Liquid-phase microextraction with in-drop derivatization combined with microvolume fluorospectrometry for free and hydrolyzed formaldehyde determination in textile samples

A new miniaturized methodology based on the combination of headspace single drop microextraction and microvolume fluorospectrometry is proposed in this work for the determination of free and hydrolyzed formaldehyde in textile samples. The proposed method is based on the extraction and in-drop derivatization of free and hydrolyzed formaldehyde using the Hantzsch reaction. The effect of experimental variables affecting the performance of the proposed method, such as fluorescence parameters, nature of the extractant phase composition (including acetylacetone concentration, pH, ammonium acetate concentration and presence of an organic solvent), sample temperature, NaCl concentration and microextraction time was carefully investigated. Under optimized conditions, instrumental detection and quantification limits were 26 and 87 μg L⁻¹, respectively, whereas procedural detection and quantification limits were 1.0 and 3.5 mg kg⁻¹, respectively. Repeatability, expressed as relative standard deviation, was 4.6% (n = 9). The method was successfully applied to the determination of free and hydrolyzed formaldehyde in several textile samples, the found results being in good agreement with those obtained with the EN ISO 14184-1:1998 method.     

Ultrasound-assisted extraction technique for establishing selenium contents in breast cancer biopsies by Zeeman-electrothermal atomic absorption spectrometry using multi-injection

A solid-liquid extraction method is developed to establish the contents of selenium in breast cancer biopsies. The method is based on the ultrasound-assisted extraction of selenium from pretreated biopsies prior to Se determination by atomic absorption spectrometry with longitudinal-Zeeman background correction. Fifty-one breast biopsies were collected from the Cies Hospital (Vigo, Spain), 32 of which correspond to tumor tissue and 19 to normal tissue (parenchyma). Difficulties arising from the samples analyzed, i.e. small samples mass (50-100 mg), extremely low Se contents and sample texture modification including tissue hardening due to formaldehyde preservation are addressed and overcome. High intensity sonication using a probe together with addition of hydrogen peroxide succeeded in completely extracting Se from biopsies. The multiple injection technique was useful to tackle the low Se contents present in some biopsies. The detection limit was 25 ng g⁻¹ of Se and the precision, expressed as relative standard deviation, was less than 10%. Se contents ranged from 0.08 to 0.4 μg g⁻¹ for parenchyma samples and from 0.09 to 0.8 μg g⁻¹ for tumor samples. In general, Se levels in tumor biopsies were higher as compared with the adjacent normal tissue in 19 patients by a factor of up to 6. Analytical data confirmed Se accumulation in the breast tumors.     

Mercury removal from contaminated water by ultrasound-promoted reduction/vaporization in a microscale reactor

A new method is described for the removal of Hg(II) at trace level from waters using an ultrasound-promoted reduction/volatilization process. The method is accomplished in a sonoreactor (100 W power; 20 kHz frequency) by adding formic acid to induce the reduction of Hg(II) to Hg(0). In contrast to other treatments, it does not introduce further foreign substances for water decontamination. A reduction mechanism is proposed, which relies on the sonolytic decomposition of formic acid to yield reducing gases such as H(2) and CO, which in turn, causes the reduction of Hg(II). After the formation of Hg(0), its removal is facilitated by the degassing effect caused by ultrasound irradiation. Hg at 100 ng/mL concentration can be removed within 30 min with a yield of 90% from a 10 mL water volume. The presence of stabilizing anions or oxidants in waters may preclude the Hg removal. Effects of experimental variables such as treatment time, amplitude of the ultrasonic probe vibration, formic acid concentration and sample volume were investigated.     

Multielemental determination in breast cancerous and non-cancerous biopsies by inductively coupled plasma-mass spectrometry following small volume microwave-assisted digestion

A microwave-assisted digestion method amenable to analysis of small size biological samples (<30 mg dry mass) has been optimized for determining twelve elements (Ag, As, Cd, Co, Cu, Cr, Mn, Mo, Ni, Pb, Se and Zn) by inductively coupled plasma-mass spectrometry (ICP-MS) in breast cancerous and non-cancerous biopsies. The use of three small volume PTFE closed vials (6-mL capacity) placed inside a conventional microwave vessel allows to drastically diminishing the volume of acid needed for digestion. A Plackett-Burman experimental design was used to evaluate the robustness of the digestion procedure. Effects of nitric acid volume, need for predigestion step, microwave power and digestion time were assessed. No significant effects were found, the digestion method being robust enough to be recommended for a routine practice. The method was successfully validated against CRM BCR 185 (bovine liver), CRM NRCC TORT-2 (lobster hepatopancreas), CRM NRCC DORM-2 (dogfish muscle) and CRM NRCC DOLT-2 (dogfish liver). Procedural detection limits ranged from 0.54 to 40 ng g(-1). Within-batch precision values were less than 3%, whereas between-batch precision values were in the range 2-11%. Forty-seven biopsies from thirty-nine women were analyzed: 20 samples corresponding to mammoplasties from healthy women and 27 samples from patients suffering from cancer pathology, 19 of which corresponded to tumour and 8 to adjacent normal tissue. After applying parametric and non-parametric statistical tests, a significant accumulation of Cu, Mn, Zn and Se in cancerous tissues was demonstrated.     

