Sequential Injection Ion Chromatography with Flow Injection Post Column Derivatization Capable of Using the Unstable Reagent Murexide to Determine Calcium and Magnesium in a Mixture

A hyphenated sequential injection ion chromatography–flow injection analysis (SIIC–FIA) system is proposed for post column derivatization capable of using murexide, an unstable but commonly available reagent, for the determination of calcium and magnesium in a mixture. A short ion exchange column was modified from a 4.6 mm × 10 mm C18 monolithic guard column. Calcium/magnesium mixture and murexide were used as model analytes and derivatizing agent, respectively. The FIA post column allows the use of unstable chromogenic reagents. The continuous flow of liquid also helped to stabilize the signal baseline during detection. A single concentration based calibration graph was demonstrated. The system requires low volumes of standard/sample (5–50 µL) and mobile phase (4.50 mL), and offers sample throughput at 8 h^?1 without the need for long column calibration. Detection limits were 0.5 and 0.1 µg for Ca²⁺ and Mg²⁺, respectively. Working ranges were 1–5 µg Ca²⁺ and 0.2–1 µg Mg²⁺. Analyses of well and drinking water samples were demonstrated and validated with the standard complexometric titration.     

Multicomponent flow injection based analysis with diode array detection and partial least squares multivariate calibration evaluation. Rapid determination of Ca(II) and Mg(II) in waters and dialysis liquids

Flow injection analysis (FIA) with multiwavelength scanning of the FIA peaks using a diode array detector (DAD) has been combined with a multivariate calibration approach applying the partial least squares (PLS) method for the data evaluation. In this way, various side effects like dilution of the reagent, high blank, absorbance changes due to the pH gradient throughout the peak and/or the other interferences can be accounted for. Thus, even with a simple FIA manifold instrumentation the satisfactory results of multicomponent analysis are obtained. The method described has been checked on analysis of binary (Ca and Mg) and ternary (Ca, Mg and Cu) mixtures with pyridylazo resorcinol (PAR) as reagent and applied for rapid determination of calcium and magnesium in dialysis liquids and waters.     

Flow Injection Analysis System Using Magnetic Beads,Screen Printed Electrodes and Magnets

Here is presented a Flow Injection Analysis (FIA) system using a flow cell with an integrated magnet, applied to biotin determination. The mixture of magnetic beads modified with streptavidin (Strep‐MB), biotin and B‐HRP is left 15 minutes under stirring and then a washing step is performed in an automatic way thanks to the external magnets coupled in the FIA system. After the immobilization of the MBs on the surface of the electrode, 3,3′,5,5′‐Tetramethylbenzidine (TMB) is injected. The linear range obtained is between 0.5 to 10 pM of biotin and the sensitivity is 85 nA/pM.     

Flow injection analysis of imidacloprid in natural waters and agricultural matrixes by photochemical dissociation, chemical reduction, and nitric oxide chemiluminescence detection

A flow injection analysis (FIA) to quantify imidacloprid was developed based upon (1) ultraviolet (254 nm) photochemical dissociation of imidacloprid to produce nitrite, (2) chemical reduction of the nitrite to nitric oxide by iodide in acid, (3) removal of gas-phase nitric oxide from the aqueous stream using a membrane separator, and (4) detection of the nitric oxide by chemiluminescent reaction with ozone. The cross-reactivity of imidacloprid with eight metabolites of imidacloprid was determined using a commercial ELISA kit and the FIA method. While the ELISA kit demonstrated varying degrees of cross-reactivity, cross-reactivity in the FIA method was observed for only the N-nitro and N-nitroso metabolites. The optimized analytical FIA method, FIA provides a linear response in imidacloprid concentration over four orders of magnitude, has a limit of detection of 5.6 pmol (1.5 ng) of imidacloprid, and exhibits an inter-day precision of 0.4%. Spike-recoveries by FIA demonstrated excellent recovery of imidacloprid in natural waters, hemlock xylem fluid, honey, and grapes with little to no interference from the matrix.     

