Simple and rapid determination of phosphorus in meat samples by WD-XRF method

The wavelength dispersive X-ray fluorescence (WD-XRF) method for phosphorus determination in meat samples has been described. The effects of sample pretreatment on the XRF analysis have been discussed. The phosphorus content determined in meat samples ranged from 603 ± 6 to 613 ± 19 mg P/100g dry mass (d.m.), depending on the sample preparation technique. The meat samples spiked with phosphates have been used for the calibration procedure. The accuracy was determined against a number of certified reference materials (SMRD 2000, RF 8414, NIST-1568A, and NIST-1549), and recovery was assayed using the standard addition procedure. The proposed method has been compared with the standard spectrophotometric method (PN-ISO 13730, 1999) of total phosphorus determination. The sample pretreatment procedure has been reduced to minimum the presented results suggest the WD-XRF method can be an alternative to the spectrophotometric analysis.     

Bioanalysis of the neuropeptide des-enkephalin-gamma-endorphin by high-performance liquid chromatography with on-line sample pretreatment using gel permeation and solid-phase isolation.

A bioanalytical method is described that allows the determination of a number of beta-endorphin-related peptides. The method is based on the application of fluorescence detection after high-performance liquid chromatography followed by post-column derivatization with o-phthaldialdehyde. Concentrations exceeding 10-25 ng/ml could be determined by using conventional fluorescence detection, whereas lower concentrations demand the use of laser-induced fluorescence detection. The sample pretreatment includes the use of on-line gel permeation, on-line solid-phase isolation and heart cutting of a peak from reversed-phase gradient elution. The sample pretreatment procedure does not discriminate between the dodecapeptide des-enkaphalin-gamma-endorphin (DE gamma E) and its metabolites in order to obtain similar recoveries for all components. The final chromatographic phase system is based on ion-pair formation, which permits the separation of DE gamma E from its metabolites and degradation products. The optimized procedure allows the determination of these peptides in plasma at concentration levels down to about 1 ng/ml, demanding a sample volume of 1 ml.     

Development of metrological models for internal standard single-point and multi-point calibrations for the assessment of tear gas weapons compliance with legislation

Tear gases are the most widely used non-lethal weapons, both by security forces and by the general public. The pepper spray, whose active agent is capsaicin, is the only self-defence aerosol allowed in Portugal, where capsaicin concentration must be below 5 g/100 mL. The cost-effective evaluation of the compliance of self-defence weapons with legislation involves the use of two measurement procedures with increasing quantitative capability. Samples are first assessed by preliminary measurement procedure based on single-point GC–MS calibration. Whenever the measurement uncertainty from this assessment makes evaluation inconclusive, the evaluation of sample compliance using multi-point GC–MS calibration is performed. Metrological models including sound criteria for the evaluation of sample compliance with legislation were developed for both measurement procedures. Such models include the evaluation of the impact of instrumental performance, calibration model, sample dilution and standards preparation on measurement uncertainty. The relative expanded uncertainty, in the studied range (capsaicin 3–7 g/100 mL), of measurements supported in single-point calibrations ranged from 10 to 22% and the ones supported on multi-point calibrations from 8 to 12% depending on capsaicin concentration and daily GC–MS repeatability. Measurements are fit for the intended use since they present a relative expanded uncertainty smaller than a target value of 30, or 15%, for measurements supported in single- or multi-point calibrations, respectively.     

On-line sample preparation and determination of phenols with a Flow-Analysis method

Summary A Flow-Analysis system has been developed to automate the phenol determination according to the German standard method DIN 38409-H16-2. The automation leads to a significant acceleration of the procedure. One analysis only lasts 3 min while the complete manual determination requires 3 h. Also the sample, solvent and reagent volumes are reduced to a tenth of the volumes demanded by the standard method. The described phenol determination is based on the integration of an airsegmented (Airsegmented-Flow-Analysis SFA) part in a Flow-Injection-Analysis (FIA) system. The main steps of the analytical procedure are: Reproducible inserting of the sample in a carrierstream, sample pretreatment and sample measuring. In the first step the sample is injected into the carrierstream. It transports the sample in the reactioncoil and than through the distillation unit. The steam distillation represents the sample preparation step; therefore an airsegmented stream is necessary. Afterwards the different phases (liquid and gas) were singled again and the distilled solution is fed into the FIA manifold. The determination itself takes place inside the FIA system. The limit of determination amounts to 0.01 mg l^–1 with a standard deviation of 1.5%. Different waste, surface and drinking water samples have been analyzed without any problems. The results correspond very well to those obtained by manual procedure.     

