人工神经网络-微分脉冲伏安法同时测定尿液中的多巴胺、尿酸及抗坏血酸

研究了多巴胺、尿酸和抗坏血酸在玻碳电极上的伏安行为.在pH 5.7的Britton - Robinson缓冲溶液中,采用微分脉冲伏安法进行电化学扫描,3种化合物均有良好的氧化峰,但其波谱重叠严重,常规伏安法难以同时测定.采用化学计量学方法中的偏最小二乘法(PLS)、主成分回归法(PCR)、径向基人工神经网络法(RBF-...     

偏最小二乘-分光光度法同时测定福美锌和代森锰农药残留量

利用紫外可见分光光度法研究了农药福美锌和代森锰与苯基荧光酮的相互作用,发现反应后的产物分别在波长为551和554 nm处最大有吸收,但光谱严重重叠.实验采集了450～700 nm波长范围吸光度数据,并对该数据进行一阶求导后用偏最小二乘法处理,据此建立了偏最小二乘-分光光度法同时测定福美锌和代森锰两种农药的新方法.福美锌和代森锰的线性范围分别为0.3～6.0和0.2～3.5 μg/mL;检出限分别为0.22和0.13 μg/mL.混合样品分析无需分离,方法简单、快速.用于水果、大米和自来水等实际样品测定.     

紫外分光光度-局部偏最小二乘回归法同时测定三种人造甜味剂

本文报道了一种简便、快速、准确地同时测定3种人造甜味剂安赛蜜、阿斯巴甜和糖精钠的方法。方法基于在p H为3.21的盐酸溶液中对安赛蜜、阿斯巴甜和糖精钠三组分混合溶液进行紫外光度测定,所得重叠光谱数据分别用偏最小二乘回归法(PLSR)、特征峰结合PLSR法和特征峰结合局部偏最小二乘回归法(LPLSR)进行处理。结果表明,选取特征波段的峰值作为自变量,采用4个局部样本做拟合的预报误差最小,总相对偏差仅为3.05%。对果汁样品进行测定,获得了很好的定量分析结果。安赛蜜、阿斯巴甜和糖精钠的定量线性范围分别为1.0~30.0 mg/L、1.0~10.0 mg/L和1.0~10.0 mg/L。     

紫外分光光度法-局部PLSR同时测定三种人造甜味剂

本文报道了一种简便、快速、准确的同时测定三种人造甜味剂安赛蜜、阿斯巴甜和糖精钠的方法。方法基于在pH为3.21的盐酸溶液中对安赛蜜、阿斯巴甜和糖精钠三组分混合溶液进行紫外光度测定,所得重叠光谱数据分别用偏最小二乘回归法（partial least squares regression,PLSR）、特征峰结合PLSR法和特征峰结合局部偏最小二乘回归法（local partial least squares regression,LPLSR）进行处理。结果表明,选取特征波段的峰值作为自变量,采用4个局部样本做拟合的预报误差最小,总相对偏差仅为3.05%。对果汁样品进行测定,获得了很好的定量分析结果。安赛蜜、阿斯巴甜和糖精钠的定量线性范围分别为1.0 - 30.0 mg/L、1.0 - 10.0 mg/L和1.0 – 10.0 mg/L。     

