Sample preparation with solid phase microextraction and exhaustive extraction approaches: Comparison for challenging cases

In chemical analysis, sample preparation is frequently considered the bottleneck of the entire analytical method. The success of the final method strongly depends on understanding the entire process of analysis of a particular type of analyte in a sample, namely: the physicochemical properties of the analytes (solubility, volatility, polarity etc.), the environmental conditions, and the matrix components of the sample. Various sample preparation strategies have been developed based on exhaustive or non-exhaustive extraction of analytes from matrices. Undoubtedly, amongst all sample preparation approaches, liquid extraction, including liquid–liquid (LLE) and solid phase extraction (SPE), are the most well-known, widely used, and commonly accepted methods by many international organizations and accredited laboratories. Both methods are well documented and there are many well defined procedures, which make them, at first sight, the methods of choice. However, many challenging tasks, such as complex matrix applications, on-site and in vivo applications, and determination of matrix-bound and free concentrations of analytes, are not easily attainable with these classical approaches for sample preparation.     

Pressurized liquid extraction versus other extraction techniques in micropreparative isolation of pharmacologically active isoflavones from Trifolium L. species

As a new sample preparation technique, pressurized liquid extraction (PLE), in combination with reversed-phase liquid chromatography (RP-LC) and photodiode-array (PDA) detection were used for the isolation and determination of phytoestrogenic isoflavones in hydrolyzed extracts obtained from aerial parts of five Trifolium L. (clover) species. To optimize the effectiveness of PLE procedure, variable extraction parameters: methanol and acetone (or their 75% aqueous solutions), as extraction solvents, temperatures (75, 100 and 125 °C) and the changeable number of static extraction cycles were tested. Additionally, two other micropreparative techniques: ultrasound-assisted extraction (UAE), and conventional solvent extraction (CSE), under optimized conditions, were also used and compared. Optimum extraction efficiency, expressed in the highest yield of biochanin A, formononetin, daidzein and genistein from plant material, with PLE, using methanol-water (75:25, v/v) as an extraction solvent, an oven temperature of 125 °C and three 5-min static extraction cycles, was obtained.     

Pressurized liquid extraction of mate tea leaves

The objective of this work is to investigate the influence of process parameters on the pressurized liquid extraction (PLE) of Ilex paraguariensis leaves. A factorial 2⁶⁻² experimental design was employed using responses as the extraction yield and the chromatographic profile of the extracts. The extraction time, polarity of solvent, amount of sample, numbers of PLE cycles, flushing volume and extraction temperature were selected as independent variables (factors). Results obtained indicated that the solvent polarity was the most significant variable in the study, while the amount of sample and extraction temperature also showed significant effect. The other variables did not present significant influence in the yield of extraction. GC/MS analysis of the extract enabled the identification of saturated hydrocarbons, fatty acids, fatty acid methyl esters, phytosterols and theobromine in the extracts. Quantitative analysis of four compounds presented in the extracts (caffeine, phytol, vitamin E and squalene) was performed by the GC/MS in the SIM mode.     

Development of pressurized liquid extraction and solid‐phase microextraction combined with gas chromatography and flame photometric detection for the determination of organophosphate esters in sediments

Organophosphate esters have been extensively used as flame retardants and plasticizers. The analysis of organophosphate esters in the environment is a hot topic because many of them are toxic and persistent. We developed a novel procedure for determining organophosphate esters in sediment. In this work, pressurized liquid extraction and solid‐phase microextraction are used for sample preparation to extract and concentrate the analytes, which are then analyzed by gas chromatography with flame photometric detection. The extraction parameters of pressurized liquid extraction were investigated and optimized by orthogonal design and then evaluated by range analysis and analysis of variance. Under the optimal conditions, the proposed procedure showed wide linear ranges (0.90–100 ng/g) with correlation coefficients ranging from 0.9921 to 0.9990. The detection limits of the method were in the range of 0.009–0.280 ng/g with standard deviations ranging from 2.2 to 9.5%. Recoveries of the proposed method ranged from 82.3 to 108.9% with relative standard deviations <8.4%. The obtained method was applied successfully to the determination of organophosphate esters in real sediments with recoveries varying from 79.8 to 107.3%. The proposed method was proved to be simple, easy, and sensitive for analyzing organophosphate esters in sediment samples.     

