Deconvolution and quantitation of unresolved mixtures in liquid chromatographic-diode array detection using evolving factor analysis

Summary A recently developed self-modeling curve resolution method based in different factor analysis techniques has been applied for the first time to the study of liquid-chromatography-diode array data under situation where the separation of two components is not achieved. Two applications are reported: the resolution and quantitation of a coeluted mixture of carbamate pesticides pirimicarb and 1-naphthol, and the estimation of the concentration profiles of the double peak obtained in the elution of the triazine metabolite chlorodiamino-s-triazine. Different methods of quantitation are compared, including Evolving Factor Analysis and Rank annihilation. Quantitation from the area of the elution profiles once the component spectra have been transformed for their area contribution to the signal, gives a relative composition for pirimicarb and naphthol pesticides which agrees with the known sample composition. In the case of the unknown triazine mixture, an approximate quantitation of the two peaks obtained for this metabolite is obtained by assuming equal signal contribution or equal maximum absorbance of the individual spectra of the two detected components.     

Analysis of environmental samples by application of multivariate curve resolution on fused high-performance liquid chromatography-diode array detection mass spectrometry data

Multivariate curve resolution-alternating least squares (MCR-ALS) is applied to solve coelution problems in liquid chromatograpy with diode array detection (DAD) and mass spectrometry (MS). Fusion of DAD and MS detector signals improved results versus those obtained using only one of the two detector signals. Application of wavelet transform to MS data before its fusion with DAD data, further help to facilitate the resolution and quantitation of the coeluted compounds under study, besides a decrease of time of analysis. Mixtures of biocide compounds in standard mixtures and in environmental samples (sediment and wastewater samples) were analyzed with estimated quantitation errors below 12%.     

加速溶剂萃取-凝胶渗透色谱净化-气相色谱快速分析动物源性食品中残留的多种有机磷农药

建立了动物源性食品猪肉、牛肉、鸡肉及鱼肉中36种有机磷农药残留的快速分析方法。以乙腈作为溶剂,对试样采用加速溶剂萃取仪萃取,自动凝胶渗透色谱仪净化预处理,N-丙基乙二胺(PSA)填料再净化,毛细管气相色谱法分离,火焰光度检测器(磷型)检测,内标法定量。该方法分离效果良好,重现性好,灵敏度、精密度高,杂质干扰少。36种有机磷农药的检测限(LOD)为0.0012 mg/kg(乙拌磷)～0.014 mg/kg(吡唑硫磷),定量限(LOQ)为0.004 mg/kg(乙拌磷)～0.047 mg/kg(吡唑硫磷)。当试样中有机磷农药的添加浓度分别为0.05,0.1,0.2 mg/kg时,回收率为58.2%～106.3%。方法的最低检测限和添加回收率均符合农药残留分析的要求。     

Characterization of subcritical water oxidation with in situ monitoring and self-modeling curve resolution

In this paper, a subcritical water oxidation (SBWO) process was monitored using self-modeling curve resolution (SMCR) of in situ UV-Vis measurements to estimate time-dependant composition profiles of reactants, intermediates and products. A small laboratory scale reactor with UV-Vis fiber-optic probes and a flow cell was used to demonstrate the usefulness of SMCR for monitoring the destruction of model compounds phenol, benzoic acid, and aniline in a dilute aqueous solutions. Hydrogen peroxide was used as the oxidizing reagent at moderate temperature (150-250 °C) and pressure (60-90 atm) in a single phase. By use of in situ monitoring, reaction times were easily determined and conditions for efficient oxidations were easily diagnosed without the need for time consuming off-line reference measurements. For selected runs, the destruction of the model compound was confirmed by gas chromatography and chemical oxygen demand (COD) measurements. Suspected intermediate oxidation products were easily detected by the use of UV-Vis spectrometry and self-modeling curve resolution, but could not be detected by gas chromatography.     

