hereditary optic neuropathy (LHON) family with complete penetrance and high percentage of recovery. Sequence analysis of the complete mitochondrial DNA revealed the presence of heteroplasmic ND6/T14484C mutation and 27 other variants, belonging to the East-Asian haplogroup B4b′d. Of those variants, a novel homoplasmic G10680A mutation substituted a threonine for a highly conserved alanine at ND4L amino acid 71, which was not found in unaffected family members and 100 normal controls. It indicated that G10680A may play a synergistic role with the primary mutation T14484C, leading to the complete penetrance of LHON in the presenting family. In addition, the other modifier factors including nuclear background, mitochondrial haplotypes and other environmental factors should account for the phenotypic variability of visual impairment in this family.

Production of Pure Ethanol from Azeotropic Solution by Pressure Swing Adsorption

Pressure swing adsorption (PSA) is attractive for final separation in the process of water removal especially for fuel ethanol production. Despite many researches on simulation and experimental works on adsorption of water on 3A zeolite in a fixed bed, none have studied a process with the actual PSA system. The purpose of this research was to study the PSA process with two adsorbers and effects of several parameters. The research also included analysis of kinetic and thermodynamic data of ethanol-water adsorption on commercial 3A zeolites in a single fixed bed. A two-level factorial design experiment was used in this research work to preliminarily screen the influence and interaction among the factors. Effects of important parameters such as initial temperature, feed concentration and feed rate were investigated. It was proven that the Langmuir isotherm could best predict the experimental results. In the PSA pilot test, the principal factors, which had effects on the performance, were feed rate, feed concentration, adsorption pressure and the cycle time. Prediction of the process efficiency in terms of ethanol recovery and enrichment was proposed in the form of regression models. The results of the study in a fixed bed adsorber could help designing a pilot-scale PSA unit. The experiments proved to be successful in terms of producing high concentration ethanol with high percentage of ethanol recovery. With further simulation work the process could be scaled up for an industrial use.

Variation in accumulation of heavy metals in different verities of sunflower seed oil with the aid of multivariate technique

In this work, three heavy metals (HMs) cadmium, lead, and zinc were determined in 16 newly breaded varieties of sunflower seed oil, using atomic absorption spectrometry, prior to use of microwave-assisted acid digestion method (MWD). The accuracy of the proposed method was studied by standard addition method and values obtained by conventional wet acid digestion methods (CAM) on same samples. The detection limit obtained from the standard addition curve was 0.327, 3.38, 10.0 ng/ml for Cd, Pb, and Zn, respectively, with high percentage recoveries. Multivariate statistical techniques (cluster and principal component analysis) were applied to modeling classes of different varieties of sunflower seed oils grown in same agricultural plot, on the basis of the analytical data of HMs. The results obtained providing sufficient information on tolerable limit of all three HMs by different varieties of sunflower oil to grow safely.

Synthesis and performance of a photocatalytic titania-hydroxyapatite composite

The photocatalytic degradation of methylene blue (MB) over a porous titania-hydroxyapatite (HAp) composite under ultraviolet radiation was studied. The catalyst was prepared by coating porous HAp with a titanium butoxide [Ti(OBu)4] sol at titania loadings of 17–49 wt%. Quantitative powder x-ray diffraction showed higher proportions of anatase as the calcination temperature increased from 500 to 800 °C due to crystallization of an amorphous precursor. The transformation of anatase to rutile was delayed until 900 °C, demonstrating the high thermal stability of the composite. Decomposition of HAp to α- and β- tricalcium phosphates takes place at 900 °C and is accompanied by the formation of perovskite at 1000 °C. A systematic study of the influence of calcination temperature and titania:HAp ratios demonstrated that for the optimal material, a surface area of 100 m2 g−1 was obtained at a titania loading of 49 wt% and calcination temperature of 600 °C. A highly dispersed suspension of finely ground titania-HAp enhanced the photodegradation of MB, allowed a high percentage recovery of catalyst, and was shown to be recyclable.

