A high-throughput method for determination of metabolites of organophosphate flame retardants in urine by ultra performance liquid chromatography–high resolution mass spectrometry

Organophosphate triesters are common flame retardants used in a wide variety of consumer products from which they can migrate and pollute the indoor environment. Humans may thus be continuously exposed to several organophosphate triesters which might be a risk for human health. An analytical method based on direct injection of 5 μL urine into an ultra performance liquid chromatography system coupled to a time-of-flight mass spectrometry has been developed and validated to monitor exposure to organophosphate triesters through their respective dialkyl and diaryl phosphate metabolites (DAPs). The targeted analytes were: di-n-butyl phosphate (DNBP), diphenyl phosphate (DPHP), bis(2-butoxyethyl) phosphate (BBOEP), bis(2-chloroethyl) phosphate (BCEP), bis(1-chloro-2-propyl) phosphate (BCPP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP). Separation was achieved in less than 3 min on a short column with narrow diameter and small particle size (50 mm × 2.1 mm × 1.7 μm). Different mobile phases were explored to obtain optimal sensitivity. Acetonitrile/water buffered with 5 mM of ammonium hydroxide/ammonium formate (pH 9.2) was the preferred mobile phase. Quantification of DAPs was performed using deuterated analogues as internal standards in synthetic urine (averaged DAP accuracy was 101%; RSD 3%). Low method limits of quantification (MLQ) were obtained for DNBP (0.40 ng mL⁻¹), DPHP (0.10 ng mL⁻¹), BDCIPP (0.40 ng mL⁻¹) and BBOEP (0.60 ng mL⁻¹), but not for the most polar DAPs, BCEP (∼12 ng mL⁻¹) and BCPP (∼25 ng mL⁻¹). The feasibility of the method was tested on 84 morning urine samples from 42 mother and child pairs. Only DPHP was found above the MLQ in the urine samples with geometric mean (GM) concentrations of 1.1 ng mL⁻¹ and 0.57 ng mL⁻¹ for mothers and children respectively. BDCIPP was however, detected above the method limit of detection (MLD) with GM of 0.13 ng mL⁻¹ and 0.20 ng mL⁻¹. While occasionally detected, the GM of DNBP and BBOEP were below MLD in both groups.     

Preparation of monoclonal antibodies against a derivative of semicarbazide as a metabolic target of nitrofurazone

Monoclonal antibodies (McAb) were produced to detect semicarbazide (SEM), a metabolite as a marker residue of nitrofurazone in animal food production. A carboxyphenyl derivative (CPSEM) of SEM was synthesized following derivatisation with 4-carboxybenzaldehyde (CBA). CPSEM was purified by recrystallization and conjugated to bovine serum albumin (BSA) or ovalbumin (OVA) as immunogen or coating antigen, respectively. Hybridomas were obtained by fusing mouse myeloma cells SP2/0 with splenocytes from the mice immunized with CPSEM-BSA. Hybridomas 1F10 and 4F2 secreting antibodies against CPSEM were obtained and subcloned. Ascites of monoclonal antibodies were prepared by injecting 1 × 10⁶ cells of hybridoma 1F10 into mice abdomen. McAb obtained from hybridoma 1F10 was highly specific for CPSEM and had no cross-reaction with various nitrofuran metabolites and a range of veterinary drugs. The sensitivity of the McAb to SEM was 0.01 ng mL⁻¹ and the IC₅₀ value was 1.3 ng mL⁻¹ (SEM in the form of CPSEM). McAb 1F10 is suitable to develop an immunoassay for SEM with sufficient sensitivity for monitoring nitrofurazone residues.     