Recent advances and trends in miniaturized sample preparation techniques

Advances in the area of sample preparation are significant and have been growing significantly in recent years. This initial step of the analysis is essential and must be carried out properly, consisting of a complicated procedure with multiple stages. Consequently, it corresponds to a potential source of errors and will determine, at the end of the process, either a satisfactory result or a fail. One of the advances in this field includes the miniaturization of extraction techniques based on the conventional sample preparation procedures such as liquid‐liquid extraction and solid‐phase extraction. These modern techniques have gained prominence in the face of traditional methods since they minimize the consumption of organic solvents and the sample volume. As another feature, it is possible to reuse the sorbents, and its coupling to chromatographic systems might be automated. The review will emphasize the main techniques based on liquid‐phase microextraction, as well as those based upon the use of sorbents. The first group includes currently popular techniques such as single drop microextraction, hollow fiber liquid‐phase microextraction, and dispersive liquid‐liquid microextraction. In the second group, solid‐phase microextraction techniques such as in‐tube solid‐phase microextraction, stir bar sorptive extraction, dispersive solid‐phase extraction, dispersive micro solid‐phase microextraction, and microextraction by packed sorbent are highlighted. These approaches, in common, aim the determination of analytes at low concentrations in complex matrices. This article describes some characteristics, recent advances, and trends on miniaturized sample preparation techniques, as well as their current applications in food, environmental, and bioanalysis fields.     

Pressurized liquid extraction as a green approach in food and herbal plants extraction: A review

Pressurized liquid extraction is a “green” technology for the extraction of nutraceuticals from foods and herbal plants. This review discusses the extraction principles and the optimization of the extraction parameters that improves the extraction efficiency. The use of different solvent mixtures and other extraction additives to enhance the efficiency of the extraction are discussed. Dynamic mode of extraction in Pressurized liquid extraction, and the use of combined and hyphenated sample preparation and analytical techniques are presented. This work discusses how different studies used Pressurized liquid extraction to enrich phenolic compounds, lignans, carotenoids, oils and lipids, essential oils and other nutraceuticals from foods and herbal plants.     

Matrix removal in state of the art sample preparation methods for serum by charged aerosol detection and metabolomics-based LC-MS

Investigations into sample preparation procedures usually focus on analyte recovery with no information provided about the fate of other components of the sample (matrix). For many analyses, however, and particularly those using liquid chromatography-mass spectrometry (LC-MS), quantitative measurements are greatly influenced by sample matrix. Using the example of the drug amitriptyline and three of its metabolites in serum, we performed a comprehensive investigation of nine commonly used sample clean-up procedures in terms of their suitability for preparing serum samples. We were monitoring the undesired matrix compounds using a combination of charged aerosol detection (CAD), LC-CAD, and a metabolomics-based LC-MS/MS approach. In this way, we compared analyte recovery of protein precipitation-, liquid-liquid-, solid-phase- and hybrid solid-phase extraction methods. Although all methods provided acceptable recoveries, the highest recovery was obtained by protein precipitation with acetonitrile/formic acid (amitriptyline 113%, nortriptyline 92%, 10-hydroxyamitriptyline 89%, and amitriptyline N-oxide 96%). The quantification of matrix removal by LC-CAD showed that the solid phase extraction method (SPE) provided the lowest remaining matrix load (48–123 μg mL⁻¹), which is a 10–40 fold better matrix clean-up than the precipitation- or hybrid solid phase extraction methods. The metabolomics profiles of eleven compound classes, comprising 70 matrix compounds showed the trends of compound class removal for each sample preparation strategy. The collective data set of analyte recovery, matrix removal and matrix compound profile was used to assess the effectiveness of each sample preparation method. The best performance in matrix clean-up and practical handling of small sample volumes was showed by the SPE techniques, particularly HLB SPE. CAD proved to be an effective tool for revealing the considerable differences between the sample preparation methods. This detector can be used to follow matrix compound elution during chromatographic separations, and the facile monitoring of matrix signal can assist in avoiding unfavourable matrix effects on analyte quantification.     

