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Modern Flow Analysis II

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Analytical Chemistry".

Deadline for manuscript submissions: closed (31 January 2022) | Viewed by 25148

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Prof. Dr. Pawel Koscielniak

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Department of Analytical Chemistry, Faculty of Chemistry, Jagiellonian University in Kraków, Gronostajowa St. 2, 30-387 Kraków, Poland
Interests: flow analysis; forensic chemistry; environmental chemistry; green analysis; analytical calibration; interference effects; optimization methods
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We announce with great pleasure the second edition of “Modern Flow Analysis II”.

Flow analysis (FA), invented successfully in the middle of 1950s, is a well-recognized and systematically developed branch of analytical chemistry. In FA systems, the analyzed sample can be processed through various physicochemical operations, including extraction, preconcentration or transformation into a chemical form most suitable for the detection used. The flow mode allows a sample to be prepared in a fast, low-cost, safe and efficient way. In addition, due to the mechanization and automation of FA processes, the final analytical results are as a rule more reliable than those obtained under non-flow conditions.

For years, special interest has been focused on instrumental progress in FA. It has been proved that samples can be efficiently treated not only in the continuous flow mode but also in the form of individual segments injected to the carrier stream. In order to decrease the sample and reagent consumption, the concepts of multisyringe and multicommutated flow systems have been introduced into analytical practice. Advances in the field of new materials have been used, amongst other things, to construct original modern detectors dedicated to measurements in the flow mode.

The last FA developments are characterized by specific features that are oriented, in general, towards “green” analytical chemistry. For instance, the gradient technique—based on the idea that the particular points of a single injection peak can be a sufficiently rich source of analytical information—is again noticed and applied. Different micro-extraction liquid–liquid and solid–liquid techniques have been ingeniously adapted to flow conditions, making possible operation with a sample drop. The tendency to make flow systems miniaturized and integrated is expressed by lab-on-valve (LOV) devices, which work sequentially to process a sample in different ways with micro-volumes of reagents. In addition, low-cost flow systems are increasingly designed using either 3D-printing technology or using paper as a body of liquid movement in lab-on-paper (LOP) devices.

I warmly invite members of the “flow family” to submit their original contributions to this Special Issue in order to present the above (and additional) modern aspects of flow analysis with special attention to those that make analytical procedures more environmentally safe and friendly.

We would be delighted if you could respond to confirm your contribution and the proposed title by 30 November 2021.

Prof. Dr. Pawel Koscielniak
Guest Editor

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

micro-extraction techniques
separation and preconcentration techniques
miniaturized flow systems
LOV systems
LOP systems
gradient technique
natural reagents
one-standard calibration procedures
flow titration
flow detectors

Related Special Issues

Modern Flow Analysis III in Molecules
Modern Flow Analysis in Molecules (14 articles)

Published Papers (12 papers)

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Research

Jump to: Review

17 pages, 1454 KiB

Open AccessArticle

Chip-Based Spectrofluorimetric Determination of Iodine in a Multi-Syringe Flow Platform with and without In-Line Digestion—Application to Salt, Pharmaceuticals, and Algae Samples

by Joana L. A. Miranda, Raquel B. R. Mesquita, Edwin Palacio, José M. Estela, Víctor Cerdà and António O. S. S. Rangel

Molecules 2022, 27(4), 1325; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27041325 - 16 Feb 2022

Cited by 3 | Viewed by 1831

Abstract

In this work, a flow-based spectrofluorimetric method for iodine determination was developed. The system consisted of a miniaturized chip-based flow manifold for solutions handling and with integrated spectrofluorimetric detection. A multi-syringe module was used as a liquid driver. Iodide was quantified from its catalytic effect on the redox reaction between Ce(IV) and As(III), based on the Sandell–Kolthoff reaction. The method was applied for the determination of iodine in salt, pharmaceuticals, supplement pills, and seaweed samples without off-line pre-treatment. An in-line oxidation process, aided by UV radiation, was implemented to analyse some samples (supplement pills and seaweed samples) to eliminate interferences and release iodine from organo-iodine compounds. This feature, combined with the fluorometric reaction, makes this method simpler, faster, and more sensitive than the classic approach of the Sandell–Kolthoff reaction. The method allowed iodine to be determined within a range of 0.20–4.0 µmol L⁻¹, with or without the in-line UV digestion, with a limit of detection of 0.028 µmol L⁻¹ and 0.025 µmol L⁻¹, respectively. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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13 pages, 1338 KiB

