Liquid chromatographic determination of aniline in table-top sweeteners based on pre-column derivatization with 1,2-naphthoquinone-4-sulfonate

A liquid chromatographic method for the determination of aniline in cyclamate sweeteners based on a pre-column derivatization with 1,2-naphthoquinone-4-sulfonate (NQS) is proposed. Aniline traces were extracted from the cyclamate samples using dichloromethane. After solvent evaporation, the dry residue was derivatized with NQS at pH 9.5 and 85 degrees C for 1 min. The aniline derivative, which was extracted from the reacting mixture, was redissolved in the eluent solution and injected into the chromatographic system. The separation of aniline derivative from other amine impurities was carried out in a C18 column using a 2% acetic acid-methanol (40:60, v/v) mobile phase. Results from the analysis of aniline in the sweetener samples with the proposed method were compared with those from the standard method. A good concordance between the two methods was observed.     

Flow-Injection Differential Spectrophotometric pH Selectivity System for the Determination of Cyclamate Contaminants

A flow-injection system with differential spectrophotometric detection is proposed for the simultaneous determination of aniline and cyclohexylamine based on their reaction with 1,2-naphthoquinone-4-sulfonate (NQS). The pH is chosen to achieve selectivity since only aniline reacts at acidic pH whereas the two amines are derivatized in basic medium. The flow manifold comprises two reactors and two detection cells for developing and monitoring the reaction under selective and general (non-selective) conditions. A double beam spectrophotometer is used for differential detection, with two flow cells placed in the sample and reference holders. Figures of merit such as sensitivity, linear range, detection limit and precision are established. The evaluation of accuracy using a series of synthetic mixtures indicates overall prediction errors of 3% and 5% for aniline and cyclohexylamine, respectively. The method is applied to the determination of amine impurities in commercial sweeteners. Good concordance between the proposed and the standard chromatographic methods is found.     

液相色谱串联质谱法测定冷冻饮品中环己基氨基磺酸钠

建立了液相色谱～串联质谱测定冷冻饮品中环己基氨基磺酸钠的方法。冷冻饮品经净化、冷冻离心后用水稀释定容,采用C18色谱柱（50mm×2．1mm,1．7μm）,以乙腈-0．01mol／L乙酸铵缓冲溶液为流动相,电喷雾离子源负离子模式（MRM）定性、定量测定环己基氨基磺酸钠。环己基氨基磺酸钠的质量浓度在2—1000μg／L范围内与峰面积呈线性关系,相关系数,=0．9999,方法的定量限为0．02mg／kg。在10—100μg／L范围内,3水平加标回收率为87．5％～101．8％,测定结果的相对标准偏差为3．0％（H=6）。该方法净化效果好,灵敏度高,能快速完成冷冻饮品中环己基氨基磺酸钠的测定。     

Flow injection kinetic spectrofluorimetric determination of trace amounts of osmium

A flow injection (FI) kinetic spectrofluorimetric method is described for the determination of osmium(IV) and the possible mechanism of catalytic reaction is discussed. The method is based on the fluorescence enhancing reaction of o-vanillin furfuralhydrazone (OVFH) with potassium bromate, which is catalyzed by Os(IV) in water medium at pH 6.10 and 45 degrees C. OVFH is newly synthesized and its ionization, IR and elemental analysis are established. Under these experimental conditions, the oxidized product of OVFH has excitation and emission maxima at 337 and 490 nm, respectively. The linear range of this method is 0-600 ng ml(-1) with the R.S.D. of 1.2%. The detection limit is 1.0 ng ml(-1) of Os(IV). A high analysis rate of 24 samples h(-1) is obtained by the FI method. The proposed method is applied successfully to determine Os(IV) in synthetic mixture and mineral samples, and the results are well consistent with the standard values.     

