增量取样量接近分析试样量时的取样——理论修正与结果

化学分析取样几乎总是一个多步骤过程,所有的步骤都会导致分析结果的总体不确定性。样品采取之后,不论后续采样过程如何精细,前期采样阶段的误差都无法在后续采样过程中更正。第一次取样是最重要的,通常其方差远远超过实验室测量的方差。但这不意味着在最终实验室分析试样制备阶段可以忽略采样理论的原理。现代分析仪器旨在处理小样本(从毫克到几克)。在这种情况下,如果样品是包含少量分析物的混合颗粒,则物料的不均匀性可能会很大以至于破坏整个分析过程。不均匀性计算和样品制备过程中基本采样误差方差的估计对于开发适用的分析程序至关重要。在样本制备的最后步骤中,新的增量本是父增量本的重要组成部分,在估算样本方差时必须考虑到这种影响。TOS提供了用于处理这些情况的工具。通过两个案例阐明了不均匀性计算的应用。在第一个例子中,评估了鸡饲料中低含量添加剂的成分不均匀性,在第二个例子中,对样品制备进行了优化,以校正用于分析硅灰石精矿中矿物杂质含量的红外仪器。在处理颗粒混合物和评估混样效率时,不均匀性评估也很重要。     

An electrochemical enrichment procedure for the determination of heavy metals by total-reflection X-ray fluorescence spectroscopy

An electrolytic separation and enrichment technique was developed for the determination of trace elements by total-reflection X-ray fluorescence spectroscopy (TXRF). The elements of interest are electrodeposited out of the sample solution onto a solid, polished disc of pure niobium which is used as sample carrier for the TXRF measurement. The electrochemical deposition leads to a high enrichment of the analytes and at the same time to a removal of the matrix. This results in substantially improved detection limits in the lower picogram per gram region. The deposited elements are directly measured by TXRF without any further sample preparation step. The homogeneous thin layer of the analytes is an ideal sample form for TXRF, because scattered radiation from the sample itself is minimized. The proposed sample preparation method is useful particularly for the analysis of heavy metals in liquid samples with for TXRF disturbing matrices, e.g. sea water.     

Determination by high-performance liquid chromatography of hydroxyurea in human plasma.

An assay using reversed-phase high-performance liquid chromatography with electrochemical detection was developed to measure hydroxyurea in plasma at concentrations suitable for pharmacokinetic studies. The sample preparation is simple, the analysis rapid and assays can be batched. The between-run precision is excellent (coefficient of variation = 2.8-4.5%) and the limit of detection is 0.02 mmol/l. Preliminary studies have shown that the method is suitable for pharmacokinetic studies.     

Determination of copper, lead and cadmium in whole blood by stripping voltammetry with the use of graphite electrodes

The problem with toxic metal ion determination in blood is the adsorption of organic compounds on the electrode surface and the formation of complexes between metal ions and organic constituents of blood. This is the reason why usually preliminary acid digestion or other sample pretreatment is used. Two kinds of electrodes have been used: “Ultra-Trace Electrode”, made from impregnated graphite (I), and thick film graphite disposable electrodes (II). The analysis of whole blood with different sample preparation methods shows, that chemical digestion is not necessary for the analysis. Electrochemical two-stage sample preparation provides the possibility for analysing whole blood with the mentioned electrodes. Thick film disposable electrodes are less sensitive to the interference of organic constituents of blood. These electrodes give the possibility to determine total cadmium, lead and copper concentration in whole blood without special sample pretreatment. The application of “Ultra-Trace Electrode” for blood analysis is possible only after preliminary pretreatment of blood by chemical digestion or electrochemical sample preparation.     

