Analytical and Bioanalytical Chemistry (v.373, #1-2)
Modern sample preparation techniques by K. Jinno (1-2).
Sorptive sample preparation – a review by E. Baltussen; C. Cramers; P. Sandra (3-22).
Most sample-enrichment procedures currently available rely on adsorption of the analytes of interest by a suitable adsorbent material. Although good performance can be obtained for many practical problems, in some cases the applicability of adsorptive sample preparation falls short, particularly for the enrichment of polar and/or high-molecular-weight compounds, especially in combination with thermal desorption. Because of the very strong retention of adsorbent materials, undesired effects such as incomplete desorption and artifact formation are observed. Polar solutes are easily adsorbed but readily undergo surface-catalyzed reactions and on desorption yield compounds different than those originally sampled. High-molecular-weight compounds cannot be desorbed because of extremely strong interactions with the adsorbent and their low volatility.To overcome some of these problems sample-preparation techniques based on polydimethylsiloxane sorption have been developed over the past 15 years. In contrast with adsorptive trapping, sorption is based on dissolution of the analytes in a liquid polymeric material. This is a much more inert means of solute retention which overcomes some of the limitations encountered when working with adsorbents. In this contribution, the basic principles of sorption, the different instrumentation used, and applications of the technique will be reviewed. The review covers the sorptive sample-preparation techniques, open-tubular trapping (OTT), solid-phase microextraction (SPME), gum-phase extraction (GPE), equilibrium gum-phase extraction (EGPE), and stir-bar-sorptive extraction (SBSE). Because of the nature of sorptive sample-preparation techniques, which perform particularly well in combination with thermal desorption, this review focuses strongly on gas chromatography as the means of chemical analysis.
Keywords: Sorptive sample preparation Gas chromatography Thermal desorption Polydimethylsiloxane
A review of modern sample-preparation techniques for the extraction and analysis of medicinal plants by Carmen W. Huie (23-30).
Sample preparation is the crucial first step in the analysis of herbs. In recent years there has been increasing interest worldwide in the use of alternative/herbal medicine for the prevention and treatment of various illnesses. Currently, however, quality-related problems (lack of consistency, safety, and efficacy) seem to be overshadowing the potential genuine health benefits of various herbal products. Thus, the development of "modern" sample-preparation techniques with significant advantages over conventional methods for the extraction and analysis of medicinal plants is likely to play an important role in the overall effort of ensuring and providing high-quality herbal products to consumers worldwide. In this article, recent developments and applications of modern sample-preparation techniques for the extraction, clean-up, and concentration of analytes from medicinal plants or herbal materials are reviewed. These modern techniques include solid-phase microextraction, supercritical-fluid extraction, pressurized-liquid extraction, microwave-assisted extraction, solid-phase extraction, and surfactant-mediated extraction.
Keywords: Sample preparation Extraction Quality control Medicinal plants Herbs
Automated sample preparation using in-tube solid-phase microextraction and its application – a review by Hiroyuki Kataoka (31-45).
Sample preparation, such as extraction, concentration, and isolation of analytes, greatly influences their reliable and accurate analysis. In-tube solid-phase microextraction (SPME) is a new effective sample preparation technique using an open tubular fused-silica capillary column as an extraction device. Organic compounds in aqueous samples are directly extracted and concentrated into the stationary phase of capillary columns by repeated draw/eject cycles of sample solution, and they can be directly transferred to the liquid chromatographic column. In-tube SPME is an ideal sample preparation technique because it is fast to operate, easy to automate, solvent-free, and inexpensive. On-line in-tube SPME-performed continuous extraction, concentration, desorption, and injection using an autosampler, is usually used in combination with high performance liquid chromatography and liquid chromatography-mass spectrometry. This technique has successfully been applied to the determination of various compounds such as pesticides, drugs, environmental pollutants, and food contaminants. In this review, an overview of the development of in-tube SPME technique and its applications to environmental, clinical, forensic, and food analyses are described.
Keywords: In-tube solid-phase microextraction Automated sample preparation Capillary column On-line analysis Hyphenated technique
Stir bar sorptive extraction–thermal desorption–capillary GC–MS applied to biological fluids by B. Tienpont; F. David; K. Desmet; P. Sandra (46-55).