Rapid determination of cyclamate in foods by solid-phase extraction and capillary electrophoresis

A method for the determination of cyclamate in food was developed using solid-phase extraction (SPE) and capillary electrophoresis (CE) with indirect ultraviolet (UV) detection. A 5-10 g sample in 0.1 mol/L hydrochloric acid was homogenized and made up to a volume of 50 mL with 0.1 mol/L hydrochloric acid. After the sample was centrifuged, 25 mL of supernatant was loaded into an Oasis HLB SPE cartridge. The cartridge was washed with 2 mL of demineralized water followed by 2 mL of 50% aqueous methanol, and cyclamate was eluted with 4.5 mL of 50% aqueous methanol. The eluate was added to a solution of sodium propionate (internal standard) for CE analysis. The cyclamate in the eluate was electrophoresed on a fused-silica capillary using 1 mmol/L hexadecyltrimethylammonium bromide and 10 mmol/L potassium sorbate as a running buffer. Detection and reference wavelengths of cyclamate determined with a UV detector were 300 and 254 nm, respectively. The calibration curves for cyclamate showed good linearity in the range of 2-1000 microg/mL and the limits of detection in beverage, fruit in syrup, jam, pickles and confectionary are sample dependent and ranged from 5-10 microg/g. The recovery of cyclamate added at a level of 200 microg/g to various kinds of foods was 93.3-108.3% and the relative standard deviation was less than 4.9% (n=3). A number of commercial samples were analyzed using the proposed method. Cyclamate was detected in one waume, two pickles, and two sunflower seeds. The quantitative values determined with CE correlated to those from high-performance liquid chromatography (HPLC) (the detected values of cyclamate in a sunflower seed measured by CE and HPLC were 3.40 g/kg and 3.51 g/kg, respectively). This analytical method for cyclamate using CE is especially suitable for use in the field.     

Determination of cyclamate in low-calorie foods by high-performance liquid chromatography with indirect visible photometry

A rapid and simple method using reversed-phase high-performance liquid chromatography combined with indirect visible photometry at 433 nm was developed to determine cyclamate in some food samples. Cyclamate was not detected in these chosen samples as its use is banned in Hong Kong. Cyclamate can easily be detected in spiked samples using a mobile phase consisting of 30 mumol dm-3 Methyl Red and 0.02 mol dm-3 phosphate buffer (pH 7.0)-methanol in a volume ratio of 3:2. The column temperature was set at 23 degrees C. The detection limit was 0.14 mmol dm-3 and the relative standard deviation of the peak area response was 0.58% for a solution containing 5.0 mmol dm-3 of cyclamate (n = 8). This method was successfully applied to the analysis of eight spiked food samples and the cyclamate recoveries for these samples ranged from 93 to 99%.     

Quantification of cyclamate and cyclohexylamine in urine samples using high-performance liquid chromatography with trinitrobenzenesulfonic acid pre-column derivatization

An HPLC isocratic method with pre-column derivatization and UV detection for the quantification of cyclamate and cyclohexylamine in urine samples is described. The method requires very little sample preparation. Free cyclohexylamine is analysed in a first run and subsequently cyclamate is analysed as cyclohexylamine, after the simple process of oxidation of the sample by means of hydrogen peroxide. Cycloheptylamine is used as internal standard. Trinitrobenzenesulfonic acid (TNBS) appears to be a good reagent for the pre-column derivatization. The time per run is 15 min; the coefficients of variation of the assays range from 1.1 to 5.5%; the limits of detection are 0.09 and 0.11 ppm for cyclohexylamine and cyclamate anion, respectively. The system described has always performed efficiently, with a high degree of stability, in daily routine work.     

Determination of cyclamate in foods by ultraperformance liquid chromatography/tandem mass spectrometry

A highly sensitive and selective method that requires minimal sample preparation was developed for the confirmation and quantitation of cyclamate in a variety of foods by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). Sample preparation consisted of homogenization followed by extraction and dilution of cyclamate with water. HPLC separation was achieved using a bridged ethyl hybrid C18 high-pressure column with a mobile phase consisting of 0.15% acetic acid and methanol. Under electrospray ionization negative conditions, quantitation was achieved by monitoring the fragment m/z = 79.7 while also collecting parent ion m/z = 177.9. Two food matrixes, diet soda and jelly, were subjected to a validation procedure in order to evaluate the applicability of the method. The cyclamate limit of detection for both matrixes was determined to be 0.050 microg/g with a limit of quantitation of 0.150 microg/g. The correlation coefficient of the calibration curves was >0.9998 from 0.0005 to 0.100 microg/mL. The method has been used for the determination of cyclamate in several foods and the results are presented.     

