Determination of Melamine in Food by SPE and CZE with UV Detection

A novel method for the determination of melamine residue in food was developed using solid-phase extraction and capillary zone electrophoresis with UV detection. Spiked samples were extracted with 1% trichloroacetic acid while 0.03 g sodium deoxycholate was used to precipitate protein in the real samples. After centrifuging and clean-up by solid-phase extraction cartridge, the extract was directly analyzed by CZE–UV. The method was validated and good results were obtained with respect to precision, repeatability and spiked recovery. The limit of detection for melamine varied between 0.25 and 0.5 mg kg^?1. The proposed method was successfully applied for the analysis of melamine in food with total recoveries ranging from 94 to 102% in the spiked range of 0.5–5 mg kg^?1, and the relative standard deviations were between 1.5 and 4.1%.     

Optimization,Validation and Application of a Capillary Zone Electrophoresis Method for the Assay of Sparfloxacin in Pharmaceutical Formulation

Abstract

A capillary zone electrophoresis (CZE) method has been developed for the determination of the antibiotic sparfloxacin in tablets. The CZE separation was performed using 75 µm×35 cm fused-silica capillary under the following conditions: 25°C; applied voltage, 12 kV; 25 mM H₃PO₄-NaOH running buffer (pH 8.5). The detection wavelength was 254 nm. Flumequine was used as internal standard (IS). The method was suitably validated with respect to linearity, limit of detection and quantification, accuracy, precision, specificity, and robustness. The calibration was linear from 10 to 60 µg mL^?1 and the limit of detection and quantification were 5.38 and 9.46 µg mL^?1, respectively. Recoveries ranging from 95.68%–102.4% were obtained in the determination of sparfloxacin that were spiked to placebos. Excipients in the commercial tablets and degraded products from different stress conditions did not interfere in the assay. The method was successfully applied to the determination of sparfloxacin in pharmaceutical tablets.     

Capillary zone electrophoresis determination of oxytetracycline in pig tissue samples at maximum residue limits

Summary The determination of the antibiotic oxytetracycline (OTC), in pig tissues was investigated by capillary zone electrophoresis (CZE) with a prior solid-phase extraction (SPE) using alkyl-bonded silica and polymeric cartridges. The methodology developed allows determination of OTC in pig kidney, liver and muscle samples with detection limits below maximum residue limit values, and the procedures to extract OTC and clean-up the matrix are simple and reliable. The limit of detection for OTC was 160, 120 and 85 μg kg⁻¹ for kidney, liver and muscle samples, respectively. The average recoveries from spiked samples (200 μg kg⁻¹ and 1600 μg kg⁻¹) were in excess of 63% with coefficients of variation between 2.0 and 9.8%. This method would be useful for routine monitoring of oxytetracycline residues in pig tissues.     

Application of SPE Using Multi-Walled Carbon Nanotubes as Adsorbent and Rapid Resolution LC-MS-MS for the Simultaneous Determination of 11 Triazine Herbicides Residues in River Water

A method for the simultaneous determination of 11 triazine herbicides residues in river water has been developed. It involves solid-phase extraction (SPE) pretreatment step and rapid resolution liquid chromatography-tandem mass spectrometry (RRLC-MS-MS). In the SPE pretreatment step, the adsorptive performance of MWCNTs material as SPE adsorbent and the elution capability of five kinds of solvents were investigated; in the LC separation step, a rapid resolution high throughput LC column, was used and the gradient elution mode adopted. The linear correlation coefficients (r ²) of the method for 11 target analytes varied between 0.9930 and 0.9980, the mean recoveries were in the range of 73.0 and 98.0% with relative standard deviations (RSD) 2.6 ~ 4.2%, the method detection limits (MDL) were all below 0.1 ng L^?1. An expanded uncertainty of not more than 20% was estimated for each analyte at the spiked concentration of 4.0 μg L^?1. The proposed method was applied to the determination of the residue concentrations of 11 pollutants in Songhuajiang River water.     