Multiresidue analysis of four pesticide residues in water dropwort (Oenanthe javanica) via pressurized liquid extraction, supercritical fluid extraction, and liquid-liquid extraction and gas chromatographic determination

The primary objective of this study was to simultaneously analyze the residues of the most commonly used pesticides, chlorpyrifos-methyl, endosulfan, EPN, and iprodione in the water dropwort, via accelerated solvent extraction (ASE), supercritical fluid extraction (SFE), and conventional solvent extraction (LLE) techniques. Residue levels were determined using GC with electron-capture detection (GC-ECD). The confirmation of pesticide identity was performed by GC-MS in a selected ion-monitoring (SIM) mode. In none of the ASE and SFE techniques were the extraction conditions optimized. Rather, the experimental variables were predicated on the author's experience. The ECD response for all pesticides was linear in the studied range of concentrations of 0.005-5.0 ppm, with correlation coefficients in excess of 0.9991. At each of the two studied fortification levels, the pesticides yielded recoveries in excess of 72% with RSDs between 1 and 19%. The LODs were achieved at a range of levels from 0.001 to 0.063 ppm, depending on the pesticide utilized. The LOQs, which ranged from 0.003 to 0.188 ppm, were lower than the maximum residue limits (MRLs) authorized by the Korean Food and Drug Administration (KFDA). All of the methods were applied successfully to the determination of pesticide residues in the real samples. It could, therefore, be concluded that any of the techniques utilized in this investigation might prove successful, given that the applied extraction conditions are wisely chosen.     

Novel sample preparation approaches in gas chromatographic analysis: Promising ideas

The development of sample preparation procedures is still a dynamic process despite a number of already proposed techniques. The main challenge in this research field is to fully replace classical procedures like liquid‐liquid extraction and solid‐phase extraction in gas chromatographic analysis. Some progress has been already achieved for the last 20 years when miniaturized techniques were incorporated in ISO standards. The current review is focused on novel approaches in sample treatment that appeared since 2010. It includes research studies describing non‐conventional instrumental design available to inspire future progress in the field. A combination of a few extraction principles and supporting with additional treatment are the main core suggested for improvement of sample preparation efficiency. This requires good compatibility of extraction media, assessment of multiple experimental parameters, and potential automatization possibilities.     

Pressurized liquid extraction of isoflavones from soybeans

Isoflavone derivatives from freeze-dried soybeans were extracted by pressurized liquid extraction (PLE) and determined by reverse-phase high performance liquid chromatography (HPLC) with both photo diode array and mass spectrometry (MS) detection. Both real and spiked samples were used in the development of the method.Several extraction solvents (methanol (MeOH) and ethanol (EtOH), 30-80% in water and water), temperatures (60-200 °C), pressures (100-200 atm), as well as the sample size (0.5-0.05 g) and cycle length (5-10 min) were studied for the optimization of the extraction protocol. The optimized extraction conditions for quantitative recoveries were: 0.1 g of sample, 100 °C, three (7 min) static extraction cycles and ethanol 70% as extracting solvent. The stability of the isoflavones during the PLE was also determined. Under PLE conditions, degradation of malonyl glucoside forms of the isoflavones takes place using temperatures higher than 100 °C whereas degradation of glucosides takes place above 150 °C. Using the optimized protocol, isoflavones can be extracted from freeze-dried soybeans without degradation.     

Comparison of mouse plasma and brain tissue homogenate sample pretreatment methods prior to high‐performance liquid chromatography for a new 1,2,4‐triazole derivative with anticonvulsant activity

The focus of the study was to develop a bio‐analytical assay for a 1,2,4‐triazole derivative from plasma and brain tissue homogenate samples. The goal was to compare analytical techniques that facilitate high accuracy with simplified sample processing. In this study, commonly used standard protein precipitation and solid‐phase extraction methods utilizing C₁₈ and cartridges of Hybrid technology were compared in terms of their ability for sample pretreatment and removal of biological matrices before high‐performance liquid chromatography quantification. Fast classical reversed‐phase chromatography on a C₁₈ column paired with selective sample preparation using Hybrid solid‐phase extraction technology resulted in the most precise bio‐analytical determination of the hydrophobic 1,2,4‐triazole derivative in both biological samples studied. The obtained recovery values were above 95% with the coefficient of variation lower than 5%.     