Efficient flow injection and sequential injection methods for spectrophotometric determination of oxybenzone in sunscreens based on reaction with Ni(II)

Spectrophotometric determination of a widely used UV-filter, such as oxybenzone, is proposed. The method is based on the complexation reaction between oxybenzone and Ni(II) in ammoniacal medium. The stoichiometry of the reaction, established by the Job method, was 1:1. Reaction conditions were studied and the experimental parameters were optimized, for both flow injection (FI) and sequential injection (SI) determinations, with comparative purposes. Sunscreen formulations containing oxybenzone were analyzed by the proposed methods and results compared with those obtained by HPLC. Data show that both FI and SI procedures provide accurate and precise results. The ruggedness, sensitivity and LOD are adequate to the analysis requirements. The sample frequency obtained by FI is three-fold higher than that of SI analysis. SI is less reagent-consuming than FI.     

Efficient flow injection and sequential injection methods for spectrophotometric determination of oxybenzone in sunscreens based on reaction with Ni(II)

Spectrophotometric determination of a widely used UV-filter, such as oxybenzone, is proposed. The method is based on the complexation reaction between oxybenzone and Ni(II) in ammoniacal medium. The stoichiometry of the reaction, established by the Job method, was 1:1. Reaction conditions were studied and the experimental parameters were optimized, for both flow injection (FI) and sequential injection (SI) determinations, with comparative purposes. Sunscreen formulations containing oxybenzone were analyzed by the proposed methods and results compared with those obtained by HPLC. Data show that both FI and SI procedures provide accurate and precise results. The ruggedness, sensitivity and LOD are adequate to the analysis requirements. The sample frequency obtained by FI is three-fold higher than that of SI analysis. SI is less reagent-consuming than FI.     

Accelerated micro-sequential injection in lab-on-valve format, applied to enzymatic assays

The assay cycle of sequential injection (SI) analysis has been greatly accelerated by simultaneously processing two sample injections within the same manifold. This is achieved through micro-miniaturization of the SI system using the lab-on-valve format (LOV), and by optimizing the assay protocol for stopped-flow reaction rate measurements. The approach has been tested on enzymatic assays of glucose and ethanol, but it is, in principle, applicable to all SI reagent-based assays. The average assay time for a single run has been shortened from 200 s to approximately 30 s. Assays were carried out at 22 degree C and 37 degree C using commercially available reagent kits. For glucose, at 22 degree C, the calibration had a linear response (r(2)= 0.9999) for the concentration range of 100-1000 ppm. At 37 degree C, the calibration was linear (r(2)= 0.9996) for 100-600 ppm glucose, but was a second order polynomial curve (r(2)= 0.9996) for 100-1000 ppm. For ethanol, at both 22 degree C and 37 degree C, the calibrations were linear for the concentration range of 50-250 ppm. The r(2) at two temperatures was 0.9994 and 0.9995, respectively. For both the glucose and ethanol assays, the relative standard deviations were below 3%. Factors affecting sampling frequency are discussed. In this work, sequential injection is shown, for the first time, to achieve sampling frequency comparable to flow injection (FI), while retaining the advantages of small reagent consumption (typically microlitres per assay), minimized waste production, full automation of assay protocols, and zero carryover.     

Electrospun electroactive nanofibers of gelatin‐oligoaniline/Poly (vinyl alcohol) templates for architecting of cardiac tissue with on‐demand drug release

In this study, grafted gelatin with oligoaniline (GelOA) was synthesized and then mixed with Poly (vinyl alcohol) (PVA). Several scaffolds with different ratio of PVA/GelOA were electrospun to fabricate electroactive scaffolds. GelOA was characterized using Fourier‐transform infrared spectroscopy (FTIR); moreover, nanofiber properties were evaluated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscope (SEM) analyses. Nanofibers diameter was decreased with aniline oligomer increment form 300 to 150 nm because of the hydrophobic nature of the aniline oligomer. Aniline oligomer electroactivity was studied using cyclic voltammetry, which exhibited two redox peaks at 0.4 and 0.6. Moreover, aniline oligomer enhancement resulted in melting point increasing from 220°C to 230°C because of the crystallinity increment. To assess the biocompatibility of nanofibers, cell viability and cell adhesion were tracked using mesenchymal stem cell (MSCs). It was revealed that the presence of aniline oligomer leads to enhancing the conductivity, thermal properties and lowering the degradation rate and drug release. Among of different scaffolds, sample with high content of GelOA shows better behavior in physical and biological properties. Accumulative drug releases under applied electrical field at 40 minutes showed that the drug release for stimulated condition is about 33% more than the unapplied electrical field one.     