银掺杂聚L-酪氨酸修饰电极同时测定多巴胺、肾上腺素和抗坏血酸

用循环伏安法制备银掺杂聚L-酪氨酸修饰玻碳电极,研究了多巴胺、肾上腺素和抗坏血酸在其电极上的电化学行为,建立了同时测定多巴胺、肾上腺素和抗坏血酸的新方法。当3种组分共存时,在磷酸盐缓冲溶液(pH6.0)中,扫描速率为140mV/s,多巴胺和肾上腺素在修饰电极上分别产生还原峰,峰电位分别为0.198和-0.205V,多巴胺和肾上腺素氧化峰重叠,峰电位为0.313V(vs.Ag/AgCl);抗坏血酸产生一个氧化峰,峰电位0.108V(vs.Ag/AgCl)。多巴胺和肾上腺素的ΔEpc=0.403V,抗坏血酸的氧化峰与多巴胺和肾上腺素的ΔEpa=0.205V,用还原峰和氧化峰可同时测定多巴胺、肾上腺素和抗坏血酸,3种组分同时测定的线性范围分别为5.0×10-6～1.0×10-4mol/L,8.0×10-6～1.0×10-4mol/L和3.0×10-5～1.0×10-3mol/L;检出限分别为5.0×10-7,8.0×10-7和5.0×10-6mol/L。本方法用于人尿液中多巴胺、肾上腺素和抗坏血酸的同时测定,结果满意。     

电化学液相微萃取-循环伏安法对海带中溴的测定

将液相微萃取与电化学法相结合,建立了快速测定海带中溴含量的电化学液相微萃取-循环伏安法(ELPME-CV).苯甲酸乙酯作为粘结剂组成碳糊电极,同时充当微液膜萃取相与样品溶液接触.在正电位下,溴离子被氧化成溴分子,溴分子经微液膜萃取富集,在负电位下还原溶出.在0.01 ～0.50 mmol/L范围内,溴的还原峰电流与溶液中溴离子浓度成正比,检出限为0.05 mmol/L.测定市售海带中溴的含量为91 μg/g,相对标准偏差为11%.     

中空纤维膜液相微萃取及常规分析用于气相色谱-质谱分析白酒中的正己酸乙酯的比较研究

应用中空纤维膜液相微萃取技术(HF-LPME),及常规分析法与气相色谱-质谱(GC-MS)联用分别测定了3种浓香型白酒中的正己酸乙酯.两种方法都采用内标法定量,内标物为乙酸正戊酯.中空纤维膜液相微萃取的优化条件为:萃取溶剂为4.0 μL正己烷,搅拌速度为1 000 r/min,萃取时间为20 min.中空纤维膜液相微萃取法及常规前处理分析法的线性范围分别为25～400 mg/L、5.0～500 mg/L,检出限分别为0.25 mg/L、0.03 mg/L,加标回收率分别为83.7%～118%、78.4%～94.2%,相对标准偏差分别为9.4%～15.6%、3.5%～4.9%.     

聚多巴胺-还原氧化石墨烯修饰电极同时测定邻苯二酚和对苯二酚

制备了聚多巴胺-还原氧化石墨烯修饰玻碳电极(PDA-rGO/GCE),以此修饰电极作为工作电极,采用循环伏安法(CV)对邻苯二酚(CC)和对苯二酚(HQ)的电化学行为进行了研究。结果表明CC和HQ在该修饰电极上的峰电流与氧化石墨烯修饰电极相比有了明显增高,并且它们的氧化峰电位差和还原峰电位差均超过110 mV,证明该修饰电极用于两种酚的同时检测是可行的。在优化实验条件下,采用微分脉冲伏安法(DPV)对CC和HQ同时进行检测,CC和HQ的峰电流与其浓度均在1.0×10~(-6)～4.0×10~(-3) mol/L范围内呈良好的线性关系,检出限(S/N=3)分别为2.0×10~(-7) mol/L和3.6×10~(-7) mol/L。以所制备的修饰电极对自来水水样和湖水水样进行了加标回收检测,回收率在97.6%～100.6%范围内。     

