Evaluation of sample preparation (grinding and sieving) of bivalves, coffee and cowpea beans for multi-element analysis

Elemental analyses of food samples require several pre-treatment steps that constitute a great potential source of errors. In this study, the influence of cryogenic, ball and knife mill devices and also sieving using different sizes of sieve (100, 300 and 500 μm) was evaluated for samples of bivalves, coffee and cowpea beans. A two-factor ANOVA was performed in each sample to test for differences between macro, micro and trace element concentrations determined by ICP OES. Results showed that the efficiency of the particle size reduction and sample homogeneity depends on the milling device and the nature of samples. Food samples may present segregation after comminution, and sieving might become a necessary step. Nevertheless, the sieve aperture has to be chosen cautiously, once it might influence the final element concentration. Overall, the expected results by employing cryogenic grinding, such as rapid sample homogenization and small particle size generated were also observed for ball mill. Contamination can be a critical issue for some elements and need to be evaluated individually.     

Comparison of sample preparation methods combined with gas chromatography with electron‐capture detection for the analysis of multipesticide residues in lotus seeds

Sample preparation is always the major bottleneck in analytical chemistry for the determination of pesticide residues. Different sample preparation methods have been proposed due to the wide variety of pesticides used and the inherent complexity of the matrices. In this study, different sample preparation methods including SPE, matrix solid‐phase dispersion, the quick, easy, cheap, efficient, rugged, and safe method, and a one‐step completion method were compared and evaluated for extracting pesticides from lotus seeds. Analysis was carried out using GC with electron‐capture detection. The results showed that good recoveries for tested pesticides were obtained by using Florisil in the four methods, and the extraction efficiency of the one‐step completion method was superior to the other three methods. The one‐step completion method was confirmed to have good linearity, reproducibility, stability, and recovery for the detection of 36 pesticides in lotus seed samples. The data collected from this study are expected to prove useful in regulating the concentration of the residues in lotus seeds, as well as in protecting human health from the hazards posed by these residues.     

Development of miniaturized sample preparation with fibrous extraction media

Introducing fine polymeric filaments as the extraction medium, a miniaturized sample preparation technique for micro-column liquid chromatography (micro-LC) has been developed along with the investigation of a reproducible preparation scheme of the extraction capillary. The polymeric filaments were packed longitudinally into either a fused-silica capillary or a polyether ether ketone (PEEK) capillary of appropriate dimensions, and the extraction capillary was installed to the injection valve in micro-LC system. The number of packed filaments should be precisely counted before the packing process to make sure the reproducible preparation of the extraction capillary. With conventional stationary phase materials for open-tubular gas chromatography, polymeric coating to the surface of the filaments was also studied in order to further enhance the extraction performance and selectivity. Coated with the polymeric material suitable for the extraction of particular analyte, a dramatic improvement on the extraction power was obtained. The results suggest that the future possibility of novel tailored fibrous extraction medium with an appropriate coating on it, especially for the analysis of complex sample matrices.     

Comparison of ultrasound-assisted leaching with conventional and acid bomb digestion for determination of metals in sediment samples

In this paper, a sample preparation method based on ultrasound assisted leaching of Pb, Cu, Zn, Ni and Mn from river and pond sediment samples under ultrasonic effect has been described. Parameters influencing leaching such as sonication time, sample amount, particle size and extractant were fully optimized. Leachatants obtained upon sonication were directly nebulised into an air-acetylene flame for fast metal determination by atomic absorption spectrometry. The best conditions for metal leaching were as follows: a 25 min sonication time, a 0.5 g sample amount (in 25 mL solvent), a particle size < 63 μm and a mixture of concentrated HNO₃-HCIO₄-HF (2:1:1, v/v/v). Analytical results for the five metals by ultrasound-assisted leaching, acid bomb and conventional digestion methods showed a good agreement, thus indicating the possibility of using mild conditions for sample preparation instead of intensive treatments inherent with the digestion methods. In addition, this method reduces the time required for all treatments (leaching or digestion, heating to dryness, cooling and separation) with acid bomb digestion method (from ∼ 8 h to ∼ 1.5 h) and conventional acid digestion method (from ∼ 14 h to ∼ 1.5 h). The accuracy of the method was tested either by comparing obtained results with those of acid bomb and conventional digestion methods or by application on a standard reference materials. The average relative standard deviation of ultrasound assisted leaching method varied between 0.7-1.9% for N = 6, depending on the analyte.     