高效液相色谱-线性离子阱串联质谱技术用于白酒中甜蜜素测定的确证分析

建立了白酒中甜蜜素的高效液相色谱-线性离子阱串联质谱测定方法。该方法可同时准确定性和定量。样品无需前处理,过膜后直接进样,由C18色谱柱分离,采用多反应监测(MRM)和触发增强子离子扫描模式检测,采集到的MRM数据用于定量测定,同时得到的高质量子离子谱图用于谱图库检索的方法进行定性确证分析。本文采用外标法定量,方法的线性范围为1.320～132.0 μg/L（r=0.9991）;检出限(信噪比为3)为0.1 μg/L;添加水平分别为2.640、26.40、100.0 μg/L的3个样品的加标回收率为96.38%～107.2%,相对标准偏差均小于9%;阳性样品的谱图匹配度均高于92%。该方法简便、准确、高效,适用于白酒中甜蜜素的测定及阳性样品的确证分析。     

固相萃取-液相色谱／串联质谱法测定黄酒中的甜蜜素

建立了黄酒中甜蜜素残留的固相萃取-液相色谱／串联质谱法（SPE—LC／MS／MS）测定方法。黄酒样品用水稀释后,弱阴离子（WAX）固相萃取小柱净化,氨化甲醇洗脱。采用HypersilGold C18色谱柱（150mm×2．1mm,5μm）,乙腈-0．1％甲酸水溶液为流动相,以电喷雾离子源负离子模式（MRM）定性、定量测定甜蜜素。甜蜜素在10～500μg／L范围内峰面积与质量浓度呈线性关系,相关系数为0．9995。取有代表性的阴性样品进行添加回收试验,在0．5—5．0mg／L范围内,回收率为81．1％-88．2％,相对标准偏差为3．65％～5．21％,方法的定量检测限为0．5mg／L。该方法净化效果好,检测灵敏度高,能同时完成黄酒中甜蜜素的定量和定性分析。     

A flow injection analysis technique for the determination of chloride using reflectance detection

A flow injection (FI) determination for chloride has been developed using the light reflectance of the precipitate formed by the reaction of chloride with silver(I) as the method of detection rather than turbidimetry, as in the previous FI method using this reaction. The dynamic range of the analysis is increased to 0-10 mM chloride with a 10 mM silver(I) reagent and to 0-50 mM chloride with a 50 mM silver(I) reagent by using this mode of detection. The ability to select the injected reagent from an option of two concentrations via the control program is incorporated into the FI system, enhancing the versatility of the analysis. The dynamic range is further extended to 100 mM chloride by measuring the signal levels at the trailing portion of the response curve. The consumption of reagent is kept to a minimum by merging injected zones of sample and reagent instead of using a constant reagent stream.     

Rapid determination of aniline metabolites of chlorpropham in potatoes by micellar electrokinetic chromatography using negative-charged mixed micelles and laser-induced fluorescence detection

A rapid, reliable method has been developed for the multi-residue analysis of aniline metabolites of chlorpropham in potato samples. The method involves the precolumn derivatization of aniline metabolites with 5-(4,6-dichloro-s-triazin-2-ylamino) fluorescein (DTAF) and their subsequent separation and determination by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection (MEKC-LIF). The optimum procedure includes a derivatization step of the aniline metabolites (3-chloroaniline, 3-chloro-4-hydroxyaniline and 3-chloro-4-methoxyaniline) at 40 degrees C for 40 min and a 5-fold dilution prior to MEKC analysis, which is conducted within about 7 min using negative-charged mixed micelles (SDS/Triton X-100) in the running buffer. Under these conditions, the DTAF-anilines were readily detected at 0.3-3.1 microg/L level with a precision of 4.8-6.4%. These results indicate that negative-charged mixed surfactant MEKC-LIF is useful as a selective, rapid, and sensitive tool for the determination of these anilines and surpasses other electrophoretic alternatives based on the use of fluorescein-isothiocyanate (FITC) as label reagent. Finally, the potato matrix showed no significant effects on the derivatization and determination of these analytes, since the analytical figures of merit for the real samples were similar to those obtained in aqueous solutions, and the average recovery at fortification levels of 10-250 microg/kg was over 97%.     