Determination of estrogens in water by HPLC-UV using cloud point extraction

A method based on cloud point extraction was developed to determine four kinds of estrogens: estriol (E3), estradiol (E2), estrone (E1), and progesterone (P) in water by high performance liquid chromatography separation and ultraviolet detection (HPLC-UV). The non-ionic surfactant Triton X-114 was chosen as extractant solvent. The parameters affecting extraction efficiency, such as concentrations of Triton X-114 and Na₂SO₄, equilibration temperature, equilibration time and centrifugation time were evaluated and optimized. Under the optimum conditions, preconcentration factors of 99 for E3, 73 for E2, 152 for E1 and 86 for P were obtained for 10 mL water sample. The detection of limitation was 0.23 ng mL⁻¹ for E3, 0.32 ng mL⁻¹ for E2, 0.25 ng mL⁻¹ for E1 and 5.0 ng mL⁻¹ for P. The proposed method was successfully applied to the determination of trace amount of estrogens in wastewater treatment plant (WWTP) effluent water and exposure water with 10 ng mL⁻¹ E2 for toxicological study in our lab. For the case of WWTP effluent water samples, no estrogen was found. The accuracy of the proposed method was tested by recovery measurements of spiked samples and good recoveries of 81.2-99.5% were obtained.     

Rapid determination of aristolochic acids I and II in herbal products and biological samples by ultra-high-pressure liquid chromatography-tandem mass spectrometry

Aristolochic acids (AAs) are a mixture of structural-related compounds, in which aristolochic acid I (AA I) and aristolochic acid II (AA II) are reported to be correlated with Aristolochic acid nephropathy (AAN). In this work, a rapid and sensitive ultra-high-pressure liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed to determine AA I and AA II in herbal products and biological fluids. By using gradient elution with a mobile phase composed of a mixture of 10 mM ammonium formate buffer (pH 3.0) and acetonitrile, AAs could be determined within 10 min. Under optimum UHPLC-MS/MS conditions, the limit of detections was 0.14 and 0.26 ng mL⁻¹ for AA I and AA II, respectively. Run-to-run repeatability and intermediate precision of peak area for AA I and AA II were less than 5.74% relative standard deviation (RSD). Accuracy was tested by spiking 10, 100 and 1000 ng mL⁻¹ in rat serum and the recoveries were within 76.5-92.9%. Matrix effects were within 78.8-127.7%. The developed method was successfully applied to determine AA I and AA II in several herbal products and to investigate their pharmacokinetic behavior in female Wister rats. The result shows that the developed UHPLC-MS/MS method is efficient, sensitive, and accurate for the determination of AA I and AA II in herbal products and biological samples.     

Simultaneous determination of psychotropic drugs in human urine by capillary electrophoresis with electrochemiluminescence detection

Amitriptyline, doxepin and chlorpromazine are often used as psychotropic drugs in treatment of the various mental diseases, and are also partly excreted by kidney. This work developed a simple, selective and sensitive method for their simultaneous monitoring in human urine using capillary electrophoresis coupled with electrochemiluminescence (ECL) detection based on end-column ECL reaction of tris-(2,2′-bipyridyl)ruthenium(II) with aliphatic tertiary amino moieties. Acetone was used as an additive to the running buffer to obtain their absolute separation. Under optimized conditions the proposed method displayed a linear range from 5.0 to 800 ng mL⁻¹ for the three drugs with the correlation coefficients more than 0.995 (n = 8). Their limits of detection were 0.8 ng mL⁻¹ (3.6 fg), 1.0 ng mL⁻¹ (4.5 fg) and 1.5 ng mL⁻¹ (6.8 fg) at a signal to noise ratio of 3, respectively. The relative standard deviations for five determinations of 20 ng mL⁻¹ amitriptyline, doxepin and chlorpromazine were 1.7%, 4.2% and 3.6%, respectively. For practical application an extract step with 90:10 heptane/ethyl acetate (v/v) was performed to eliminate the influence of ionic strength in sample. The recoveries of amitriptyline, doxepin and chlorpromazine at different levels in human urine were between 83% and 93%, which showed that the method was valuable in clinical and biochemical laboratories for monitoring amitriptyline, doxepin and chlorpromazine.     

