Enhanced Sensitivity in Flow Injection Analysis Using a Long Pathlength Liquid Waveguide Capillary Flow Cell for Spectrophotometric Detection

ABSTRACTA continuous flow analysis system, composed of a 1.2-cm laboratory-made antibubble flow cell and a spectrophotometer, was established. The system was evaluated for the determination of nitrite, phosphate, and silicate. Different from flow injection analysis and other flow analysis modes, an injection or multiposition valve was not needed. Even better, the system was free from interferences from air bubbles without the use of a debubbler device or electronic bubble gate. Without the formation of air bubbles, the chemical reaction was accelerated using a water bath. The experimental parameters for nutrient analysis, including reagent concentration, flow strategy, flow rate, and reaction temperature, were optimized based on a univariate experimental design. The carry-over effect was comprehensively evaluated and may be ignored using this protocol. The established system and analytical methods were especially suitable for laboratories with only basic instruments and limited budgets. The system had the advantages of high sample throughput (>60 h−1); great convenience without valve utilization; long linear dynamic ranges (0.2–80 µM for nitrite, 0.3–14 µM for phosphate, and 0.5–120 µM for silicate); low detection limits (0.06 µM for nitrite, 0.08 µM for phosphate, and 0.11 µM for silicate); and high recovery values (91.5 ± 1.01 to 108.7 ± 3.18%). In addition to water samples, national reference materials were analyzed, and the results were in good agreement with the certified values.

A rapid and precise assay for peroxide as ‘active oxygen’ in products, by flow injection analysis in a high pressure system with spectrophotometric detection

The application of inverse spectrophotometric detection in flow injection is introduced and its potential illustrated by a possible application to the determination of nitrite by its reaction with cerium(IV).A single manifold was employed with two reagent concentrations, namely 10 and 20 g l–1, of cerium(IV) ammonium sulphate in 0.5 M sulphuric acid. The working ranges are 10–200 and 200–1000 mg l–1, respectively, for a ca. 30-µl sample injection and the sampling rate is between 60 and 75 injections per hour. The 200–1000 mg l–1 system was applied to the determination of nitrite in culture media and the results were compared with those given by a manual diazotisation method.The same manifold with a smaller sample loop was also employed to demonstrate the extension of the technique to provide chemical back-off. A working range of approximately 2500 mg l–1 of nitrite can be covered anywhere between 1000 and 9000 mg l–1 simply by selection of a suitable reagent concentration.

Sequential flow injection spectrophotometric determination of nitrite and nitrate in various samples

New interface for coupling flow-injection and capillary electrophoresis

The quantitative analysis of protein mixtures is pivotal for the understanding of variations in the proteome of living systems. Therefore, approaches have been recently devised that generally allow the relative quantitative analysis of peptides and proteins. Here we present proof of concept of the new metal-coded affinity tag (MeCAT) technique, which allowed the quantitative determination of peptides and proteins. A macrocyclic metal chelate complex (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)) loaded with different lanthanides (metal(III) ions) was the essential part of the tag. The combination of DOTA with an affinity anchor for purification and a reactive group for reaction with amino acids constituted a reagent that allowed quantification of peptides and proteins in an absolute fashion. For the quantitative determination, the tagged peptides and proteins were analyzed using flow injection inductively coupled plasma MS, a technique that allowed detection of metals with high precision and low detection limits. The metal chelate complexes were attached to the cysteine residues, and the course of the labeling reaction was followed using SDS-PAGE and MALDI-TOF MS, ESI MS, and inductively coupled plasma MS. To limit the width in isotopic signal spread and to increase the sensitivity for ESI analysis, we used the monoisotopic lanthanide macrocycle complexes. Peptides tagged with the reagent loaded with different metals coelute in liquid chromatography. In first applications with proteins, the calculated detection limit for bovine serum albumin for example was 110 amol, and we have used MeCAT to analyze proteins of the Sus scrofa eye lens as a model system. These data showed that MeCAT allowed quantification not only of peptides but also of proteins in an absolute fashion at low concentrations and in complex mixtures.