Multielement analysis of whole blood by high resolution inductively coupled plasma mass spectrometry

An analytical method using double focusing sector field inductively coupled plasma mass spectrometry (ICP-SMS) for rapid simultaneous determination of 50 elements in digested human blood is described. Sample preparation consisted of microwave digestion with nitric acid followed by dilution with ultrapure water. The importance of controlling possible contamination sources at different sample preparation and analysis stages in order to achieve adequate method detection limits (MDL) is emphasised. Correction for matrix effects was made using scandium, indium and lutecium as internal standards. Accuracy of the data for elements suffering from spectral interferences was improved by applying either a high resolution capability of the ICP-SMS or mathematical corrections. Different approaches for accuracy assessment in blood analysis are evaluated. Additional information on trace elements concentration in selected blood reference materials is given. The between-batch precision was assessed from replicate analysis (including sample preparation) of reference materials and was better than 10% RSD for 21 elements and better than 30% RSD for 36 elements under consideration. A statistical summary for results obtained for 31 blood samples from non-exposed subjects is presented. The majority of elements tested was found in the samples at concentrations higher than MDL.     

Quasi in situ XPS study of anion intercalation into HOPG from the ionic liquid [EMIM][BF4]

Highly oriented pyrolytic graphite (HOPG) electrodes were electrochemically oxidized in the ionic liquid [EMIM][BF₄]. Both, the electrolyte and the electrode surface were investigated using X-ray photoelectron spectroscopy (XPS) after electrochemical treatment. For that purpose an electrochemical preparation chamber was attached to the ultra high vacuum system allowing for preparation of electrodes in non-aqueous electrolyte and subsequent sample transfer under inert nitrogen atmosphere. The XP-spectra of all species detected on the oxidized HOPG surface show core level shifts towards lower binding energies referring to a Fermi level shift and proving that a graphite intercalation compound was formed. Anion intercalation occurs together with co-intercalation of cations at 2 V vs. carbon quasi-reference electrode and is found to be irreversible. XPS analysis of the ionic liquid prior to and after electrochemical treatment indicates a change in electrolyte composition.     

Molecularly Imprinted Polymers Combined with Electrochemical Sensors for Food Contaminants Analysis

Detection of relevant contaminants using screening approaches is a key issue to ensure food safety and respect for the regulatory limits established. Electrochemical sensors present several advantages such as rapidity; ease of use; possibility of on-site analysis and low cost. The lack of selectivity for electrochemical sensors working in complex samples as food may be overcome by coupling them with molecularly imprinted polymers (MIPs). MIPs are synthetic materials that mimic biological receptors and are produced by the polymerization of functional monomers in presence of a target analyte. This paper critically reviews and discusses the recent progress in MIP-based electrochemical sensors for food safety. A brief introduction on MIPs and electrochemical sensors is given; followed by a discussion of the recent achievements for various MIPs-based electrochemical sensors for food contaminants analysis. Both electropolymerization and chemical synthesis of MIP-based electrochemical sensing are discussed as well as the relevant applications of MIPs used in sample preparation and then coupled to electrochemical analysis. Future perspectives and challenges have been eventually given.     

Multielement analysis of whole blood by high resolution inductively coupled plasma mass spectrometry

An analytical method using double focusing sector field inductively coupled plasma mass spectrometry (ICP-SMS) for rapid simultaneous determination of 50 elements in digested human blood is described. Sample preparation consisted of microwave digestion with nitric acid followed by dilution with ultrapure water. The importance of controlling possible contamination sources at different sample preparation and analysis stages in order to achieve adequate method detection limits (MDL) is emphasised. Correction for matrix effects was made using scandium, indium and lutecium as internal standards. Accuracy of the data for elements suffering from spectral interferences was improved by applying either a high resolution capability of the ICP-SMS or mathematical corrections. Different approaches for accuracy assessment in blood analysis are evaluated. Additional information on trace elements concentration in selected blood reference materials is given. The between-batch precision was assessed from replicate analysis (including sample preparation) of reference materials and was better than 10% RSD for 21 elements and better than 30% RSD for 36 elements under consideration. A statistical summary for results obtained for 31 blood samples from non-exposed subjects is presented. The majority of elements tested was found in the samples at concentrations higher than MDL. Received: 23 November 1998 / Revised: 6 January 1999 / Accepted: 12 January 1999     

