Christina Vakh

Flow Analysis: A Novel Approach For Classification

ABSTRACT We suggest a novel approach for classification of flow analysis methods according to the conditions under which the mass transfer processes and chemical reactions take place in the flow mode: dispersion-convection flow methods and forced-convection flow methods. The first group includes continuous flow analysis, flow injection analysis, all injection analysis, sequential injection analysis, sequential injection chromatography, cross injection analysis, multi-commutated flow analysis, multi-syringe flow injection analysis, multi-pumping flow systems, loop flow analysis, and simultaneous injection effective mixing flow analysis. The second group includes segmented flow analysis, zone fluidics, flow batch analysis, sequential injection analysis with a mixing chamber, stepwise injection analysis, and multi-commutated stepwise injection analysis. The offered classification allows systematizing a large number of flow analysis methods. Recent developments and applications of dispersion-convection flow methods and forced-convection flow methods are presented.

A fully automated effervescence assisted dispersive liquid-liquid microextraction based on a stepwise injection system. Determination of antipyrine in saliva samples

A first attempt to automate the effervescence assisted dispersive liquid-liquid microextraction (EA-DLLME) has been reported. The method is based on the aspiration of a sample and all required aqueous reagents into the stepwise injection analysis (SWIA) manifold, followed by simultaneous counterflow injection of the extraction solvent (dichloromethane), the mixture of the effervescence agent (0.5 mol L(-1) Na2CO3) and the proton donor solution (1 mol L(-1) CH3COOH). Formation of carbon dioxide microbubbles generated in situ leads to the dispersion of the extraction solvent in the whole aqueous sample and extraction of the analyte into organic phase. Unlike the conventional DLLME, in the case of EA-DLLME, the addition of dispersive solvent, as well as, time consuming centrifugation step for disruption of the cloudy state is avoided. The phase separation was achieved by gentle bubbling of nitrogen stream (2 mL min(-1) during 2 min). The performance of the suggested approach is demonstrated by determination of antipyrine in saliva samples. The procedure is based on the derivatization of antipyrine by nitrite-ion followed by EA-DLLME of 4-nitrosoantipyrine and subsequent UV-Vis detection using SWIA manifold. The absorbance of the yellow-colored extract at the wavelength of 345 nm obeys Beers law in the range of 1.5-100 µmol L(-1) of antipyrine in saliva. The LOD, calculated from a blank test based on 3σ, was 0.5 µmol L(-1).

An automatic chemiluminescence method based on the multi-pumping flow system coupled with the fluidized reactor and direct-injection detector: Determination of uric acid in saliva samples

A novel approach for the automatic chemiluminescence (CL) analysis of the complex samples is proposed. A multi-pumping flow system was successfully combined with fluidized reactor and direct-injection CL detector. The possibility of the approach was demonstrated on the determination of uric acid in saliva samples. Uric acid is clinically important analyte and its determination in biological fluids is related to human organism dysfunctions, such as gout. For the first time, the fast luminol - N-bromosuccinimide (NBS) reaction in an alkaline medium was used for the CL determination of uric acid in saliva samples. The CL intensity is greatly quenched in the presence of the analyte. The method includes on-line separation of uric acid from the saliva samples based on fluidized beds strategy using anion-exchange resin Dowex® 2×8 followed by the elution and CL determination using a direct-injection CL detector. The stroke pulsations of the solenoid micro-pumps provided the floating of the anion exchange resin in a sample phase and uric acid separation from the sample matrix into a sample pre-treatment block of flow system. To obtain efficient elution of analyte an eluent circulation was applied. Under the optimal conditions, the detector response for uric acid was linear in the logarithmic concentration ranges from 6·10-6 to 1·10-3molL-1. The limit of detection, calculated from a blank test based on 3σ, was 2·10-6molL-1. Fluidized bed strategy allows us to exclude saliva matrices influence on the luminol-NBS CL reaction, which results in improved selectivity. The applicability of the method developed is demonstrated with the help of real sample analysis. The obtained results are confirmed by reference HPLC-UV method.

Automated alkaline-induced salting-out homogeneous liquid-liquid extraction coupled with in-line organic-phase detection by an optical probe for the determination of diclofenac

A fully automated alkaline-induced salting-out homogeneous liquid-liquid extraction (AI-SHLLE) procedure coupled with in-line organic-phase detection by an optical probe has been suggested. Diclofenac was used as a proof-of-concept analyte. The method is based on the oxidation of diclofenac with potassium ferricyanide in an alkaline medium followed by separation of the acetonitrile phase from the homogeneous sample solution and simultaneous extraction of the derivative. Sodium hydroxide serves as both the alkaline agent for the derivatization of diclofenac and as the salting-out agent for the acetonitrile-rich phase formation. Absorbance of the derivative in the acetonitrile-rich phase was measured in-line using an optical probe. The calibration graph was linear over the range of 2.5-60µmolL-1 with the regression coefficient equal to 0.9997. The LOD calculated from the calibration plot based on 3σ was 0.8µmolL-1. The sample throughput was 7 samplesh-1. The method was applied for the determination of diclofenac in spiked saliva samples and pharmaceutical preparations and the results were compared with those obtained by the reference method.