Colloidal gold nanoparticle probe-based immunochromatographic assay for the rapid detection of chromium ions in water and serum samples

An immunochromatographic assay (ICA) using gold nanoparticles coated with monoclonal antibody (McAb) for the detection of chromium ions (Cr) in water and serum samples was developed, optimized and validated. Gold nanoparticles coated with affinity-purified monoclonal antibodies against isothiocyanobenzyl-EDTA (iEDTA)-chelated Cr³⁺ were used as the detecting reagent in this completive immunoassay-based one-step test strip. The ICA was investigated to measure chromium speciation (Cr³⁺ and Cr⁶⁺ ions) in water samples. Chromium standard samples of 0–80 ng mL⁻¹ in water were determined by the test strips. The results showed that the visual lowest detection limit (LDL) of the test strip was 50.0 ng mL⁻¹. A portable colorimetric lateral flow reader was used for the quantification of Cr. The results indicated that the linear range of the ICA with colorimetric detection was 5–80 ng mL⁻¹. The ICA was also validated for the detection of chromium ions in serum samples. The test trips showed high stability in that they could be stored at 37 °C for at least 12 weeks without significant loss of activity. The test strip also showed good selectivity for Cr detection with negligible interference from other heavy metals. Because of its low cost and short testing time (within 5 min), the test strip is especially suitable for on-site large-scale screening of Cr-polluted water samples, biomonitoring of Cr exposure, and many other field applications.     

Application of dispersive liquid-liquid microextraction for the analysis of triazophos and carbaryl pesticides in water and fruit juice samples

In this work, a simple, rapid and sensitive sample pretreatment technique, dispersive liquid-liquid microextraction (DLLME) coupled with high performance liquid chromatography-fluorescence detection (HPLC-FLD), has been developed to determine carbamate (carbaryl) and organophosphorus (triazophos) pesticide residues in water and fruit juice samples. Parameters, affecting the DLLME performance such as the kind and volume of extraction and dispersive solvents, extraction time and salt concentration, were studied and optimized. Under the optimum extraction conditions (extraction solvent: tetrachloroethane, 15.0 μL; dispersive solvent: acetonitrile, 1.0 mL; no addition of salt and extraction time below 5 s), the performance of the proposed method was evaluated. The enrichment factors for the carbaryl and triazophos were 87.3 and 275.6, respectively. The linearity was obtained in the concentration range of 0.1-1000 ng mL⁻¹ with correlation coefficients from 0.9991 to 0.9999. The limits of detection (LODs), based on signal-to-noise ratio (S/N) of 3, ranged from 12.3 to 16.0 pg mL⁻¹. The relative standard deviations (RSDs, for 10 ng mL⁻¹ of carbaryl and 20 ng mL⁻¹ of triazophos) varied from 1.38% to 2.74% (n = 6). The environmental water (at the fortified level of 1.0 ng mL⁻¹) and fruit juice samples (at the fortified level of 1.0 and 5.0 ng mL⁻¹) were successfully analyzed by the proposed method, and the relative recoveries of them were in the range of 80.4-114.2%, 89.8-117.9% and 86.3-105.3%, respectively.     

Production and characterization of a broad-specificity polyclonal antibody for O,O-diethyl organophosphorus pesticides and a quantitative structure-activity relationship study of antibody recognition