Modified Screen-Printed Electrode for Potentiometric Determination of Copper(II) in Water Samples

Modified screen printed (SPE) and carbon paste electrodes (CPE) with phenanthroline–tetraphenyl borate ionophore [Phen:TPB] were fabricated for the determination of copper(II). The modified electrodes have linear responses over a wide concentration range (1 × 10^?6–1 × 10^?2 mol·L^?1) of copper(II) ion at 25 °C with divalent cationic slopes of 29.85 ± 0.58 and 29.45 ± 0.81 mV·decade^?1 and exhibit a detection limit of 1 × 10^?6 mol·L^?1 for SPE and CPE. The selectivity coefficient was measured using the match potential method in acetate buffer of pH = 4.2. The modified SPE and CPE sensors show high selectivity and sensitivity for determination of copper(II) and also show stable and reproducible response over a period of five and three months for SPE and CPE sensors, respectively. This method can be used for determination of copper(II) in water, soil, plant and fish tissue samples and the results obtained agreed with those obtained with atomic absorption spectrometer (AAS).     

Improvements in analytical methodology for the determination of frequently consumed illicit drugs in urban wastewater

Rapid and sensitive analytical methodology based on ultra high-performance liquid chromatography-tandem mass spectrometry has been developed for the determination of widely consumed drugs of abuse (amphetamines, MDMA, cocaine, opioids, cannabis and ketamine) and their major metabolites in urban wastewaters. Sample clean-up and pre-concentration was performed by a generic off-line SPE procedure using Oasis HLB. Special effort was made to incorporate amphetamine, which was found highly problematic in the wastewater samples tested, including an additional clean-up with Oasis MCX SPE and dispersive primary secondary amine. Correction for possible SPE losses or degradation during storage was made by the use of isotope-labelled internal standards (ILIS), available for all compounds, which were added to the samples as surrogates. Although ILIS were also efficient for matrix effects correction, the strong ionization suppression observed was not eliminated; therefore, a four-fold dilution prior to SPE was applied to influent wastewaters and a low injection volume was selected (3 μL), in order to reach a compromise between matrix effects, chromatographic performance and sensitivity. The method was validated at 25 and 200 ng L^?1 (effluent), and 100 and 800 ng L^?1 (influent), obtaining limits of quantification (i.e. the lowest level that the compound can be quantified and also confirmed with at least two MS/MS transitions) between 0.4–25 ng L^?1 (effluent) and 2–100 ng L^?1 (influent). The applicability of the method was demonstrated by analysis of 14 influent and 14 effluent wastewater samples collected over 2 weeks in Castellón (Spain) within a European collaborative study.     

SPE then RP-LC for Simultaneous Analysis of Cyromazine and its Metabolite Melamine in Liquid Milk and Egg

Solid-phase extraction (SPE) and reversed-phase liquid chromatography (RP-LC) have been used for simple, sensitive simultaneous analysis of cyromazine and melamine residues in liquid milk and eggs. The conditions used for SPE and LC were investigated and optimized. A combined cation-exchange–reversed-phase cartridge was used for clean-up, and an ODS (C₁₈) column (150 mm × 4.6 mm i.d., 5-μm particles) with 62:38 (v/v) 5 mm sodium lauryl sulfate (pH 3.4)–acetonitrile as mobile phase was used for RP-LC. Under the optimum conditions the method limit of detection (LOD) for both cyromazine and melamine was 6.2 μg kg^?1 for liquid milk samples, and 11.5 μg kg^?1 for egg samples. Average recovery of cyromazine and melamine from milk samples was 90.3%, RSD 4.6–5.6%, and 99.6%, RSD 3.2–4.7%, respectively. Average recovery of cyromazine and melamine from egg samples was 85.3%, RSD 1.0–4.7%, and 89.6%, RSD 3.1–5.0%, respectively. The method enables detection of melamine and cyromazine at levels as low as 20.7 μg kg^?1 in liquid milk and 38.3 μg kg^?1 in egg.     