Degradation of atrazine and several organophosphorus pesticides in oranges

The degradation of atrazine and four organophosphorus pesticides (chlorpyriphos, fenamiphos, methidathion and methyl-parathion) in oranges was studied. Oranges were immersed in a Milli-Q water solution spiked with 10 mg litre-1 of each pesticide for one day, allowing their adsorption on the orange peel. Then, the oranges were rinsed with Milli-Q water and left outdoors to expose them to natural ambient conditions for two weeks. In parallel, an aqueous solution containing 1 mg litre-1 of each pesticide was placed in a Pyrex flask, which was tightly closed, and exposed to the same ambient conditions. Both samples (orange peel and Milli-Q water) were analyzed periodically by gas chromatography coupled to a nitrogen-phosphorus detector. The pesticide degradation in both samples could be described using a first-order degradation curve. Half-lives varied from 14.5 to more than 30 days in aqueous solution and from 2.3 to 4.1 days in oranges for organophosphorus pesticides, while those for atrazine were 3.1 days and 14.2 days, respectively. The presence of some organophosphorus degradation products in water samples after storage under the above conditions was confirmed by gas chromatography-mass spectrometry.     

Alternative calibration approaches for LC-MS quantitative determination of coeluted compounds in complex environmental mixtures using multivariate curve resolution

Different calibration approaches including external calibration, standard addition and internal standard are evaluated for quantification of coeluted compounds in liquid chromatography with MS spectrometry detection in scan mode and using multivariate curve resolution. These different calibration approaches are proposed to cope with sensitivity changes and matrix effects encountered in the analysis of complex natural environmental samples. By using them, multivariate curve resolution analysis of MS data in scan mode gave similar quantitative results to those obtained by LC-MS in selected ion monitoring (SIM) mode (in both cases errors were below 16% for internal standard combined with standard addition strategy), and it provided at the same time a means of analyte confirmation via their resolved pure MS spectra, and a means to gather a larger amount of information about the whole chromatographic process and to facilitate the simultaneous determination of multiple analytes in the same chromatographic run using the same experimental and instrumental conditions.     

有机溶剂对某些有机磷农药的MECC洗提影响的研究

以有机磷农药甲基对硫磷、对硫磷等为被试验物质，探讨了在十二烷基硫酸钠、硼砂电解液中加入甲醇、乙醇、异丙醇、乙腈等有机溶剂对某些有机磷农药的毛细管胶束电动色谱分离的影响。并从电解液的物理化学性质和毛细管色谱动力学两方面阐明了其影响机理     

Local resolution of two-way data from multicomponent equilibria

A self-modeling curve resolution (SMCR) method is proposed to calculate concentration and spectral profiles for the two-way spectral data from an equilibrium containing several chemical components. The proposed method has three main distinctive steps: (i) fixed size moving window evolving factor analysis (FSMWEFA) is used to identify the selective and zero concentration regions for a desired component, (ii) orthogonal projection resolution (OPR) is used to calculate its concentration profile and (iii) the component striping is done directly to resolve other components. The results of simulated and real polyprotic acid dissociation equilibria showed that the proposed combined method performs well even in situation when the successive stepwise equilibrium constants are close to each other. The applicability of method for resolving the triprotic acid system with rank deficiency due full spectral overlapping of two involved chemical species also is shown.     

Screening and Determination of Pesticides from Various Classes in Natural Water without Sample Preparation by Ultra HPLC–High-Resolution Quadrupole Time-of-Flight Mass Spectrometry

A rapid screening and determination of 59 pesticides from various classes in natural water without sample preparation by high-resolution ultra HPLC–quadrupole time-of-flight mass spectrometry is proposed. The matrix effect is considered on an example of waters with a high (mineral) and low (artesian) salt concentration. It is demonstrated that pesticides can be determined in water using the calibration curve method with an insignificant matrix effect (neonicotinoids, carbamates, and derivatives of uracil, pyridine, and benzoic and aryloxycarboxylic acids) and the standard addition method with a significant matrix effect (triazines, triazinones, triazoles, imidazoles, pyridazinones, organophosphorus compounds, and urea derivatives). The limits of detection were 0.01–10 ng/mL; the analytical ranges for pesticides were 0.04–50 (100) ng/mL. The relative standard deviation of the results does not exceed 15%; the analysis time is 10–15 min.     