Polyclonal antibody (PAb) with broad-specificity for O,O-diethyl organophosphorus pesticides (OPs) against a generic hapten, 4-(diethoxyphosphorothioyloxy)benzoic acid, was produced. The obtained PAb showed high sensitivity to seven commonly used O,O-diethyl OPs in a competitive indirect enzyme-linked immunosorbent assay (ciELISA) using a heterologous coating antigen, 4-(3-(diethoxyphosphorothioyloxy)phenylamino)-4-oxobutanoic acid. The 50% inhibition value (IC₅₀) was 348 ng mL⁻¹ for parathion, 13 ng mL⁻¹ for coumaphos, 22 ng mL⁻¹ for quinalphos, 35 ng mL⁻¹ for triazophos, 751 ng mL⁻¹ for phorate, 850 ng mL⁻¹ for dichlofenthion, and 1301 ng mL⁻¹ for phoxim. The limit of detection (LOD) met the ideal detection criteria of all the seven OP residues. A quantitative structure-activity relationship (QSAR) model was constructed to study the mechanism of antibody recognition using multiple linear regression analysis. The results indicated that the frontier-orbital energies (energy of the highest occupied molecular orbital, E_HOMO, and energy of the lowest unoccupied molecular orbital, E_LUMO) and hydrophobicity (log of the octanol/water partition coefficient, log P) were mainly responsible for the antibody recognition. The linear equation was log(IC₅₀) = −63.274E_HOMO + 15.985E_LUMO + 0.556 log P − 25.015, with a determination coefficient (r²) of 0.908.     

Monolithic silica spin column extraction and simultaneous derivatization of amphetamines and 3,4-methylenedioxyamphetamines in human urine for gas chromatographic-mass spectrometric detection

A simple, sensitive, and specific method with gas chromatography-mass spectrometry was developed for simultaneous extraction and derivatization of amphetamines (APs) and 3,4-methylenedioxyamphetamines (MDAs) in human urine by using a monolithic silica spin column. All the procedures, such as sample loading, washing, and elution were performed by centrifugation. APs and MDAs in urine were adsorbed on the monolithic silica and derivatized with propyl chloroformate in the column. Methamphetamine-d₅ was used as an internal standard. The linear ranges were 0.01-5.0 μg mL⁻¹ for methamphetamine (MA) and 3,4-methylenedioxymethamphetamine (MDMA) and 0.02-5.0 μg mL⁻¹ for amphetamine (AP) and 3,4-methylenedioxyamphetamine (MDA) (coefficient of correlation ≧0.995). The recovery of APs and MDAs in urine was 84-94%, and the relative standard deviation of the intra- and interday reproducibility for urine samples containing 0.1, 1.0, and 4.0 μg mL⁻¹ of APs and MDAs ranged from 1.4% to 13.6%. The lowest detection limit (signal-to-noise ratio ≧ 3) in urine was 5 ng mL⁻¹ for MA and MDMA and 10 ng mL⁻¹ for AP and MDA. The proposed method can be used to perform simultaneous extraction and derivatization on spin columns that have been loaded with a small quantity of solvent by using centrifugation.     

Study on the resonance Rayleigh scattering spectra of the interactions of palladium (II)-cephalosporins chelates with 4,5-dibromofluorescein and their analytical applications

In pH 2.8-3.8 BR buffer medium, the third generation cephalosporin antibiotics (TGCs) such as ceftazidime (CZD), ceftriaxone (CTRX), cefoperazone (CPZ), and cefotaxime (CFTM) react with palladium(II) (Pd(II)) to form 1:2 yellowish-brown cationic chelates, which further react with 4, 5-dibromofluorescein (DBF) to form 1:3 brown ion-association complexes. As a result, not only the spectra of absorption and fluorescence are changed, but also the resonance Rayleigh scattering (RRS) is enhanced greatly and the new RRS spectra are observed. The four TGCs products have similar spectral characteristics and their maximum RRS wavelengths are all located at 291 nm. The quantitative determination ranges and the detection limits of the four TGCs are 0.0065-1.0 μg mL⁻¹ and 2.0 ng mL⁻¹ for CZD, 0.0070-1.1 μg mL⁻¹ and 2.2 ng mL⁻¹ for CTRX, 0.0090-1.6 μg mL⁻¹ and 2.7 ng mL⁻¹ for CPZ, and 0.014-2.2 μg mL⁻¹ and 4.2 ng mL⁻¹ for CFTM, respectively. The optimum conditions of the reactions and the effects of foreign substances are investigated, and the composition of ion-association complexes is discussed also. Based on the ion-association reaction, a highly sensitive, simple and rapid method has been proposed to the determination of TGCs.     