SPE HG-AAS method for the determination of inorganic arsenic in rice—results from method validation studies and a survey on rice products

The present paper describes the development, validation and application of a method for inorganic arsenic (iAs) determination in rice samples. The separation of iAs from organoarsenic compounds was done by off-line solid-phase extraction (SPE) followed by hydride generation atomic absorption spectrometry (HG-AAS) detection. This approach was earlier developed for seafood samples (Rasmussen et al., Anal Bioanal Chem 403:2825–2834, 2012) and has in the present work been tailored for rice products and further optimised for a higher sample throughput and a lower detection limit. Water bath heating (90 °C, 60 min) of samples with dilute HNO₃ and H₂O₂ solubilised and oxidised all iAs to arsenate (As^V). Loading of buffered sample extracts (pH 6?±?1) followed by selective elution of arsenate from a strong anion exchange SPE cartridge enabled the selective iAs quantification by HG-AAS, measuring total arsenic (As) in the SPE eluate. The in-house validation gave mean recoveries of 101–106 % for spiked rice samples and in two reference samples. The limit of detection was 0.02 mg kg^?1, and repeatability and intra-laboratory reproducibility were less than 6 and 9 %, respectively. The SPE HG-AAS method produced similar results compared to parallel high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (ICP-MS) analysis. The SPE separation step was tested collaboratively, where the laboratories (N?=?10) used either HG-AAS or ICP-MS for iAs determination in a wholemeal rice powder. The trial gave satisfactory results (HorRat value of 1.6) and did not reveal significant difference (t test, p?>?0.05) between HG-AAS and ICP-MS quantification. The iAs concentration in 36 rice samples purchased on the Danish retail market varied (0.03–0.60 mg kg^?1), with the highest concentration found in a red rice sample.      

Determination of Flavonoid Markers in Honey with SPE and LC using Experimental Design

Determination of flavonoid markers quercetin, hesperetin, and chrysin, found in north Iranian citrus honey samples, was carried out by solid phase extraction (SPE) and isocratic liquid chromatographic separation using central composite design. Optimum conditions for SPE were achieved using 10 mL methanol/water (13:87, v/v, pH = 7) as the washing solvent and 4 mL methanol for elution. Good clean-up and high recovery >90% were observed for all analytes. The use of water/ACN/THF/AcOH (54:36:5:5, v/v) was found to serve as the optimum mobile phase composition and allowed for the separation of analytes from endogenous compounds present in honey. SPE parameters, such as maximum loading capacity and breakthrough volume, were also determined for each analyte. Limit of detection, linear range, recovery, repeatability of retention times, and peak heights were 3.11 × 10^?8–4.44 × 10^?8 g g^?1, 0.50–50.0 μg mL^?1 (R ² > 0.99), 90.7–96.9%, 3.0–3.6%, and 1.0–2.6%, respectively. Precision of the overall analytical procedure, estimated by five replicate measurements for quercetin, hesperetin and chrysin in citrus honey, as well as the relative standard deviations were 4.3%, 3.8%, and 5.5%, respectively.     

多壁碳纳米管固相萃取净化-高效液相色谱法测定猪肉和鸡肉中的磺胺多残留

建立了多壁碳纳米管为吸附剂的固相萃取净化-高效液相色谱-紫外检测测定猪肉和鸡肉中多种磺胺类药物多残留的方法。样品采用乙腈提取,多壁碳纳米管固相萃取净化,NaH₂PO₄缓冲溶液（pH 5.5~6.0）溶解上样,5%（v/v）丙酮-正己烷淋洗,丙酮-二氯甲烷（1：1,v/v）洗脱。色谱分离以50 mmol/L NaH₂PO₄-乙腈（7：3,v/v）为流动相,方法的线性范围为0.01~1.00 mg/L,线性相关系数大于0.998,检出限（LOD）为0.003 mg/L,定量限（LOQ）为0.01 mg/L。在0.02~0.2 mg/kg添加范围内,9种磺胺类药物的回收率高于70%,RSD低于8%,表明多壁碳纳米管对磺胺类药物具有较强的吸附富集能力。该方法简便、准确可用于动物组织及产品中磺胺药物残留的检测。     