Determination of substituted purines in body fluids by micellar electrokinetic capillary chromatography with direct sample injection.

Many substituted purines (theobromine, caffeine, paraxanthine, theophylline and uric acid, as well as other methylated xanthines and uric acids) can easily be separated and analysed in one run using micellar electrokinetic capillary chromatography with a boratephosphate buffer containing 75 mM sodium dodecyl sulphate (pH approximately 9). Serum, saliva and urine samples collected after the self-administration of caffeine and serum samples from patients receiving theophylline or caffeine pharmacotherapy were screened for substituted purines. The data presented show the ease of using on-column multi-wavelength detection for investigating the feasibility of direct sample application, the characterization of sample pretreatment procedures and peak confirmation by comparing absorption spectra. It is shown that the determination of purines in serum and saliva samples, including therapeutic concentrations of caffeine and theophylline, can be accomplished without any sample pretreatment, whereas sample extraction is required for the determination of purines in urine. Quantitative data for the determination of micromolar amounts of theophylline (samples from adult patients) and caffeine (samples from infants born prematurely) in serum samples compared well with data obtained by non-isotopic immunoassays. Micellar electrokinetic capillary chromatography with the direct injection of serum or saliva samples requires only microlitre volumes of sample and several different compounds can be determined within a few minutes.     

Improved Sensing of Capsaicin with TiO2 Nanoparticles Modified Epoxy Graphite Electrode

The presented research focuses on the electrochemical determination of capsaicin, a lipophilic alkaloid which originates hotness in chili peppers. An electrochemical sensor based on epoxy‐graphite composite with the modification of titanium dioxide (TiO₂) nanoparticles is developed for the determination of this alkaloid. The measurements were carried out in glycine buffer at pH 2.5 using cyclic voltammetry. Two linear concentration ranges were obtained from 6 to 75 μM (R=0.99) and from 12 to 138 μM, with a detection limit of 5.34 μM and 11.3 μM capsaicin, for 1^st and 2^nd oxidation peak, respectively. The main advantage of developed sensor is its repeatability and robustness against fouling; the relative standard deviation (RSD) value was 2.53 % (n=10). This voltammetric sensing procedure has successfully been applied to quantify capsaicin in various real samples such as hot chili sauce and pharmaceutical preparations.     

Determination of aluminium and chromium in serum by atomic absorption spectrometry

Summary The optimal conditions for the determination of aluminium and chromium in blood serum are proposed. Several sample pretreatment procedures for the purpose are compared. The best results are obtained by sample dilution with nitric acid (0.1 mol/l) and addition of Mg(NO₃)₂ as modifier with a magnesium concentration of 0.2 mg/ml. This procedure has been used for studying the intestinal intake of aluminium by patients after oral administration of aluminium compounds.     

Electrochemical Sensor for Sensitive Determination of Capsaicin Using Pd Decorated Reduced Graphene Oxide

In this work, the reduced graphene oxide functionalized with poly dimethyl diallyl ammonium chloride (PDDA) modified palladium nanoparticles (PDDA‐rGO/Pd) had been facile synthesized and used as the sensing layer for sensitive determination of capsaicin. The prepared composite was characterized by transmission electron microscopy, UV‐visible absorption spectroscopy. The image demonstrated that Pd nanoparticles were uniformly distributed on the graphene surface. The electrochemical properties of the prepared sensor were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that the nanocomposite exhibits attractive electrocatalytic activity towards the oxidation of capsaicin. This attributed to the synergistic action of the excellent properties of Pd nanoparticles and graphene nanosheets. Under optimized conditions, the electrochemical sensor possessed a dynamic linear range from 0.32 μM to 64 μM with a detection limit of 0.10 μM (S/N=3) for capsaicin detection. Moreover, the cost‐effective and simple fabrication procedure, good reproducibility and stability as well as acceptable accuracy for capsaicin determination in actual samples are also the main advantages of this method, which might have broad application in other amide alkaloid detection.     

