José Luis Capelo

Comparison of ultrasound-assisted extraction and microwave-assisted digestion for determination of magnesium, manganese and zinc in plant samples by flame atomic absorption spectrometry

In this paper, a sample preparation method based on acid extraction of magnesium, manganese and zinc from plant tissue by means of high intensity probe ultrasonication is described. Acid extracts obtained upon sonication were directly nebulised into an air-acetylene flame for fast metal determination by atomic absorption spectrometry. Parameters influencing extraction such as sonication time, ultrasound amplitude, sample mass, particle size, extractant composition and volume were fully optimised. Optimum conditions for metal extraction were as follows: a 3-min sonication time, a 30% ultrasonic amplitude, a 0.1-g sample mass, a particle size less than 50 mum, a 0.3% m/v HCl concentration in the extractant solution and a 5-ml extractant volume. Six plant samples used in the human diet were analysed, the concentration range of the three metals approximately being in the range of 1500-3000 mug g(-1) for Mg, 30-735 mug g(-1) for Mn and 20-45 mug g(-1) for Zn. Limits of detection corresponding to the ultrasound-assisted extraction method were 0.10, 1.26 and 0.65 mug g(-1) for Mg, Mn and Zn, respectively. Between-batch precision, expressed as R.S.D., was about 0.5, 1.5 and 1% for Mg, Mn and Zn, respectively. Analytical results for the three metals by ultrasound-assisted extraction and microwave-assisted digestion showed a good agreement, thus indicating the possibility of using mild conditions for sample preparation instead of intensive treatments inherent with the digestion method. The advantages and drawbacks of ultrasound-assisted extraction in respect to the microwave-assisted digestion are discussed.

Trends in ultrasonic-based equipment for analytical sample treatment

The recent developments achieved in ultrasonic equipment urges the need for the revision of its applications in analytical chemistry. In the present work, the last ultrasonic devices are easily presented and their applications for sample treatment are critically discussed. Comments are given on edge areas of research, such as proteomics or polymer science, which are presently taking advantage of ultrasonic sample treatments. Future applications and trends for ultrasonic-based handling approaches are also given and commented.

Overview on modern approaches to speed up protein identification workflows relying on enzymatic cleavage and mass spectrometry-based techniques.

Recent tools addressed to accelerate the different steps of the sample treatment for protein identification in modern workflows are reviewed and critically commented in this manuscript. Heating, microspin columns, ultrasonic energy, high pressure, infrared energy, microwave energy, alternating electric fields and microreactors are outlined as useful tools that can be used to accelerate all or some of the following steps for in-gel or in-liquid based approaches for protein identification: (i) protein dissolution/denaturation, (ii) protein reduction, (iii) protein alkylation and (iv) protein digestion. The advantages and drawbacks, along with the main differences among the different tools are also commented. Future prospects for hyphenation of methods are also discussed. Researchers are informed also in this work regarding the main problems to be found when implementing any of the above mentioned methods.

Micro-focused ultrasonic solid–liquid extraction (μFUSLE) combined with HPLC and fluorescence detection for PAHs determination in sediments: optimization and linking with the analytical minimalism concept

Analytical minimalism is a concept that deals with the optimization of all stages of an analytical procedure so that it becomes less time, cost, sample, reagent and energy consuming. The guide-lines provided in the USEPA extraction method 3550B recommend the use of focused ultrasound (FU), i.e., probe sonication, for the solid-liquid extraction of Polycyclic Aromatic Hydrocarbons, PAHs, but ignore the principle of analytical minimalism. The problems related with the dead sonication zones, often present when high volumes are sonicated with probe, are also not addressed. In this work, we demonstrate that successful extraction and quantification of PAHs from sediments can be done with low sample mass (0.125g), low reagent volume (4ml), short sonication time (3min) and low sonication amplitude (40%). Two variables are here particularly taken into account for total extraction: (i) the design of the extraction vessel and (ii) the solvent used to carry out the extraction. Results showed PAHs recoveries (EPA priority list) ranged between 77 and 101%, accounting for more than 95% for most of the PAHs here studied, as compared with the values obtained after soxhlet extraction. Taking into account the results reported in this work we recommend a revision of the EPA guidelines for PAHs extraction from solid matrices with focused ultrasound, so that these match the analytical minimalism concept.

Ultrasonic-assisted matrix solid-phase dispersion as an improved methodology for the determination of pesticides in fruits

An ultrasonic-assisted matrix solid-phase dispersion (UA-MSPD) method has been developed for extracting and cleaning-up 15 organophosphorus pesticides (OPPs) and 9 triazines in fruits. Using reversed phase octasilyl-derivatised silica (C8) as dispersant and ethyl acetate as extraction solvent, two sonication devices, an ultrasonic bath and a sonoreactor, were tested for speeding and increasing the efficiency of the MSPD process. A standard MSPD and a heating-assisted MSPD procedure were also done. Gas chromatography-mass spectrometry was used for analyte determination. 1-min sonication with the sonoreactor at 50% amplitude provided the best results, with reproducibilities below 15% for the pesticides studied. The general low detection limits (1-42microgkg(-1)) ensure proper determination at maximum allowed residue levels set in current legislations, except for dimethoate and disulfuton. The analytical performance of the method was evaluated for apples, pear and apricot, showing little or no matrix effect.

Trends in selenium determination/speciation by hyphenated techniques based on AAS or AFS.