Development of an automated on-line solid-phase extraction-high-performance liquid chromatographic method for the analysis of aniline, phenol, caffeine and various selected substituted aniline and phenol compounds in aqueous matrices

A fully automated solid-phase extraction (SPE)-high-performance liquid chromatographic method has been developed for the simultaneous analysis of substituted anilines and phenols in aqueous matrices at the low- to sub-microg/l level. Diode array and electrochemical detection operated in tandem mode were used for analyte detection. Two new polymeric sorbent materials (Hysphere-GP and Hysphere-SH) were evaluated for the on-line SPE of substituted anilines and phenols from aqueous matrices and their performance was compared with the PRP-1 and PLRP-S sorbents. Hysphere-GP sorbent packed in 10 x 2 mm cartridges was found to give better results in terms of sensitivity and selectivity of the overall analytical method. The proposed analytical method was validated for the analysis of these compounds in Axios river water that receives industrial, communal and agricultural wastes. The detection limits for all the compounds range between 0.05 and 0.2 microg/l, except for aniline and phenol which have detection limits of 0.5 and 1 microg/l, respectively (aniline detected by electrochemical detection). The recoveries for all the compounds are higher than 75% except for aniline (6%), phenol (50%) and 3-chlorophenol (67%). Finally, in order to evaluate the efficiency of the Hysphere-GP (10 x 2 mm) cartridges for sample stabilization and storage, the stability of the compounds of interest at the sorbed state onto these cartridges has been evaluated under three different temperature regimes (deep freeze, refrigeration, 20 degrees C).     

Flow Injection Determination of Oxalate Based on Its Catalytic Effect on the Oxidation of p-Chloride Aniline by Dichromate

In a sulfuric acid medium, oxalate exhibits a strong catalytic effect on the oxidation of p-chloride aniline(ClBN) by dichromate, and the red oxidation product of ClBN has a maximum absorhancy at 520 nm. Based on this founding, a new FI method for determining oxalate was developed. A calibration curve of oxalate in the range of 0.40—17.0μg/mL was obtained. The detection limit was 0.10μg/mL. Sampling rate was 103-samples/h. The possible interference by the co-existing substances or ions was examined. This new method was applied to the determination of micro amounts of oxalate in real samples with satisfactory results.     

Determination of Cr(III) in urine, blood serum and hair using flow injection chemiluminescence analysis

A flow injection (FI) chemiluminescence method for the determination of Cr(III) in blood serum, urine and hair samples is reported. It is based on the chromium-catalyzed light emission from the luminol oxidation by hydrogen peroxide. The apparatus consists of an FI system with a flow cell formed by a coiled transparent tube suitable for chemiluminescence detection. The specificity of the method is achieved in presence of EDTA. The detection limit under optimum conditions is 0.01 μg L^–1 of Cr(III). Precision and accuracy were evaluated by determining Cr(III) concentrations in urine standards from the National Institute of Standard and Technology (NIST).     

Simultaneous square-wave voltammetric determination of aspartame and cyclamate using a boron-doped diamond electrode

A simple and highly selective electrochemical method was developed for the simultaneous determination of aspartame and cyclamate in dietary products at a boron-doped diamond (BDD) electrode. In square-wave voltammetric (SWV) measurements, the BDD electrode was able to separate the oxidation peak potentials of aspartame and cyclamate present in binary mixtures by about 400 mV. The detection limit for aspartame in the presence of 3.0x10(-4) mol L(-1) cyclamate was 4.7x10(-7) mol L(-1), and the detection limit for cyclamate in the presence of 1.0x10(-4) mol L(-1) aspartame was 4.2x10(-6) mol L(-1). When simultaneously changing the concentration of both aspartame and cyclamate in a 0.5 mol L(-1) sulfuric acid solution, the corresponding detection limits were 3.5x10(-7) and 4.5x10(-6) mol L(-1), respectively. The relative standard deviation (R.S.D.) obtained was 1.3% for the 1.0x10(-4) mol L(-1) aspartame solution (n=5) and 1.1% for the 3.0x10(-3) mol L(-1) cyclamate solution. The proposed method was successfully applied in the determination of aspartame in several dietary products with results similar to those obtained using an HPLC method at 95% confidence level.