Ta-doped multifunctional bioactive nanostructured films

Ta-doped multifunctional bioactive nanostructured films (MuBiNaFs) were deposited by DC magnetron sputtering or ion implantation assisted magnetron sputtering of composite (Ti,Ta)C + Ca 3(PO 4) 2 and (Ti,Ta)C + CaO targets produced by self-propagating high-temperature synthesis method. The films were characterized in terms of their structure, elemental and phase composition using X-ray diffraction, transmission electron microscopy, X-ray photoelectron, Raman, and IR spectroscopy. The films deposited in an Ar atmosphere consisted of (Ti,Ta)C, Ti x O y , and CaO phases in an amorphous matrix with P–O, C–O, and O–H bonding. In the films deposited in a gaseous mixture of Ar + 14%N 2, apart from the (Ti,Ta)(C,N), Ti x O y , and CaO phases, the indication of diamond-like carbon, bcc Ta and traces of P–O bonding were observed. The MuBiNaFs demonstrated high hardness in the range of 38–44 GPa, Young's modulus 310–350 GPa, high percentage of elastic recovery 70–75%, low friction coefficient down to 0.17–0.25 (both in air and under physiological solution) and two orders of magnitude lower wear rate compared with Ti substrate. Ti ion implantation of growing films was shown to be an effective instrument to decrease their high internal stress. Static water contact angle measurements indicated hydrophilic nature of film surfaces. The electrochemical tests demonstrated that the Ta-doped films had positive values of corrosion potential with low current density. In vitro studies showed that cultured IAR-2 epitheliocytes and MC3T3-E1 osteoblastic cells were well spread on the surface of films and their actin cytoskeleton was well organized. Osteoblastic cells had a high rate of proliferation on all examined films and expressed alkaline phosphatase activity, an early-stage differentiation marker. The MuBiNaF revealed a high level of biocompatibility and biostability at experiments in vivo.

Spectrophotometric estimation of ambroxol hydrochloride and cetirizine hydrochloride in tablets

A simple, rapid, accurate, precise and reproducible simultaneous equation method has been developed for simultaneous estimation of ambroxol hydrochloride and cetirizine hydrochloride in tablets. Ambroxol hydrochloride has absorbance maxima at 243 nm, while cetirizine hydrochloride has absorbance maxima at 229 nm in glass-distilled water. The method developed involves no separation or extraction process.The proposed methods were successfully applied to the determination of ambroxol hydrochloride and cetirizine hydrochloride in tablets, with high percentage of recovery, good accuracy, and acceptable precision. Different analytical performance parameters such as linearity, precision, accuracy, limit of detection, limit of quantitation, and robustness were determined according to International Conference on Harmonization ICH Q2B guidelines. Results of analysis of formulation given as percentage of label claim ± relative standard deviation were found to be 99.27 ± 0.8083 and 102.43 ± 1.5357 for ambroxol hydrochloride and cetirizine hydrochloride respectively. Results of recovery studies given as percentage of label claim ± relative standard deviation were found to be 99.88 ± 0.3811 and 100.36 ± 2.0480 for ambroxol hydrochloride and cetirizine hydrochloride respectively.

RP-HPLC and Spectrophotometric Estimation of Ambroxol Hydrochloride and Cetirizine Hydrochloride in Combined Dosage Form.

Rapid, precise, accurate, specific and sensitive reverse phase liquid chromatographic and absorbance ratio spectrophotometric methods have been developed for the simultaneous analysis of ambroxol hydrochloride and cetirizine hydrochloride in their tablet formulation. The chromatographic methods were standardized using a HIQ SIL-C18 column (250×4.6 mm i.d., 10 μm particle size) with UV detection at 229 nm and mobile phase consisting of methanol-acetonitrile-water (40:40:20, v/v/v). Ambroxol hydrochloride and cetirizine hydrochloride have absorbance maxima at 243 nm and 229 nm, respectively. The isoabsorptive wavelength for both the drugs was 236 nm. For absorbance ratio method developed, wavelengths selected were 243 nm and 236 nm. The proposed methods were successfully applied to the determination of ambroxol hydrochloride and cetirizine hydrochloride in tablets, with high percentage of recovery, good accuracy and acceptable precision. Different analytical performance parameters such as linearity, precision, accuracy, limit of detection, limit of quantitation and robustness were determined according to International Conference on Harmonization ICH Q2B guidelines. Results of analysis of the developed method were compared by performing ANOVA.

Spectrophotometric estimation of ambroxol hydrochloride and cetirizine hydrochloride in tablets

A simple, rapid, accurate, precise and reproducible simultaneous equation method has been developed for simultaneous estimation of ambroxol hydrochloride and cetirizine hydrochloride in tablets. Ambroxol hydrochloride has absorbance maxima at 243 nm, while cetirizine hydrochloride has absorbance maxima at 229 nm in glass-distilled water. The method developed involves no separation or extraction process. The proposed methods were successfully applied to the determination of ambroxol hydrochloride and cetirizine hydrochloride in tablets, with high percentage of recovery, good accuracy, and acceptable precision. Different analytical performance parameters such as linearity, precision, accuracy, limit of detection, limit of quantitation, and robustness were determined according to International Conference on Harmonization ICH Q2B guidelines. Results of analysis of formulation given as percentage of label claim ± relative standard deviation were found to be 99.27 ± 0.8083 and 102.43 ± 1.5357 for ambroxol hydrochloride and cetirizine hydrochloride respectively. Results of recovery studies given as percentage of label claim ± relative standard deviation were found to be 99.88 ± 0.3811 and 100.36 ± 2.0480 for ambroxol hydrochloride and cetirizine hydrochloride respectively.

