Flow-batch analysis

Spectrophotometric determination of phosphate using sodium molybdate and its field application to the simultaneous measurement with ammonium in seawater

Phosphate (PO43-) and ammonium (NH4+), two major components of the phosphorus and nitrogen cycles, respectively, play vital roles in aquatic ecosystems. Very few studies have reported methods for the simultaneous determination of PO43- and NH4+ in seawater. Additionally, when ammonium molybdate solution was employed as a chromogenic reagent for the simultaneous determination of both PO43- and NH4+ in a single analysis system, there was a possibility of cross-contamination. In this study, a spectrophotometric method for the simultaneous determination of PO43- and NH4+ in seawater was established. To prevent interference from ammonium molybdate, sodium molybdate was used in the phosphomolybdenum blue reaction, yielding satisfactory results. The indophenol blue method was used for the determination of NH4+. The reagent concentrations for the determination of PO43- and NH4+ were optimized, and the effect of salinity on the determination was investigated. The effect of salinity can be effectively ignored by setting the residence time for the reaction. The developed method was validated, with limit of detection observed to be 0.02 and 0.06 μM for PO43- and NH4+, respectively. The working range of the method was observed to be 15 μM for PO43- and 12 μM for NH4+, with the relative standard deviations (1 μM, n = 20) of 2.5 % and 1.9 %. The results obtained using the proposed method were in agreement with the reference method. Furthermore, the proposed method was successfully applied for the on-site monitoring of diurnal variation of PO43- and NH4+ in surface seawater.

A compact flow-batch analyzer equipped with mini piezoelectric pumps and image-based volume control

Flow-batch analyzers demand meticulous volume control for successful application in quantitative determinations, with the incorporation of high-efficiency pumps and valves recommended for their construction. However, routine recalibrations are frequently needed to uphold the accuracy of manipulated volumes, highlighting the value of exploring new alternatives for volume control and measurement, with less sophisticated apparatus. In this work a compact Flow-Batch (FB) analyzer with piezoelectric micropumps was developed to perform standard addition calibration, incorporating image-based detection to perform volume control. The instrument was evaluated by quantitatively determining Cr(VI), NO2-, and Fe(II) in water samples, combining RGB-based colorimetry with established spectrophotometric methods. The results demonstrate that a comprehensive analysis with five standard additions can be completed in approximately 10 minutes, maintaining a suitable linear correlation (R2 > 0.99) and precision (0.4 ≤ RSD ≤ 12.1%). Recoveries between 90% and 105% for analyte levels below Brazilian regulatory limits underscore the accuracy of the proposed approach. The study confirms that digital image monitoring provides an elegant alternative for controlling solution volumes in FB systems, eliminating the need for more robust pumps with precisely controlled flow rates.

Relevant insights and concepts overlooked throughout the development of flow analysis. A tutorial

The conceptual expansion, fast development, and general acceptance of flow analysis are consequence of its adherence to the principles of green and white analytical chemistry, and chemical derivatization plays an essential role in this context. Through the flow analysis development, however, some of its potentialities and limitations have been overlooked. This is more evident when the involved modifications in flow rates, timing and/or manifold architecture deteriorate the analytical signals. These aspects have not always been systematically investigated, and are addressed here in relation to flow analyzers with UV-Vis spectrophotometric detection. Novel strategies for solution handling, guidance for dealing with the aforementioned analytical signal deterioration, and an alternative possibility for exploiting differential aspiration are presented. The concept of blank reagent carrier stream is proposed.

A miniaturized flow batch chemical vapor generation system for Hg determination in fish by ICP-MS

A new flow batch (FB) system for chemical vapor generation (CVG) is proposed for mercury (Hg) determination in fish. An inductively coupled plasma mass spectrometer was used as a detector. Low-cost peristaltic mini pumps were used to propel the solutions and different configurations of FB systems (reactor/gas/liquid separator) were studied. The proposed configuration of the FB-CVG system allows good sensitivity, low limit of detection (LOD) and low consumption of reagents and sample solutions. In summary, only 1 mL of reductant, 1 mL of acid and 0.16 mL of sample are needed. The proposed method has good linearity, precision (better than 5 %), LOD of 0.008 μg g-1 and LOQ of 0.012 μg g-1, and high sample throughput, allowing 90 measurements/h. The accuracy of the method was evaluated through the analysis of a certified reference material (DOLT-4 Dogfish Liver), whose result is in good agreement with certified value (t-test with 95 % confidence level) and the quantification limit meets current legislations, of 1.0 μg g-1 (Brazil) and 0.3 μg g-1 (EU). In addition, analyte recovery test was done, where Hg recovery was better than 95 %, demonstrating the good analytical performance of the method. To demonstrate the applicability of the method, five samples of fish tissue (muscle) were analyzed. The proposed FB-CVG system, in addition to being low cost, is robust and requires only the volume of reagents necessary for Hg vapor generation, producing a very low amount of waste. It can be concluded that the proposed system can be used for routine analysis for Hg determination in fish tissue. It is worth noting that with the appropriate adjustments, the system can be coupled to different Hg detectors.

