Testing shelled corn for aflatoxin, Part I: estimation of variance components

The variability associated with testing lots of shelled corn for aflatoxin was investigated. Eighteen lots of shelled corn were tested for aflatoxin contamination. The total variance associated with testing shelled corn was estimated and partitioned into sampling, sample preparation, and analytical variances. All variances increased as aflatoxin concentration increased. With the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentration. Test results on a lot with 20 parts per billion aflatoxin using a 1.13 kg sample, a Romer mill, 50 g subsamples, and liquid chromatographic analysis showed that the total, sampling, sample preparation, and analytical variances were 274.9 (CV = 82.9%), 214.0 (CV = 73.1 %), 56.3 (CV = 37.5%), and 4.6 (CV = 10.7%), respectively. The percentage of the total variance for sampling, sample preparation, and analytical was 77.8, 20.5, and 1.7, respectively.     

Sampling hazelnuts for aflatoxin: uncertainty associated with sampling, sample preparation, and analysis

The variability associated with the aflatoxin test procedure used to estimate aflatoxin levels in bulk shipments of hazelnuts was investigated. Sixteen 10 kg samples of shelled hazelnuts were taken from each of 20 lots that were suspected of aflatoxin contamination. The total variance associated with testing shelled hazelnuts was estimated and partitioned into sampling, sample preparation, and analytical variance components. Each variance component increased as aflatoxin concentration (either B1 or total) increased. With the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentration. The sampling, sample preparation, and analytical variances associated with estimating aflatoxin in a hazelnut lot at a total aflatoxin level of 10 ng/g and using a 10 kg sample, a 50 g subsample, dry comminution with a Robot Coupe mill, and a high-performance liquid chromatographic analytical method are 174.40, 0.74, and 0.27, respectively. The sampling, sample preparation, and analytical steps of the aflatoxin test procedure accounted for 99.4, 0.4, and 0.2% of the total variability, respectively.     

Nickel species analysis of human colonic tissue using liquid chromatography,gel electrophoresis and mass spectrometry

Studies to specify metal-binding species, such as metalloproteins that are present in trace amounts in colonic cell cytosol, using chromatographic separation methods in combination with inductively coupled plasma mass spectrometry (ICP-MS) as element-specific detection require an optimised sample preparation regarding the solubilisation of the proteins. Focus should be taken to avoid metal contamination, enzymatic digestion by different proteases and oxidation. In this article different sample preparation methods are studied to find a suitable method for the isolation and characterisation of Ni species previously found in cytosols from normal and malignant tissues of the human colon. The total Ni concentrations of the cytosols were determined as well as the total protein content. Thus, a Ni-containing protein could be isolated from cytosols of malignant human colonic tissues using size-exclusion chromatography with ICP-MS for element-specific detection. Ni-containing species in the molecular mass range from 10,000 to 20,000 Da were found and pre-concentrated. The determination of the molecular mass of the species was performed through online coupling of reversed-phase chromatography with electrospray ionisation quadrupole time-of-flight MS. Using identical chromatographic conditions and ICP-MS the detected protein was shown to contain Ni.     

Coupling of biological sample handling and capillary electrophoresis.

The analysis of biological samples (e.g., blood, urine, saliva, tissue homogenates) by capillary electrophoresis (CE) requires efficient sample preparation (i.e., concentration and clean-up) procedures to remove interfering solutes (endogenous/exogenous and/or low-/high-molecular-mass), (in)organic salts and particulate matter. The sample preparation modules can be coupled with CE either off-line (manual), at-line (robotic interface), on-line (coupling via a transfer line) or in-line (complete integration between sample preparation and separation system). Sample preparation systems reported in the literature are based on chromatographic, electrophoretic or membrane-based procedures. The combination of automated sample preparation and CE is especially useful if complex samples have to be analyzed and helps to improve both selectivity and sensitivity. In this review, the different modes of solid-phase (micro-) extraction will be discussed and an overview of the potential of chromatographic, electrophoretic (e.g., isotachophoresis, sample stacking) and membrane-based procedures will be given.     