GPC–HPLC–MS/MS法测定食用油中天然辣椒素、二氢辣椒素和合成辣椒素含量

以动植物油脂为实验材料,建立了测定食用油中天然辣椒素、二氢辣椒素和合成辣椒素含量的凝胶渗透色谱–高效液相色谱–串联质谱(GPC–HPLC–MS/MS)法。样品经凝胶渗透色谱净化后,采用液相色谱串联质谱法(HPLC–ESI–MS/MS)分析,多反应监测模式(MRM)下外标法定量。在0.1~5.0μg/L范围内线性良好,天然辣椒素、二氢辣椒素和合成辣椒素的相关系数分别为0.999 6,0.999 8,0.999 8,检出限为0.5μg/kg。在5μg/kg添加水平下,空白加标回收率为71.5%~82.5%,测定结果的相对标准偏差为3.0%~8.3%(n=6)。该方法样品处理过程简便快捷,测定结果准确,可满足实验室大量、快速分析的需求。     

Determination of polycyclic aromatic hydrocarbons in water by solid-phase microextraction and liquid chromatography.

This study describes the determination of polycyclic aromatic hydrocarbons (PAHs) in water using high-performance liquid chromatography (HPLC) coupled with fluorescence detection (FLD). Because individual PAHs are generally present in water only at trace levels, a sensitive and accurate determination technique is essential. The separation and detection of five PAHs were run completely within 25 min by the HPLC/FLD system with an analytical C18 column, a fluorescence detection, and acetonitrile-water gradient elution. Calibration graphs were linear with very good correlation coefficients (r > 0.9998), and the detection limits were in the range of 2-6 ng/l for five PAHs. Solid phase microextraction (SPME) was performed for sample pretreatment prior to HPLC-FLD determination, and the governing parameters were investigated. Compared to conventional methods, SPME has high recovery, saves considerable time, and reduces solvents waste. The extraction efficiencies of five PAHs were above 88% and the extraction times were 35 min in one pretreatment procedure. One particular discovery is that 1.5 M sodium monochloroactate (ClCH2COONa) can improve the extraction yield of PAH compounds more than other inorganic salts. The SPME-HPLC-FLD technique provides a relatively simple, convenient, practical procedure, which was here successfully applied to determine five PAHs in water from authentic water samples.     

Exploitation of a short monolithic column for in‐line separation and preconcentration: Environmental friendly determination of the emerging pollutant salicylic acid in natural waters

Salicylic acid is an emerging environmental contaminant, usually found at ng/L concentrations in natural waters. Its quantification usually involves liquid chromatography‐tandem mass spectrometry, which requires complex and costly instrumentation as well as time‐consuming sample pretreatment, typically involving large solvent volumes. In this work, sequential injection chromatography was exploited to develop a fast, green, cost‐effective, and highly sensitive procedure for fluorimetric determination of salicylic acid in natural waters. Analyte preconcentration directly on the chromatographic column (on‐column preconcentration) was exploited to improve detectability, yielding an enrichment factor of 122 (1.75 mL of sample) and takes only 8.5 min per determination. A detection limit of 20 ng/L, a linear response range from 0.06 to 5.00 µg/L, coefficients of variation lower than 3.0% (n = 10), and recoveries within 86 and 114% were estimated. The procedure was applied for the analyses of freshwater samples and results agreed with those obtained by liquid chromatography‐tandem mass spectrometry at the 95% confidence level. The proposed procedure encompasses in‐line concentration, isolation/separation, and detection, without the need for sample clean‐up, thus minimizing the consumption of organic solvents and risk of analyte losse.     