Consecutive spectrophotometric determination of phosphate and silicate in a sequential injection lab-at-valve flow system

A new highly sensitive and selective sequential injection lab-at-valve spectrophotometric method for the consecutive determination of silicate and phosphate is described. The proposed method is based on the formation of specific ion-association complexes (IAs) of 12-heteropolymolybdates of phosphorus and silicon (12-MSC) with Astra Phloxine. The addition of an external reaction chamber (RC) to the SIA manifold made it possible to significantly improve the conditions for the formation of the analytical form used. The formation of the IA took place in the RC; the solution is mixed by passing an air flow through it. The interfering effect on the determination of phosphate from silicate was completely eliminated by choosing an acidity at which the rate of 12-MSC formation is very low. The use of secondary acidification in the determination of silicate led to the complete exclusion of the influence of phosphate. The tolerable ratio of phosphate to silicate and vice versa is about 100-times, which allows the analysis of most real samples without the use of masking agents or complex separation steps. The determination ranges are 3.0-60 μg L^-1 for phosphate as P(V) and 2.8-56 μg L^-1 for silicate as Si(IV) at a throughput of 5 samples h^-1. The detection limits are 5.0 and 3.8 μg L^-1 for phosphate and silicate, respectively. Silicate and phosphate were determined in the tap water, river water, mineral water, main water of the Krivoy Rog (Ukraine) region, and the certified reference material of carbon steel.

Development of a low-cost semi-automated robotic orthophosphate system for batch analysis

Monitoring the level of nutrients in soil and their availability for crops can be time-consuming or require expensive instrumentation. This work describes a low-cost (<€500) portable, semi-automated colourimetric orthophosphate (PO₄^3-) analyser supplemented with 3D printed parts. Colour development was based on the phosphomolybdenum blue formation coupled with spectrophotometric detection using a low-cost LED-photodiode assembly. The batch analysis technique required only minimal autonomous additions of reagents to the reaction vessel. In addition, the reaction time was reduced with vigorous automated stirring of the small quantity of reactants. Continuous monitoring of the absorbance throughout the reaction also decreased contact time, eliminating the prerequisite of a blank and warm-up time, customarily associated with colourimetric measurements. The semi-automated Robotic Orthophosphate System (saROS) has a linear dynamic range between 10-750 μg L^-1 P-PO₄^3-, and a limit of detection of 3 μg L^-1 P-PO₄^3- with good repeatability (RSD of 2.4%). In addition to portability and low cost, the prototype is an accurate and reproducible device for measuring phosphorus in aquatic ecosystems and soil extracts.

Lab-In-Syringe automation of deep eutectic solvent-based direct immersion single drop microextraction coupled online to high-performance liquid chromatography for the determination of fluoroquinolones

Lab-In-Syringe direct immersion single drop microextraction is proposed as an automated sample pretreatment methodology and coupled online to HPLC with fluorescence detection for the determination of fluoroquinolones in environmental waters. For the first time, a drop of a natural deep eutectic solvent (NADES), synthesized from hexanoic acid and thymol, has been used as an extractant in automated single-drop microextraction. The extraction procedure was carried out within the 5 mL void of an automatic syringe pump. A 9-position head valve served the aspiration of all required solutions, air, waste disposal, and hyphenation with the HPLC instrument. Sample mixing during extraction was done by a magnetic stirring bar placed inside the syringe. Only 60 μL of NADES were required omitting toxic classical solvents and improving the greenness of the proposed methodology. By direct injection, linear working ranges between 0.1 and 5 μg L^-1 were achieved for all fluoroquinolones. The limit of quantification values and enrichment factors ranged from 20 ng L^-1 to 30 ng L^-1 and 35 to 45, respectively. Accuracies obtained from the analysis of spiked surface water and wastewater treatment plant effluent analysis at two concentration levels (0.5 and 4 μg L^-1) ranged from 84.6% to 119.7%, with RSD values typically <3%.

Chemical Derivatization in Flow Analysis

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.