A novel stacking method of repetitive large volume sample injection and sweeping MEKC for determination of androgenic steroids in urine

In this research, a novel stacking capillary electrophoresis method, repetitive large volume sample injection and sweeping MEKC (rLVSI-sweeping MEKC) were developed to analyze the presence of three androgenic steroids considered as sport doping drugs, testosterone (T), epitestosterone (E) and epitestosterone glucuronide (EG) in urine. This method provides better sensitivity enhancement than the traditional large volume sample stacking-sweeping strategies due to sensitivity enhancement by repetitive injections. This multiple sampling method enhances sensitivity of monitoring of urine samples by UV detection (254 nm). Firstly, the phosphate buffer was filled into an uncoated fused silica capillary and the samples were injected into the capillary at 10 psi for 20 s, and then stacked at −10 kV for 1 min using phosphate buffer containing SDS. The above injecting and stacking steps were repeated five times. Finally, separation was performed at −20 kV, using phosphate buffer containing methanol, SDS and (2-hydroxypropyl)-β-cyclodextrin. Method validation showed that calibration plots were linear (r ≧ 0.997) over a range of 5-200 ng mL⁻¹ for T, 20-200 ng mL⁻¹ for E and 0.5-500 ng mL⁻¹ for EG. The limits of detection were 1.0 ng mL⁻¹ for T, 5.0 ng mL⁻¹ for E and 200.0 pg mL⁻¹ for EG. When evaluating precision and accuracy, values of RSD and RE in intra-day (n = 3) and inter-day (n = 5) analysis were found to be less than 10.0%. Compared with the simple LVSS-sweeping, which is also a stacking strategy, this method further improves sensitivity up to 25 folds (∼2500 folds with MEKC without preconcentration). This method was applied to monitor 10 athletes’ urine, and did not detect any analyte. The novel stacking method was feasible for monitoring of doping by sportsmen.     

Improved porous silicon microarray based prostate specific antigen immunoassay by optimized surface density of the capture antibody

Enriching the surface density of immobilized capture antibodies enhances the detection signal of antibody sandwich microarrays. In this study, we improved the detection sensitivity of our previously developed P-Si (porous silicon) antibody microarray by optimizing concentrations of the capturing antibody. We investigated immunoassays using a P-Si microarray at three different capture antibody (PSA – prostate specific antigen) concentrations, analyzing the influence of the antibody density on the assay detection sensitivity. The LOD (limit of detection) for PSA was 2.5 ng mL⁻¹, 80 pg mL⁻¹, and 800 fg mL⁻¹ when arraying the PSA antibody, H117 at the concentration 15 μg mL⁻¹, 35 μg mL⁻¹, and 154 μg mL⁻¹, respectively. We further investigated PSA spiked into human female serum in the range of 800 fg mL⁻¹ to 500 ng mL⁻¹. The microarray showed a LOD of 800 fg mL⁻¹ and a dynamic range of 800 fg mL⁻¹ to 80 ng mL⁻¹ in serum spiked samples.     

Ligandless dispersive liquid-liquid microextraction for the separation of trace amounts of silver ions in water samples and flame atomic absorption spectrometry determination

In this article, a new ligandless dispersive liquid-liquid microextraction method has been developed for preconcentration of trace quantities of silver as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach, carbon tetrachloride and ethanol were used as extraction and dispersive solvents. Several factors that may be affected on the extraction process, like, extraction solvent, disperser solvent, the volume of extraction and disperser solvent, pH of the aqueous solution and extraction time were optimized. Under the optimal conditions, the calibration curve was linear in the range of 5.0 ng mL⁻¹ to 2.0 μg mL⁻¹ of silver with R² = 0.9995 (n = 9) and detection limit based on three times the standard deviation of the blank (3S_b) was 1.2 ng mL⁻¹ in original solution. The relative standard deviation for eight replicate determination of 0.5 μg mL⁻¹ silver was ±1.5%. The high efficiency of dispersive liquid-liquid microextraction to carry out the determination of silver in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of silver in standard and water samples with satisfactory results.     