Measuring Concentrations of Insulin-Like Growth Factor-I with an Enzyme-Linked Immunosorbent Antibody Assay in Plasma Samples from Holstein Cows

This study describes the use of a commercial nonextraction ELISA to quantify total concentrations of insulin-like growth factor-I (IGF-I) in plasma samples from Holstein cows fed pasture-based diets varying in dry matter and metabolizable energy density. The assays were conducted using the protocols provided by the manufacturer. The ELISA was verified for linearity, accuracy in measuring IGF-I from spiked plasma samples, and precision involving variation within and between assays. Validation also involved comparing results of the ELISA against an established RIA after defatted plasma samples were subjected to acid gel HPLC to dissociate and separate IGF and IGF binding protein complexes. Validation results had low coefficients of variation (CV; intraassay CV of less than 6% and interassay CV of less than 8%) and a high recovery percentage of IGF-I (79%) from samples spiked with unbound IGF-I. The coefficients of determination between the ELISA and the RIA reference assay were 0.90 in 2 separate assays. Associations between the RIA and the ELISA were higher, and the limits of agreement at 95% confidence intervals were narrower compared with those between the RIA and a modified ELISA procedure in which IGF binding protein complexes were extracted using HPLC. The samples were obtained from cows sampled over a period of 5 wk. These results demonstrated that the DSL-10-2800 nonextraction IGF-I ELISA was acceptably specific and sufficiently sensitive to be used to measure the extent and patterns of change in the plasma concentrations of IGF-I in samples from lactating Holstein cows.

Recovery of precious metals by using chemically modified waste paper

Waste newsprint paper was chemically modified with p-aminobenzoic acid to prepare a sorption active gel. This gel proved useful for the selective uptake of gold, palladium and platinum over other coexisting metal ions such as copper, nickel, zinc and iron. A remarkably high capacity for Au(III) was observed together with a moderate uptake of Pt(IV) and Pd(IV). Furthermore, Au(III) was reduced to elemental gold which formed aggregates. A high percentage recovery of the precious metal ions (85–95%) and regeneration of the gel was attained by using a mixture of 0.15 M thiourea and 1 M HCl. Repeated cycles of uptake and elution by using a column packed with this new sorbent indicated that the gel is suitable for industrial application in continuous mode.

Achieving Proposed Federal Concentrations using Reduced Specimen Volume for the Extraction of Amphetamines from Oral Fluid

This article details the rapid extraction of amphetamines from oral fluid using low specimen volume, low sorbent bed mass, and fast gas chromatography with mass selective detection. The collection of a known amount of sample volume coupled with high percentage recovery of drug from the collection pad has allowed oral fluid to be increasingly employed as the specimen of choice for the detection of drug use in various applications. Additionally, low specimen volume for confirmation is required, so that adequate test volume remains for second analysis in case of batch failure or for testing at a different laboratory facility. The extracts were prepared using low bed mass sorbent, so less conditioning, washing, and elution solvent further reduced the overall cost of sample preparation. The limits of quantitation for the assay were 25 ng/mL; the intraday precision of the assays (n = 5) ranged from 0.3 to 3.99%; interday precision ranged from 0.72 to 4.6% for the amphetamine class. The percentage recovery of the drugs from the collection pads ranged from 85.4 to 89.1% (n = 6). The process lends itself to widely available automated processing instrumentation and significantly increases the efficiency of laboratories providing high-volume oral fluid analysis for drugs of abuse.