Assessment of immobilized yeast for the separation and determination of platinum in environmental samples by flow-injection chemiluminescence and electrothermal atomic absorption spectrometry

The yeast Saccharomyces cerevisiae immobilized in calcium alginate beads was used for separation and subsequent determination of Pt in environmental samples by flow-injection chemiluminescence (FI-CL) and electrothermal atomic absorption spectrometry (ETAAS). The application of a yeast column resulted in an increase in the tolerable matrix ions concentration compared to direct measurements by both detection techniques. The developed FI-CL method of Pt determination based on the catalytic effect of Pt(IV) ions on luminol oxidation in alkaline medium is characterized by a low limit of detection (0.15 ng mL^?1), and good sensitivity and precision, and can be used for analysis of Pt in water samples. Determination of Pt in more complex environmental samples can be carried out by ETAAS (LOD?=?6 ng mL^?1) after introduction of a column clean-up step with 10 mM nitric acid. The accuracy of the method was confirmed by analyzing the certified reference material of platinum ore (SARM-7), spiked grass, and road dust samples.     

Analysis of triallate residue and degradation rate in wheat and soil by liquid chromatography coupled to tandem mass spectroscopy detection with multi-walled carbon nanotubes

A modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method for the analysis of triallate residue in wheat and soil was developed and validated. Multi-walled carbon nanotubes were used as clean-up sorbent. The residual levels and dissipation rates of triallate in wheat and soil were determined by liquid chromatography–tandem mass spectrometry. The limit of quantification was established as 0.01, 0.02 and 0.05 mg kg^?1 for soil, wheat and wheat plant samples, respectively. The average recoveries of triallate ranged from 77% to 108% at fortified levels of 0.01–0.5 mg kg^?1 with relative standard deviations of 3.0–8.4% (n = 5). From residue trials at three geographical experimental plots in China, the results showed that the half-lives of triallate in soils were 1.13–1.63 days. For trials applied according to the label recommendation, the final residues of triallate in wheat at harvest time were all below 0.05 mg kg^?1 (the maximum residue levels of China, Japan, Korea and the US).     

Hexafluoroisopropanol-induced coacervation in aqueous mixed systems of cationic and anionic surfactants for the extraction of sulfonamides in water samples

Hexafluoroisopropanol (HFIP)-induced coacervation in aqueous mixed systems of catanionic surfactants of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS) was described in detail, and its application in the extraction of strongly polar sulfonamides (SAs) was investigated. With 10 % (v/v) HFIP inclusion, coacervation formation and two-phase separation occur in a wide range of SDS/DTAB mole ratios (88:12～0:100 mol/mol) and total surfactant concentrations (10～200 mmol/L). The interactions between HFIP and DTAB play an important role in coacervation formation. The HFIP-induced SDS–DTAB coacervation extraction proves to be an efficient method for the extraction and preconcentration of SAs. Both hydrophobic interaction and polar interactions (hydrogen–bond, electrostatic, and π-cation) contribute to the distribution of SAs into coacervate phase. The proposed HFIP-induced SDS–DTAB coacervation extraction combined with HPLC–UV was employed for the extraction and quantitative determination of SAs in environmental water samples. Limits of detection were 1.4～2.5 ng mL^?1. Excellent linearity with correlation coefficients from 0.9990 to 0.9995 was obtained in the concentration of 0.01～10 μg mL^?1. Relative recoveries were in the range of 93.4～105.9 % for analysis of the lake, underground, and tap water samples spiked with SAs at 0.01, 1.0, and 10 μg/mL, respectively. Relative standard deviations were 0.7～3.2 % for intraday precision and 1.3～4.6 % for interday precision (n?=?3). Concentration factors were 17～49 for three water samples spiked with 0.01 μg/mL SAs. The results demonstrate that the proposed extraction method is feasible for the preconcentration and determination of trace SAs in real water samples. Graphical abstract