Ultrasonic-assisted leaching of trace metals from sediments as a function of pH

The effects of ultrasonication on the leaching of trace metals form sediments as a function of pH have been investigated using atomic absorption spectrometry. Cu, Pb, Ni, Zn and Mn were leached from sediments by ultrasonic effect using phthalate buffers at pH values of 2.2-6.0. Parameters influencing leaching, such as leaching time, solution matrix, wet or dry sample and final pH were evaluated. Results from ultrasonic leaching experiments were comparable to those of conventional procedure. In addition, this ultrasonic-assisted leaching method reduces the time required for conventional method approximately from 12 h to 25 min. Depending on the metal and sample type, metal removal increased linearly or exponentially with decreasing pH. The accuracy of the method was tested by comparing obtained results with this of conventional method. The average relative standard deviation (R.S.D.) of ultrasonic-assisted leaching method (ULM) varied between 1.71 and 3.00% for N = 36, depending on the analyte. This technique shows promise for studying chemical and biological availability and uptake/release processes for metals in sediment and soil as a function of pH.     

化学衍生与萃取联用技术在生物样品预处理中的应用

近年来各种萃取技术与化学衍生联用的模式作为一种新型样品处理技术广泛应用于生物样品预处理.这种联用技术不仅能有效去除样品基质,还能有效改善极性大、挥发性强、热稳定性差的目标分析物的回收率,提高方法的选择性和灵敏度.研究者根据待分析物及衍生试剂性质选取不同的联用模式.本文评述了萃取技术与化学衍生联用模式以及其在生物样品预处理中的应用.     

On-line monitoring of Soxhlet extraction by chromatography and mass spectrometry to reveal temporal extract profiles

Soxhlet extraction is a popular sample preparation technique used in chemical analysis. It enables liberation of molecules embedded in complex matrices (for example, plant tissues, foodstuffs). In most protocols, samples are analyzed after the extraction process is complete. However, in order to optimize extraction conditions and enable comparisons between different types of extraction, it would be desirable to monitor it in real time. The main development of this work is the design and construction of the interface between Soxhlet extractor and GC–MS as well as ESI-MS system. The temporal extract profiles, obtained in the course of real-time GC–MS monitoring, have been fitted with mathematical functions to analyze extraction kinetics of different analytes. For example, the mass transfer coefficients of pinene, limonene and terpinene in lemon sample, estimated using the first-order kinetic model, are 0.540 h⁻¹, 0.507 h⁻¹ and 0.722 h⁻¹, respectively. On the other hand, the Peleg model provides the following extraction rates of pinene, limonene and terpinene: 0.370 nM h⁻¹, 0.216 nM h⁻¹ and 0.596 nM h⁻¹, respectively. The results suggest that both first-order kinetic and Peleg equations can be used to describe the progress of Soxhlet extraction. On-line monitoring of Soxhlet extraction reveals extractability of various analytes present in natural samples (plant tissue), and can potentially facilitate optimization of the extraction process.     

Preparation steps in environmental trace element analysis - facts and traps

The laboratory of CERVA is for several decades involved in the Belgian environmental research. The activity was associated to national monitoring programs dealing with trace metal pollution of all compartments of the environment (sea and river waters, sediments and organisms but also soils, plants, animal and food samples). Such a monitoring dealing with the total analyte contents in samples needed a comprehensive development of the whole methodology associated to the analyses using atomic absorption and emission spectroscopy techniques. This includes measurement but also preparation steps. The latter is the subject of this work. Long-term experience has shown that precisely sample preparation is the most critical part of the analysis because it is responsible for the largest and often hidden sources of errors. Errors due to contaminations may be usually overcome if necessary precautions are taken concerning reagents, tools and the manner of working. The problem is different for analyte losses: in this case, the responsible factor is an inappropriate methodology. This is particularly true for preparation of solid samples that have to be brought in a solution in order to satisfy needs of introduction systems of most spectroscopic techniques utilized in routine laboratories. For some types of samples (e.g. animal tissues), the dissolution is not a problem: it may be readily achieved by several procedures. This is not the case for samples that contain silicates in their matrix (e.g. soils, sediments, plants) because their complete dissolution cannot be ensured by a simple procedure. This review describes the present knowledge regarding possibilities and errors that concern preparation steps. In addition, possible effects of the preparation procedure on the quality of measurement are also systematically discussed.     