Development of membrane electrodes for selective determination of some antiepileptic drugs in pharmaceuticals, plasma and urine

Newly developed, simple, low-cost and sensitive ion-selective electrodes have been proposed for determination of some antiepileptic drugs such as lamotrigine, felbamate, and primidone in their pharmaceutical preparations as well as in biological fluids. The electrodes are based on poly(vinyl chloride) membranes doped with drug-tetraphenyl borate (TPB) or drug-phosphotungstic acid (PT) ion-pair complexes as molecular recognition materials. The novel electrodes displayed rapid Nernstian responses with detection limits of approximately 10(-7) M. Calibration graphs were linear over the ranges 5.2 x 10(-7)-1.0 x 10(-3), 1.5 x 10(-6)-1.0 x 10(-3), and 2.6 x 10(-7)-1.0 x 10(-3 )M for drug-TPB and 5.8 x 10(-7)-1.0 x 10(-3), 1.8 x 10(-7)-1.0 x 10(-3), and 6.6 x 10(-7)-1.0 x 10(-3) M for drug-PT electrodes, respectively, with slopes ranging from 52.3 to 62.3 mV/decade. The membranes developed have potential stability for up to 1 month and proved to be highly selective for the drugs investigated over other ions and excipients. The results show that the selectivity of the ion-selective electrodes is influenced significantly by the plasticizer. The proposed electrodes were successfully applied in the determination of these drugs in pharmaceutical preparations in four batches of different expiry dates. Statistical Student's t test and F test showed insignificant systematic error between the ion-selective electrode methods developed and a standard method. Comparison of the results obtained using the proposed electrodes with those found using a reference method showed that the ion-selective electrode technique is sensitive, reliable, and can be used with very good accuracy and high percentage recovery without pretreatment procedures of the samples to minimize interfering matrix effects.

A sensitive method for detection of EGFR gene mutations in plasma

18027 Background: Somatic mutations in the tyrosine kinase (TK) domain of the EGFR gene are associated with clinical response to TK inhibitors in patients with non-small cell lung cancer. An assay that detects such mutations in the plasma would provide a noninvasive technique to assess suitability for TK inhibitor therapy. Here we describe: 1) the development of a sensitive assay to detect the E746-A750 deletion in the TK domain of EGFR in plasma; and 2) optimization of the method for plasma DNA extraction. Methods: Our assay uses Mse I to specifically digest wild-type (WT) genomic DNA (gDNA) to reduce non-specific amplification. After digestion, samples are PCR- amplified using 1 unlabeled primer and 1 FAM-labeled primer spanning the E746-A750 deletion region and fluorescence detected with an automated analyzer. Serial dilution studies were conducted using H1650 gDNA (del E746-A750 cell line) diluted in WT gDNA after Mse I digestion. To assess detection of the deletion in plasma, 3–4 mL whole blood was spiked with 1–37 ng H1650 gDNA; gDNA from the separated plasma was then extracted (silica column/2-propanol precipitation), digested with Mse I, and amplified as above. Several extraction methods were evaluated using pooled plasma samples and PBS spiked with 10–350 ng gDNA: silica column, magnetic bead, phenol:chloroform, and 2-propanol precipitation. Results: Digestion of the WT EGFR allele followed by deletion-specific fluorescent PCR allowed detection of caof ca. 1 copy of the del E746-A750 EGFR gene (10 pg gDNA) diluted to 0.001%. Furthermore, del E746-A750 was successfully detected in 1/5 the final DNA volume (5 μl) in all spiked blood samples. Magnetic bead-based DNA extraction yielded the highest percent recovery of gDNA from PBS (69% recovery of the 10-ng sample). Phenol:chloroform extraction gave the highest yield with pooled plasma samples. Conclusions: The combination of an optimized DNA extraction method, clearing the plasma DNA sample of amplifiable WT DNA by restriction digestion, and mutation-specific fluorescent PCR provides a highly sensitive assay for detection of somatic mutations in plasma. No significant financial relationships to disclose.

Application of surfactants and microemulsions to the extraction of pyrene and phenanthrene from soil with three different extraction methods

In the present work, the use of surfactants and oil-in-water (O/W) microemulsions as alternative extractants in accelerated solvent extraction (ASE) for the extraction of polycyclic aromatic hydrocarbons (pyrene and phenanthrene) from soils was investigated. In particular, the effect of each individual component within the microemulsions, i.e., oil phase, surfactant and co-surfactatnt, and extraction conditions on the percentage recovery was systematically studied. When compared to the water and organic solvent, the important findings were that the common surfactant solutions at the concentrations above their critical micelle concentrations (CMC) were shown to enhance the percentage recovery at the lower extraction temperature. Moreover, the highest percentage recovery can be obtained using microemulsion as the extractant. The chemical component within the microemulsions and relative amounts of the oil phase appeared to play a much more significant role in ensuring high percentage recovery. Finally, an overall comparison between the percentage recoveries obtained with ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and ASE using organic solvents, surfactants and microemulsions as extractants was exhibited.

