Design of novel,simple, and inexpensive 3D printing-based miniaturized electrochemical platform containing embedded disposable detector for analytical applications

This paper describes the development of a novel, simple, and inexpensive electrochemical device containing an integrated and disposable three-electrode system for detection. The base of this platform consists on a PDMS structure containing microchannels which were prototyped using 3D-printed molds. Pencil graphite leads were inserted into these microchannels and utilized as working, counter and reference electrodes in a novel design. Morphological analysis and electrochemical experiments with benchmark redox probes were carried out in order to evaluate the performance and characterize the miniaturized device proposed. Even using inexpensive materials and a simple fabrication protocol, the electrochemical platform developed provided good repeatability and reproducibility over a low cost (ca. $2 per device), acceptable lifetime (ca. 250 voltammetric runs) and extremely reduced consumption of samples and reagents (order of µL). As proof of concept, the analytical feasibility of the platform was investigated through the simultaneous determination of dopamine (DOPA) and acetaminophen (AC). The two analytes showed linear dependence on the concentration range from 1 to 15 µM and the LODs achieved were 0.21 µM for DOPA and 0.29 µM for AC. Moreover, the platform was successfully applied on the determination of DOPA and AC in spiked blood serum and urine samples. The results obtained with the device described here were better than some reports in literature that use more costly electrodic materials and complex modification steps for the detection of the same analytes.     

Prediction of the bed-load transport by gas–liquid stratified flows in horizontal ducts

Solid particles can be transported as a mobile granular bed, known as bed-load, by pressure-driven flows. A common case in industry is the presence of bed-load in stratified gas–liquid flows in horizontal ducts. In this case, an initially flat granular bed may be unstable, generating ripples and dunes. This three-phase flow, although complex, can be modeled under some simplifying assumptions. This paper presents a model for the estimation of some bed-load characteristics. Based on parameters easily measurable in industry, the model can predict the local bed-load flow rates and the celerity and the wavelength of instabilities appearing on the granular bed.     

Determination of cadmium,copper and lead in alumina based catalysts by direct solid sampling graphite furnace atomic absorption spectrometry

Trace impurities of Cd, Cu and Pb were determined in alumina based catalysts using direct solid sampling graphite furnace atomic absorption spectrometry (DSS-GF AAS). The analyzed catalysts are widely used in petrochemical processes. The following analytical parameters were evaluated: pyrolysis and atomization temperatures, feasibility of calibration with aqueous solutions, the necessity for palladium as chemical modifier and the sample mass introduced into the atomizer. Test samples between 0.05 and 8.5 mg were used. Palladium was investigated as chemical modifier but no improvement in analytical performance was obtained and its use was considered unnecessary for all elements. The results obtained by DSS-GF AAS were compared with those of inductively coupled plasma optical emission spectrometry (ICP OES) and also with conventional solution analysis by GF AAS (Sol-GF AAS). Characteristic masses were 1.4, 9 and 20 pg, for Cd, Cu and Pb, respectively. Using DSS-GF AAS the relative standard deviation was always less than 10% and the results agreed with those obtained by Sol-GF AAS and ICP OES. Calibration using aqueous solutions showed good linearity within the working range (R² better than 0.99). Limits of detection (3σ, n = 10) for Cd, Cu and Pb using the proposed procedure were 0.2, 22, and 1.2 ng g^− 1, respectively.     