Determination of organochlorine pesticides in water using microwave assisted headspace solid-phase microextraction and gas chromatography

A coupled technique, microwave-assisted headspace solid-phase microextraction (MA-HS-SPME), was investigated for one-step in situ sample pretreatment for organochlorine pesticides (OCPs) prior to gas chromatographic determination. The OCPs, aldrin, o,p'-DDE, p,p'-DDE, o,p'-DDT, p,p'-DDT, dieldrin, alpha-endosulfan, beta-endosulfan, endosulfan sulfate, endrin, delta-HCH, gamma-HCH, heptachlor, heptachlor epoxide, methoxychlor and trifluralin were collected by the proposed method and analyzed by gas chromatography with electron-capture detection (GC-ECD). To perform the MA-HS-SPME, six types of SPME fibers were examined and compared. The parameters affecting the efficiency in MA-HS-SPME process such as sampling time and temperature, microwave irradiation power, desorption temperature and time were studied to obtain the optimal conditions. The method was developed using spiked water samples such as field water and with 0.05% humic acid in a concentration range of 0.05-2.5 microg/l except endosulfan sulfate in 0.25-2.5 microg/l. The detection was linear over the studied concentration range with r2>0.9978. The detection limits varied from 0.002 to 0.070 microg/l based on S/N=3 and the relative standard deviations for repeatability were <15%. A certified reference sample of OCPs in aqueous solution was analyzed by the proposed method and compared with the conventional liquid-liquid extraction procedure. These results are in good agreement. The results indicate that the proposed method provides a very simple, fast, and solvent-free procedure to achieve sample pretreatment prior to the trace-level screening determination of organochloride pesticides by gas chromatography.     

Determination of mercury by differential-pulse anodic-stripping voltammetry with various working electrodes Application to the analysis of natural water sediments

Four types of working electrode (glassy-carbon and gold rotating-disk electrodes and two types of gold-film electrode) have been used in determination of traces of mercury by differential-pulse anodic-stripping voltammetry, and the analytical parameters of the procedures compared. The technique has been applied to the analysis of river sediments. The lowest limit of detection (0.02 μg/l.) was obtained with the gold rotating-disk electrode. Two procedures have been found optimal for analyses of sediment samples; determination with the gold rotating-disk electrode and solution-exchange after the preelectrolysis, and determination with the gold-film electrode prepared in situ in the sample extract. The sample pretreatment involved a separation of the 0.45–63 μm fraction, mineralization with a mixture of hydrochloric and nitric acids (3:1 or 1:3) under atmospheric pressure in a fused silica vessel, followed by irradiation with ultraviolet light, after addition of hydrogen peroxide (to destroy organic matter). The most serious interference is from iron; this can be prevented by adding fluoride or pyrophosphate. The procedure is an alternative to the AAS determination of the total mercury content in sediments, especially with heavily polluted samples (mercury concentrations up to 0.01%).     

Flow-injection on-line oxidizing fluorimetry and solid phase extraction for determination of thioridazine hydrochloride in human plasma

A simple, sensitive and specific fluorimetric method has been developed for the determination of thioridazine hydrochloride in human plasma involving solid phase extraction (SPE). In a flow-injection system, thioridazine hydrochloride is on-line oxidized into a strongly fluorescent compound with a lead dioxide solid-phase reactor and the fluorescence intensity is measured with a fluorescence detector (λ_ex = 349 nm, λ_em = 429 nm). A comparison of plasma sample pretreatment between SPE procedure and precipitation method was made and the results showed that SPE procedure was better than precipitation method. Under the optimum conditions, the fluorescence intensity is proportional to the concentration of thioridazine hydrochloride in the range from 0.015 to 2.000 μg mL⁻¹. The detection limit is 5.5 ng mL⁻¹ of thioridazine hydrochloride and the relative standard deviation is 1.06%. This method has been applied to determination of thioridazine hydrochloride in real patients plasma samples with the results compared with those obtained by HPLC method.     

Fast and Selective Determination of Pesticides in Water by Automated On-Line Solid Phase Extraction Liquid Chromatography Tandem Mass Spectrometry

An automated on line-solid phase extraction (SPE) liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of 17 polar pesticides in water. Minimizing sample pretreatment and using a fast chromatographic separation, the method allowed a sample to be processed in 15 minutes. The MS analysis was performed by Data Dependent Acquisition, using the triggered Multiple Reaction Mode function that provided analyte confirmation, thus enhancing selectivity without compromising sensitivity. In fact, the optimized method enabled the determination of the considered pesticides at the ultratrace level, with detection limits in the range 0.07–1.65 ng/L (propazine and atrazine-desisopropyl, respectively); the only exception was linuron that showed a slightly higher detection limit (12.2 ng/L). The optimized method was then applied to real water samples; five pesticides were determined in river water, in the range 1.17–14.2 ng/L, while four were measured in drinking water, in the range 0.91–2.25 ng/L.     