Objective To establish a catalytic spectrophotometric method for determination of iodine in water without the use of highly toxic arsenic reagents with good precision and accuracy. Methods A new flow injection catalytic spectrophotometry method for determination of iodine in water was established by combining flow injection analysis (FIA) with a new catalytic spectrophotometry for determination of iodine with no need of arsenic reagent. The standard curve linearity, sample detection limit, precision and accuracy of different iodine content ranges(0 - 250, 0 - 1 200 μg/L) were tested. The test result was compared with that of the arsenic-based catalytic spectrophotometry recommended by the iodine deficiency disorders monitoring program in China(recommended monitoring method). Results A calibration relation of C = aA2 + bA + d (C: iodine concentration, A: measuring absorbance peak area from FIA) of the new method existed in the range of 0 - 250 and 0 - 1 200 μg/L. The linear correlative coefficient were both 0.999 9. The detection limit for iodine in water was 0.3 μg/L. The FIA peak shape of the sample tube with the lowest content is determined, and the sensitive iodine signal is detected. The water samples with different iodine content ranges were determined in parallel for 6 times, and the coefficient of variation (CV) was 0.2% - 2.7%; the recoveries ranged from 95.0% to 105.0%, and the total average recovery was 100.3%. The measured values of water iodine standard material GBW 09113e [(8.2 ± 1.2) μg/L] and GBW 09114d [(62.0 ± 6.0) μg/L] in the standard curve of different iodine contents were all within the uncertainty range of the given value. There was no significant difference between the results of recommended monitoring method and the new method(t = 0.781, P > 0.05). Conclusions The new method for measuring water iodine has a wide standard curve range, high sensitivity, and good precision and accuracy. The instrument is easy to operate, and no need for toxic arsenic reagent. The method is a reliable method for water iodine detection. Key words: Iodine; Water; Arsenic; Flow injection analysis; Catalytic spectrophotometry

Chapter 1 - Flow Injection Analysis: Its Origins and Progress

A community-wide intercomparison exercise for the determination of dissolved iron in seawater

Application of reducing column for metal speciation by flow injection analysis : Spectrophotometric Determination of Iron(III) and Simultaneous Determination of Iron(II) and Total Iron

A rapid and sensitive flow injection analysis (FIA) with spectrophotometric detection by a Ti(IV)-porphyrin reagent is described for the determination of oxalate in foods using an immobilized oxalate oxidase reactor to yield hydrogen peroxide. The reagent is an aqueous solution of oxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV), TiO(tpypH4)4+, which reacts with hydrogen peroxide to form a monoperoxo complex, TiO2(tpypH4)4+, having an absorption peak at 450nm. The absorbance was proportional to the concentration of hydrogen peroxide. The flow-injection manifold comprised a two-channel system with an immobilized oxalate oxidase column. A linear relation was observed between the absorbance and the oxalate concentration ranging from 5×10-7to 2.5×10-4M (r=0.999), and 25 samples could be analyzed in one hour. The relative standard deviation for ten replicate measurements was 0.48% at 2.5×10-5M (500pmol/injection). The application of this system for the determination of oxalate in foods gave satisfactory results. A good correlation (r=0.996) was seen between the results obtained by the proposed method and by the conventional method using a commercial F-kit.

Comparison of spectrophotometric and potentiometric detection for the determination of water using Karl Fischer method under flow injection analysis conditions

For more than a decade, immunoassay methods have held great promise for use not only in their classic clinical applications but also in food, pesticides, process and quality control, industrial fermentations, etc. A great number of publications have appeared in these fields. Flow injection analysis (FIA) is a technique that allows the automatic analysis of a large number of samples and/or continuous monitoring, and it has been proven to be applicable to a variety of analytical problems. Nevertheless, antibody-supported flow injection systems have received relatively little attention. Only recently, the advantage of the specificity inherent to most immune reactions began to be exploited in FIA procedures. Flow injection coupled to immunoassays (FIIA) is arising as a powerful tool for the development of analytical protocols, and the application of FIA techniques is expected to contribute enormously in improving the speed and quality of immunoassays. This article gives an overview on the application...

The application of strongly reducing agents in flow injection analysis : part 2. Chromium(II)

An ion chromatographic method with post-column derivatization and spectrophotometric detection is presented for the determination of nitrate and nitrite (NOx) in baby food. NOx residues found naturally or added as preservatives were extracted from baby foods and determined by using ion chromatography with post-column derivatization and spectrophotometric detection. Nitrate was reduced to nitrite online by post-column reduction using vanadium(lll) chloride and heat. Nitrite reacted with Griess reagent to produce a dye that was detected at 525 nm. The use of V(III) and heat to promote the reduction of nitrate to nitrite online is a novel feature of this detection system. The determination of incurred NOx residues in samples by using AOAC Method 993.03 yielded results comparable to those obtained by ion chromatography with spectrophotometric detection. The toxic and carcinogenic metal cadmium used in the AOAC Method to reduce the nitrate to nitrite was avoided. The proposed method provides simultaneous determination of nitrate and nitrite. Average recoveries of nitrate and nitrite residues ranged from 82 to 107% for fortification levels of 25-400 ppm.