The field of selenium speciation has been studied for decades and the growing interest in this field seems never to reach a plateau. Although powerful techniques based on mass spectrometry are nowadays used for selenium determination/speciation, few laboratories can support the high cost of such techniques. The hyphenation of chromatography to atomic absorption or atomic fluorescence spectrometry (AAS or AFS) is still a reliable and low-cost alternative for routine laboratories. In this work we present the most important parameters dealing with selenium speciation along with the latest trends in this subject, namely in the items related with sample treatment and hyphenation techniques with AAS and AFS detection.

Solid-liquid extraction of copper from slurried samples using high intensity probe sonication for electrothermal atomic absorption spectrometry.

A fast and simple method is proposed for determination of copper by electrothermal atomic absorption spectrometry in biological samples. Pulverized solid samples were placed in autosampler cups, slurried in an acidic diluent and subsequently treated by sonication under optimized conditions. Parameters influencing extraction such as sonication time, ultrasound amplitude, acid concentration and particle size were optimized so that quantitative copper recovery could be achieved. Quantitative recoveries for copper in mussel tissue were obtained using a 3 min sonication time, a 60% ultrasound amplitude, a 3% V/V HNO(3) concentration along with a particle size of the solid particles less than 50 microm. Under these extraction conditions, quantitative recovery of copper was also seen to be achieved for several certified reference materials such as BCR 278 mussel tissue, NRCC DORM-2 dogfish muscle and BCR CRM 60 (Lagarosiphon major) aquatic plant. The LOD of copper in the biological samples was 0.16 microg g(-1) when a sample mass of 10 mg were slurried in a volume of 1.5 ml. When comparing within- and between-batch precision values no significant differences occurred, hence indicating good homogeneity at the 10 mg mass level. Potential advantages of the method proposed over conventional slurry sampling such as an improved precision, since the representative subsample is the whole mass weighed in the autosampler cup, a decreased build-up of carbonaceous residues inside the graphite tube and the removal of volumetric and sedimentation errors can be anticipated.

Ultrasound-assisted extraction of cadmium from slurried biological samples for electrothermal atomic absorption spectrometry

Cadmium was determined in biological materials by electrothermal atomic absorption spectrometry after ultrasound-assisted treatment of slurried samples prepared in the autosampler cups with an acidic diluent. Parameters influencing Cd extraction into the liquid phase of the slurry, such as ultrasound amplitude, sonication time, particle size, acid concentration and sample mass used for preparing the slurry, were investigated. Quantitative recoveries of Cd from mussel tissue were obtained using a 20% amplitude, a 1 min sonication time and 3% nitric acid, demonstrating that the resulting supernatant in the autosampler cup can be used for sampling. Particle size had no effect on Cd extraction from mussel tissue in the range 200 μm, the recovery being quantitative. Extraction of Cd from several CRMs, such as BCR CRM 60 (Lagarosiphon major) Aquatic Plant, BCR CRM 278 Mussel Tissue, NRCC DORM-2 Dogfish Muscle and NRCC DOLT-2 Dogfish Liver, was also successful under the conditions mentioned above along with the original particle size distribution provided for these materials. Non-quantitative extraction was obtained with materials that have a typical inorganic matrix, such as BCR CRM 145R Sewage Sludge and BCR CRM 320 River Sediment. Homogeneity testing was carried out by comparison of between- and within-batch precision as well as homogeneity factors. The LOD for Cd in the solid biological samples was 0.019 μg g –1 when a 10 mg sample mass was slurried in a volume of 1.5 ml. In all cases, an acceptable homogeneity was observed even when using a sample mass of 10 mg for slurry preparation. In addition, the proposed approach for analyte extraction should provide further advantages in comparison with conventional slurry sampling, such as an improved precision, since the representative sub-sample is the whole mass taken for slurry preparation, lower background signals and a decreased build-up of carbonaceous residues inside the graphite tube.

Ultrasonic-assisted enzymatic digestion (USAED) for total elemental determination and elemental speciation: A tutorial

Due to its potential as sample treatment for Analytical Chemistry, the Ultrasonic-Assisted Enzymatic Digestion (USAED) for total elemental determination and elemental speciation is described under the most recent achievements published in literature, focusing on the variables that critically affect the performance of this relatively new sample treatment, such as the type of enzymes or the type of ultrasonic system used for the acceleration of the solid-liquid extraction process. Moreover, analytical chemists are aware of common errors produced in data interpretation concerning USAED. In addition, a guide for the rapid application of this methodology is also provided along with detailed explanations. Finally, future trends regarding USAED are also given and commented.

Gas chromatography mass spectrometry determination of acaricides from honey after a new fast ultrasonic-based solid phase micro-extraction sample treatment.

A method is reported for the determination of acaricides (amitraz, bromopropylate, coumaphos and fluvalinate) from honey by gas chromatography mass spectrometry after a new fast solid phase micro-extraction, SPME, procedure. Six different fibers were assessed for micro-extraction purpose studying the following variables: (i) SPME coating, (ii) extraction temperature, (iii) extraction time, (iv) desorption conditions and (v) agitation conditions. The new ultrasonic bath technology providing different sonication frequencies (35 and 130kHz) and different working modes (Sweep, Standard and Degas) was studied and optimized for speeding up the acaricide micro-extraction. The best extraction results were achieved with the polyacrylate fiber. The extraction process was done in 30min using the ultrasonic bath at 130kHz in the Standard mode. Quality parameters of the proposed method show a good precision (<11%) and detection and quantitation limits lower than 6 and 15ng/g, respectively, except for fluvalinate. Eleven Portuguese commercial honey samples were analyzed with the developed method in order to assess the performance of the method with real samples and to determine whether the concentration of acaricides in honey exceed their maximum residue levels (MRLs). Acaricide residues detected were lower than those established by the legislation.