影响离子色谱测量准确性的因素

介绍了离子色谱测量过程中色谱条件的变化、样品前处理方法和操作过程等因素对测量结果准确性的影响,提出了相应的解决措施和校准方法.以实际样品测定为例介绍了样品前处理过程中待测组分浓度和形态的变化,对定量分析结果造成的误差及修正方法.     

Selective separation and determination of quercetin from red wine by molecularly imprinted nanoparticles coupled with HPLC and ultraviolet detection

In this study, a highly sensitive and selective sample pretreatment procedure using molecularly imprinted silica nanoparticles was developed for the extraction and determination of quercetin in red wine samples coupled with high‐performance liquid chromatography with ultraviolet detection. The imprinted silica nanoparticles were prepared in the presence of N‐acryoyl‐l ‐aspartic acid (functional monomer), quercetin (template), azobisisobutyronitrile (initiator) and methylene bisacrylamide (cross‐linker) and methanol/water (porogen) via surface‐initiated reversible addition‐fragmentation chain transfer polymerization. Surface characterization was performed and several imprinting parameters were investigated, and the results indicated that adsorption of quercetin on the imprinted silica nanoparticles followed a pseudo‐first‐order adsorption isotherm with a maximum adsorption capacity at 26.4 mg/g within 60 min. The imprinted silica nanoparticles also showed satisfactory selectivity towards quercetin as compared with its structural analogues. Moreover, the imprinted nanoparticles preserved their recognition ability even after five adsorption–desorption cycles. Meanwhile, the nanoparticles were successfully applied to selective extraction of quercetin from red wine with a high recovery (99.7–100.4%). The limit of detection was calculated to be 0.058 μg/mL with a correlation coefficient 0.9996 in the range of 0.2–50 μg/mL. As a result, the developed selective extraction method using molecular imprinting technology simplifies the sample pretreatment procedure before determination of quercetin in real samples.     

Determination of selenium in infant foods using electrothermal atomic absorption spectrometry with direct slurry sample introduction

Slurry sampling electrothermal atomic absorption (SS ETAAS) was applied to the development of a sensitive and precise method for selenium determination in infant foods without sample pretreatment. Suspensions prepared in a medium containing 0.1% Triton X-100, 0.5 or 5% v/v concentrated HNO₃ were directly introduced into the furnace. The accuracy of the procedure was confirmed by analysis of a standard reference material and comparison with hydride generation atomic absorption spectrometric (HGAAS) procedure. The characteristic mass is 44 pg and detection limit 0.43 μg·l⁻¹.     

Magnetic solid‐phase extraction for determination of sulpiride in human urine and blood using high‐performance liquid chromatography

A novel and efficient sample preconcentration technique based on the Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) coated with silica (SiO₂) has been developed for extraction and determination of sulpiride. The functionalized MNPs showed excellent dispersibility in aqueous solution and were applied to magnetic solid‐phase extraction of sulpiride from human urine and blood prior to high‐performance liquid chromatography analysis. The separation, preconcentration and desorption procedure was completed in 10 min. Optimal experimental conditions, including sample pH, the amount of the MNPs, eluent type and volume, and the ultrasonication time were studied and established. The method showed good linearity for the determination of sulpiride in the concentration range of 10–1000 ng/mL in urine and blood. The recovery of the method was in the range between 91.2 and 97.5%, and the limit of detection was 2 ng/mL for sulpiride in human blood and urine. The results indicated that the present procedure is a suitable pretreatment method for biological samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Kinetic determination of creatinine in biological fluids by stopped-flow injection analysis

Summary A kinetic photometric method for the determination of creatinine in biological fluids based on the Jaffé reaction and the use of a flow injection manifold where the reacting plug is halted prior to detection is proposed. The wide linear range of the calibration curve obtained (between 3 and 150 g ml^–1) allows the determination of the analyte in serum and urine. The kinetic measurements require no sample pretreatment (urine samples need dilution). The proposed method compares favourably with the standard recommended procedure.