Integration of electrochemistry in micro-total analysis systems for biochemical assays: Recent developments

Micro-total analysis systems (μTAS) integrate different analytical operations like sample preparation, separation and detection into a single microfabricated device. With the outstanding advantages of low cost, satisfactory analytical efficiency and flexibility in design, highly integrated and miniaturized devices from the concept of μTAS have gained widespread applications, especially in biochemical assays. Electrochemistry is shown to be quite compatible with microanalytical systems for biochemical assays, because of its attractive merits such as simplicity, rapidity, high sensitivity, reduced power consumption, and sample/reagent economy. This review presents recent developments in the integration of electrochemistry in microdevices for biochemical assays. Ingenious microelectrode design and fabrication methods, and versatility of electrochemical techniques are involved. Practical applications of such integrated microsystem in biochemical assays are focused on in situ analysis, point-of-care testing and portable devices. Electrochemical techniques are apparently suited to microsystems, since easy microfabrication of electrochemical elements and a high degree of integration with multi-analytical functions can be achieved at low cost. Such integrated microsystems will play an increasingly important role for analysis of small volume biochemical samples. Work is in progress toward new microdevice design and applications.     

Nickel Amperometric Detector Prepared by Electroless Deposition for Microchip Electrophoretic Measurement of Alcohols and Sugars

Nickel was deposited directly at the end of an electrophoretic glass microchip using an electroless deposition procedure leading to an attractive amperometric detector for sugars and alcohols. Such direct electroless deposition of nickel at the end of the separation chip greatly simplifies the preparation of on‐chip electrochemical detectors. Variables affecting the preparation and operation of the new detector are characterized and optimized. The integrated capillary electrophoresis‐electrochemical detection microsystem was evaluated for the separation of alcohols and sugars in connection to assays of different beer and wine samples. Linear calibration plots and favorable detection limits are found that meet the needs of real sample (wine and beer) analyses. This represents the first example of using nickel electrode and detecting alcohols on microchip platforms.     

Sample Preparation of Energy Materials for X‐ray Nanotomography with Micromanipulation

X‐ray nanotomography presents an unprecedented opportunity to study energy storage/conversion materials at nanometer scales in three dimensions, with both elemental and chemical sensitivity. A critical step in obtaining high‐quality X‐ray nanotomography data is reliable sample preparation to ensure that the entire sample fits within the field of view of the X‐ray microscope. Although focused‐ion‐beam lift‐out has previously been used for large sample (few to tens of microns) preparation, a difficult undercut and lift‐out procedure results in a time‐consuming sample preparation process. Herein, we propose a much simpler and direct sample preparation method to resolve the issues that block the view of the sample base after milling and during the lift‐out process. This method is applied on a solid‐oxide fuel cell and a lithium‐ion battery electrode, before numerous critical 3D morphological parameters are extracted, which are highly relevant to their electrochemical performance. A broad application of this method for microstructure study with X‐ray nanotomography is discussed and presented.     

Measurement uncertainty from physical sample preparation: estimation including systematic error