Pressurized liquid extraction in environmental analysis

A critical evaluation of recent literature utilizing pressurized liquid extraction (PLE) for environmental analysis is presented by compound class. Overall, the extraction efficiency of PLE, using the appropriate solvent, temperature and pressure for extraction, is similar to that of Soxhlet extraction. PLE has been used for some classes of compounds that are thermally labile (e.g., explosives) and may require acidic conditions for extraction (e.g., organometallic compounds). References to recent applications are presented emphasizing studies which utilize unspiked, natural matrices and studies that compare PLE to alternate extraction techniques.     

Optimizing pressurized liquid extraction of microbial lipids using the response surface method

Response surface methodology (RSM) was used for the determination of optimum extraction parameters to reach maximum lipid extraction yield with yeast. Total lipids were extracted from oleaginous yeast (Rhodotorula glutinis) using pressurized liquid extraction (PLE). The effects of extraction parameters on lipid extraction yield were studied by employing a second-order central composite design. The optimal condition was obtained as three cycles of 15 min at 100°C with a ratio of 144 g of hydromatrix per 100 g of dry cell weight. Different analysis methods were used to compare the optimized PLE method with two conventional methods (Soxhlet and modification of Bligh and Dyer methods) under efficiency, selectivity and reproducibility criteria thanks to gravimetric analysis, GC with flame ionization detector, High Performance Liquid Chromatography linked to Evaporative Light Scattering Detector (HPLC-ELSD) and thin-layer chromatographic analysis. For each sample, the lipid extraction yield with optimized PLE was higher than those obtained with referenced methods (Soxhlet and Bligh and Dyer methods with, respectively, a recovery of 78% and 85% compared to PLE method). Moreover, the use of PLE led to major advantages such as an analysis time reduction by a factor of 10 and solvent quantity reduction by 70%, compared with traditional extraction methods.     

Appraisal of “classic” and “novel” extraction procedure efficiencies for the isolation of polycyclic aromatic hydrocarbons and their derivatives from biotic matrices

In this study the extraction efficiency of pressurized liquid extraction (PLE), employing different extraction solvent mixtures under different extraction conditions, was compared with extraction efficiencies of commonly used procedures, Soxhlet extraction and extraction enhanced by sonication. Spruce needles and fish tissue were selected as test samples. Purification of obtained extracts was carried out by gel permeation chromatography (GPC) employing gel Bio-Beads S-X3. Identification and quantitation of target PAHs was performed by high-performance liquid chromatography with fluorescence detection (HPLC–FLD).

Within optimisation of PLE conditions, temperature of extraction, type of solvent, duration and number of static cycles as well as the influence of sample pre-treatment (drying, homogenisation, etc.) were tested. Comparison of the extraction efficiency of PLE with the efficiencies of the other techniques was done under the optimised conditions, i.e. sample slurry obtained by desiccation with anhydrous sodium sulphate, extracted at 100 °C in 1 cycle lasting 5 min. Hexane:acetone (1:1, v/v) was chosen as the most suitable extraction solvent for isolation of analytes from test samples.

Comparison of mentioned isolation techniques with respect to the amount of co-extracts, procedure blank levels and time and solvent volume demands was also done.     

Extraction techniques based on solid state and connected with liquid chromatography

Extraction methods applied in analysis of water samples can be named as liquid chromatography. Very often, these techniques are used as sample preparation method before another analytical method such gas chromatography or high performance liquid chromatography. The subject of this review is to compare the extraction techniques of liquid samples and discuss their characteristics in comparison with liquid chromatography. Some new extraction techniques are described, and some characteristic parameters are compared.     