Ionic liquids as a tool for determination of metals and organic compounds in food analysis

Ionic liquids (ILs) are non-molecular solvents, which are mainly characterized as possessing low melting points, low-to-negligible vapor pressures, and high thermal stability. Their unique solvation properties, coupled to the fact that they can be structurally tailored for specific applications, have increased study of ILs in many areas of fundamental and applied chemistry. Thus, ILs have successfully been utilized as novel solvents in different extraction and microextraction schemes in recent years, but mainly with environmental samples.Food samples are quite complicated matrices from an analytical point of view. They contain a large range of chemical substances, and sometimes they also have a high fat content. Even with the most advanced analytical techniques, food sampling and food-sample preparation prior to the analytical determination are labor-intensive and time-consuming, and normally require relatively large amounts of organic solvents.In this review, we summarize the most recent analytical developments aimed at employing ILs as a tool in food analysis. We discuss practical applications to determine metals and organic compounds in food samples of quite different natures, with special emphasis to the extraction step at which the IL is introduced, and the advantages of the IL-based methods developed over conventional extraction methods.     

Atomic spectrometric methods for the determination of metals and metalloids in automotive fuels - A review

Gasoline, diesel, ethanol and more recently also biodiesel are the four types of fuel used for automobile, truck and other transportation vehicle. The presence of metallic and metalloid species in automotive fuels is undesirable, except in the form of additives in order to improve specific characteristics of the fuel. Metallic or metalloid elements may derive from the raw product, such as nickel and vanadium in petroleum-based fuel or phosphorus in biodiesel, or they may be introduced during production and storage, such as copper, iron, nickel and zinc in case of petroleum-based fuel and alcohol or sodium and potassium in the case of biodiesel. The most famous additive to fuel is undoubtedly lead, the use of which has been banned or drastically reduced now in many countries of the world. The problems related to the trace element content may be economic, such as fuel degradation and poisoning of automotive catalysts, and/or environmental, such as the emission of metal compounds to the atmosphere. The analytical methods that have been developed for metal and metalloid quantification in automotive fuel are reviewed in this article. The main atomic spectrometric techniques used for trace metal and metalloid determination in fuels, particularly atomic absorption spectrometry with flames, graphite furnaces and with chemical vapor generation, and inductively coupled plasma coupled with optical emission and mass spectrometry are presented, including the different sample preparation procedures proposed for these techniques.     

An extraction technique for analytical sample preparation in aqueous solution based on controlling dispersion of ionic surfactant assemblies in isotachophoretic migration

An extraction technique for analytical sample preparation in aqueous solution has been developed based on controlling dispersion of ionic surfactant assemblies. An extraction technique was realized based on controlling dispersion of the ionic surfactant assemblies in their isotachophoretic migration during the extraction by arranging the solutions of leading electrolyte, ionic surfactant and terminating electrolyte in order and applying voltage. Potential of the technique for analytical sample preparation in aqueous solution has been demonstrated by extracting a model sample of four alkylphenones, which were analyzed by HPLC after the extraction. The extraction showed concentration effects on all the four alkylphenones of butyrophenone, valerophenone, hexanophenone and heptanophenone in the model sample. The enrichment factors were 5.29, 7.70, 7.25 and 7.49 for the four alkylphenones of butyrophenone, valerophenone, hexanophenone and heptanophenone, respectively. Linear relationship was obtained with all the four alkylphenones between their chromatographic peak areas before and after the extraction in the range of concentration from 0.05 ppm to 1.5 ppm. The RSD of the chromatographic peak areas in triplicate extractions was 7.97%, 3.75%, 2.91% and 4.45% for butyrophenone, valerophenone, hexanophenone and heptanophenone, respectively. Advantages of the extraction technique developed include ease of operation, low reagent cost, no consumption of organic solvents and no requirement for additional phase separation.     

Influence of two grinding methods on the uncertainty of determinations of heavy metals in atomic absorption spectrometry/electrothermal atomisation of plant samples

 Chemical analyses of trace elements are affected by relatively high analytical errors due to the different steps of the laboratory procedures: samples grinding, mineralisation and instrumental measurements. In the present communication, the influence of the grinding phase on the global uncertainty of Pb, Cd, Ni and Cr determinations in plant samples by the classical method of atomic absorption spectrometry/electrothermal atomisation (AAS-ETA) after dry ashing is quantified. Two grinding machines, a planetary mill with balls and jars of agate versus a stainless steel grinder were compared by analysing leaf samples of cucumber, strawberry, kiwivines, apple trees and grapevines from agricultural experimental plots under controlled conditions. Variance components due to the difference between grinding methods and experimental plots were estimated. Further, the simultaneous effects of the grinding methods on all considered metals have been evaluated by analysis of variance. With the stainless steel grinder, on average, higher levels of the considered heavy metals were obtained (up to 67% of the mean values). On average, the increments were similar for metals contained in steel (Ni and Cr) and those not contained (Pb and Cd). The true causes of these differences need further investigation to determine whether the higher metal detection is due to possible contamination, to a different grinding quality or to other reasons. Finally, the grinding methods did not seem to affect the combined uncertainty of the analyses. Received: 3 November 1997 · Accepted: 29 November 1997     