A methodology is proposed, which employs duplicated primary sampling and subsequent duplicated physical preparation coupled with duplicated chemical analyses. Sample preparation duplicates should be prepared under conditions that represent normal variability in routine laboratory practice. The proposed methodology requires duplicated chemical analysis on a minimum of two of the sample preparation duplicates. Data produced from the hierarchical design is treated with robust analysis of variance (ANOVA) to generate uncertainty estimates, as standard uncertainties ('u' expressed as standard deviation), for primary sampling (ssamp), physical sample preparation (sprep) and chemical analysis (sanal). The ANOVA results allow the contribution of the sample preparation process to the overall uncertainty to be assessed. This methodology has been applied for the first time to a case study of pesticide residues in retail strawberry samples. Duplicated sample preparation was performed under ambient conditions on two consecutive days. Multi-residue analysis (quantification by GC-MS) was undertaken for a range of incurred pesticide residues including those suspected of being susceptible to loss during sample preparation procedures. Sampling and analytical uncertainties dominated at low analyte concentrations. The sample preparation process contributed up to 20% to the total variability and had a relative uncertainty (Uprep%) of up to 66% (for bupirimate at 95% confidence). Estimates of systematic errors during physical sample preparation were also made using spike recovery experiments. Four options for the estimation of measurement uncertainty are discussed, which both include and exclude systematic error arising from sample preparation and chemical analysis. A holistic approach to the combination and subsequent expression of uncertainty is advised.     

Basal plasma-catecholamine-level determination using HPLC-ED and different sample cleanup techniques

Summary Reversed phase HPLC with electrochemical detection was used for the determination of basal adrenaline, dopamine and noradrenaline levels in human plasma. These compounds demonstrated good stability during different stages of collection and long-term storage. Using a new electrochemical detector and improving mobile phase parameters, we obtained a detection limit of 2 pg per injection. Good separation of dihydroxyphenylacetic acid was also attained, which is important in investigations with intensive care patients. Good accuracy and precision, demonstrated in the daily quality control measurements taken over a five month period, verified the reliability of the chromatographic separation. However, there was a decrease in the recovery of very low amounts of catecholamines, added to fresh frozen plasma that had previously been made catecholamine-free. According to the widely-accepted extraction method of Anton and Sayre, it is argued that the un-known affinity of catecholamines to acid-prepared aluminium oxide (in comparison to catecholamine —protein binding constants) explains the low accuracy in measurement at very low plasma levels. We thus compared this sample preparation method to recently published extraction procedures.     

Electrochemical solid-phase nanoextraction of copper(II) on a magnesium oxinate-modified carbon paste electrode by cyclic voltammetry

Solid-phase nanoextraction is a sample preparation technique, which combines nanotechnology with analytical chemistry, and brings analytical chemistry to a higher level, particularly for complex system analysis. This paper describes a typical example of electrochemical solid-phase nanoextraction and electrochemical detection. Trace amounts of copper (5.0?×?10^?13?mol/L) were extracted by electrochemical solid-phase nanoextraction on to the magnesium oxinate nanoparticle-modified carbon paste electrode surface in a pH?7.2 phosphate buffer system at ?0.50 V for 100 s. The extraction is achieved by the cation exchange between copper(II) in the aqueous solution and magnesium(II) from the magnesium oxinate nanoparticles on the electrode surface. The extracted copper shows an irreversible anodic peak at about 0.2 V (vs. saturated calomel electrode). The peak current is proportional to the scan rate, which shows this to be a surface-controlled process. The oxidation peak current is proportional to the logarithm of the copper concentration in the range 5.0?×?10^?13?～?5.0?×?10^?7?M with a slope of 2.215. This powerful method uses the carbon paste electrode to combine extraction with electrochemical analysis.     

Chromatographic quantitation at losses of analyte during sample preparation. Application of the modified method of double internal standard

Known methods of quantitative chromatographic analysis (calibration, external standard, internal standard and standard addition) require the application of sample preparation techniques without significant losses of analytes. If this condition cannot be satisfied, the compensation of these losses should be provided. The modification of known method of quantitative chromatographic analysis (double internal standard), implying the addition of two homologues (previous and following) of target analytes as internal standards into initial samples is considered. This approach permits us to compensate significant losses both analytes and standards at all stages of sample preparation. The advantages of this method are demonstrated on the examples of liquid-liquid extraction, head space analysis (HSA), distillation of volatile compounds with volatile solvents (concentration in condensates) and evaporation of volatile solvents (concentrating in the residues of solvents). In all cases the application of two homologues as internal standards provides accurate results (the typical relative errors are within 1-6%) at the values of a factor of composition distortion of initial samples (K', the definition is suggested) from 0.2 up to 4. These results are in accordance with general relationships between variations in any physicochemical properties of organic compounds within homologous series. The single found exception was the evaporation of volatile solvents (the open phase transition process) when to get the results with relative errors not more then +10% requires the minimal changes in the composition of initial samples (K' values should not be more then approximately 1.5).     