Self-modeling curve resolution analysis of on-line vibrational spectra of polymerisation and transesterification

This article discusses the potential of self-modeling curve resolution analysis (SMCR) for the evolution of on-line vibrational spectral data of polymerisation and transesterification. After the general introduction of the SMCR approach, representative SMCR techniques like orthogonal projection analysis (OPA) and simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) are briefly outlined. As examples the SMCR analysis of the Raman spectra of the block copolymerisation of styrene and 1,3-butadiene and that of the near-infrared (NIR) spectra of the melt-extrusion transesterification of ethylene-vinylacetate copolymer will be illustrated. In the last part of this review paper, a new powerful SMCR method that we have recently proposed is demonstrated.     

Self-modeling curve resolution (SMCR) by particle swarm optimization (PSO)

Particle swarm optimization (PSO) combined with alternating least squares (ALS) is introduced to self-modeling curve resolution (SMCR) in this study for effective initial estimate. The proposed method aims to search concentration profiles or pure spectra which give the best resolution result by PSO. SMCR sometimes yields insufficient resolution results by getting trapped in a local minimum with poor initial estimates. The proposed method enables to reduce an undesirable effect of the local minimum in SMCR due to the advantages of PSO. Moreover, a new criterion based on global phase angle is also proposed for more effective performance of SMCR. It takes full advantage of data structure, that is to say, a sequential change with respect to a perturbation can be considered in SMCR with the criterion. To demonstrate its potential, SMCR by PSO is applied to concentration-dependent near-infrared (NIR) spectra of mixture solutions of oleic acid (OA) and ethanol. Its curve resolution performances are compared with SMCR with evolving factor analysis (EFA). The results show that SMCR by PSO yields significantly better curve resolution performances than those by EFA. It is revealed that SMCR by PSO is less sensitive to a local minimum in SMCR and it can be a new effective tool for curve resolution analysis.     

Methods of the decomposition of spectra of various origin in the analysis of complex mixtures

Different algorithms of the decomposition of spectral curves are compared by the precision of identification and quantitative analysis of complex mixtures. The available conventional methods of self-modeling curve resolution (SIMPLISMA, MCR-ALS) and algorithms implementing the independent component analysis (MILCA, SNICA) are used. The results are illustrated by a series of examples of different spectral signals (UV, IR, Raman, fluorescence).     

微波辅助萃取-分散固相萃取-气相色谱质谱法测定茶叶中23种农药残留

建立了微波辅助萃取-分散固相萃取净化-气相色谱质谱法（GC-MS）快速测定茶叶中23种农药残留量的方法. 茶叶样品用乙腈进行微波辅助萃取（MAE）,提取液经分散固相萃取（DSPE）净化处理. 采用DB-17MS毛细管色谱柱分离后,选择离子监测模式下（SIM）质谱法进行测定. 23种农药组分在0.01~0.50 mg/mL质量浓度范围内呈线性关系,相关系数r2大于0.995,方法测定低限（10S/N）为0.005~0.01 mg/kg. 以空白绿茶为基体,在4个标准添加水平0.01、0.05、0.10、0.25 mg/kg进行加标回收试验,加标平均回收率为70%~105%,相对标准偏差为3.0%~8.2%.     

Direct Analysis of Natural Waters by Electron Spray Ionization and High-Resolution Time-of-Flight Mass Spectrometry Detection. Determination of Pesticides of Various Classes

The possibility of directly determining 36 pesticides (derivatives of urea, triazines, triazoles, imidazoles, carbamates, triazinones, benzamides, and pyridazinones and organophosphorus pesticides) by electrospray ionization with high-resolution quadrupole time-of-flight mass spectrometry in natural waters is demonstrated. A significant matrix effect is observed in the determination of pesticides in natural waters, and the use of the standard addition method is proposed for their determination in test samples, both undiluted and diluted with deionized water. The analytical range of the analytes was 0.5–50 ng/mL. The relative standard deviation of the results does not exceed 10%; the time required for the analysis is 10–15 min.     