Open AccessArticle

Novel Integrated Flow-Based Steam Distillation and Titration System for Determination of Volatile Acidity in Wines

by Justyna Paluch, Joanna Kozak, Karolina Mermer, Iwona Molęda, Marcin Wieczorek, Sławomir Kalinowski and Paweł Kościelniak

Molecules 2021, 26(24), 7673; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26247673 - 18 Dec 2021

Viewed by 2268

Abstract

Novel integrated flow-based steam distillation and titration system with spectrophotometric detection was developed for determination of volatile acidity in wines. Using the system, the distillation procedure was carried out in an automatic manner, starting with introducing into a heated steam distillation module a sample and subjecting it to steam distillation. Under selected conditions, all the analyte was transferred to the distillate; therefore, the system did not require calibration. The collected distillate and titrant were introduced into the next monosegments in varying proportions, in accordance with the developed titration procedure, and directed to the detection system to record the titration curve. The titration was stopped after reaching the end point of titration. Procedures for distillation and titration were developed and verified separately by distillation of acetic acid, acetic acid in the presence of tartaric acid as well as acetic acid, tartaric acid, and titratable acidity, with precision (relative standard deviation) and accuracy (relative error) for both procedures lower than 6.9 and 5.6%, respectively. The developed steam distillation and titration systems were used to determine volatile acidity in samples of white and rosé wines separately and as the integrated steam distillation and titration system, both with precision lower than 9.4% and accuracy better than 6.7%. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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9 pages, 597 KiB

Open AccessArticle

Determination of N-Acetyl-l-cysteine Ethyl Ester (NACET) by Flow Injection Analysis and Spectrophotometric Detection Using Different Thiol-Sensitive Ligands

by Lea Kukoc-Modun, Tomislav Kraljević, Dimitrios Tsikas, Njegomir Radić and Darko Modun

Molecules 2021, 26(22), 6826; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26226826 - 11 Nov 2021

Cited by 3 | Viewed by 2173

Abstract

A new flow injection spectrophotometric method for the determination of N-acetyl-l-cysteine ethyl ester (NACET) was developed and validated. The method is based on the reduction of Cu(II)-ligand complexes to chromophoric Cu(I)-ligand complexes with the analyte. The studied ligands were neocuproine (NCN), bicinchoninic acid (BCA) and bathocuproine disulfonic acid (BCS). The absorbance of the Cu(I)-ligand complex was measured at 458, 562 and 483 nm for the reactions of NACET with NCN, BCA and BCS, respectively. The method was validated in terms of linear dynamic range, limit of detection and quantitation, accuracy, selectivity, and precision. Experimental conditions were optimized by a univariate method, yielding linear calibration curves in a concentration range from 2.0 × 10⁻⁶ mol L⁻¹ to 2.0 × 10⁻⁴ mol L⁻¹ using NCN; 2.0 × 10⁻⁶ mol L⁻¹ to 1.0 × 10⁻⁴ mol L⁻¹ using BCA and 6.0 × 10⁻⁷ mol L⁻¹ to 1.2 × 10⁻⁴ mol L⁻¹ using BCS. The achieved analytical frequency was 90 h⁻¹ for all three ligands. The method was successfully employed for NACET determination in pharmaceutical preparations, indicating that this FIA method fulfilled all the essential demands for the determination of NACET in quality control laboratories, as it combined low instrument and reagent costs with a high sampling rate. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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16 pages, 2951 KiB

Open AccessArticle

Sequential Injection System for Analysis of Degree Brix, Orthophosphate and pH in Raw Sugarcane Juice Applicable to Sugar Industry

by Phoonthawee Saetear, Nattinee Saechua and Kamonthip Sereenonchai

Molecules 2021, 26(21), 6484; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26216484 - 27 Oct 2021