Determination of cadmium and lead in mussels by electrothermal atomic absorption spectrometry using an ultrasound-assisted extraction method optimized by factorial design

A simple and rapid method is described for the quantitative extraction and determination of Cd and Pb in mussel tissue (Mytilus edulis). The method is based on the quantitative ultrasound-assisted extraction (i.e. sample mass at mg level) of the two metals using diluted nitric acid as extractant. The extraction procedure is carried out in autosampler cups of the graphite furnace (typically, less than 20 mg). A two-level full factorial design (2⁴) was applied to optimize the variables influencing the ultrasound extraction process. These variables were: extraction time, ultrasound amplitude, nitric acid concentration and particle size. Optimization results showed that acid concentration and particle size were the more significant variables. Determination of Cd and Pb in extracts obtained after ultrasound treatment was carried out by Electrothermal Atomic Absorption Spectrometry. The method was validated by statistically comparing the metal contents found with the certified ones corresponding to the BCR 278 mussel tissue. No significant differences were observed for P = 0.05. LODs for Cd and Pb in mussel tissue were 0.019 and 0.37 μg g^–1. RSDs values (corresponding to between-batch precision for n = 5) were 2.2 and 6.7% for Cd and Pb, respectively. The method was applied to measure the contents of Cd and Pb in mussels used as pollution bioindicators from the Galician coast (Ria de Vigo, Spain).     

Specific peptides as alternative to antibody ligands for biomagnetic separation of Clostridium tyrobutyricum spores

Nowadays, the reference method for the detection of Clostridium tyrobutyricum in milk is the most-probable-number method, a very time-consuming and non-specific method. In this work, the suitability of the use of superparamagnetic beads coated with specific antibodies and peptides for bioseparation and concentration of spores of C. tyrobutyricum has been assessed. Peptide or antibody functionalized nanoparticles were able to specifically bind C. tyrobutyricum spores and concentrate them up to detectable levels. Moreover, several factors, such as particle size (200 nm and 1 μm), particle derivatization (aminated and carboxylated beads), coating method, and type of ligand have been studied in order to establish the most appropriate conditions for spore separation. Results show that concentration of spore is favored by a smaller bead size due to the wider surface of interaction in relation to particle volume. Antibody orientation, related to the binding method, is also critical in spore recovery. However, specific peptides seem to be a better ligand than antibodies, not only due to the higher recovery ratio of spores obtained but also due to the prolonged stability over time, allowing an optimal recovery of spores up to 3 weeks after bead coating. These results demonstrate that specific peptides bound to magnetic nanoparticles can be used instead of traditional antibodies to specifically bind C. tyrobutyricum spores being a potential basis for a rapid method to detect this bacterial target.     

The furan approach to azacyclic compounds

We describe an efficient new approach to the synthesis of azacyclic compounds that extends our recently developed methodology based on the oxidation of a furan ring with singlet oxygen followed by an intramolecular hetero Michael addition. The new approach gives access to the readily opened bicyclic lactones and novel tricyclic heterocycles containing the piperidine ring.     

Straightforward α-carbamoylation of NADH-like dihydropyridines and enol ethers

The protonation of NADH-like dihydropyridines and cyclic enol ethers generates reactive cationic intermediates, which interact with isocyanides to afford α-carbamoylated heterocycles after an aqueous quenching, in Ugi and Passerini-type reactions, thus broadening the scope of these multicomponent processes.     

Microvolume turbidimetry for rapid and sensitive determination of the acid labile sulfide fraction in waters after headspace single-drop microextraction with in situ generation of volatile hydrogen sulfide

In this work, we demonstrate the feasibility of applying headspace single-drop microextraction with in-drop precipitation for the quantitative determination of the acid labile sulfide fraction (H₂S, HS⁻, and S²⁻ (free sulfide), amorphous FeS and some metal sulfide complexes-clusters as ZnS) in aqueous samples by microvolume turbidimetry. The methodology lies in the in situ hydrogen sulfide generation and subsequent sequestration into an alkaline microdrop containing ZnO₂²⁻ and exposed to the headspace above the stirred aqueous sample. The ZnS formed in the drop was then determined by microvolume turbidimetry. The optimum experimental conditions of the proposed method were: 2 μL of a microdrop containing 750 mg L⁻¹ Zn(II) in 1 mol L⁻¹ NaOH exposed to the headspace of a 20-mL aqueous sample stirred at 1600 rpm during 80 s after derivatization with 1 mL of 6 mol L⁻¹ HCl. An enrichment factor of 1710 was achieved in only 80 s. The calibration graph was linear in the range of 5-100 μg L⁻¹ with a detection limit of 0.5 μg L⁻¹. The repeatability, expressed as relative standard deviation, was 5.8% (N = 9). Finally, the proposed methodology was successfully applied to the determination of the acid labile sulfide fraction in different natural water samples.     

Optimization of digestion methods for sewage sludge using the Plackett-Burman saturated design

The Plackett-Burman saturated factorial design was used to select optimized dissolution conditions for sewage sludge samples. Three different digestion methods were applied: i) microwave oven digestion in a domestic oven with Parr-type reactors; ii) microwave oven digestion with controlled-pressure reactors; iii) pressure bomb reactor heated on a hot plate. The three methods were validated by statistically comparing the metal contents found with the certified ones of the sewage sludge sample (BCR 145R). No significant differences were obtained and the RSD values were lower than 3% in all cases. The metals were determined by flame-AAS. The variables studied were the following: microwave power; digestion time; predigestion; volume of hydrochloric acid; volume of hydrofluoric acid; volume of nitric acid. The operative advantages offered by microwave digestion with controlled-pressure reactors were also considered. Received: 23 July 1997 / Revised: 31 October 1997 / Accepted: 5 November 1997