A new sample preparation method, stir bar sorptive extraction (SBSE), has been evaluated for the enrichment of organic solutes from biological fluids such as urine and blood. In SBSE, a stir bar coated with a polydimethylsiloxane layer is stirred for a given time in the sample. After sampling the stir bar is placed in a thermal desorption unit coupled on-line to capillary gas chromatography–mass spectrometry (SBSE–TD–CGC–MS). The principle and operation of SBSE are presented. Total profiling and target compound analysis have been selected as applications to illustrate the performance of SBSE–TD–CGC–MS (MSD). It is demonstrated that a variety analytes ranging from biological markers (phenols, hormones, fatty acids) to artificial contaminants (recreational drugs, plasticizers) can be enriched with high sensitivity. For polar solutes, in-situ derivatization can enhance both recovery into the polydimethylsiloxane (PDMS) layer and chromatographic analysis. Two types of derivatization have been applied, derivatization with ethyl chloroformate and with acetic acid anhydride. Linearity, detectability, and repeatability are illustrated by the determination of 1-hydroxypyrene in a urine sample from a smoker.
Keywords: Stir bar sorptive extraction Thermal desorption Capillary gas chromatography–mass spectrometry Biological fluids Quantitative analysis
Simultaneous determination of preservatives in beverages, vinegar, aqueous sauces, and quasi-drug drinks by stir-bar sorptive extraction (SBSE) and thermal desorption GC–MS by Nobuo Ochiai; Kikuo Sasamoto; Masahiko Takino; Satoru Yamashita; Shigeki Daishima; Arnd C. Heiden; Andreas Hoffmann (56-63).
A method for the simultaneous determination of seven preservatives – sorbic acid, benzoic acid, and p-hydroxybenzoic acid ethyl, isopropyl, propyl, isobutyl, and butyl esters – in beverages, vinegar, aqueous sauces, and quasi-drug drinks has been developed using the stir-bar sorptive extraction technique then thermal desorption GC–MS analysis. The extraction conditions – pH, sample volume, extraction temperature, salt addition, and extraction time – were examined.d5-Benzoic acid and p-hydroxybenzoic acid sec-butyl ester were added as surrogate internal standards to compensate for the effect of sample matrix and coexisting analytes on the sorptive extraction. The linearity of the method was good over the concentration range from 1 to 1000 µg mL–1 for sorbic acid, 10–1000 µg mL–1 for benzoic acid, and 0.1–100 µg mL–1 for p-hydroxybenzoic acid ethyl, isopropyl, propyl, isobutyl, and butyl esters, and the correlation coefficients were higher than 0.9984. The limit of detection ranged from 0.015 to 3.3 µg mL–1. The recoveries (95–105%) and precision (RSD: 0.86–6.0%) of the method were examined by analyzing a sparkling soft drink, white wine, red wine, balsamic vinegar, soy sauce, and quasi-drug drink samples fortified at the 5 to 50 µg mL–1 level.
Keywords: Preservatives Stir-bar sorptive extraction (SBSE) Thermal desorption GC–MS
Solid-phase microextraction and on-line methylation gas chromatography for aliphatic carboxylic acids by Yaqian Liu; Seong R. Cho; Neil D. Danielson (64-69).
Methylation of carboxylic acids upon syringe injection of a mixture of the acid sample and phenyltrimethylammonium hydroxide (PTMAH) into the GC injection port is a convenient but under-utilized derivatization procedure. To minimize potential instrumental problems due to the sample matrix, it was shown that solid-phase microextraction (SPME) is effective for the absorption of both the carboxylic acid (RCOOH) and PTMAH permitting on-line methylation from the fiber. A comparison of three fibers, polydimethylsiloxane (PDMS), polyacrylate (PA), and carboxene/PDMS for decanoic and stearic acids showed the carboxene/PDMS fiber was about five times more effective for the extraction of the RCOOH-PTMAH mixture dissolved in methanol. The optimum fiber absorption time was about 20 min and the optimum desorption time in the injection port held at 280 °C was about 5–10 min. The optimum PTMAH/RCOOH ratio was about 125:1. Linearity for C18:0 at 3.3×10–6–3.3×10–4 M was demonstrated by GC-MS with a detection limit of 1 µM. This SPME method is also effective for the methylation of C18:1, C18:2, and C18:3 fatty acids. Transesterification of olive oil using PTMAH and then on-line methylation either by the syringe method or by SPME gave comparable fatty acid methyl ester profiles.