Resolution of chemical species in flow injection analysis by using self-modeling curve resolution

Mixtures can be resolved into their components by separation, spectrometric and kinetic (chemical) procedures, which have varying degrees of efficiency. Chemometric methods of data processing have proved useful for increasing resolution, especially in spectral and chromatographic procedures. This study shows that chemometric methods are also useful for kinetic flow-injection methods based on chemical reactions combined with multichannel spectral detection, where neither the reaction nor the detector provides adequate resolution. The problem of background absorbance of a sample in a flow-injection system with an ultraviolet/visible photodiode array detector is solved by applying a self-modeling curve resolution method. The example used is a mixture of methyl violet and phenolphthalein.     

Multiresidue Method for the Determination of Organophosphorus Pesticides in Still Wine and Fortified Wine Using Solid-Phase Microextraction and Gas Chromatography – Tandem Mass Spectrometry

A SPME-GC-MS/MS method for the determination of eight organophosphorus pesticides (azinphos-methyl, chlorpyriphos, chlorpyriphos-methyl, diazinon, fenitrothion, fenthion, malathion, and methidathion) in still and fortified wine was developed. The extraction procedure is simple, solvent free, and without any sample pretreatment. Limits of detection (LOD) and quantitation (LOQ) values in the range 0.1–14.3 µg/L and 0.2–43.3 µg/L, respectively, were obtained. The LOQ values are below the maximum residue levels (MRLs) established by European Regulation for grapes, with the exception of methidathion. Coefficients of correlation (R²) higher than 0.99 were obtained for the majority of the pesticides, in all different wines analyzed.     

Elimination of Matrix Interferences in GC‐MS Analysis of Pesticides by Entropy Minimization

Gas chromatography‐mass spectrometry (GC‐MS ) is an important analytical technique for the analysis of organophosphorus pesticides in food products. Because of the complex matrices of food products, multiple preprocessing steps are required prior to performing the GC‐MS analysis. Despite that, it is difficult to totally eliminate the interference of complex matrix background. In this work, we introduce an entropy minimization technique that can eliminate the need for comprehensive preprocessing steps to detect organophosphorus pesticides in a fortified orange juice sample. The pure mass spectra and extracted‐ion chromatograms of the pesticides were extracted and reconstructed. The results achieved higher National Institute of Standard and Technology (NIST ) match scores in comparison to the conventional background subtraction technique. Taken together, the entropy minimization technique is capable of providing rapid qualitative and quantitative analyses of complex GC‐MS data. This technique is expected to have great potential for natural products and food analysis applications.     

高效液相色谱串联质谱法对栀子中11种有机磷农药残留的检测

建立了高效液相色谱串联质谱法检测栀子中11种有机磷农药残留量的分析方法。样品以乙腈为提取溶剂,采用超声波辅助提取,经Carb/PSA固相萃取柱净化,液质联用仪测定。11种有机磷农药在125~2 000μg/L范围内线性良好,相关系数为0.9955~0.9998。在50、100、500μg/kg 3个添加水平的平均加标回收率为84%~107%,相对标准偏差为1.4%~10.9%。     

Cleaning of extracts of cereal crop samples with aluminosilicate in the determination of pesticides by gas chromatography with mass-spectrometric detection

A procedure for the determination of 23 pesticides from different classes (organophosphorus and organochlorine compounds, synthetic pyrethroids, and triazoles) in cereal crops is proposed. It is based on sample preparation according to the QuEChERS method with the subsequent cleaning of the extract with natural aluminosilicate and the determination of analytes by gas chromatography with mass-spectrometric detection. The limits of the quantitative determination of pesticides are ~0.005 mg/kg. The relative standard deviation does not exceed 0.02. The duration of analysis is 35–40 min.