Cited by 7 | Viewed by 2613

Abstract

This work presents, for the first time, a new sequential injection analysis (SIA) method to simultaneously analyze degree Brix, orthophosphate and pH in raw cane juice. These key parameters relate to price of harvested sugarcane and quality of cane juice for sugar production. The SIA system employed two detectors: the first detector is a diode-array spectrophotometer, equipped with a regular flow cell, for measurements of degree Brix and orthophosphate. Quantitative of degree Brix (°Bx; ca. % (w/w) sucrose) was based on manipulation of the schlieren effect at the interface between plugs of sample and water. Orthophosphate analysis was carried out based on the molybdenum blue method with significant reduction in consumption of the reagents. Compensation of the schlieren effect from sucrose for determination of orthophosphate was achieved by using a dual-wavelength spectrometric detection. Second detector is a pH-sensing device, called ion-selective field-effect transistors (ISFET). The ISFET is based on the current through the ISFET arising according to the H⁺ concentration in solution. Our developed SIA system provides linear calibration graphs fitting for purpose in analysis of sugarcane juice (pH: 0–14, °Bx: 1.0–7.0 and P₂O₅: 20–200 mg L⁻¹). Simultaneous analysis of sugarcane juice for pH, °Bx and P₂O₅ is carried out within 5 min (12 sample per h). Precision of SIA system is acceptable (RSD < 3%). Our SIA system gave quantitative results insignificantly different, as compared with conventional methods for analysis of pH, °Bx and P₂O₅ in sugarcane juice. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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12 pages, 2844 KiB

Open AccessArticle

Multisyringe Flow Injection Analysis of Tropomyosin Allergens in Shellfish Samples

by Bruno Coulomb, Fabien Robert-Peillard, Najib Ben Ali Gam, Salwa Sadok and Jean-Luc Boudenne

Molecules 2021, 26(19), 5809; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26195809 - 25 Sep 2021

Cited by 1 | Viewed by 1427

Abstract

This paper presents the development and the application of a multisyringe flow injection analysis system for the fluorimetric determination of the major heat-stable known allergen in shrimp, rPen a 1 (tropomyosin). This muscle protein, made up of 284 amino acids, is the main allergen in crustaceans and can be hydrolyzed by microwave in hydrochloric acid medium to produce glutamic acid, the major amino acid in the protein. Glutamic acid can then be quantified specifically by thermal conversion into pyroglutamic acid followed by chemical derivatization of the pyroglutamic acid formed by an analytical protocol based on an OPA-NAC reagent. Pyroglutamic acid can thus be quantified between 1 and 100 µM in less than 15 min with a detection limit of 1.3 µM. The method has been validated by measurements on real samples demonstrating that the response increases with the increase in the tropomyosin content or with the increase in the mass of the shrimp sample. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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11 pages, 1282 KiB

Open AccessArticle

Development of CE-C⁴D Method for Determination Tropane Alkaloids

by Małgorzata Gołąb, Martyna Przybyłowska, Petr Kubáň, Petra Itterheimová and Michał Woźniakiewicz

Molecules 2021, 26(19), 5749; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26195749 - 22 Sep 2021

Cited by 5 | Viewed by 2118

Abstract

A fast method for the determination of tropane alkaloids, using a portable CE instrument with a capacitively coupled contactless conductivity detector (CE-C⁴D) was developed and validated for determination of atropine and scopolamine in seeds from Solanaceae family plants. Separation was obtained within 5 min, using an optimized background electrolyte consisting of 0.5 M acetic acid with 0.25% (w/v) β-CD. The limit of detection and quantification was 0.5 µg/mL and 1.5 µg/mL, respectively, for both atropine and scopolamine. The developed method was validated with the following parameters—precision (CV): 1.07–2.08%, accuracy of the assay (recovery, RE): 101.0–102.7% and matrix effect (ME): 92.99–94.23%. Moreover, the optimized CE-C⁴D method was applied to the analysis of plant extracts and pharmaceuticals, proving its applicability and accuracy. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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10 pages, 2079 KiB

Open AccessArticle

A Simple Minimized System Based on Moving Drops for Antioxidant Analysis Using a Smartphone

by Sutasinee Apichai, Kajorngai Thajee, Thanawat Pattananandecha, Chalermpong Saenjum and Kate Grudpan

Molecules 2021, 26(19), 5744; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26195744 - 22 Sep 2021