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Simultaneous Determination of Eight Typical Biogenic Amines by CZE with Capacitively Coupled Contactless Conductivity Detection

A novel method has been developed for simultaneous determination of eight typical biogenic amines (BAs) based on CZE with capacitively coupled contactless conductivity detection (CZE–C⁴D). On-column C⁴D was used for direct quantification of these nonUV-absorbing amine compounds without derivatization. The effects of various experimental factors on separation and detection were investigated. Under the optimum conditions, spermine, spermidine, histamine, putrescine, cadaver, β-phenylethylamine, tyramine, and tryptamine can be well separated within 24 min at the separation voltage of 16 kV in 150 mmol L^?1 18-crown-6/500 mmol L^?1 acetic acid running buffer, and the excitation voltage and frequency of C⁴D were 60 V and 550 kHz, respectively. A good linear relationship could be obtained between the peak area and the concentration of each BA at three orders of magnitude; the limits of detection were in the range of 44.3–149 ng mL^?1. This proposed method has been successfully applied for the analysis of BAs in water and hard liquor samples.     

Electrochemical Characterization of and Stripping Voltammetry at Screen Printed Electrodes Modified with Different Brands of Multiwall Carbon Nanotubes and Bismuth Films

A screen-printed electrode sensor has been fabricated by modifying the carbon ink surface with different brands of multiwall carbon nanotubes (MWCNTs) and bismuth film (BiF) for the determination of traces of lead, cadmium and zinc ions by square wave anodic stripping voltammetry. The MWCNTs, from three different sources, were functionalized and dispersed in Nafion (MWCNT-Nafion) solution and placed on screen printed electrodes (MWCNT-Nafion/SPE); bismuth films were then prepared by ex-situ plating of bismuth onto the MWCNT-Nafion/SPE electrodes. The electrochemical characteristics of BiF/MWCNT-Nafion/SPE/ were examined by electrochemical impedance spectroscopy and showed differences; the charge transfer resistance tends to decrease with negative applied potentials. After optimizing the experimental conditions, the square-wave peak current signal is linear in the nmol L^?1 range. The lowest limit of detection found for the separate determination of lead, cadmium and zinc were 0.7 nmol L^?1, 1.5 nmol L^?1, and 11.1 nmol L^?1, respectively, with a 120 s deposition time.     

Determination of carbamates at trace levels in water and cucumber by capillary liquid chromatography

A sensitive and reliable method using capillary HPLC with UV-diode array detection (DAD) has been developed and validated for trace determination of carbamate pesticides in cucumber and environmental water samples. The analytes, including carbofuran, carbaryl, methiocarb, promecarb, benthiocarb and fenoxycarb, present legal residue levels regulated by the EU Council Directive 98/83/EC on drinking water and by the Regulation (EC) No. 396/2005 on vegetables. A previous off-line solid-phase extraction (SPE) procedure was required for preconcentration and sample clean-up. The separation was achieved using a C₁₈ column (150?mm?×?0.5?mm I.D, 5?µm particle size) and a mobile phase consisting of ACN?:?water using gradient mode, with a flow rate of 10?µl min^?1. Taking advantages of the characteristics of capillary HPLC, low volume of sample and solvents were required, achieving limits of detection for the studied compounds ranged from 10.0–29.6?ng l^?1 for water samples and 1.8–5.6?µg kg^?1 for cucumber, using UV-detection. Recoveries studies for fortified samples, at three different concentration levels, were carried out obtaining recoveries ranging from 70.0 to 111.1% and relative standard deviations (RSDs) lower than 10.6%.     