Applications of ethylammonium and propylammonium nitrate solvents in liquid-liquid extraction and chromatography

Ethyl- and propylammonium nitrate are novel ionic solvents, liquid at room temperature, suitable for use as selective solvents for the isolation of analytes containing proton donor functional groups (alcohols, amines, phenols, carboxylic acids, etc.) by liquid-liquid distribution. These solvents form immiscible solvent pairs with non-polar aliphatic and aromatic hydrocarbons, ethers and alkyl halide solvents (e.g., methylene chloride, chloroform). Analytes can be recovered from the ionic solvents by back-extraction into ah organic solvent after dilution with water or pH buffer or, preferably, by extractive derivatization when gas chromatography is used for the analyses, avoiding the accumulation of salt on the column that results in poor baseline stability. Alkylation, acylation and particularly silylation are suitable methods for extractive derivatization using standard reaction conditions. Applications are presented for the isolation of polar analytes from an urban dust, shale oil and urine samples and for the determination of low-molecular-weight alcohols in gasahol and glycerol in soap. Liquid-liquid chromatographic systems with the liquid organic salt as stationary phase can be used to predict distribution constants for a particular separation and for the separation of polar solutes, particularly isomeric compounds possessing a proton donor functional group.     

Analytical methods for the assessment of endocrine disrupting chemical exposure during human fetal and lactation stages: A review

In the present work, a review of the analytical methods developed in the last 15 years for the determination of endocrine disrupting chemicals (EDCs) in human samples related with children, including placenta, cord blood, amniotic fluid, maternal blood, maternal urine and breast milk, is proposed. Children are highly vulnerable to toxic chemicals in the environment. Among these environmental contaminants to which children are at risk of exposure are EDCs —substances able to alter the normal hormone function of wildlife and humans—. The work focuses mainly on sample preparation and instrumental techniques used for the detection and quantification of the analytes. The sample preparation techniques include, not only liquid–liquid extraction (LLE) and solid-phase extraction (SPE), but also modern microextraction techniques such as extraction with molecular imprinted polymers (MIPs), stir-bar sorptive extraction (SBSE), hollow-fiber liquid-phase microextraction (HF-LPME), dispersive liquid–liquid microextraction (DLLME), matrix solid phase dispersion (MSPD) or ultrasound-assisted extraction (UAE), which are becoming alternatives in the analysis of human samples. Most studies focus on minimizing the number of steps and using the lowest solvent amounts in the sample treatment. The usual instrumental techniques employed include liquid chromatography (LC), gas chromatography (GC) mainly coupled to tandem mass spectrometry. Multiresidue methods are being developed for the determination of several families of EDCs with one extraction step and limited sample preparation.     

Development and validation of methods for the trace determination of phthalates in sludge and vegetables

A routine method which is simple, quick and precise has been set up and validated for phthalate analysis in environmental samples (tomato plants and sewage sludges). Six phthalates have been studied simultaneously: dimethylphthalate, diethylphthalate, di-n-butylphthalate, n-butylbenzylphthalate, di-2-ethyl-hexyl phthalate (DEHP) and di-n-octylphthalate. Optimization of sample, solvent extraction uses a Soxtec apparatus and extract purification with an a solid-phase extraction cartridge allows between 90 and 110% recovery of phthalates. Precise, sensitive and selective identification and quantifying of analytes is by GC-MS in the single ion monitoring mode. This protocol allows analytes with concentrations as low as 10 microg/kg dry matter (DM) to be determined from small (1-2 g DM) samples. This analytical method has been applied to the phthalate transfer study for agricultural recycling of sludges, where phthalate bioavailability has been studied in aquiculture using two types of experiments. Tomatoes have been grown in containers where the trace organics have been directly introduced as pure substances, and in a second experiment under the same growth conditions, sewage sludge has replaced the pure substances. Transfer of these trace organics has been followed into the various parts of the tomato plant and in general only the DEHP is worthy of note although its percentage transfer remains very low even in an experiment designed to maximize this.     