Spectrophotometric determination of silicon in silicates by flow-injection analysis

A flow-injection spectrophotometric method has been developed for the accurate, continuous determination of silicon in silicate rocks. A rock sample solution is prepared by fusion with a 1:1 mixture of lithium carbonate and boric acid and subsequent dissolution of the cake in 1 M hydrochloric acid. The preparation technique is the same as that used for the determination of total iron, aluminium, calcium, titanium, and phosphorus in silicate rocks by flow-injection spectrophotometry. Because of the marked polymerization of silicic acid in acid solution, silicic acid is depolymerized in alkaline medium after a simple cation-exchange column filtration of the rock sample solution and then determined by a static or an FIA spectrophotometric method. The FIA system consists of two channels which carry the carrier solution and molybdate reagent, and allows the colour reaction to proceed under controlled conditions. The FIA system permits high throughput of 70 samples per hour. The procedure has been applied to a variety of standard silicate rocks of the U.S. Geological Survey and the Geological Survey of Japan, and gave satisfactory agreement with the recommended values.     

Spectrophotometric determination of calcium in zirconium powder by use of murexide

An accurate spectrophotometric method is proposed for the determination of calcium in zirconium powder by use of murexide. A 0.4-g sample is dissolved in hydrofluoric and sulphuric acids, the solution evaporated to fumes of sulphuric acid, and a mercury cathode electrolysis made if more than 0.05% copper or nickel is present. Ammoniacal precipitation in the presence of ammonium chloride separates zirconium and other elements and an aliquot of filtrate is collected, equivalent to 0.2 g of sample. The ammonium salts are destroyed with nitric and hydrochloric acids and the calcium is determined with murexide. The high reagent blank is shown to be due to the reagent grade nitric acid, hydrochloric acid, and ammonium hydroxide.     

A simple method for water discrimination based on an light emitting diode (LED) photometer

This work describes the use of a multi-LED photometer for discrimination of mineral water samples, employing chromogenic reagents and chemometric techniques. Forty-five water samples (including 7 different brands of mineral water and samples of deionised, distilled and tap waters) were analysed in a monosegmented flow system, using three different chromogenic reagents (murexide, PAR and eriochrome black T) in a pH 10.0 NH₃/NH₄⁺ buffer in separate injections. Measurements were performed at 470, 500, 525, 562, 590, 612, 636 and 654 nm. Analyses were carried out using PCA, employing data sets including absorbance values obtained with one, two or all three reagents, which comprise 8, 16 or 24 variables, respectively. The best result was obtained with the data set from murexide and eriochrome black T, providing a clear distinction between 9 groups (distilled and deionised waters were classified in the same group). Based on the loading values, it was possible to select four wavelengths (470, 500, 590 and 654 nm) that provided a similar discrimination. With the use of these four LED, an HCA was performed, providing discrimination between 8 groups at a similarity level of 0.88. A model based on SIMCA allowed correctly classifying 94% of the samples. The discrimination between different groups is due to the metal ion contents in the water samples, mainly calcium and magnesium. Therefore, the use of common complexing reagents, such as murexide and erichrome black T, a multi-LED photometer and chemometric techniques provide an easy and simple method for water discrimination.     

Fabrication of Photoelectrochemical Glucose Biosensor in Flow Injection Analysis System Using ZnS/CdS‐Carbon Nanotube Nanocomposite Electrode

In this work, a photoamperometric glucose biosensor based on glucose oxidase (GODx) was developed in flow injection analysis (FIA) system using ZnS‐CdS quantum dot (QD) modified multiwalled carbon nanotube/glassy carbon electrode (ZnS‐CdS/MWCNT/GCE). Cyclic voltammograms of the proposed electrode (GODx/ZnS‐CdS/MWCNT/GCE) showed a pair of well‐defined reversible redox peak attributing that direct electron transfer between the protein and electrode. The current of the reduction peak became more cathodic in the presence of O₂ due to the electrocatalytic activity of the electrode towards the reduction of dissolved O₂, but reduction current shifted to a less negative value upon addition of glucose in the solution. The obtained CV currents were affected by the irradiation of the electrode surface. Thus, the photoelectrochemical biosensing of glucose in the FIA system was studied by monitoring of the changes in the electrocatalyzed reduction peak current of dissolved O₂ at the proposed electrode dependent on glucose concentration. The proposed photoelectrochemical FIA method has a linear response to glucose ranging from of 0.01 to 1.0 mM with detection limit of 3.0 μM under optimized conditions. Photoelectrochemical biosensor was successfully fabricated in FIA system for selective, sensitive and repeatable detection of glucose and has been satisfactorily applied to determination of glucose in real sample.     

