A fully automated linear polyacrylamide coating and regeneration method for capillary electrophoresis of proteins

Surface modification of the inner capillary wall in CE of proteins is frequently required to alter EOF and to prevent protein adsorption. Manual protocols for such coating techniques are cumbersome. In this paper, an automated covalent linear polyacrylamide coating and regeneration process is described to support long‐term stability of fused‐silica capillaries for protein analysis. The stability of the resulting capillary coatings was evaluated by a large number of separations using a three‐protein test mixture in pH 6 and 3 buffer systems. The results were compared to that obtained with the use of bare fused‐silica capillaries. If necessary, the fully automated capillary coating process was easily applied to regenerate the capillary to extend its useful life‐time.     

Analytical strategy photodegradation/chemiluminescence/continuous-flow multicommutation methodology for the determination of the herbicide Propanil

The present paper is dealing with an analytical strategy based on coupling photodegradation, chemiluminescence and multicommutation continuous-flow methodology for the determination of the pesticide Propanil, a common herbicide. The pesticide solution is inserted as small segments sequentially alternated with segments of the solution for adjusting the suitable medium for the photodegradation. Both flow-rates (sample and medium) are adjusted to required time for photodegradation, 2.0 min; and then, the resulting solution is also sequentially inserted as segments alternated with segments of the oxidizing solutions system, 1.00 × 10⁻⁴ mol l⁻¹ potassium permanganate in 2.00 mol l⁻¹ sulphuric acid medium. The calibration range, from 10 μg l⁻¹ to 25 mg l⁻¹, resulted in a linear behaviour over the range 10 μg l⁻¹-5 mg l⁻¹ and fitting the linear equation: I = 780.30C + 95.28; correlation coefficient 0.9999. The limit of detection was 8 μg l⁻¹ and the sample throughput 20 h⁻¹. After testing the influence of a large series of potential interferents the method is applied to water samples obtained from different places and to one formulation. The method is valid for the determination of other pesticides from the same chemical family, namely: alachlor, flumetsulam, furalaxyl and ofurace. Calibration graphs, limits of detection, repeatability and determination in water samples are obtained for each reported pesticide.     

A Method for the polarographic determination of the stability constants of mixed complexes

A new method for determining the stability constants of mixed complexes is proposed which is especially appropriate when only the mixed complex 1:1:1 is formed. In order to verify this method, the coordinate system Pb(II)-SCN^?-NO^?₃ has been studied polarographically in aqueous medium of a constant ionic strength of μ = 1.0 M. Using our knowledge of the stability constants of simple complexes and applying this method we obtain β₁₁ = 8 for the mixed complex.     

The potentiometric determination of stability constants of macrocyclic ethers using linear regression techniques

Summary The stability constants of various stoichiometries of NaCl complexes of the macrocyclic ethers of 15-crown-5, benzo-15-crown-5, 18-crown-6 and benzo-18-crown-6 were measured by maintaining identical initial ion-ligand concentrations [A ₀ ⁺ ]=[L_o] and using the expression of the stability constant _i of a complex formation, 1/_i[L_o]^n+m–1=(1–nP)ⁿ(1–mP)^m/P where P=P_AL/[1+P_AL(m–1)]. The potentiometric measurements were carried out in water with a glass membrane electrode in a computer-ion meter system.Submitted to IUPAC, International Symposium on Macrocyclic Ligands for the Design of New Materials, 1992, Surrey, UK     

A battery-powered,computerized instrument for the field-based determination of fluoride by the ion-selective electrode technique

Battery-powered complementary metal-oxide semiconductor (CMOS) electronic devices are used to develop computerized instrumentation based on an ion-selective electrode for environmental monitoring in the field. The development of CMOS-based instrumentation for the determination of fluoride in drinking water, river water, lake water and sea water is described. The instrument is portable and completely field-programmable. Under software control, the equilibrium potential and fluoride concentration, based on a double standard-addition method, are calculated. The associated temperature, date and time form part of the data-logging record. Data obtained in the field are shown to compare satisfactorily with those obtained on samples which were stored and returned to the laboratory for examination by conventional mains-powered instrumentation. Accuracy is good and precision is only slightly poorer than that of mains-powered laboratory instrumentation.     

Comparison of continuous-flow microextraction and static liquid-phase microextraction for the determination of p-toluidine in Chlamydomonas reinhardtii

In this study, two microextraction methods, viz. continuous-flow microextraction (CFME) and static liquid-phase microextraction (s-LPME), were optimized and compared for the determination of p-toluidine in water and Chlamydomonas reinhardtii samples. The calibration curve for p-toluidine was linear in the concentration range of 0.01-5 microg/mL, and the squared regression coefficients (r(2)) for the lines were up to 0.999 for both CFME and s-LPME treatments. Detection limits in CFME and s-LPME were 8.2 ng/mL and 4.9 ng/mL, based on a signal-to-noise (S/N) ratio of 3, respectively. The precision was tested, in five replicates, by analysis of a 100-ng/mL standard solution of p-toluidine and the relative standard deviations were 5.43 and 3.08% for CFME and s-LPME, respectively. The concentration factors were 5.5 and 14.4 for CFME and s-LPME, respectively. s-LPME has a higher extraction efficiency, lower detection limit, and higher concentration factor than that of CFME. Additionally, the s-LPME method is precise and reproducible, and requires only a 3.0-microL microdrop of extraction solvent. Therefore, this procedure is more convenient in use, and viable for qualitative and quantitative analysis of p-toluidine in water and biota samples.     