Miniaturized preconcentration methods based on liquid–liquid extraction and their application in inorganic ultratrace analysis and speciation: A review

Liquid–liquid extraction (LLE) is widely used as a pre-treatment technique for separation and preconcentration of both organic and inorganic analytes from aqueous samples. Nevertheless, it has several drawbacks, such as emulsion formation or the use of large volumes of solvents, which makes LLE expensive and labour intensive. Therefore, miniaturization of conventional liquid–liquid extraction is needed. The search for alternatives to the conventional LLE using negligible volumes of extractant and the minimum number of steps has driven the development of three new miniaturized methodologies, i.e. single-drop microextraction (SDME), hollow fibre liquid-phase microextraction (HF-LPME) and dispersive liquid–liquid microextraction (DLLME). The aim of this paper is to provide an overview of these novel preconcentration approaches and their potential use in analytical labs involved in inorganic (ultra)trace analysis and speciation. Relevant applications to the determination of metal ions, metalloids, organometals and non-metals are included.     

X射线荧光分析中熔融制样条件的研究

本文研究了熔融制样时熔融温度、熔融时间和脱模剂的加入量对分析结果的影响。研究结果表明,随着熔融温度的升高和熔融时间的加长,分析结果的总值将随之增大。相反,脱模剂量的增加会使分析结果降低。通过对熔融样品时产生的升华物的研究,发现在熔触过程中,四硼酸锂比样品以更大的比例逸出熔融体,从而造成了样品在分析圆片中的相对浓缩。而且在高温熔融时,钾和钠比样品中的其他元素例如硅、铝、铁、钛、钙、镁等更易于逸失。制样条件的不同引起样品和熔剂逸失的比例会有变化,它直接影响测定的结果,这证明了在X射线荧光光谱分析中保持制样条件一致的重要性。     

A solid-liquid extraction approach to elucidate the chemical availability of metals in soil and sediment assuming Langmuir isotherm behaviour

In an earlier paper (Anal. Chim. Acta 514 (2004) 137) we claimed that the maximal extractability of a metal from soil or sediment for a user-defined extractant, i.e. the chemical availability in that particular extractant, may be biased as a result of inadequate volume to mass (V/m) ratios. Correcting for that artifact using an implementation of the simple linear isotherm model gave good results although we cautioned the general applicability. In this paper we will theoretically derive the limitations of that approach based on the more general assumption that sorption processes are described by a Langmuir isotherm.NIST reference material 8704 was extracted with 1 mol l⁻¹ NaOAc (adjusted to pH 5) to experimentally verify the applicability of the Langmuir isotherm approach and illustrate the deviations obtained for some metals using the linear isotherm approach. Of the seven metals measured (Cr, Co, Ni, Cu, Zn, Cd, and Ba) only for Cr and Cu severe discrepancies between both approaches were found, which could be traced back to non-linear isotherm behaviour. Moreover, the Langmuir isotherm approach showed that the above mentioned extractability artifact is even more serious than earlier assumed applying the linear isotherm approach.     

Analytical methods for the determination of fluoroquinolones in solid environmental matrices

We present a critical review of the analytical procedures proposed in the past decade for the determination of fluoroquinolones (FQs) by chromatographic methods in solid environmental matrices. We emphasize the overall analytical procedure, from sampling to final detection. We devote special attention to sample preparation, highlighting the problems involved in the analysis of real complex matrices, mainly soil, sediment, manure and sludge. We compare the different extraction techniques in terms of efficiency, time taken and environmental impact, pointing out advantages and drawbacks. We provide an overview on the role of photochemistry in the degradation of FQs in soils and sediments, and we underline the central position of analytical chemistry in environmental monitoring because FQs are emerging pollutants.     

Microextraction methods for the determination of phthalate esters in liquid samples: A review

1,2‐Benzenedicarboxylic acid esters, commonly referred to as phthalate esters, form a group of compounds that are mainly used as plasticizers in polymers. Because phthalate esters are not chemically bound to the plastics, they can be released easily from products and migrate into the food or water that comes into direct contact. Due to their widespread use, they are considered as ubiquitous environmental pollutants. Phthalate esters are regarded as endocrine disrupting compounds by means of their carcinogenic effect. Phthalate esters can be analyzed by gas chromatography or high‐performance liquid chromatography, however, their sensitivity and selectivity limit their direct use for determination of phthalates at very low level of concentrations exist in environmental samples with complex matrices. Therefore a sample pretreatment prior to their analysis is necessary. In this review, the historical development and overview of sample preparation methodologies have briefly been discussed and a comprehensive application of these methods in combination with different analytical techniques for preconcentration and determination of phthalate esters in various matrices have been summarized. Finally, a critical comparison of the different approaches in terms of enrichment factors achieved, extraction efficiency, precision, selectivity and simplicity of operation is provided.