微分脉冲溶出伏安法结合化学计量学测定醚类除草剂

在pH=6.82的Britton-Robinson缓冲溶液中,采用循环伏安法和微分脉冲溶出伏安法对醚类除草剂甲羧除草醚(Bifenox)和三氟羧草醚(Acifluofen)的伏安行为进行了研究,发现吸附时间为50 s时此电化学体系达到平衡,而且微分脉冲溶出伏安法能给出较高的灵敏度,甲羧除草醚和三氟羧草醚分别在-685 mV和-700 mV处具有良好还原峰,但由于峰电位接近而谱峰重叠,很难分别测定.本文采用化学计量学方法来解析重叠峰并完成这两种除草剂的定量分析.甲羧除草醚和三氟羧草醚的测定线性范围分别为0.02～0.18 μg·5mL~(-1)和0.02～0.16 μg·5mL~(-1),检出限分别为0.0073 μg·5mL~(-1)和0.0068 μg·5mL~(-1).利用该方法对水样中的甲羧除草醚和三氟羧草醚进行直接测定,获得了较好的定量分析结果.     

芦丁在纳米金修饰玻碳电极上的电化学行为及其测定

采用循环伏安法将纳米金电沉积于玻碳电极表面,制备了纳米金修饰玻碳电极(NG/GCE).在pH3.29的Britton-Robinson(B-R)缓冲溶液中,用循环伏安法研究了芦丁在NG/GCE上的电化学行为.结果表明,NG/GCE对芦丁的氧化还原反应有良好的电催化作用.用方波伏安法测得芦丁的还原峰电流与其浓度在2.0×10-8～2.0×10-6mol/L范围内呈线性关系,检出限为1.0×10-8mol/L(S/N=3).     

Simultaneous Voltammetric Determination of Three Herbicides in Food and Water Samples with the Aid of Chemometrics

Differential pulse stripping voltammetry method(DPSV) was applied to the determination of three herbicides,ametryn,cyanatryn,and dimethametryn.It was found that their voltammograms overlapped strongly,and it is difficult to determine these compounds individually from their mixtures.With the aid of chemometrics,classical least squares(CLS),principal component regression(PCR) and partial least squares(PLS),voltammogram resolution and quantitative analysis of the synthetic mixtures of the three compounds were successfully performed.The proposed method was also applied to the analysis of some real samples with satisfactory results.     

Simultaneous determination of three fluoroquinolones by linear sweep stripping voltammetry with the aid of chemometrics

A linear sweep stripping voltammetric (LSSV) method has been researched and developed for simultaneous quantitative determination of mixtures of three antibiotic drugs, ofloxacin, norfloxacin and ciprofloxacin. It relies on reductive reaction of the antibiotics at a mercury electrode in a Britton-Robinson buffer (pH 3.78). The voltammograms of these three compounds overlap strongly, and show non-linear character. Thus, it is difficult to analyse the compounds individually in their mixtures. In this work, chemometrics methods such as classical least squares (CLS), principal component regression (PCR), partial least squares (PLS) and radial basis function-artificial neural networks (RBF-ANN) were applied for the simultaneous determination of these compounds. The prediction performance of the calibration models constructed on the basis of these methods was compared. It was shown that satisfactory quantitative results were obtained with the use of the RBF-ANN calibration model relative prediction error (RPE_T) of 8.1% and an average recovery of 101%. This method is able to accommodate non-linear data quite well. The proposed analytical method based on LSSV was applied for the analysis of ofloxacin, norfloxacin and ciprofloxacin antibiotics in bird feedstuffs and their spiked samples, as well as in eye drops with satisfactory results.     

Resolution of mixtures of three nonsteroidal anti-inflammatory drugs by fluorescence using partial least squares multivariate calibration with previous wavelength selection by Kohonen artificial neural networks

A spectrofluorometric method for the quantitative determination of flufenamic, mefenamic and meclofenamic acids in mixtures has been developed by recording emission fluorescence spectra between 370 and 550 nm with an excitation wavelength of 352 nm. The excitation–emission spectra of these compounds are deeply overlapped which does not allow their direct determination without previous separation. The proposed method applies partial least squares (PLS) multivariate calibration to the resolution of this mixture using a set of wavelengths previously selected by Kohonen artificial neural networks (K-ANN). The linear calibration graphs used to construct the calibration matrix were selected in the ranges from 0.25 to 1.00 μg ml⁻¹ for flufenamic and meclofenamic acids, and from 1.00 to 4.00 μg ml⁻¹ for mefenamic acid. A cross-validation procedure was used to select the number of factors. The selected calibration model has been applied to the determination of these compounds in synthetic mixtures and pharmaceutical formulations.     