Optimization of a rapid microwave assisted extraction method for the liquid chromatography–electrospray-tandem mass spectrometry determination of isoflavonoid aglycones in soybeans

A very fast chromatographic separation of isoflavonoids genistein, daidzein, formononetin and biochanin A was developed on a C18 high-speed column under isocratic conditions. The method was validated in terms of detection limits, quantitation limits (LOQs), linearity and precision. LOQs in 0.04–0.2 μg/g range were calculated, making feasible the determination of these compounds of nutritional concern at trace levels. Good linearity was demonstrated over three concentration orders of magnitude for each analyte ( r 2 0.990–1.000). The intra-day and inter-day repeatability was evaluated in terms of relative standard deviation (RSD%) at two concentration levels for each analyte (RSD% <9%). An optimization strategy was adopted to find the best conditions for the extraction of isoflavonoid aglycones from yellow soybeans using microwave-assisted extraction. The most relevant parameters resulted to be the microwave power, the extraction time and the acid concentration, optimal values being 600 W, 1 min and 12 M, respectively. When performing sample treatment on a fortified soybean sample, high recovery percentage was obtained for both compounds (94 ± 8% for daidzein and 97 ± 5% ( n = 4) for genistein). The concentration level at which daidzein and genistein were found in the soybean sample were 1.21 ± 0.15 mg/g and 2.38 ± 0.09 mg/g ( n = 4), respectively.

Implementación y evaluación de dos métodos deconservación y generación de la base de datos del banco de cepas y genes del Instituto de Biotecnología de la Universidad Nacional de Colombia (IBUN)

76 cepas de las familias Enterobacteriaceae y Pseudomonadaceae fueron conservadas por el método semistock en papel filtro y 68 de las mismas por el método stock de criopreservación, en el banco de cepas y genes del Instituto de Biotecnología de la Universidad Nacional de Colombia (IBUN). La eficacia de los métodos de preservación se realizó mediante la evaluación de la viabilidad a las 24 horas de conservación y fue calculado el porcentaje de recuperación. En conclusión, la preservación en papel filtro y criopreservación son adecuados métodos semistock y stock, respectivamente; ya que el 73.7% de los microorganismos de la familia Enterobacteriaceae y el 82.3% de los microorganismos de la familia Pseudomonadaceae, presentaron un porcentaje de recuperación mayor al 50%. Por otra parte, se implementó una base de datos elaborada en el software Access ®, la cual se implementó con éxito en el IBUN y en la página Web de la Universidad Nacional de Colombia en la dirección electrónica www.ibun.unal.edu.co/instituto/cepario , que está disponible al público en general.

Determination of lanthanides by source excited energy dispersive X-ray fluorescence (EDXRF) method after preconcentration with ammonium pyrrolidine dithiocarbamate (APDC)

A new analytical procedure for determination of lanthanides in environmental samples after chemical separation from major matrix elements on DOWEX 50W-X8 resin followed by preconcentration with chelating agent ammonium pyrrolidine dithiocarbamate (APDC) and analyses of thin targets by energy dispersive X-ray fluorescence (EDXRF) method using 109Cd as the source of excitation was presented. Characteristic Lα X-ray lines of the lanthanides were used for calculations of the net peak area and mass concentrations. The influence of pH value of the solution and addition of organic matter on the complexation was investigated. Percentage of recovery of each lanthanide after separation on DOWEX 50W-X8 resin was also determined. Accuracy of the method was tested on standard reference materials and real environmental samples (red mud material). For that purpose samples of standard reference materials and red mud were prepared as thick targets and directly analyzed (without the separation step) by EDXRF method using 241Am as the excitation source. In that case lanthanides concentrations were determined over their characteristic Kα X-ray lines and results were compared with those obtained after separation/preconcentration step described above. Results showed that selected lanthanides made stable complexes with APDC in the alkaline medium with the maximum recovery at pH = 8. The presence of organic matter slightly modified the complexation by means of somewhat higher recovery percentage at pH lower than 7 and approx. 20% lower recovery at pH higher than 7. Recovery of the elements after separation on DOWEX 50W-X8 resin and preconcentration with APDC at pH = 8 varied from 91.4% (Pr) to only 24.9% in the case of Dy. Concentrations of lanthanides measured in standard reference material and environmental samples of red mud after microwave digestion, separation on DOWEX 50W-X8 resin, preconcentration with APDC at pH = 8 and recalculation on the percentage of recovery were in good agreement with certified values in the case of SRM as well as with the concentrations obtained by direct determination over Kα lines using 241Am excitation source in the case of red mud leading to the conclusion that presented method was applicable for the determination of lanthanides in real environmental samples.