Large-scale flow analysis: From repetitive assays to expert analyzers

Flow analysis is usually associated with repetitive assays, as all samples of a batch are generally handled in the same way. By exploiting computer-controlled devices (e.g. pumps, valves, injectors, commuters, and samplers), this scenario has been expanded, as a proper manifold dimensioning can be set for each sample. Initially, this dimensioning relied on previous information about each sample, added to the operating software prior to analysis of a given sample lot. Further, real-time decisions relying on feedback mechanisms started to be exploited for improving the analytical figures of merit, simplifying the laboratory management, and allowing real-time system optimization and fault detection. This is the essence of the expert flow analyzers, which involve manifold re-dimensioning by means of flow/manifold programming, often relying on multicommutation. The development of flow analysis from repetitive to real-time defined assays, the involved terminology, and trends on further development are highlighted in this review. Applications involve segmented and unsegmented flow analysis of agronomical, clinical, environmental, industrial, pharmaceutical, and geological samples.

Flow-Batch Sample Preparation for Fractionation of the Stress Signaling Phytohormone Salicylic Acid in Fresh Leaves

Salicylic acid (SA) is an important stress signaling phytohormone and plays an essential role in physiological processes in plants. SA fractionation has been carried out batchwise, which is not compatible with the high analytical demand in agronomical studies and increases susceptibility to analytical errors. In this context, a novel flow-batch sample preparation system for SA fractionation on fresh plant leaves was developed. It was based on microwave-assisted extraction with water and conversion of the conjugated species to free SA by alkaline hydrolysis. Free and total SA were quantified by fluorimetry after separation by sequential injection chromatography in a C18 monolithic column. The proposed procedure is directly applicable to plant leaves containing up 16 mg kg^-1 SA, with a limit of detection of 0.1 mg kg^-1 of SA, coefficient of variation of 3.0% (n = 10), and sampling rate of 4 samples h^-1. The flow-batch sample preparation system was successfully applied to SA fractionation in sugarcane, corn, and soybean leaves without clogging or increasing in backpressure. The proposed approach is simple, less time-consuming, and more environmentally friendly in comparison to batchwise procedures.

The Automation Technique Lab-In-Syringe: A Practical Guide

About eight years ago, a new automation approach and flow technique called "Lab-In-Syringe" was proposed. It was derived from previous flow techniques, all based on handling reagent and sample solutions in a flow manifold. To date Lab-In-Syringe has evidently gained the interest of researchers in many countries, with new modifications, operation modes, and technical improvements still popping up. It has proven to be a versatile tool for the automation of sample preparation, particularly, liquid-phase microextraction approaches. This article aims to assist newcomers to this technique in system planning and setup by overviewing the different options for configurations, limitations, and feasible operations. This includes syringe orientation, in-syringe stirring modes, in-syringe detection, additional inlets, and addable features. The authors give also a chronological overview of technical milestones and a critical explanation on the potentials and shortcomings of this technique, calculations of characteristics, and tips and tricks on method development. Moreover, a comprehensive overview of the different operation modes of Lab-In-Syringe automated sample pretreatment is given focusing on the technical aspects and challenges of the related operations. We further deal with possibilities on how to fabricate required or useful system components, in particular by 3D printing technology, with over 20 different elements exemplarily shown. Finally, a short discussion on shortcomings and required improvements is given.

Photogeneration of silver nanoparticles induced by UV radiation and their use as a sensor for the determination of chloride in fuel ethanol using a flow-batch system

Photogeneration of silver chloride nanoparticles (AgCl-NPs) in fuel ethanol was used as a sensor for the spectrophotometric determination of chloride. A low-power UV radiation source (germicidal lamp) was placed close to a flow-batch chamber and a 3D-built support for the reaction chamber was used to couple fiber optic cables in the orthogonal direction with the UV-lamp beam, allowing the monitoring of nanoparticle formation in real-time using a spectrophotometer. The nanoparticles were characterized via high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and UV-vis spectroscopy. Most of the particles exhibited a spherical shape with an average diameter of 18 nm. The absorbance maximum was observed at 440 nm and was used for chloride determination in fuel ethanol. Under the optimized working conditions, the system exhibited a linear response from 0.05 to 0.8 mg L^-1 chloride, with a limit of detection (95%) and coefficient of variation (n = 8) were estimated to be 12 μg L^-1 chloride and 2.2%, respectively. The intra- and inter-day precisions (coefficient of variation) were 2.4% and 2.8%, respectively. This working range (0.05-0.8 mg L^-1) for the determination of chloride at low concentrations met the limit required by Brazilian legislation (limit of 1.0 mg kg^-1). Analyses of fuel ethanol were performed without sample treatment and the obtained results were compared with those obtained by ion-chromatography. No significant differences were observed between the two methods at the 95% confidence level.