植物激素样品前处理方法的研究进展

植物激素是植物中一类含量很低,却对植物生长发育等生命过程起重要调控作用的有机化合物。近年色谱/质谱联用技术不断发展,已成为植物激素分析的常用方法,而样品前处理则是色谱分析过程中的一个关键环节,所以高选择性和高回收率的前处理方法对于植物激素的分析至关重要。根据植物激素的化学性质,本文将其分为酸碱性植物激素、油菜素甾醇、植物多肽3类,并对相应的前处理方法加以综述,特别是近年来发展起来的新方法。内容包括前处理方法的原理、装置、萃取材料以及衍生试剂等,相关内容主要围绕本研究组的痕量植物激素研究工作展开,最后对研究趋势做了简短展望。     

Liquid chromatography–mass spectrometry methods for urinary biomarker detection in metabonomic studies with application to nutritional studies

The effects of sample preparation and chromatographic method differences on the classification and recovery of metabolic biomarkers from UPLC‐MS measurements on urine samples of humans exposed to different dietary interventions have been investigated. Eight volunteers consumed three high‐fat meals (rich in saturated, monounsaturated and polyunsaturated fatty acids, respectively) in randomized order with a washout period in between. For each participant, urine samples were obtained prior to and at three timed intervals after each meal. Samples were processed either by dilution (1 : 4) or by liquid–liquid extraction and then run under two different gradient conditions. For each analysis method, a total of 96 observations (eight participants, four time points, three diets) were measured. The total ion count chromatograms were analyzed using partial‐least‐squares discriminant analysis. All three dietary classes could be discriminated irrespective of sample preparation and chromatographic method. However, the main discriminating metabolites varied according to sample preparation, indicating that sample treatment and chromatographic conditions influence the ability to extract biomolecular information. Diluted samples showed higher m/z compounds (ca 400 u) while liquid–liquid extraction samples showed low m/z at the same retention time span. Optimized methods for metabolite identification (e.g. organic acids) were statistically inferior to global screening for mixed compound identification, confirming that multiple compound class‐based metabolic profiles are likely to give superior metabonomic (diagnostic) classification, although great care has to be taken in the interpretation in relation to matrix effects. Copyright © 2009 John Wiley & Sons, Ltd.     

Recent advances in metal‐organic frameworks and covalent organic frameworks for sample preparation and chromatographic analysis

In the field of analytical chemistry, sample preparation and chromatographic separation are two core procedures. The means by which to improve the sensitivity, selectivity and detection limit of a method have become a topic of great interest. Recently, porous organic frameworks, such as metal‐organic frameworks (MOFs) and covalent organic frameworks (COFs), have been widely used in this research area because of their special features, and different methods have been developed. This review summarizes the applications of MOFs and COFs in sample preparation and chromatographic stationary phases. The MOF‐ or COF‐based solid‐phase extraction (SPE), solid‐phase microextraction (SPME), gas chromatography (GC), high‐performance liquid chromatography (HPLC) and capillary electrochromatography (CEC) methods are described. The excellent properties of MOFs and COFs have resulted in intense interest in exploring their performance and mechanisms for sample preparation and chromatographic separation.     

大气颗粒物中有机物色谱分析的样品制备技术

大气颗粒物中有机物成分分析对深入研究大气颗粒物对人类健康、环境、气候、生态的影响,解析气溶胶来源,制定颗粒物控制相关法规,以及风险管理方法具有重要意义。由于颗粒物中的有机组分种类繁多,分析复杂,目前仅10%~20%的有机物得到了定性和定量分析。因此,大气细颗粒中有机物的分析已成为环境分析领域的优先发展方向。色谱是大气颗粒物中有机物分析的主要方法,而样品制备则是影响分析速度和精度的关键步骤。本文对颗粒物中有机组分色谱分析前的样品制备方法进行了综述,介绍了索氏提取、超声辅助提取、微波辅助提取、加压溶剂提取等溶剂提取方法以及热解吸提取方法,并重点介绍了这些方法在大气颗粒物样品处理中的应用,总结了各种方法的优缺点。     

Preparation of samples of plant material for chromatographic analysis

The selection, collection, and preliminary treatment of plant material samples are discussed. Stages of sample preparation and extraction techniques presently used are described, and the most recent examples of sample preparation for chromatographic analysis are reviewed. Recent applications of gas chromatography for the assessment of emission of volatile organic compounds by plants are also described.     