Keywords: Solid-phase microextraction Pyrolytic methylation
SPME determination of volatile aldehydes for evaluation of in-vitro antioxidant activity by Elena E. Stashenko; Miguel A. Puertas; Jairo R. Martínez (70-74).
The in-vitro antioxidant activity of natural (essential oils, vitamin E) or synthetic substances (tert-butyl hydroxy anisole (BHA), Trolox) has been evaluated by monitoring volatile carbonyl compounds released in model lipid systems subjected to peroxidation. The procedure employed methodology previously developed for the determination of carbonyl compounds as their pentafluorophenylhydrazine derivatives which were quantified, with high sensitivity, by means of capillary gas chromatography with electron-capture detection. Linoleic acid and sunflower oil were used as model lipid systems. Lipid peroxidation was induced in linoleic acid by the Fe2+ ion (1 mmol L–1, 37 °C, 12 h) and in sunflower oil by heating in the presence of O2 (220 °C, 2 h). The change in hexanal (the main lipoxidation product) concentration found in the lipid matrix subjected to oxidation with and without the substance being tested was used to calculate the antioxidant protection effect. These procedures were employed to evaluate the antioxidant activity of the essential oils of cilantro (Coriander sativum L.), fennel (Foeniculum vulgare Mill.), rosemary (Rosmarinus officinalis L.), "salvia negra" (Lepechinia schiedeana), and oregano (Origanum vulgare L.), and the well-known antioxidants BHA, vitamin E, and Trolox, its water-soluble analog. In the sunflower oil system, the essential oils had a stronger protective effect against lipid peroxidation than BHA, vitamin E, and Trolox within the range of concentrations examined (1–20 g L–1). The highest protecting effect, corresponding to a 90% drop in hexanal release, was observed for cilantro oil at 10 g L–1.
Keywords: Antioxidant Pentafluorophenylhydrazine Lipoxidation On-fiber derivatization Essential oils
Cryogenic oven-trapping gas chromatography for analysis of volatile organic compounds in body fluids by K. Watanabe-Suzuki; A. Ishii; O. Suzuki (75-80).
Cryogenic oven-trapping (COT) with capillary GC has been successfully applied to analysis of chloroform, dichloromethane, trichloroethylene, diethyl ether, the components of solvent thinner (ethyl acetate, benzene, n-butanol, toluene, and others), xylene isomers, cyanide, ethanol, hexanes, general anesthetics, and styrene in human body fluids. This COT–GC technique was compared with headspace solid-phase microextraction (SPME) coupled with GC for some volatile organic compounds (VOC); for all compounds compared the sensitivity achieved using COT–GC was more than ten times higher than for headspace SPME–GC. The COT–GC method is recommended for widespread use in forensic and environmental toxicology, because it is simple, requires no special GC operations, and yet enables high sensitivity and high resolution.
Keywords: Cryogenic oven-trapping Volatile organic compounds Gas chromatography Headspace extraction Cryo-focusing
Miniaturized solid-phase extraction as a sample preparation technique for the determination of phthalates in water by Yoshihiro Saito; Yuji Nakao; Motohiro Imaizumi; Yoriko Morishima; Yoshiaki Kiso; Kiyokatsu Jinno (81-86).
Miniaturized solid-phase extraction (SPE) has been developed and successfully employed for the determination of organic species in water samples by liquid chromatography (LC). The method is based on the concept of a microscale extraction technique using a fused-silica capillary column for gas chromatography (GC), so-called in-tube solid-phase microextraction (SPME). The extraction conditions, such as the extraction time and flow-rate for the extraction and desorption process, were investigated as well as the effect of the internal structure of the extraction capillary on the efficiency. By inserting a stainless steel wire into the extraction capillary to reduce the internal volume of the capillary with the same surface area of the coating, an improved extraction and pre-concentration effects were obtained. Further pre-concentration was accomplished by the extraction device with a novel fiber-in-tube configuration. The direct coupling of the extraction method with a LC system has made it possible to determine low levels of phthalates in water samples without high consumption of organic solvents. The system developed must have potential applications for the analysis of environmental and biological samples in aqueous sample matrices.