A PLS-based extractive spectrophotometric method for simultaneous determination of carbamazepine and carbamazepine-10,11-epoxide in plasma and comparison with HPLC

Carbamazepine (CBZ) undergoes enzyme biotransformation through epoxidation with the formation of its metabolite, carbamazepine-10,11-epoxide (CBZE). A simple chemometrics-assisted spectrophotometric method has been proposed for simultaneous determination of CBZ and CBZE in plasma. A liquid extraction procedure was operated to separate the analytes from plasma, and the UV absorbance spectra of the resultant solutions were subjected to partial least squares (PLS) regression. The optimum number of PLS latent variables was selected according to the PRESS values of leave-one-out cross-validation. A HPLC method was also employed for comparison. The respective mean recoveries for analysis of CBZ and CBZE in synthetic mixtures were 102.57 (+/-0.25)% and 103.00 (+/-0.09)% for PLS and 99.40 (+/-0.15)% and 102.20 (+/-0.02)%. The concentrations of CBZ and CBZE were also determined in five patients using the PLS and HPLC methods. The results showed that the data obtained by PLS were comparable with those obtained by HPLC method.     

Simultaneous determination of potassium guaiacolsulfonate, guaifenesin, diphenhydramine HCl and carbetapentane citrate in syrups by using HPLC-DAD coupled with partial least squares multivariate calibration

A simple and rapid analytical procedure was proposed for the determination of chromatographic peaks by means of partial least squares multivariate calibration (PLS) of high-performance liquid chromatography with diode array detection (HPLC-DAD). The method is exemplified with analysis of quaternary mixtures of potassium guaiacolsulfonate (PG), guaifenesin (GU), diphenhydramine HCI (DP) and carbetapentane citrate (CP) in syrup preparations. In this method, the area does not need to be directly measured and predictions are more accurate. Though the chromatographic and spectral peaks of the analytes were heavily overlapped and interferents coeluted with the compounds studied, good recoveries of analytes could be obtained with HPLC-DAD coupled with PLS calibration. This method was tested by analyzing the synthetic mixture of PG, GU, DP and CP. As a comparison method, a classsical HPLC method was used. The proposed methods were applied to syrups samples containing four drugs and the obtained results were statistically compared with each other. Finally, the main advantage of HPLC-PLS method over the classical HPLC method tried to emphasized as the using of simple mobile phase, shorter analysis time and no use of internal standard and gradient elution.     

Simultaneous Determination of Three Synthetic Glucocorticoids by Differential Pulse Stripping Voltammetry with the Aid of Chemometrics

Abstract

A novel voltammetric method for simultaneous determination of the glucocorticoid residues prednisone, prednisolone, and dexamethasone was developed. All three compounds were reduced at a mercury electrode in a Britton–Robinson buffer (pH 3.78), and well-defined voltammetric waves were observed. However, the voltammograms of these three compounds overlapped seriously and showed nonlinear character, and thus, it was difficult to analyze the compounds individually in their mixtures. In this work, two chemometrics methods, principal component regression (PCR) and partial least squares (PLS), were applied to resolve the overlapped voltammograms, and the calibration models were established for simultaneous determination of these compounds. Under the optimum experimental conditions, the limits of detection (LOD) were 5.6, 8.3, and 16.8 µg l^?1 for prednisone, prednisolone, and dexamethasone, respectively. The proposed method was also applied for the determination of these glucocorticoid residues in the rabbit plasma and human urine samples with satisfactory results.     