Flow analysis with chemiluminescence detection: recent advances and applications

This article highlights the most important developments in flow analysis with chemiluminescence (CL) detection, describing different flow systems that are compatible with CL detection, detector designs, commonly applied CL reactions and approaches to sample treatment. Recent applications of flow analysis with CL detection (focusing on outputs published since 2010) are also presented. Applications are classified by sample matrix, covering foods and beverages, environmental matrices, pharmaceuticals and biological fluids. Comprehensive tables are provided for each area, listing the specific sample matrix, CL reaction used, linear range, limit of detection and sample treatment for each analyte. Finally, recent and emerging trends in the field are also discussed.

Automated IR determination of petroleum products in water based on sequential injection analysis

The simple and easy performed automated method for the IR determination of petroleum products (PP) in water using extraction-chromatographic cartridges has been developed. The method assumes two stages: on-site extraction of PP during a sampling by using extraction-chromatographic cartridges and subsequent determination of the extracted PP using sequential injection analysis (SIA) with IR detection. The appropriate experimental conditions for extraction of the dissolved in water PP and for automated SIA procedure were investigated. The calibration plot constructed using the developed procedure was linear in the range of 3-200 μg L(-1). The limit of detection (LOD), calculated from a blank test based on 3σ was 1 µg L(-1). The sample volume was 1L. The system throughput was found to be 12 h(-1).

Simultaneous determination of iron (II) and ascorbic acid in pharmaceuticas based on flow sandwich technique.

The simple and easy performed flow system based on sandwich technique has been developed for the simultaneous separate determination of iron (II) and ascorbic acid in pharmaceuticals. The implementation of sandwich technique assumed the injection of sample solution between two selective reagents and allowed the carrying out in reaction coil two chemical reactions simultaneously: iron (II) with 1,10-phenanthroline and ascorbic acid with sodium 2,6-dichlorophenolindophenol. For achieving of excellent repeatability and considerable reagent saving the various parameters such as flow rate, sample and reagent volumes, reaction coil length were also optimized. The limits of detection (LODs) obtained by using the developed flow sandwich-type approach were 0.2 mg L(-1) for iron (II) and 0.7 mg L(-1) for ascorbic acid. The suggested approach was validated according to the following parameters: linearity and sensitivity, precision, recoveries and accuracy. The sampling frequency was 41 h(-1).

An automated salting-out assisted liquid-liquid microextraction approach using 1-octylamine: On-line separation of tetracycline in urine samples followed by HPLC-UV determination

An automated salting-out assisted liquid-liquid microextraction (SALLME) procedure based on a flow system was developed as new approach for pretreatment of complex sample matrix. In this procedure 1-octylamine was investigated as novel extractant for the SALLME. The procedure involved aspiration of the 1-octylamine and sample solution into a mixing chamber of a flow system followed by their air-bubble mixing resulting to isotropic solution formation. To provide phase separation a salting-out agent solution was added into the mixing chamber. After phase separation, the micellar 1-octylamine phase containing analyte was mixed with methanol and transported to a HPLC-UV system. To demonstrate the efficiency of the suggested approach, the automated procedure was applied for the HPLC-UV determination of tetracycline as a proof-of-concept analyte in human urine samples. Under the optimal conditions, the detector response of the analytes was linear in the concentration ranges of 0.5-20 mg L-1. The limit of detection, calculated from a blank test based on 3σ, was 0.17 mg L-1. The results demonstrate that the developed approach is highly cost-effective, simple and rapid.

A novel flow injection chemiluminescence method for automated and miniaturized determination of phenols in smoked food samples

An easily performed fully automated and miniaturized flow injection chemiluminescence (CL) method for determination of phenols in smoked food samples has been proposed. This method includes the ultrasound assisted solid-liquid extraction coupled with gas-diffusion separation of phenols from smoked food sample and analytes absorption into a NaOH solution in a specially designed gas-diffusion cell. The flow system was designed to focus on automation and miniaturization with minimal sample and reagent consumption by inexpensive instrumentation. The luminol - N-bromosuccinimide system in an alkaline medium was used for the CL determination of phenols. The limit of detection of the proposed procedure was 3·10-8·molL-1 (0.01mgkg-1) in terms of phenol. The presented method demonstrated to be a good tool for easy, rapid and cost-effective point-of-need screening phenols in smoked food samples.

Effervescence assisted dispersive liquid–liquid microextraction followed by microvolume UV-Vis spectrophotometric determination of surfactants in water

ABSTRACT The novel and simple methods for the sensitive determination of cationic and anionic surfactants in water based on effervescence assisted dispersive liquid–liquid microextraction and microvolume UV-Vis spectrophotometry have been developed. The method involves ion-pair extraction of cationic and anionic surfactants with organic dyes (methyl orange and azure A, respectively) during the dispersion of extraction solvent (CHCl3) by CO2 bubbles which are formed by the injection of a mixture of the extraction solvent and proton donor solvent into the sample solution which contains carbonate-ions as effervescency agent. The analytical performance of the proposed procedure was compared with the conventional dispersive liquid–liquid microextraction. Appropriate experimental conditions for both methods were investigated. The absorbances of the colored extracts at wavelengths of 440 and 625 nm obey Beers law within the range of 0.1–5.0 mg/L for both cationic and anionic surfactants. The limit of detection (LOD) obtained using the effervescence assisted extraction method was 30 µg/L for cationic and anionic surfactants. The proposed methods were successfully applied to determination of surfactants in water samples.