Cited by 5 | Viewed by 1670

Abstract

In this paper, a novel antioxidant analysis is proposed using a simple minimized device based on moving drops as solution handling and a smartphone as a detector. This approach is based on the colorimetric determination of the scavenging activity against 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^•), expressed as the half-maximal inhibitory concentration (IC₅₀), vitamin C equivalent antioxidant capacity (VCEAC), and Trolox equivalent antioxidant capacity (TEAC). A small drop of the positive control or the samples moves by eluting an ethanol drop down by the force of gravity to react with a DPPH^• drop in the detection zone. The color change of DPPH^• is monitored by a smartphone camera, and the color signals are processed using Adobe Photoshop software. The magenta-to-yellow ratio was successfully applied to evaluate the percentage of DPPH^• inhibition with no significant difference compared with the reference spectrophotometric method at a confidence level of 95%. The total phenolic content (TPC) was measured using the Folin–Ciocalteu assay. An application to Miang (fermented tea leaf extract) showed the consonant relationship between the scavenging activity of DPPH^• and TPC. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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9 pages, 1886 KiB

Open AccessArticle

Determination of Lead Employing Simple Flow Injection AAS with Monolithic Alginate-Polyurethane Composite Packed In-Valve Column

by Piyanat Issarangkura Na Ayutthaya, Chonnipa Yeerum, Kullapon Kesonkan, Kanokwan Kiwfo, Kate Grudpan, Norio Teshima, Hiroya Murakami and Monnapat Vongboot

Molecules 2021, 26(15), 4397; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26154397 - 21 Jul 2021

Cited by 2 | Viewed by 2171

Abstract

A simple flow injection FlameAAS for lead determination with an alginate-polyurethane composite (ALG-PUC) monolithic in-valve column has been developed. The ALG-PUC monolithic rod was prepared by mixing methylene diphenyl diisocyanate with polyol and sodium alginate with the ratio of 2:1:1 by weight for a 5 min polymerization reaction. It was then put into a column (0.8 cm i.d × 11 cm length) situated in a switching valve for the FI set up. A single standard calibration could be obtained by plotting the loaded µg Pb²⁺ vs. FI response (absorbances). The loaded µg Pb²⁺ is calculated: μg Pb²⁺ = FR_load × LT × C_Pb²⁺, where the FR load is the flow rate of the loading analyte solution (mL min⁻¹), LT is the loading time (min), and C_Pb²⁺ is the Pb²⁺ concentration (µg mL⁻¹). A linear calibration equation was obtained: FI response (absorbances) = 0.0018 [µg Pb²⁺] + 0.0032, R² = 0.9927 for 1–150 µg Pb²⁺, and RSD of less than 20% was also obtained. Application of the developed procedure has been demonstrated in real samples. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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11 pages, 236 KiB

Open AccessArticle

Comprehensive Assessment of Flow and Other Analytical Methods Dedicated to the Determination of Zinc in Water

by Paweł Kościelniak, Paweł Mateusz Nowak, Joanna Kozak and Marcin Wieczorek

Molecules 2021, 26(13), 3914; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26133914 - 26 Jun 2021

Cited by 5 | Viewed by 1895

Abstract

An original strategy to evaluate analytical procedures is proposed and applied to verify if the flow-based methods, generally favorable in terms of green chemistry, are competitive when their evaluation also relies on other criteria. To this end, eight methods for the determination of zinc in waters, including four flow-based ones, were compared and the Red–Green–Blue (RGB) model was exploited. This model takes into account several features related to the general quality of an analytical method, namely, its analytical efficiency, compliance with the green analytical chemistry, as well as practical and economic usefulness. Amongst the investigated methods, the best was the flow-based spectrofluorimetric one, and a negative example was that one involving a flow module, ICP ionization and MS detection, which was very good in analytical terms, but worse in relation to other aspects, which significantly limits its overall potential. Good assessments were also noted for non-flow electrochemical methods, which attract attention with a high degree of balance of features and, therefore, high versatility. The original attempt to confront several worldwide accepted analytical strategies, although to some extent subjective and with limitations, provides interesting information and indications, establishing a novel direction towards the development and evaluation of analytical methods. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

17 pages, 4889 KiB

Open AccessArticle

Simple and Equipment-Free Paper-Based Device for Determination of Mercury in Contaminated Soil

by Hikmanita Lisan Nashukha, Jirayu Sitanurak, Hermin Sulistyarti, Duangjai Nacapricha and Kanchana Uraisin