A critical comparison of computer programs for the potentiometric determination of stability constants

The performance of five of the best-known computer programs LETAGROP, SCOGS, MINIQUAD, SUPERQUAD and ESTA, is critically discussed. All these programs are based on least-squares refinement procedures but differ in some important aspects: (a) the definition of the residuals function; (b) the minimization procedure; (c) the statistical and weighting parameters. Each of these aspects is evaluated and the programs are compared on this basis.     

A new micro-cell for continuous-flow pulsed voltammetric analysis

The effect of p-toluenesulfonate and trifluoromethanesulfonate supporting electrolytes on the polarographic reduction of some alkaline earth and transition metal ions in N,N-dimethylformamide and acetonitrile has been investigated. Trifluoromethanesulfonate behaved similarly to perchlorate in dimethylformamide, while the half-wave potentials in p-toluenesulfonate supporting electrolyte shift to more negative potentials than those in perchlorate. in acetonitrile, the half-wave potentials shift to more negative potentials in trifluoromethanesulfonate than in perchlorate. The effect of the supporting electrolyte on the shift of the half-wave potential can be explained as the ion-pair formation between the divalent cation to be reduced and the supporting electrolyte anion.     

Comparison of efficiencies between single-drop microextraction and continuous-flow microextraction for the determination of methomyl in natural waters

Two liquid-phase microextraction (LPME) approaches, static direct-immersed single-drop microextraction (DI-SDME) and continuous-flow microextraction (CFME), were used to extract methomyl in water samples and their respective extraction efficiencies were compared. Several important parameters affecting extraction efficiency such as the type of extraction solvent, solvent drop volume, stirring speed or flow rate, extraction time and salt concentration were optimised. The optimised conditions were as follows: 3.0-µL tetrachloroethane (C₂H₂Cl₄) as the extraction solvent, 15% NaCl (w/v), 15 min extraction time and stirring speed at 600 rpm for DI-SDME; 3.5-µL C₂H₂Cl₄ as the extraction solvent, 15% NaCl (w/v), 21 min extraction time and flowing rate at 0.8 mL min^?1 for CFME. Under the previous optimal conditions, the linear range, detection limit (S/N = 3) and precision (RSD, n = 6) were 5.0-5000 ng mL^?1, 1.5 ng mL^?1, 6.9% for DI-SDME, and 4.0–10000 ng mL^?1, 2.5 ng mL^?1, 4.6% for CFME, respectively. Lake and river water samples were successfully analysed by DI-SDME and CFME. The result demonstrated that both SDME and CFME techniques are simple, low cost and amity to environment. As a result, the two approaches have tremendous potential in trace analysis of methomyl in natural waters.     

A stability indicating HPLC method for the determination of electrochemically controlled release of risperidone

A rapid stability indicating reversed-phase high-performance liquid chromatography (HPLC) method is developed for the determination of the electrochemically controlled risperidone release from a novel drug delivery system, based on the intrinsically conducting polymer (ICP), polypyrrole. The chromatographic separation was carried out on a C(18) column using acetonitrile-potassium dihydrogen phosphate (45:55, v/v, pH 6.5; 0.05 M) as the mobile phase. The isocratic flow is at 1.0 mL/min, with a runtime of 6 min, and the UV detection is at 237 nm. This provided a calibration curve linear over the range of 1-100 μg/mL. Intra-day and inter-day accuracy range between 98.4% and 102.6%, and the RSD for precision is <1.43%. The limit of detection and quantitation were determined to be 0.001 μg/mL and 0.01 μg/mL, respectively. The analytical method confirmed risperidone is stable for the oxidizing electric potential and the acidic environment involved during the manufacture and operation of the novel drug delivery system. The rate of risperidone release from polypyrrole depended on electrical stimulation applied to the polymer. This HPLC method is significantly faster than previously published methods and is the first to investigate the effect of an oxidizing potential on risperidone stability, which is essential for the evaluation of controlled delivery from an ICP-based system.     