Determination of biologically active low-molecular-mass thiols in human blood. III. Highly sensitive narrow-bore isocratic reversed-phase high-performance liquid chromatography with fluorescence detection

The fast isocratic narrow-bore reversed-phase high-performance liquid chromatographic method employing fluorescence detection is described for the precise reproducible simultaneous measurement of total homocysteine, cysteine and glutathione in human blood. Sample preparation involves conversion of disulfides to free thiols with triphenylphosphine, precipitation of proteins with sulfosalicylic acid, and conjugation of thiols with monobromobimane. Optimized sample preparation conditions as well as chromatographic conditions allowed to obtain reliable quantitative results within the concentration range corresponding to the levels of these thiols in human blood in norm and pathology. The detection limit was approximately 70 amol for all labeled aminothiols. The proposed method for these compounds analysis includes simple sample preparation, high selectivity, good linearity (r2>0.998), high reproducibility (within-run precision for derivatized aminothiol peaks area RSD<1.8% for three times consequently injected sample); high reliability and the small sample volume (1 microl) required for analysis make it suitable for clinical studies.     

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.     

样品前处理-色谱分析在线联用技术的研究进展

样品前处理是色谱分析中耗时最多、最容易引起误差的关键环节,因此有关样品前处理技术与色谱分析的在线联用的研究已成为分析化学的前沿课题。本文综述了近年来各种样品前处理技术与色谱分析在线联用的研究进展,包括固相萃取、固相微萃取与液相微萃取、膜辅助萃取、场作用辅助萃取、气相萃取、热解吸以及微芯片分离技术。     

A new method for solvent-free application of polymers and inorganic materials to ferromagnetic wires used for pyrolysis-capillary gas chromatographic studies

A method is described that enables soluble and insoluble samples to be applied to ferromagnetic wires. The principle of the method consists in pressing the sample on to a flattened Curie-point wire at a pressure of 15 tonnes. It is shown that this method is suitable for a wide variety of polymers and for inorganic materials. As the pyrolysis—gas chromatographic results obtained are not only influenced by the pyrolysis itself but also to a large extent by the gas chromatographic process, a number of considerations are given with respect to the use of capillary gas chromatography in combination with a Curie-point pyrolyser. The sample application technique described has also been used to check the inertness of the chromatographic system by the preparation of Curie wires loaded with Tenax. These wires have been used for the “injection” of volatile compounds, such as a Grob mixture, with the pyrolyser system.     

The Analysis of Penicillins in Biological Fluids and Pharmaceutical Preparations by High-Performance Liquid Chromatography: A Review

Abstract

High performance liquid chromatographic methods for the analysis of penicillins in biological fluids and pharmaceutical preparations are reviewed. In particular, sample preparation and handling procedures, chromatographic conditions and detection methods are discussed. A summary of published high performance liquid chromatographic assays for individual penicillins is included.     

Simultaneous determination of fluoride and monofluorophosphate in toothpastes by supressed ion chromatography

Suppressed ion chromatography with a highly selective and high capacity anion-exchange column is used for the determination of anionic compounds in ten commercially available toothpastes. Minimal sample preparation is needed, requiring only dilution and filtration over a solid-phase extraction cartridge. Quantitative analysis of fluoride and monofluorophosphate, as well as chloride, nitrate, orthophosphate, and sulfate is achieved in one chromatographic run with a total analysis time of 25 minutes. Optimized analytical conditions are validated in terms of accuracy, precision, and total uncertainty, and the results demonstrate the reproducibility of ion chromatography. The coefficient of determination for the anions ranges from 0.9896 to 0.9997. The spiked recoveries for the anions are 88–108%. The change in the fluoride content of the toothpaste with storage time is investigated.     