Ligandless-solidified floating organic drop microextraction method for the preconcentration of trace amount of cadmium in water samples

In this article, a new ligandless solidified floating organic drop microextraction (LL-SFODME) method has been developed for preconcentration of trace amount of cadmium as a prior step to its determination by flow injection-flame atomic absorption spectrometry (FI-FAAS). The methodology is based on the SFODME of cadmium with 1-dodecanol in the absence of chelating agent. Several factors affecting the microextraction efficiency, such as, pH, sodium dodecylbenzenesulfonate (SDBS) concentration, extraction time, stirring rate and temperature were investigated and optimized. Under optimized experimental conditions an enhancement factor of 205 was obtained for 100 mL of sample solution. The calibration graph was linear in the range of 1.0-25.0 ng mL⁻¹, the limit of detection (3s) was 0.21 ng mL⁻¹ and the limit of quantification (10s) was 0.62 ng mL⁻¹. The relative standard deviation (RSD) for 10 replicate measurements of 10 ng mL⁻¹ cadmium was 4.7%. The developed method was successfully applied to the extraction and determination of cadmium in standard and several water samples and satisfactory results were obtained.     

Multiplex detection of tumor markers with photonic suspension array

A novel photonic suspension array was developed for multiplex immunoassay. The carries of this array were silica colloidal crystal beads (SCCBs). The codes of these carriers are the characteristic reflection peak originated from their structural periodicity, and therefore they do not suffer from fading, bleaching, quenching, and chemical instability. In addition, because no dyes or materials related with fluorescence are included, the fluorescence background of SCCBs is very low. With a sandwich format, the proposed suspension array was used for simultaneous multiplex detection of tumor markers in one test tube. The results showed that the four tumor markers, α-fetoprotein (AFP), carcinoembryonic antigen (CEA), carcinoma antigen 125 (CA 125) and carcinoma antigen 19-9 (CA 19-9) could be assayed in the ranges of 1.0-500 ng mL⁻¹, 1.0-500 ng mL⁻¹, 1.0-500 U mL⁻¹ and 3.0-500 U mL⁻¹ with limits of detection of 0.68 ng mL⁻¹, 0.95 ng mL⁻¹, 0.99 U mL⁻¹ and 2.30 U mL⁻¹ at 3σ, respectively. The proposed array showed acceptable accuracy, detection reproducibility, storage stability and the results obtained were in acceptable agreement with those from parallel single-analyte test of practical clinical sera. This technique provides a new strategy for low cost, automated, and simultaneous multiplex immunoassay.     

Development and validation of a high-throughput double solid phase extraction-liquid chromatography-tandem mass spectrometry method for the determination of tetrodotoxin in human urine and plasma

A sensitive analytical method for the determination of tetrodotoxin (TTX) in urine and plasma matrices was developed using double solid phase extraction (C18 and hydrophilic interaction liquid chromatography) and subsequent analysis by HPLC coupled with tandem mass spectrometry. The double SPE sample cleanup efficiently reduced matrix and ion suppression effects. Together with the use of ion pair reagent in the mobile phase, isocratic elution became possible which enabled a shorter analysis time of 5.5 min per sample. The assay results were linear up to 500 ng mL⁻¹ for urine and 20 ng mL⁻¹ for plasma. The limit of detection and limit of quantification were 0.13 ng mL⁻¹ and 2.5 ng mL⁻¹, respectively, for both biological matrices. Recoveries were in the range of 75-81%. To eliminate the effect of dehydration and variations in urinary output, urinary creatinine-adjustment was made. TTX was quantified in eight urine samples and seven plasma samples from eight patients suspected of having TTX poisoning. TTX was detected in all urine samples, with concentrations ranging from 17.6 to 460.5 ng mL⁻¹, but was not detected in any of the plasma samples. The creatinine-adjusted TTX concentration in urine (ranging from 7.4 to 41.1 ng μmol⁻¹ creatinine) correlated well with the degree of poisoning as observed from clinical symptoms.     