LC and SPE Determination of Chlorophacinone in Corn Grains, Soil and Rat Plasma

A liquid chromatographic method was used for the analysis of chlorophacinone in corn, soil and rat plasma. Sample preparation differed from corn, soil and serum. Simple liquid extraction procedures were applied to soil and corn; solid phase extraction using Oasis HLB cartridges and easy protocol was used for plasma. Liquid chromatography was on X-terra C18 column. The mobile phase used did not contain ion-pairing reagent, it was constituted with methanol/ammonium bicarbonate (0.01 M, pH = 7), 70/30, v/v at 1 mL min⁻¹. UV detection was by using photodiode detector operating at 282 nm. Complete validation of the proposed procedure for corn, soil and serum was made.     

Application of totally automated on-line sample clean up for prostanoid extraction and HPLC separation

Summary The aim of this study has been the evaluation of an automated system for on-line sample preparation using solid phase extraction and HPLC purification for the measurement of prostanoids in urine. We have established the optimum precolumn and column conditions for this analysis. The manual extraction —HPLC procedure furnishes lower recoveries and higher coefficients of variation than those obtained by the automated on-line procedure. The automated system has been applied to prostanoid analysis of human urine samples from subjects exposed to lead.     

Basic principles,recent trends and future directions of microextraction techniques for the analysis of aqueous environmental samples

Microextraction-based sample preparation techniques have exhibited remarkable importance in analytical chemistry since they were first developed in the 1980s. The application of these techniques involves efficient and, at the same time, environmentally-friendly analytical methodologies. They are also generally faster when compared with classical sample preparation techniques, requiring low solvent and sample volumes, and also allowing for automated or semi-automated procedures. This paper provides an overview of the basic principles of sample preparation techniques and the important applications and developments that have taken place in this area over the past five years. These procedures include solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), bar adsorptive microextraction (BAμE), rotating disk sorptive extraction (RDSE), micro solid-phase extraction (μ-SPE) and liquid-phase microextraction (LPME). The main variations are discussed with a focus on recent applications in the analysis of environmental water samples. Lastly, some of the trends and perspectives associated with these outstanding microextraction sample preparation approaches are highlighted.     

Characterisation and determination of fullerenes: A critical review

A prominent sector of nanotechnology is occupied by a class of carbon-based nanoparticles known as fullerenes. Fullerene particle size and shape impact in how easily these particles are transported into and throughout the environment and living tissues. Currently, there is a lack of adequate methodology for their size and shape characterisation, identification and quantitative detection in environmental and biological samples. The most commonly used methods for their size measurements (aggregation, size distribution, shape, etc.), the effect of sampling and sample treatment on these characteristics and the analytical methods proposed for their determination in complex matrices are discussed in this review. For the characterisation and analysis of fullerenes in real samples, different analytical techniques including microscopy, spectroscopy, flow field-flow fractionation, electrophoresis, light scattering, liquid chromatography and mass spectrometry have been reported. The existing limitations and knowledge gaps in the use of these techniques are discussed and the necessity to hyphenate complementary ones for the accurate characterisation, identification and quantitation of these nanoparticles is highlighted.     

Sample preparation for planar chromatography

High-performance thin-layer chromatography has favorable properties for high-throughput separations with a high matrix tolerance. Sample preparation, however, is sometimes required to control specific matrix interferences and to enhance the detectability of target compounds. Trends in contemporary applications have shifted from absorbance and fluorescence detection to methods employing bioassays and mass spectrometry. Traditional methods (shake-flask, heat at reflux, Soxhlet, and hydrodistillation) are being challenged by automated instrumental approaches (ultrasound-assisted and microwave-assisted solvent extraction, pressurized liquid extraction, and supercritical fluid extraction) and the quick, easy cheap, efficient, rugged, and safe extraction method for faster and streamlined sample processing. Liquid-liquid extraction remains the most widely used approach for sample clean-up with increasing competition from solid-phase extraction. On-layer sample, clean-up by planar solid-phase extraction is increasingly used for complex samples and in combination with heart-cut multimodal systems. The automated spray-on sample applicator, the elution head interface, biological detection of target and non-target compounds, and straightforward mass spectrometric detection are highlighted as the main factors directing current interest toward faster and simpler sample workflows, analysis of more complex samples, and the determination of minor contaminants requiring high concentration factors.