Joanna Kozak

Tyrosinase-based biosensor for determination of bisphenol A in a flow-batch system

A tyrosinase-based amperometric biosensor is proposed for determination of bisphenol A (BPA) in a flow-batch monosegmented sequential injection system. The enzyme was entrapped in a sol-gel TiO2 matrix modified with multi-walled carbon nanotubes (MWCNTs), polycationic polymer poly(diallyldimethylammonium chloride), (PDDA) and Nafion. Morphology of TYR/TiO2/MWCNTs/PDDA/Nafion matrix composite was studied via scanning electron microscopy (SEM). Electrochemical behavior of the developed biosensor towards bisphenol A was examined and analytical characteristics were assessed with respect to linear range, biosensor sensitivity, limit of detection, long term stability, repeatability and reproducibility. Linear range of biosensor response was found between 0.28 and 45.05 µM with high sensitivity of 3263 µA mM(-1) cm(-2) and detection limit 0.066 µM. The approach was successfully employed for determination of BPA in natural samples.

An automatic, vigorous-injection assisted dispersive liquid–liquid microextraction technique for stopped-flow spectrophotometric detection of boron

A novel automatic vigorous-injection assisted dispersive liquid-liquid microextraction procedure based on the use of a modified single-valve sequential injection manifold (SV-SIA) was developed and applied for determination of boron in water samples. The major novelties in the procedure are the achieving of efficient dispersive liquid-liquid microextraction by means of single vigorous-injection (250 µL, 900 µL s(-1)) of the extraction solvent (n-amylacetate) into aqueous phase resulting in the effective dispersive mixing without using dispersive solvent and after self-separation of the phases, as well as forwarding of the extraction phase directly to a Z-flow cell (10 mm) without the use of a holding coil for stopped-flow spectrophotometric detection. The calibration working range was linear up to 2.43 mg L(-1) of boron at 426nm wavelength. The limit of detection, calculated as 3s of a blank test (n=10), was found to be 0.003 mg L(-1), and the relative standard deviation, measured as ten replicable concentrations at 0.41 mg L(-1) of boron was determined to be 5.6%. The validation of the method was tested using certified reference material.

Simple flow injection method for simultaneous spectrophotometric determination of Fe(II) and Fe(III).

The method is based on spectrophotometric determination of Fe(II) and Fe(III) at a single wavelength (530 nm) with the use of a dedicated reversed-flow injection system. In the system, EDTA solution is injected into a carrier stream (HNO(3)) and then merged with a sample stream containing a mixture of sulfosalicylic acid and 1,10-phenanthroline as indicators. In an acid environment (pH≅3) the indicators form complexes with both Fe(III) and Fe(II), but EDTA replaces sulfosalicylic acid, forming a more stable colourless complex with Fe(III), whereas Fe(II) remains in a complex with 1,10-phenenthroline. As a result, the area and minimum of the characteristic peak can be exploited as measures corresponding to the Fe(III) and Fe(II) concentrations, respectively. The analytes were not found to affect each others signals, hence two analytical curves were constructed with the use of a set of standard solutions, each containing Fe(II) and Fe(III). Both analytes were determined in synthetic samples within the concentration ranges of 0.05-4.0 and 0.09-6.0 mg L(-1), respectively, with precision less than 1.5 and 2.6% (RSD) and with accuracy less than 4.3 and 5.6% (RE). The method was applied to determination of the analytes in water samples collected from artesian wells and the results of the determination were consistent with those obtained using the ICP-OES technique.

Review of Univariate Standard Addition Calibration Procedures in Flow Analysis

The calibration procedures related to the standard addition method and used in flow analysis are critically reviewed. All examples met in the literature are considered with respect to their facilities for overcoming the interferences. It is disclosed that the flow techniques give a chance to add the standard(s) to a sample by different manners allowing the analytical result to be calculated by either interpolative or extrapolative way. However, from among various calibration procedures those of extrapolative character are distinguished as they are exclusively able to compensate the multiplicative interference effect in wide range of the interferent(s) concentration. It is also shown how the flow standard addition approaches can be employed to solve different analytical problems and—on the other hand—why some of them reveal limited usefulness for calibration purposes. The particular groups of calibration procedures are compared with each other and discussed in terms of their analytical performance.

Generalized Calibration Strategy in Analytical Chemistry

A novel calibration methodology named ‘the generalized calibration strategy’ (GCS) is presented that is aimed at verifying and improving the accuracy of analytical determinations. It is based on integration of calibration methods together with such operations as standard addition and sample dilution. At each stage of the sample dilution, the analytical result is estimated on the basis of six values, which are differently resistant to errors caused by interference and non-linearity effects. The process of stepwise elimination of both effects is controlled by comparison of these values. A dedicated flow system is presented. The GCS can be adapted to calibration by all well-known methods: conventional, internal standard, and indirect. This novel calibration strategy has been tested on indirect determination of chlorites in water samples by UV/Vis spectrophotometry.