A naked-eye based strategy for semiquantitative immunochromatographic assay

It is critical to develop a cost-effective quantitative/semiquantitative assay for rapid diagnosis and on-site detection of toxic or harmful substances. Here, a naked-eye based semiquantitative immunochromatographic strip (NSI-strip) was developed, on which three test lines (TLs, TL-I, TL-II and TL-III) were dispensed on a nitrocellulose membrane to form the test zone. Similar as the traditional strip assay for small molecule, the NSI-strip assay was also based on the competitive theory, difference was that the analyte competed three times with the capture reagent for the limited number of antibody binding sites. After the assay, the number of TLs developed in the test zone was inversely proportional to the analyte concentration, thus analyte content levels could be determined by observing the appeared number of TLs. Taking aflatoxin B₁ as the model analyte, visual detection limit of the NSI-strip was 0.06 ng mL⁻¹ and threshold concentrations for TL-I–III were 0.125, 0.5, and 2.0 ng mL⁻¹, respectively. Therefore, according to the appeared number of TLs, the following concentration ranges would be detectable by visual examination: 0–0.06 ng mL⁻¹ (negative samples), and 0.06–0.125 ng mL⁻¹, 0.125–0.5 ng mL⁻¹, 0.5–2.0 ng mL⁻¹ and >2.0 ng mL⁻¹ (positive samples). That was to say, compared to traditional strips the NSI-strip could offer more parameter information of the target analyte content. In this way, the NSI-strip improved the qualitative presence/absence detection of traditional strips by measuring the content (range) of target analytes semiquantitatively.     

Silica gel-polyethylene glycol as a new adsorbent for solid phase extraction of cobalt and nickel and determination by flame atomic absorption spectrometry

In this paper a novel solid phase extraction method to determine Co(II) and Ni(II) using silica gel-polyethylene glycol (Silica-PEG) as a new adsorbent is described. The method is based on the adsorption of cobalt and nickel ions in alkaline media on polyethylene glycol-silica gel in a mini-column, elution with nitric acid and determination by flame atomic absorption spectrometry. The adsorption conditions such as NaOH concentration, sample volume and amount of adsorbent were optimized in order to achieve highest sensitivity. The calibration graph was linear in the range of 0.5-200.0 ng mL⁻¹ for Co(II) and 2.0-100.0 ng mL⁻¹ for Ni(II) in the initial solution. The limit of detection based on 3S_b was 0.37 ng mL⁻¹ for Co(II) and 0.71 ng mL⁻¹ for Ni(II). The relative standard deviations (R.S.D.) for ten replicate measurements of 40 ng mL⁻¹ of Co(II), and Ni(II) were 3.24 and 3.13%, respectively. The method was applied to determine Co(II) and Ni(II) in black tea, rice flour, sesame seeds, tap water and river water samples.     