Creatinine biosensor based on ammonium ion selective electrode and its application in flow-injection analysis

A new, highly sensitive, fast responding and stable potentiometric biosensor for creatinine determination is developed. The biosensor is based on an ammonium ion-selective electrode. Creatinine deiminase (EC 3.5.4.21) is chemically immobilized on the surface of the polymeric ion-sensitive membrane in the form of monomolecular layer using a simple, one-step carbodiimide covalent attachment method. The resulting enzyme electrodes are useful for measurement under flow injection analysis (FIA) conditions. The biosensors exhibit excellent operational and storage stability. The enzyme electrodes retain over 70% of initial sensitivity after ten weeks of work under FIA conditions. The storage stability at 4 °C is longer than half a year without loss of sensitivity. Under optimized conditions near 30 samples per hour can be analyzed and the determination range (0.02-20.0 mmol l⁻¹) fully covers creatinine concentrations important from clinical and biomedical point of view. The simple biosensor/FIA system has been successfully used for determination of creatinine in urine, serum and posthemodialysate samples.     

Measurement of total alkali and phenol in process liquor by FIA

Flow injection analysis (FIA) has been applied to the determination of total phenol and total alkali in high concentration alkaline phenoxide liquors as it occurs in industrial process streams. The total alkali content and total phenol content in samples containing 20–50% (w/v) sodium phenoxide can be directly measured without mutual interference. The first is measured by peak width measurement based FIA with conductimetric detection utilizing an electronic circuit to permit automatic measurement from minima to minima. The total phenol is measured by the Berthelot reaction using NaOCl and ammonia to form indophenol blue, monitored at 660 nm with a light emitting diode-based detector.     

Flow injection analysis of potassium using an all-solid-state potassium-selective electrode as a detector

The concentration of potassium was determined by a combination of flow injection analysis (FIA) with an all-solid-state potassium sensor detection. The all-solid-state potassium-selective electrode possessing long-term potential stability was fabricated by coating an electroactive polypyrrole/poly(4-styrenesulfonate) film electrode with a plasticized poly(vinyl chloride) membrane containing valinomycin. The simple FIA system developed in this laboratory demonstrated sensitivity identical to that in the batch system and achieved considerably rapid assay (150 samples h⁻¹). Analyses of soy sauce and control serum samples by this FIA system yielded results in good agreement with those obtained by conventional measurements.     

流动注射光纤荧光探针动力学法测定铁的研究

研究了8-苯胺基-1-萘磺酸作为表面活性剂胶束荧光探针的性质,并将其用作动力学分析的荧光指示剂。建立了以铁(Ⅲ)催化过氧化氢氧化ANS-Brij35体系荧光猝灭反应为基础,用流动注射和光导纤维技术测定痕量铁的动力学分析新方法。该法线性范围为5～300ng/mL,检测下限为2ng/mL,绝对检出量为0.2ng,对20ng/mL铁(Ⅲ)进行11次测定相对标准偏差为0.27%,可直接用于人发、纯铝和铝合金中铁的测定。     

Micro-flow injection system for the urinary protein assay

A urinary protein assay has been investigated, employing a micro-flow injection analysis (μFIA) combined with an adsorptive separation of protein from analyte. The adsorptive separation part of protein in the artificial urine with ceramic hydroxyapatite is integrated on the μFIA chip, since the interference of other components coexisting in urine occurs in the conventional FIA system. The typical FI peak can be obtained following the adsorption–elution process of the protein prior to the detection, and the protein concentration in artificial urine can be quantitatively determined.     

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

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.     