Development of a Flow Injection Manifold for Napropamide Determination by Photo-Induced Chemiluminescence

A new, rapid, and simple method is proposed for the determination of the pesticide napropamide by photo-induced chemiluminescence detection coupled with a flow injection analysis (FIA) system. The emission was obtained by oxidation with periodate in basic medium, of the photoproducts generated on-line by UV irradiation (254 nm) of napropamide in acidic SDS (sodium dodecyl sulfate) medium. The flow method, in combination with the solid phase extraction (SPE) performed off-line with C₁₈ cartridges, allowed the determination of this pesticide over the 0.8–14.0 µ gL^?1 range, with a limit of detection of 0.3 µ gL^?1. The relative standard deviation (n = 9) at 2.5 µ gL^?1 level was 4.3% for the combined FIA-SPE system. After testing the influence of several potential interfering compounds, including ions and other pesticides, the method was successfully applied to the determination of napropamide in spiked water samples with recoveries between 96–103%.     

Matrix solid-phase dispersion extraction of organophosphorous pesticides from beeswax

Beeswax is a complex mixture of lipophilic compounds and other components such as aliphatic alcohols and carotenoids. Then, extraction and clean-up for pesticide analysis in beeswax is a challenge. In this work, a multiresidue method for the analysis of dichlorvos (DCV), diazinon, malathion, methyl parathion and coumaphos (CMF) in beeswax was developed. The proposed approach is based on matrix solid-phase dispersion extraction. The adsorbent for sample clean-up was studied and a simplex-centroid cubic statistical design was applied to evaluate pure solvents and their binary and ternary mixtures to elute the analytes. Finally, Florisil and ethyl acetate were chosen as solid support and eluting solvent, respectively. After extraction, pesticides were separated and detected by gas chromatography/mass spectrometry. The method achieved acceptable recoveries (70–85%; except for DCV, 24–38%) with relative standard deviations below 5%. The repeatability of the method was lower than 8% and interday variability was below 12%. The limit of detection (LOD) for the analytes varies between 0.2 and 2.6 µg?kg^?1 and limit of quantification from 0.93 to 8.8 µg?kg^?1. LOD reached for CMF was below the maximum residue limit allowed by the legislation of the United States and Canada.     

Preconcentration of beryllium via octadecyl silica gel microparticles doped with aluminon, and its determination by flame atomic absorption spectrometry

A simple and sensitive method is presented for solid phase extraction (SPE) and preconcentration of trace quantities of beryllium using octadecyl silica gel modifed with aurin tricarboxylic acid (aluminon). Beryllium is then determined by flame atomic absorption spectroscopy. Parameters affecting SPE such as pH, sample solution and eluent flow rate, type, concentration and volume of eluent, interfering ions and breakthrough volume, were investigated. Under optimal conditions, the beryllium ions were retained on the sorbent at pH 6–6.7, while 3.0 mL of 0.05 mol L^?1 HNO₃ is sufficient to elute the ions. The limit of detection (LOD) based on 3σ was 0.8 µg L^?1 for 250 mL sample solution and 5 mL 0.05 mol L^?1 HNO₃ as eluent. The LOD can reach 0.1 µg L^?1 for 1 L sample solution and 3 mL of 0.05 mol L^?1 HNO₃. The accuracy and precision (RSD %) of the method is >90% and <10%, respectively. The method was applied to the determination of beryllium in aqueous samples.     

Simultaneous Determination of Fluoroquinolones, Tetracyclines and Sulfonamides in Chicken Muscle by UPLC–MS–MS

A rapid and sensitive analytical method for the simultaneous determination of four fluoroquinolones, four tetracyclines and six sulfonamides in chicken muscle using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC–MS–MS) has been developed and validated. Samples were extracted with McIlvaine buffer-acetonitrile, defatted with n-hexane, and analyzed by UPLC–MS–MS. Solvent delay technique was applied in the analysis to remove the non-volatile phosphate and carry out farther on-line SPE clean-up. Satisfactory recoveries (55–110%) of all the veterinary drugs were demonstrated in 1, 10 and 20 μg kg^?1 spiked levels with the overall RSD for intra- and inter-day of 14 analytes less than 18%. The LOD and LOQ were 0.3 and 1.0 μg kg^?1, respectively. Quantitative results of 103 real samples indicated that the present method was suitable for the quantitative analysis of real samples.