Microsphere based continuous-flow immunoassay in a microfluidic device for determination of clinically relevant insulin levels

This paper describes a miniaturized microsphere-based immunoassay integrated into a microfluidic device for rapid quantitation of insulin. Analysis of bionic pancreas studies have revealed that the rates of absorption of insulin analogs vary from patient to patient, and even within patients on different occasions. Thus development of an approach to monitor insulin continuously allows the pharmacokinetic characteristics of insulin analogs to be determined in real-time. The authors have developed a microsphere-based continuous flow assay in a microfluidic chip that allows for the detection of insulin within seconds with high sensitivity and specificity. The method was applied to near real-time monitoring of clinical samples. Calibration plot were established for different insulin analogs such as insulin aspart (Novolog), insulin lispro (Humalog), and regular human insulin (RHI) and the insulin detection limit was 0.26 ng.mL^?1 (44 pM). This sensitivity allows to detect the fasting insulin levels of T1D patients, which are reported in the range of 50–180 pM (0.3–1 ng.mL^?1), after treatment with subcutaneous insulin administration. This fast approach was also applied to sera collected in intervals from T1D patients after a bolus of insulin aspart delivery. The insulin profile obtained by this method is similar to the basal and peak insulin levels as determined using the standard non-continuous ELISA reference method. In our perception, this assay will improve healthcare by personalizing diagnostics for better clinical outcome and provide real-time feedback on sensing and actuation.

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Graphical abstract Schematic illustration of the microfluidic microsphere based Microfluidic Lab-On-Chip device for near real-time insulin monitoring.

     

A simple linear sweep voltammetric method for the determination of double-stranded DNA with malachite green

In pH 3.5 Britton—Robinson buffer solution double-stranded (ds) DNA can react with malachite green (MG) to form an interaction complex, which resulted in the decrease of the electrochemical response of MG, MG had a well-defined second-order derivative linear sweep voltammetric peak at −0.73 V (vs. SCE). After the addition of dsDNA into MG solution, the reductive peak current decreased with the positive shift of peak potential, which was the typical characteristic of intercalation. Based on the interaction, an indirect electrochemical determination method for dsDNA was established. The optimum conditions for the reaction were investigated and there were little or no interferences from the commonly coexisting substances. The decrease of peak current was linear with the concentration of dsDNA over the range of 0.8–12.0 μg cm⁻³ with the linear regression equation as ΔI _p″/nA = 91.70 C/(μg cm⁻³) + 74.55 (n = 10, γ = 0.990). The detection limit was calculated as 0.46 μg cm⁻³ (3σ). The method had high sensitivity and was further applied to the dsDNA synthetic samples with satisfactory result. The interaction mechanism was discussed with the intercalation of DNA-MG to form a supramolecular complex and the stoichiometry of the supramolecular complex was calculated by electrochemical method with the binding number 3 and the binding constant 2.35 × 10¹⁵ (mol dm⁻³)⁻³.     

Compact optical instrument for simultaneous determination of oxygen and carbon dioxide

A multi-analyte platform based on a portable instrument is presented that enables oxygen and carbon dioxide to be determined in sample gases. The use of four sensing channels (two channels for each analyte to provide redundancy) warrants high system reliability. The sensing scheme in case of oxygen is based on the quenching of the phosphorescence of the platinum octaethylporphyrin complex. In case of carbon dioxide, a secondary inner-filter effect is exploited that is caused by a pH indicator whose color is reversibly changed. The sensing membranes were placed directly on the detectors and on the light sources so to make additional optical element dispensable, reduce system costs, avoid problems related to optical alignment, optimize the efficiency of data acquisition, and enable facile replacement of sensors. The resulting microcontroller-based system is immune against optical and electrical interferences, contains simple digital signal processing circuitry, and has low power consumption. The response of the system to the two gases was modeled, and calibration curves are corrected for effects of temperature. The instrument was characterized in terms of cross-sensitivity and dynamic response. It can determine oxygen and carbon dioxide in terms of volume percentage.

Direct determination of total carbonate salts in soil samples by continuous-flow piezoelectric detection

Two new methods for the determination of total carbonate salts, as CaCO₃, in soil by continuous-flow piezoelectric (PZ) detection are proposed. Both use a piezoelectric flow cell and a manifold including a dynamic gas extraction device to purge gaseous CO₂ released by the sample solution upon acidification. One of the methods involves monitoring the pressure generated by the CO₂ produced upon addition of hydrochloric acid; in the other, the CO₂ is quantified by using a quartz crystal coated with tetramethylammonium fluoride tetrahydrate (TMAF). The precision of both methods is compared with that of the officially endorsed method. The proposed methods allow calcium carbonate amounts over the ranges 10-100 mg and 2-15 mg, respectively, to be determined. Both were applied to the determination of CaCO₃ in soil samples. The standard deviation and throughput achieved were 2.7% and 30 samples per hour, respectively, with the pressure-based method; and 6.0% and six samples per hour, respectively, with the mass-based method.     

Direct spectrophotometric determination of thiocyanate in serum and urine with a continuous-flow analyzer

A spectrophotometric method for the rapid measurement of thiocyanate in serum and urine without separation from interfering substances is described. Thiocyanate reacts immediately with chloramine-T in presence of iron(III) chloride catalyst to give cyanogen chloride, which reacts with a mixture of γ-picoline (4-methylpyridine) and barbituric acid to form a soluble violet—blue product, which is measured at 605 nm. Other components of physiological fluids react more slowly and do not interfere if the reaction time of the chlorinating step is kept very short. The proposed procedure is compared with a highly selective method, based on the oxidation of thiocyanate to cyanide, and good agreement was obtained for both serum and urine. The method is readily adapted to a continuous-flow procedure with a Technicon AutoAnalyzer.