Stereoselective determination of hydroxychloro-quine and its major metabolites in human urine by solid-phase microextraction and HPLC

The enantioselective analysis of hydroxychloroquine (HCQ) and its major metabolites was achieved by HPLC and solid-phase microextraction. The chromatographic separation was performed on a Chiralcel OD-H column using hexane/methanol/ethanol (96:2:2, v/v/v) plus 0.2% diethylamine as the mobile phase, at the flow rate of 1.3 mL/min. The main extraction parameters were optimized. The best condition was achieved by the addition of 10% NaCl and 1 mL phosphate buffer 1 mol/L pH 11 to 3 mL human urine. The extraction was conducted for 40 min at 25 degrees C and the desorption time was 3 min using methanol (100%). PDMS-DVB 60 microm fiber was used in this study. The mean recoveries were 9.3, 9.2, and 14.4% for HCQ, desethylhydroxychloroquine (DHCQ), and desethylchloroquine (DCQ), respectively. The method was linear over the range of 50-1000 ng/mL for HCQ enantiomers and over the range of 42-416 ng/mL for DCQ and DHCQ enantiomers. Within-day and between-day precision and accuracy assays for HCQ and its metabolites were lower than 15%. The preliminary 48 h urinary excretion study performed in human urine showed to be stereoselective. The amount of (+)-(S)-enantiomer excreted was higher than its antipode.     

Examination of Pt(111)/Ru and Pt(111)/Os surfaces: STM imaging and methanol oxidation activity

Ruthenium and osmium were deposited in submonolayer amounts on Pt(111) single crystal surfaces using the previously reported ‘spontaneous deposition’ procedure [Chrzanowski et al., Langmuir, 13 (1997) 5974]. Such surfaces were first explored using ex situ scanning tunneling microscopy (STM) to image the deposition characteristics of ruthenium and osmium islands on Pt(111). It was found that, using the spontaneous deposition procedure, a maximum coverage of 0.20 ML ruthenium is formed on the surface after 120 s of exposure to a RuCl₃ solution in 0.1 M HClO₄. A homogeneous deposition on the Pt(111) surface was found, with no observed preferential deposition on step edges or surface defect sites. In contrast, in the spontaneous deposition of osmium, osmium clusters form preferentially at, though not limited to, surface defect sites and step edges. Osmium island deposition occurs at a greater rate than ruthenium on Pt(111), and possible explanations are presented. Methanol activity on the Pt(111)/Ru and Pt(111)/Os surfaces is also studied, using the coverage values determined to yield the highest activity for methanol electro-oxidation (0.20 ML coverage for Ru and 0.15 ML for Os). At potentials more negative than 0.40 V vs. RHE, the Pt(111)/Ru surface yields a higher surface activity than Pt(111)/Os. However, at potentials more positive than 0.04 V, Pt(111)/Os exhibits demonstrably higher surface activity. The relevance of this data is discussed and future avenues of interest are indicated.     

Characterization of cyclodextrin glycosyltransferase from Bacillus firmus strain No. 37

The enzyme cyclod extringly cosyltransferase (CGTase), EC2.4.1.19, which produces cyclodextrins (CDs) from starch, was obtained from Bacillus firmus strain no. 37 isolated from Brazilian soil and characterized in the soluble form using as substrate 100 g/L of maltodextrin in 0.05 M Tris-HCl buffer, 5 mM CaCl₂, and appropriate buffers. Enzymatic activity and its activation energy were determined as a function of temperature and pH. The activation energy for the production of β- and γ-CD was 7.5 and 9.9 kcal/mol, respectively. The energy of deactivation was 39 kcal/mol. The enzyme showed little thermal deactivation in the temperature range of 35–60°C, and Arrhenius-type equations were obtained for calculating the activity, deactivation, and half-life as a function of temperature. The molecular weight of the enzyme was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, giving 77.6k Da. Results for CGTase activity as a function of temperature gave maximal activity for the production of β-CD at 65°C, pH 6.0, and 7 1.5 mmol of β-CD/(min·mg of protein), whereas for γ-CD it was 9.1 m mol of γ-CD/(min·mg of protein) at 70°C and pH 8.0. For long contact times, the bestuse of the enzymatic activity occurs at 60°C oratalower temperature, and the reaction pH may be selected to increase the vield of a desired CD.     