Keywords: Miniaturization Fiber-in-tube solid-phase extraction Sample preparation Liquid chromatography Capillary electrochromatography
Homogeneous liquid–liquid extraction and micellar electrokinetic chromatography using sweeping effect concentration system for determination of trace amounts of several polycyclic aromatic hydrocarbons by Yoshitaka Takagai; Shukuro Igarashi (87-92).
A powerful capillary electrophoresis (CE) method, with preconcentration in excess of 100,000-fold, has been developed by using a specific characteristic of perfluoro surfactants. Highly sensitive determination and separation of polycyclic aromatic hydrocarbons (PAH) were achieved by following a combination of two kinds of efficient preconcentration method using perfluoro surfactants. The two preconcentration methods combined were homogeneous liquid–liquid extraction for off-line concentration and a sweeping method as on-line concentration. Five PAH (1,2,3,4-dibenzanthracene, 1,2,5,6-dibenzanthracene, benzo(a)pyrene, benzo(e)pyrene, and pyrene) were investigated, and were completely separated. When the concentration-factor (volume ratio) was 8335-fold, the determination limits were in the range 10–10 to 10–9 mol L–1. The maximum concentration-factor (volume ratio) obtained was 125,000-fold. Addition and recovery experiments were performed for three kinds of natural water (rain water, river water, and spring water).
Keywords: Homogeneous liquid–liquid extraction method Micellar electrokinetic chromatography Sweeping method Fluoro surfactant Polycyclic aromatic hydrocarbons Preconcentration
Ultrasound-assisted extraction in the determination of arsenic, cadmium, copper, lead, and silver in contaminated soil samples by inductively coupled plasma atomic emission spectrometry by Ari Väisänen; Reijo Suontamo; Janne Silvonen; Jukka Rintala (93-97).
An extraction method was developed for the determination of toxic elements in contaminated soil samples by inductively coupled plasma atomic emission spectrometry (ICP-AES). The determination of arsenic, cadmium, lead, and silver in ultrasound-assisted extracts of SRM 2710 and SRM 2711 by ICP-AES was carried out with high accuracy and precision (RSD<3.7%). The certified concentrations of the SRMs were obtained for arsenic, cadmium, lead, and silver by using an ultrasound-assisted extraction method with a digestion solution of (1+1)-diluted aqua regia. The determination of copper in SRMs by the ultrasound-assisted extraction method and analysis by ICP-AES failed to obtain the certified concentrations at the 95% level of confidence using (±2 s) as confidence limits of the mean. However, the same results were observed with the use of the microwave digestion method and reflux, which is the ISO 11466 standard method. The analysis of the SRMs showed that the ultrasound-assisted extraction method is highly comparable with the other methods used for such purposes. The major advantages of the ultrasound-assisted extraction method compared to the microwave and reflux methods are the high treatment rate (50 samples simultaneously in nine minutes) and low reagent usage, the main benefit of which are the low chloride and nitrate concentrations in the extracts.
Keywords: Ultrasound-assisted extraction ICP-AES Elemental analyses Toxic metals Contaminated soil
On-line filtration system for determining total chromium and chromium in the soluble fraction of industrial effluents by flow injection flame atomic absorption spectrometry by I. López-García; B. Merino Meroño; N. Campillo; M. Hernández-Córdoba (98-102).
Two manifolds were assessed for the purpose of determining both the total chromium content and that present as a soluble form in industrial effluents by flow injection flame atomic absorption spectrometry (FI-FAAS). To determine the chromium content in the soluble fraction the samples were used without additional treatment, a 0.45 µm filter being included in the FI system. To determine the total chromium content, the samples were acidified with nitric acid 20% (v/v) and heated for 30 s in a microwave oven (temperatures of about 70 °C were reached). The problem posed by the very different concentration range in which total and soluble chromium are present was overcome by using programmed flow rate methodology and by only partially emptying the sample loop. A personal computer controlled both the rotation speed of a peristaltic pump and the volume of sample injected into the system, thus obtaining the dispersion degree required. Using the manifold proposed, the chromium content in the soluble fraction can be determined in the 0.5–20 µg mL–1 range using a 10 µg mL–1 single standard for calibration. To determine the total chromium content, a calibration line in the 20–200 µg mL–1 range was obtained using a single 50 µg mL–1 chromium standard solution. The reliability of the semi-automatic devices was verified by comparing the results obtained with those found by treating the samples and using both FAAS in a conventional way and a spectrophotometric method using diphenylcarbazide at the 95% confidence level (ANOVA test). The proposed procedures showed a RSD lower than ±3%.