Molecules 2021, 26(7), 2004; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26072004 - 01 Apr 2021

Cited by 12 | Viewed by 2429

Abstract

This work presents a simple and innovative protocol employing a microfluidic paper-based analytical device (µPAD) for equipment-free determination of mercury. In this method, mercury (II) forms an ionic-association complex of tetraiodomercurate (II) ion (HgI₄²⁻_(aq)) using a known excess amount of iodide. The residual iodide flows by capillary action into a second region of the paper where it is converted to iodine by pre-deposited iodate to liberate I_2(g) under acidic condition. Iodine vapor diffuses across the spacer region of the µPAD to form a purple colored of tri-iodide starch complex in a detection zone located in a separate layer of the µPAD. The digital image of the complex is analyzed using ImageJ software. The method has a linear calibration range of 50–350 mg L⁻¹ Hg with the detection limit of 20 mg L⁻¹. The method was successfully applied to the determination of mercury in contaminated soil and water samples which the results agreed well with the ICP-MS method. Three soil samples were highly contaminated with mercury above the acceptable WHO limits (0.05 mg kg⁻¹). To the best of our knowledge, this is the first colorimetric µPAD method that is applicable for soil samples including mercury contaminated soils from gold mining areas. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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13 pages, 2519 KiB

Open AccessArticle

Development and Validation of an Automated Zone Fluidics-Based Sensor for In Vitro Dissolution Studies of Captopril Using Total Error Concept

by Theano D. Karakosta, Paraskevas D. Tzanavaras and Constantinos K. Zacharis

Molecules 2021, 26(4), 824; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26040824 - 05 Feb 2021

Cited by 1 | Viewed by 1500

Abstract

In the present research, a zone fluidics-based automated sensor for the analysis of captopril in in vitro dissolution samples is reported. Captopril is reacted under flow conditions with Ni(II) (10 mmol L⁻¹) in alkaline medium (0.15% v/v NH₃) to form a stable derivate, which is monitored spectrophotometrically at 340 nm. The chemical and instrumental parameters were carefully investigated and optimized. The validation of the developed method was performed in the range of 5 to 120% of the expected maximum concentration using the accuracy profiles as a graphical decision-making tool. The β-expectation tolerance intervals did not exceed the acceptance criteria of ±10%, which means that 95% of future results will be encompassed in the defined bias limits. The variation of the relative bias ranged between −2.3% and 3.5% and the RSD values for repeatability and intermediate precision were lower than 2.3% in all cases. The limit of detection (LOD), and the lower and the upper limit of quantification (LLOQ, ULOQ) were satisfactory and found to be 1%, 5% and 120% (corresponding to 0.6, 2.78 and 66.67 μg mL⁻¹ in dissolution medium). The developed method was successfully applied for the analysis of captopril in dissolution tests of two commercially available batches. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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Review

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20 pages, 767 KiB

Open AccessReview

Chemical Derivatization in Flow Analysis

by Fábio R. P. Rocha and Elias A. G. Zagatto

Molecules 2022, 27(5), 1563; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27051563 - 26 Feb 2022

Cited by 1 | Viewed by 2021

Abstract

Chemical derivatization for improving selectivity and/or sensitivity is a common practice in analytical chemistry. It is particularly attractive in flow analysis in view of its highly reproducible reagent addition(s) and controlled timing. Then, measurements without attaining the steady state, kinetic discrimination, exploitation of unstable reagents and/or products, as well as strategies compliant with Green Analytical Chemistry, have been efficiently exploited. Flow-based chemical derivatization has been accomplished by different approaches, most involving flow and manifold programming. Solid-phase reagents, novel strategies for sample insertion and reagent addition, as well as to increase sample residence time have been also exploited. However, the required alterations in flow rates and/or manifold geometry may lead to spurious signals (e.g., Schlieren effect) resulting in distorted peaks and a noisy/drifty baseline. These anomalies can be circumvented by a proper flow system design. In this review, these aspects are critically discussed mostly in relation to spectrophotometric and luminometric detection. Full article

(This article belongs to the Special Issue Modern Flow Analysis II)

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