Simple HPLC-EC Method for the Simultaneous Determination of Biogenic Amines and Their Main Metabolites in Small Rat Brain Regions

Abstract

A simple and reliable procedure for the simultaneous determination of dopamine (DA), serotonin (5-HT) and their acidic metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy indoleacetic acid (5-HIAA) using high-performance liquid chromatography with electrochemical detection has been developed. Minimal sample preparation is required before injection into the liquid chromatograph. The present method can be applied to the analysis of several rat brain regions. The procedure offers good possibilities for routine analysis of biogenic amines and their acidic metabolites in the picogram range.     

High Performance Liquid Chromatographic Determination of Phenylenediamines in Aqueous Environmental Samples

Abstract

The use of high performance liquid chromatography (HPLC) for the determination of phenylenediamines has been studied. Detection limits using both ultraviolet (UV) and electrochemical (EC) detectors have been determined and EC is superior in most cases. Chromatographic conditions and sample preparation procedures are described for many phenylenediamines of environmental significance.     

干果类食品的样品前处理与分析检测方法研究进展

坚果、果脯等干果类食品含有丰富的营养成分,深受国内外广大消费者的喜爱。但这些食品在果实生产、加工、储运时会使用农药或产生霉变等,造成干果中农药、重金属、霉菌毒素或添加剂等有害成分残留,甚至超过国家限量要求,带来严重的食品安全问题。因此,加强干果类食品的质量监督具有重要的经济和社会意义。但干果类食品基质复杂,有害物质种类多,结构和性质差异大,含量低,其分析检测需要快速高效的样品前处理技术和准确灵敏的分析检测方法。该文主要综述了近十年来干果类食品中有害物质的样品前处理及分析检测方法研究进展。其中样品前处理方法主要包括各种场辅助萃取法、相分离法和衍生化萃取方法等。场辅助萃取法主要是借助超声波和微波场等外场(协同)作用加快干果中有害物质的溶出速度,提高其萃取效率。相分离法,包括固相(微)萃取、分散固相萃取和液相(微)萃取法等,具有溶剂消耗少、分离富集效率高的优势,是干果样品分析中较常使用的前处理方法。该文还重点介绍了干果中各类有害成分分析检测技术,主要包括色谱、原子光谱、无机质谱、电化学分析等常规实验室方法,以及一些适用于现场分析的快速检测技术,并以此为基础,展望了干果类食品中有害物质分析检测技术的发展趋势。     

Routine determination of urinary free catecholamines by high-performance liquid chromatography with electrochemical detection

A simple and reliable high-performance liquid chromatographic method is described for the routine determination of the free catecholamines (norepinephrine, epinephrine and dopamine) in urine. The catecholamines are isolated from urine samples using small affinity chromatography columns prepacked with immobilised m-aminophenylboronic acid, separated by ion-pair reversed-phase liquid chromatography and quantified by electrochemical detection. Total analysis, including sample preparation time, is achieved in less than 30 min with analytical recoveries of 92-96% for all three catecholamines. Long-term stability and reproducibility of the liquid chromatographic system is attained by selection of optimised conditions for chromatographic separation with a formate mobile phase and produces detection limits of 1.4, 1.8 and 2.2 nmol/l for norepinephrine, epinephrine and dopamine, respectively, in urine samples and day-to-day coefficients of variation of less than 6%. Furthermore, the affinity isolation gels can be reused a minimum of ten times providing a rapid and cost-effective means of sample preparation.