Continuous melting and ion chromatographic analyses of ice cores

A new method for determining concentrations of organic and inorganic ions in ice cores by continuous melting and contemporaneous ion chromatographic analyses was developed. A subcore is melted on a melting device and the meltwater produced is collected in two parallel sample loops and then analyzed simultaneously by two ion chromatographs, one for anions and one for cations. For most of the analyzed species, lower or equal blank values were achieved with the continuous melting and analysis technique compared to the conventional analysis. Comparison of the continuous melting and ion chromatographic analysis with the conventional analysis of a real ice core segment showed good agreement in concentration profiles and total amounts of ionic species. Thus, the newly developed method is well suited for ice core analysis and has the advantages of lower ice consumption, less time-consuming sample preparation and lower risk of contamination.     

Search on ruggedness of fast gas chromatography-mass spectrometry in pesticide residues analysis

In this study, suitability of fast gas chromatography-mass spectrometry (GC-MS) on a narrow-bore column with a programmed temperature vaporizer for the analysis of pesticide residues in non-fatty food was evaluated. The main objectives were ruggedness and stability of chromatographic system with regards to co-extractives injected. The chromatographic matrix induced response enhancement was found to be strongly dependent on the concentration of residues and is reaching up to 700% compared to the pesticides solutions in a neat solvent. However, the responses of pesticides in matrix-matched standards at different concentration levels do not significantly change during 130 injections. Response enhancement/or decrease is influenced by the sample preparation technique. External calibration with matrix-matched calibration standards should, therefore, provide results with good precision also at the concentration level of 0.005 mg kg(-1). Special attention is given to the performance of the chromatographic column and retention gap with regards to peak widths, peak tailing and different sample preparation methods. During approximately 460 matrix sample injections, the performance of the analytical column was acceptable. GC-MS set-up with 0.15 mm i.d. column can be successfully utilized for the pesticide residues analysis.     

Determination of amphetamine and methadone in human urine by microextraction by packed sorbent coupled directly to mass spectrometry: An alternative for rapid clinical and forensic analysis†

Speed and low cost, together with regulatory approval, are the most important requirements of clinical assays. Therefore, a fast and automated on‐line sample preparation method is essential for the routine analysis of biological samples. Microextraction by packed sorbent is an option for optimal sample preparation due to its easy automation, minimal requirements for the sample and elution solvent volumes, elimination of evaporation and reconstitution steps, and ability to integrate sample preparation and injection into one step. The use of effective sample preparation steps circumvents the need for chromatographic separation and therefore allows more rapid and less expensive sample analysis in clinical and forensic practice. Two biologically active compounds, amphetamine and methadone, were chosen as representative drugs of abuse for the application of microextraction by packed sorbent coupled directly to mass spectrometry. The developed method was validated, with the results confirming the suitability of the combination of these techniques for the analysis of biological samples. The approach was confirmed to be appropriate for use in clinical and forensic practice with regard to cost and time requirements for analysis.     

Use of computerized pattern recognition in the study of the cuticular hydrocarbons of imported fire ants. I. Introduction and characterization of the cuticular hydrocarbon patterns of Solenopsis invicta and S. richteri

A method is described in which gas chromatographic (GC) data obtained from cuticular hydrocarbons are treated by methods of pattern recognition. Based on a recently described sample preparation procedure, GC data are normalized to eliminate slight variations in chromatographic conditions and converted into the proper format for discriminant analysis by computer. The results of several methods of data treatment and display are discussed, based upon the chemometric system package, ARTHUR. The approach has the advantage of largely removing operator bias.     

Sample preparation for chromatographic analysis of food.

Sampling, homogenisation and sample preparation prior to chromatographic injection of food analytes are designed to enhance accuracy and precision. The reduction of inherent errors introduced by these steps requires the analyst's attention as a matter of course. Methods and examples of minimising errors in each step are reviewed.