Tyrosinase biosensor for benzoic acid inhibition-based determination with the use of a flow-batch monosegmented sequential injection system

Amperometric tyrosinase based biosensor for benzoic acid determination with the use of a flow-batch monosegmented sequential injection system is proposed. The functioning of the biosensor is based on the inhibition effect of benzoic acid on the biocatalytic activity of tyrosinase, polyphenol oxidase. In the biosensor, tyrosinase is entrapped in titania gel modified with multiwalled carbon nanotubes (MWCNT) and Nafion. The procedure of optimization of experimental conditions affecting the biosensor response, as well as its analytical characteristics and results of the approach verification using synthetic samples and a reference material are presented. The developed biosensor exhibits linear range up to 2.46μM, good sensitivity toward benzoic acid (1.06μAμM(-1)) and low detection limit (0.03μM). The approach has been applied to benzoic acid determination in a real beverage sample giving the result consistent with that obtained using the HPLC method.

Calibration by the gradient ratio-standard addition method in flow injection flame atomic absorption spectrometry

Abstract A calibration method has been developed which is realised in the flow injection analysis (FIA) by the gradient technique. According to this method two transient peaks, one for a sample and the other for a sample with standard addition, are recorded and compared point by point in the entire defined time range. The analytical result is estimated on the basis of information gained about the local analyte concentrations in the sample zone. The method allows the results to be reliable when both the non-linear calibration dependence and the interference effect occur. As an example, calcium in synthetic samples containing silicon, phosphate, aluminium, vanadium and titanium, and also in iron ore sample, were determined by flame atomic absorption spectrometry (FAAS). It has been proved, that the method can be effective in overcoming even extremely strong interferences, providing analytical results with average accuracy equal to ca. 5% and with precision 2–3 times inferior to that obtained by conventional FI calibration.

Complementary dilution method: A new version of calibration by the integrated strategy

Abstract A novel version of the integrated approach to calibration is presented as “the complementary dilution method” (CDM). In the series of six solutions a standard and a sample are suggested to be complementarily diluted with each other and with the blank solution, hence four linear calibration graphs may be constructed on the basis of the measurement data obtained. The analyte concentration in a sample is estimated by four values calculated in both the interpolative and extrapolative way. When comparing statistically these values with one to another, the calibration errors caused by both the non‐linear and interference effect can be detected. The flow injection system designed for realization of the CDM method is presented. The manners how the system can be adapted to examination and elimination of the calibration errors are described. The usefulness and performance of the CDM method have been confirmed experimentally on the examples of the iron determination by UV/VIS spectrophotometry and the calcium and magnesium determination by flame atomic absorption spectrometry.

Review and classification of univariate interpolative calibration procedures in flow analysis

A novel classification system introducing three main categories of the calibration methods—interpolative, extrapolative, and indicative—is suggested once more to be used in analytical chemistry. Then the univariate interpolative calibration procedures developed in the flow analysis are reviewed. In contrast to other similar reports, the present article does not present them with respect to instrumental aspects but as to how the measurement data recorded are interpreted and transformed into the analytical results. On such a basis, five groups of the calibration approaches have been specified. Finally, the particular groups of methods are compared with each other and discussed in terms of their analytical performance.

Simultaneous spectrophotometric flow injection determination of phosphate and silicate.

A method for the simultaneous determination of phosphate and silicate based on spectrophotometric measurement at 385 nm of a single peak using a flow injection system with two component calibration is described. In the system, a stream of sample containing both analytes is merged with a stream of ammonium molybdate to form (at 1<pH<2) molybdophosphoric and molybdosilicic acids. Total absorbance of the compounds is registered in a form of a constant signal. Simultaneously, oxalic acid solution is injected into a carrier stream (H2SO4) and then merged with the stream of sample containing the mixture of heteropolyacids. A characteristic peak is registered as a result of selective decomposition of molybdophosphoric acid by oxalic acid. The area (or the absorbance measured at the constant signal) and the absorbance measured at the minimum of the peak can be used as measures corresponding to the phosphate and silicate concentrations, respectively. The time of the peak registration is about 3 min. Two-component calibration with the use of four standard solutions of the phosphate/silicate concentrations established in accordance with 2(2) factorial design was applied. Phosphate and silicate can be determined within the concentration ranges of 0.20-15.00 and 0.20-20.00 mg L(-1), with precision less than 2.7 and 0.9% (RSD), respectively and accuracy better than 6.2% (RE). The detection limit is 0.054 and 0.092 mg L(-1) for phosphate and silicate, respectively. The method was applied to determination of the analytes in certified reference materials of groundwater, wastewater, and river water giving results consistent with the certified values.