Increasing the scope and power of flow-injection analysis through chemometric approaches

The objective of this paper is to illustrate how chemometrics can enhance the scope and power of flow injection analysis (FIA) by considering a few simple but representative cases where the ability of chemometrics to improve performance is not readily apparent. In principle, there are two phases when chemometrics can be usefully combined with FIA: first when developing an FIA method and, second, when treating raw data acquired from an FIA detection system. The most obvious application of chemometrics for the FIA practitioner is to use experimental design to replace the obsolete, but too often used one-variable-at-a-time approach when optimising an FIA method. Therefore, methods for screening variables and system optimisation are discussed. Raw data acquired from most FIA systems are first-order data, containing information about the dispersed sample plug. However, the information that is extracted when using FIA for routine purposes is of zero-order: predominantly peak height values. It is shown by a simple example that a chemometric approach in such cases can again provide additional useful information about the sample. First-order spectral data and second-order data more or less require a chemometrics approach for successful analysis, and examples of such applications are briefly discussed.     

Fabrication of a fiberglass-packed channel in a microchip for flow injection analysis

A novel fiberglass-packed channel in a microchip has been fabricated for flow injection analysis (FIA) based on the in situ polymerization of methyl methacrylate (MMA). MMA prepolymer molding solution containing an ultraviolet initiator was sandwiched between a poly(methyl methacrylate) (PMMA) cover plate and a PMMA base plate bearing a glycerol-permeated fiberglass bundle and exposed to UV light. During the UV-initiated polymerization, the fiberglass bundle was embedded in the PMMA substrate to form a fiberglass-packed microchannel. When the glycerol in the fiberglass bundle was flushed away with water, the obtained porous fiberglass-packed microchannel could serve as an electroosmotic pump and a FIA channel. Scanning electron micrographs offer insights into the fiber-based microchip. The analytical performance of the FIA system has been demonstrated by detecting catechol in connection with end-column amperometric detection. The fiber- based microchips can be fabricated by the new approach without the need for complicated and expensive lithography-based microfabrication techniques, indicating great promise for the low-cost production of microchips, and should find a wide range of applications.     

Open-access liquid chromatography/mass spectrometry in a drug discovery environment

The use of open-access mass spectrometry to monitor synthetic chemistry reactions, and also the integrity and purity of new chemical entities, has been a part of the medicinal chemist's tool-box for more than 5 years. Originally in our group at Wyeth Research there were two open-access methods available to the chemists, flow injection analysis (FIA) and liquid chromatography/mass spectrometry (LC/MS). The FIA method was approximately 3 min long, while the LC/MS method was approximately 20 min long (including an 8 min gradient). Within the first 2 years, the total number of open-access analyses increased by approximately 125%. It is interesting, however, that the number of LC/MS analyses increased by more than 285%. This is attributed to the fact that the chemists began using the LC/MS data to monitor reactions and also to check final product integrity and purity. In addition, the number of chemists performing parallel synthesis reactions has increased; thus, individual chemists can produce sample sets of up to 100 vials. This paper describes the implementation of new methodology, which accommodates the need for much faster run times and also the ability to acquire alternating positive and negative ion spectra within the same run. In addition, the instrument has been configured to e-mail the resulting processed data report to the submitting chemist. Several methods have been developed, including structure elucidation using in-source collision-induced dissociation (CID) and night-time analysis. The LC/MS methods for this system are described herein and are applicable to both industrial and academic synthetic chemistry optimization efforts.     

Spectrophotometric determination of the stability constant of the Eu(III)-murexide complex

The values of the stability constants of the Ca(II) and lanthanide(III) complexes of murexide reported in the literature were determined without proper correction for binding of buffer ions to the metal ion. The constants are best determined without a buffer present. Accurate values of conditional stability constants for the Eu(III)—murexide complex (relative standard deviation better than 3%), of the differential molar absorptivity of the Eu(III)—murexide complex with respect to murexide at 480 nm (relative standard deviation better than 0.5%) and of the molar absorptivity of murexide at 520 and at 506 nm (precision better than 0.4%) at pH 5.0 and 6.5 at 15, 25 and 35° are reported. The accuracy and precision of the concentration of metal ion solution determined by using these conditional stability constants are discussed.