Development of an Integrated Syringe-Pump-Based Environmental-Water Analyzer ( iSEA) and Application of It for Fully Automated Real-Time Determination of Ammonium in Fresh Water

The development of a multipurpose integrated syringe-pump-based environmental-water analyzer ( iSEA) and its application for spectrophotometric determination of ammonium is presented. The iSEA consists of a mini-syringe pump equipped with a selection valve and laboratory-programmed software written by LabVIEW. The chemistry is based on a modified indophenol method using o-phenylphenol. The effect of reagent concentrations and sample temperatures was evaluated. This fully automated analyzer had a detection limit of 0.12 μM with sample throughput of 12 h^-1. Relative standard deviations at different concentrations (0-20 μM) were 0.23-3.36% ( n = 3-11) and 1.0% ( n = 144, in 24 h of continuous measurement, ∼5 μM). Calibration curves were linear ( R² = 0.9998) over the range of 0-20 and 0-70 μM for the detection at 700 and 600 nm, respectively. The iSEA was applied in continuous real-time monitoring of ammonium variations in a river for 24 h and 14 days. A total of 1802 samples were measured, and only 0.4% was outlier data (≥3 sigma residuals). Measurements of reference materials and different aqueous samples ( n = 26) showed no significant difference between results obtained by reference and present methods. The system is compact (18 cm × 22 cm × 24 cm), portable (4.8 kg), and robust (high-resolution real-time monitoring in harsh environments) and consumes a small amount of chemicals (20-30 μL/run) and sample/standards (2.9 mL/run).

Lab-In-Syringe automation of stirring-assisted room-temperature headspace extraction coupled online to gas chromatography with flame ionization detection for determination of benzene, toluene, ethylbenzene, and xylenes in surface waters

Online coupling of Lab-In-Syringe automated headspace extraction to gas chromatography has been studied. The developed methodology was successfully applied to surface water analysis using benzene, toluene, ethylbenzene, and xylenes as model analytes. The extraction system consisted of an automatic syringe pump with a 5 mL syringe into which all solutions and air for headspace formation were aspirated. The syringe piston featured a longitudinal channel, which allowed connecting the syringe void directly to a gas chromatograph with flame ionization detector via a transfer capillary. Gas injection was achieved via opening a computer-controlled pinch valve and compressing the headspace, upon which separation was initialized. Extractions were performed at room temperature; yet sensitivity comparable to previous work was obtained by high headspace to sample ratio V_HS/V_Sample of 1.6:1 and injection of about 77% of the headspace. Assistance by in-syringe magnetic stirring yielded an about threefold increase in extraction efficiency. Interferences were compensated by using chlorobenzene as an internal standard. Syringe cleaning and extraction lasting over 10 min was carried out in parallel to the chromatographic run enabling a time of analysis of <19 min. Excellent peak area repeatabilities with RSD of <4% when omitting and <2% RSD when using internal standard corrections on 100 μg L^-1 level were achieved. An average recovery of 97.7% and limit of detection of 1-2 μg L^-1 were obtained in analyses of surface water.

A soft material for chromium speciation in water samples using a chemiluminescence automatic system

A soft material formed by multiwall carbon nanotubes and 1-butyl-3-methyl imidazolium chloride was used as sorbent material to perform the chromium speciation in natural waters. This soft material was not yet used for the speciation of metals as chromium. Thus, a multicommutated flow system containing a minicolumn packed with the soft material was designed. The procedure was based on the capacity of the sorbent to retain Cr(VI) as Cr₂O₇⁼ and allow to pass Cr(III) through the column. Then, a fully automated flow-batch analysis system was developed to quantify both species using chemiluminescence detection. Thus, Cr(III) was determined as catalyst of the luminol and hydrogen peroxide reaction and Cr(VI) as oxidant of luminol reaction. This represents a new approach because the oxidation of luminol using Cr₂O₇⁼ has not been reported in literature. The variables of the two systems were optimized. The limits of detection were 1.4 μg L^-1 for Cr(VI) and 4.0 μg L^-1 for Cr(III). The precision of the method was 3.8% and 7.0% for Cr(VI) and Cr(III), respectively. The present method was applied to real water samples with recoveries between 95% and 107%. Besides, these results were in accordance with those obtained using inductive coupled plasma-optical emission spectrometry technique.