Simultaneous determination of naproxen, salicylic acid and acetylsalicylic acid by spectrofluorimetry using partial least-squares (PLS) multivariate calibration

Determination of naproxen, salicylic acid and acetylsalicylic acid has been carried out in mixtures of up to three components by recording emission fluorescence spectra between 300 and 520 nm with an excitation wavelength of 290 nm. The excitation-emission spectra of these compounds are strongly overlapped, which does not permit their direct determination without previous separation by conventional methodologies. Here, a method is proposed for the determination of these chemicals by the use of a full-spectrum multivariate calibration method, partial least-squares (PLS). The experimental calibration matrix was designed with 18 samples. The concentrations were varied between 0.1 and 1.0 mug ml(-1) for naproxen, 0.5 and 5.0 mug ml(-1) for salicylic acid and from 2.0 to 12.0 mug ml(-1) for acetylsalicylic acid. The cross-validation method was used to select the number of factors. To check the accuracy of the proposed method, the optimized model, obtained using PLS-1, was applied to the determination of these compounds in pharmaceuticals and human serum samples previously spiked with different amounts of each chemical.     

Simultaneous determination of vitamin B12 and its derivatives using some of multivariate calibration 1 (MVC1) techniques

Resolution of binary mixtures of vitamin B12, methylcobalamin and B12 coenzyme with minimum sample pre-treatment and without analyte separation has been successfully achieved by methods of partial least squares algorithm with one dependent variable (PLS1), orthogonal signal correction/partial least squares (OSC/PLS), principal component regression (PCR) and hybrid linear analysis (HLA). Data of analysis were obtained from UV-vis spectra. The UV-vis spectra of the vitamin B12, methylcobalamin and B12 coenzyme were recorded in the same spectral conditions. The method of central composite design was used in the ranges of 10-80mgL(-1) for vitamin B12 and methylcobalamin and 20-130mgL(-1) for B12 coenzyme. The models refinement procedure and validation were performed by cross-validation. The minimum root mean square error of prediction (RMSEP) was 2.26mgL(-1) for vitamin B12 with PLS1, 1.33mgL(-1) for methylcobalamin with OSC/PLS and 3.24mgL(-1) for B12 coenzyme with HLA techniques. Figures of merit such as selectivity, sensitivity, analytical sensitivity and LOD were determined for three compounds. The procedure was successfully applied to simultaneous determination of three compounds in synthetic mixtures and in a pharmaceutical formulation.     

A flow-through fluorimetric sensing device for determination of alpha- and beta-naphthol mixtures using a partial least-squares multivariate calibration approach

A single flow-through optosensor spectrofluorimetric system is proposed for the resolution of mixtures of alpha- and beta-naphthol at mug l(-1) levels using a partial least-squares (PLS) calibration approach. The sensor was developed in conjunction with a monochannel flow-injection analysis system with fluorimetric detection using Sephadex QAE A-25 resin as an active sorbent substrate in the flow cell and the second derivative of the native synchronous fluorescence spectra of analytes as analytical signal. In the manifold, the solutions of naphthol (at pH 10.0) were injected in a carrier stream of KCl (0.15 M)/NaOH (10(-2) M). Because of the strong spectral overlap, the mixture could not be resolved by conventional spectrofluorimetry. The non-additive behaviour of the fluorescence signals revealed an interaction in the system, which was not found by working in the solution only (without the sorbent support). This interaction, probably due to the environment of the analytes on the solid phase, made impossible their simultaneous determination. So, the use of synchronous fluorescence spectroscopy or even its derivative signal could not resolve satisfactorily the mixture. The simultaneous determination of both naphthol has been carried out by recording the signal of the second-derivative synchronous fluorescence (Deltalambda=170 nm) spectra between 200 and 450 nm and a PLS multivariate calibration treatment. The optimum number of factors was selected by using the cross-validation method. After validating the proposed method, it was applied to the determination of these compounds in natural waters with different amounts of each chemical.