Keywords: Chromium determination Flow injection Flame atomic absorption spectrometry FI-AAS AAS
Determination of Cr3+, CrO4 2–, and Cr2O7 2– in environmental matrixes by high-performance liquid chromatography with diode-array detection (HPLC–DAD) by S. Cathum; C. Brown; W. Wong (103-110).
A high-performance liquid chromatographic method with diode array detection (HPLC–DAD), based on chelation with ammonium pyrrolidinedithiocarbamate (APDC), has been developed for the determination of chromium species. Determination of Cr3+, CrO4 2–, and Cr2O7 2– was performed for standards and synthetic environmental matrixes. This method is robust, rugged, and can be used for rapid routine determination of chromium species with high precision and reliability. Sample pretreatment is simple. The method is capable of discriminating not only between Cr(III) and Cr(VI) but also between the chemical forms of Cr(VI) – CrO4 2– and Cr2O7 2–. By analysis of numerous samples the method has been shown to be selective, sensitive, and free from matrix interference, which is crucial for the determination of chromium species in difficult-to-analyze environmental matrixes. This method has been validated by means of an interlaboratory study. Although different speciation techniques were used during this study, there was good agreement between results from the two laboratories. The method detection limits were 7 and 4 mg L–1 for Cr3+ and Cr2O7 2–, respectively. Recoveries of the analytes from spiked samples were 98% and 100% for Cr3+ and Cr2O7 2–, respectively. Both were based on a 10-mL sample volume spiked with 0.4 mg L–1 chromium.
Keywords: Chromium Chelation HPLC–DAD Speciation Environmental analysis
A new simple and rapid electrochemical method for the determination of hydroxyl radical generated by Fenton reaction and its application by Hong Zou; Chao Tai; Xue-Xin Gu; Ruo-Hua Zhu; Qi-Hua Guo (111-115).
A simple and rapid electrochemical method to detect the hydroxyl radical is described. This method employed the reaction between ·OH and dimethyl sulfoxide (DMSO) to generate quantitatively formaldehyde, which then reacted with hydrazine hydrochloride at pH 6.2. The product showed a second-order derivative cathodic wave with the peak potential of –1.08 V( vs SCE) by single sweep oscillopolarography. The electrochemical behavior of the product was investigated by single sweep oscillopolarography and cyclic voltammetry. The experimental conditions for the measurement were optimized and the scavenging activity of some flavonoids on hydroxyl radicals was studied.
Keywords: Hydroxyl radical Fenton reaction Flavonoids Hydrazine hydrochloride Oscillopolarography,
Electroanalytical methods for determination of the metal content and acetic-acid-available metal fractions in soils by Joanna Kowalska; Beata Krasnodêbska-Ostrêga; Jerzy Golimowski (116-118).
The pseudo-total and available arsenic, cadmium, and lead content of soils have been determined by stripping voltammetry with a hanging-mercury-drop electrode and by atomic absorption spectrometry with electrothermal atomization. For determination of pseudo-total metals microwave digestion with a mixture of HNO3 and HClO4, with and without addition of HF, was investigated. The single-extraction procedure with 0.43 mol L–1 CH3COOH, proposed by BCR, was used to assess the availability of metals in soils. The results obtained were validated by analysis of a certified reference material.
Keywords: Soils Arsenic Cadmium Lead Single extraction Voltammetry
A flow system with in-line blank correction applied to the spectrophotometric determination of total iron and chromium (VI) in wastewaters by I. Morais; M. Souto; A. Rangel (119-122).
A flow system using the sample as the carrier with a propulsion device located after the detector is presented. This approach allows the correction of the intrinsic color of the sample, as it provides baseline adjustment for each sample. A confluence situated just after the selection valve allows the sample composition to be adjusted for the colorimetric measurement. The developed methodology was applied to the colorimetric determination of total Fe and Cr (VI) in wastewaters at 0.1–6.0 mg L–1 and 0.03–1.0 mg L–1, respectively. RSDs lower than 3% and a sampling rate of approximately 40 h–1 were obtained.
Keywords: Flow system Total iron Chromium (VI) Blank correction Wastewaters