Development, validation and application of a method based on DI-SPME and GC-MS for determination of pesticides of different chemical groups in surface and groundwater samples

A simple and rapid method based on solid-phase micro extraction (SPME) technique followed by gas chromatography-mass spectrometry with selected ion monitoring (GC-MS, SIM) was developed by the simultaneous determination of 16 pesticides of seven different chemical groups [Six organophosphorus (trichlorfon, diazinon, methyl parathion, malathion, fenthion and ethyon), three pyrethroids (bifenhin, permethrin, cypermethrin), two imidazoles (imazalil and prochloraz), two strobilurins (azoxystrobin and pyraclostrobin), one carbamate (carbofuran), one tetrazine (clofentezine), and one triazole (difenoconazole)] in water. The pesticides extraction was done with direct immersion mode (DI-SPME) of the polyacrilate fiber (PA 85 µm). The extraction temperature was adjusted to 50 °C during 30 min, while stirring at 250 rpm was applied. After extraction, the fiber was introduced in the GC injector for thermal desorption for 5 min. at 280 °C. The method was validated using ultra pure water samples fortified with pesticides at different concentration levels and shows good linearity in the concentrations between 0.05 and 250.00 ng mL^− 1. The LOD and LOQ ranged, from 0.02 to 0.30 ng mL^− 1 and 0.05 to 1.00 ng mL^− 1, respectively. Intra-day and inter-day precisions were determined in two concentration levels (5.00 and 50.00 ng mL^− 1). Intra-day relative standard deviation (%R.S.D.) ranged between 3.6 and 13.6%, and inter-day (%R.S.D.) ranged between 6.3 and 18.5%. Relative recovery tests were carried out spiking the ultra pure sample with standards in three different concentration levels 0.20, 5.00 and 50.00 ng mL^− 1. The recovery at 0.20 ng mL^− 1 level varied from 86.4 ± 9.4% to 108.5 ± 10.5%, at 5.00 ng mL^− 1 level varied from 77.5 ± 10.8% to 104.6 ± 9.6% and at 50.00 ng mL^− 1 level varied from 70.2 ± 4.6% to 98.4 ± 8.5%. The proposed SPME method was applied in twenty-six water samples collected in the “Platô de Neópolis”, State of Sergipe, Brazil. Methyl parathion was detected in five samples with an average concentration of 0.17 ng mL^− 1 and bifenthrin, pyraclostrobin and azoxystrobin residues were found in three samples with average concentrations of 2.28, 3.12 and 0.15 ng mL^− 1, respectively.     

Effect of dimensions of multi-walled carbon nanotubes on its enrichment efficiency of metal ions from environmental waters

The effect of dimensions (length and external diameter) of multi-walled carbon nanotubes (MWCNTs) on its preconcentration efficiency towards some metal ions (Pb²⁺, Cd²⁺, Cu²⁺, Zn²⁺ and MnO₄⁻) from environmental waters prior to their analysis by flame atomic absorption spectroscopy (FAAS) was investigated. MWCNTs (as-received from the manufacturer) of various external diameters and lengths were involved. Other variables optimized included effects of pH of water sample, composition and volume of eluent, mass of the MWCNTs, breakthrough volume and coexisting ions. Maximum recovery of metal ions was obtained at pH 9 where it was thought that precipitation of metals as their hydroxides played the major factor in metals uptake by MWCNT. It was suggested that the use of appropriate dimensions of MWCNTs may support the trapping process of the precipitated metal hydroxides by MWCNTs. It was found that long MWCNT of length 5-15 μm and external diameter 10-30 nm gave the highest enrichment efficiency towards almost all the targeted metal ions. It could be used for preconcentration of MnO₄⁻, Cu²⁺, Zn²⁺ and Pb²⁺ with almost full recovery; but not for Cd²⁺ due to its low recovery. The optimized solid phase extraction (SPE) procedure was capable of determining metal ions in the linear range 20-100 ng mL⁻¹ (except for Zn²⁺ from 20 to 150 ng mL⁻¹). Detection limits were 0.709 ng mL⁻¹ for MnO₄⁻, 0.278 ng mL⁻¹ for Pb²⁺, 0.465 ng mL⁻¹ for Cu²⁺, 0.867 ng mL⁻¹ for Zn²⁺. Application of the optimized SPE procedure to environmental waters (tap water, reservoir water and stream water) gave spike recoveries of the metals in the range of 81-100%.