Determination of rare earth elements in USGS rock standards by isotope dilution mass spectrometry and comparison with neutron activation and inductively coupled plasma atomic emission spectrometry

Rare earth element (REE) concentrations in United States Geological Survey (USGS) rock standards AGV-1, GSP-1, G-2 and PCC-1 were determined by isotope dilution mass spectrometry (IDMS), neutron activation and inductively coupled argon plasma atomic emission spectrometric techniques. The procedure involved acid digestion of samples in PTFE pressure bombs and group separation of REEs by an ion-exchange method. For IDMS an additional separation step using α-hydroxyisobutyric acid as an eluent was used in a cation-exchange column to split the REEs into subgroups. Comparison of the results with literature values showed that the IDMS values are the most precise and accurate. However, the precisions and the accuracies of the other techniques are acceptable.     

Grafting of cyclodextrins onto filter paper

Grafting of cyclodextrins and cyclodextrins derivatives on cellulosic surface, such as paper or filter paper, provides hosting cavities that can include a large variety of chemicals for specific cellulose finishing. In this study grafting of monocholorotriazinyl-β-cyclodextrin (MCT-β-CD) and β-cyclodextrin (β-CD) to filter paper has been performed. β-cyclodextrin has been bonded to filter paper using 1,4-butanediol diglycidyl ether as the crosslinking agent. The untreated and treated filter papers were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), demonstrating the covalent binding of cyclodextrins to filter paper. The quantification of β-CD and MCT-β-CD grafted to filter paper was determined by the dye extinction method with the inclusion of phenolphthalein. The final β-CD content amounted to 15.9 μmol per gram of support (1.8% by weight), and 72.8 μmol per gram of support (11.3% by weight) for MCT-β-CD.     

MUTATIONAL INTERACTIONS BETWEEN NEAR-UV RADIATION AND DNA DAMAGING AGENTS IN Escherichia coli: THE ROLE OF NEAR-UV-INDUCED MODIFICATIONS IN GROWTH AND MACROMOLECULAR SYNTHESIS

Abstract— The mutational interactions between near-ultraviolet (near-UV, 334 nm, 365 nm) radiation and DNA damaging agents (far-UV (254 nm) and ethyl-methanesulphonate (EMS)) were studied in strains of Escherichia coli B/r trp thy with different susceptibilities to near-UV-induced growth delay (wild-type, rel and srd ). Far-UV induced reversion to tryptophan independence is reduced while forward mutation to streptomycin is enhanced by prior exposure of the rel+ srd+ strains to near-UV radiation. The observed interactions are reduced ( rel ) or absent ( srd ) in the two mutant strains as are the corresponding growth and macromolecular synthesis delays normally observed after near-UV treatment. Quantitatively, the degree of interaction induced by near-UV pre-treatment correlates closely with the degree of protein synthesis inhibition. We propose a mechanism for the contrasting interactions at the two genetic loci based on the different pathways by which pre-mutagenic lesions may be processed. The primary chromophore for the mutational interactions would appear to be 4-thiouracil-containing transfer RNA.     

Flow injection potentiometric determination of saccharin in dietary products with relocation of filtration unit

A flow injection potentiometric procedure for saccharin determination in dietary products is proposed. Saccharin is precipitated as mercurous saccharinate and the excess of the mercurous cation is potentiometrically measured using a silver wire coated with a mercury film as the working electrode. A filter unit is used to avoid contact between the precipitate and the electrode surface. With relocation in the flow manifold, the accumulated precipitate is removed on-line. Sucrose, glucose, aspartame, sodium cyclamate and sodium benzoate do not interfere when present in amounts similar to those observed in commercial products. Results are comparable with those obtained by UV-spectrophotometry and the correlation coefficient between methods is equal to 0.9930. A linear relationship between DeltaE (mV) and the logarithm of saccharin concentration was obtained in the saccharin concentration range 2 x 10(-3) - 1 x 10(-2)M. The sampling frequency is 60/hour and only 0.76 mg of Hg(2+)(2) is consumed in each determination.