Fully-automated magnetic stirring-assisted lab-in-syringe dispersive liquid–liquid microextraction for the determination of arsenic species in rice samples

Fully-automated magnetic stirring-assisted lab-in-syringe dispersive liquid–liquid microextraction (MAS-LIS-DLLME), combined with graphite furnace atomic absorption spectrometry (GFAAS) was developed for the fast and efficient separation and preconcentration of trace levels of inorganic arsenic species in rice samples. This totally automated analytical procedure combines the advantages of lab-in-syringe flow system and dispersive liquid–liquid microextraction (DLLME) aiming at separation of trace arsenite and arsenate species from natural matrix for the first time. With a single syringe pump that is coupled with a multiposition valve, the whole lab-in-syringe microextraction process including cleaning, mixing, microextraction, phase separation, and target analyte collection was implemented in a fully-automated way. Significant factors of the MAS-LIS-DLLME method were sample acidity, concentration of the chelating agent, amounts of ionic liquids (ILs), aspiration speed and matrix interference. Using the present method, the limits of detection (LODs) for As(v) was 0.005 μg L⁻¹. The relative standard deviation (RSDs) for seven replicate measurements of 2.0 μg L⁻¹ of As(v) was 3.7%. The linear dynamic range (LDR) was 0.04–5.0 μg L⁻¹ and the determination coefficients was 0.9990. Under the optimum conditions, the developed totally automated analytical procedure was successfully applied for the trace arsenite and arsenate species studies in natural rice samples and standard reference materials with satisfactory results.

The schematic of the MAS-LIS-DLLME system. D, detection system; SP, syringe pump; SV, three-way solenoid valve; W, waste; MPV, multiposition valve.

Online coupling of fully automatic in-syringe dispersive liquid-liquid microextraction with oxidative back-extraction to inductively coupled plasma spectrometry for sample clean-up in elemental analysis: A proof of concept

A proof of concept of a novel automatic sample cleanup approach for metal assays in troublesome matrixes as a front-end sample pre-treatment to inductively coupled plasma optical emission spectroscopy - ICP-OES - is herein presented. Target metals, namely, copper, lead, and cadmium were complexed in-system quantitatively using ammonium pyrrolidine dithiocarbamate (APDC) and transferred into a minute volume of toluene as extractant employing lab-in-syringe magnetic stirring-assisted dispersive liquid-liquid microextraction (LIS-MSA-DLLME). After discharge of the sample, the analytes were back-extracted into nitric acid and injected on-line into ICP-OES. To promote and expedite this process in-syringe, advantage was taken from oxidative decomposition of the chelate by potassium iodate, reported in this article for the first time. Experimental conditions for LIS-MSA-DLLME were optimized by Box-Benkhen multivariate analysis using the geometric mean of analyte recoveries as the desirability function. Times of extraction and back-extraction of 300s and 100s, respectively, pH 5.5 at 30mmol/L acetate, 300µL of extraction solvent, and 600µmol/L of APDC were finally applied. Online interfacing to ICP-OES for back-extract analysis yielded average repeatabilities for Cd, Cu, and Pb of 2.9%, 3.5%, and 3.5% with limits of detections (3s) of 1.9, 1.4, and 5.6ng/mL, respectively. Oxidative back-extraction was proven reliable for the determination of metal species in coastal seawater, surrogate digestive fluids and soil leachates with recovery values for Cd, Cu, and Pb ranging from 90% to 118%, 68% to 104%, and 86% to 112%, respectively.

Sulphate radical generation through interaction of peroxymonosulphate with Co(II) for in-line sample preparation aiming at spectrophotometric flow-based determination of phosphate and phosphite in fertilizers

An advanced oxidative process relying on the interaction of peroxymonosulphate and cobalt(II) was implemented for generating the sulphate radicals in flow analysis, in order to accomplish in-line sample preparation thus improving the spectrophotometric determination of phosphate and phosphite in liquid foliar fertilizers. To this end, a flow-batch system with a heated chamber was designed. The sample was handled twice, with and without the step of phosphite oxidation to phosphate, and the formed orthophosphate was quantified after interaction with the vanadate-molybdate reagent. Phosphite was determined as the difference in analytical signals corresponding to sample handling with and without the oxidation step. Influence of Co(II) on the peroxymonosulphate activation, reagent concentrations and added volumes, acidity, temperature and heating time were investigated like aiming at to improve analytical recovery and measurement repeatability, as well as the and system ruggedness. The 6.6-20.0mgL(-1) P2O5 standards were in-line prepared from a single stock solution. Detection limits were estimated as 0.8 and 0.1mgL(-1) for P2O5 and P-PO4. Twenty-four samples are were run per hour, and results are were in agreement with those obtained by the official procedure.

Recent advances in flow injection analysis

A dynamic development of methodologies of analytical flow injection measurements during four decades since their invention has reinforced the solid position of flow analysis in the arsenal of techniques and instrumentation of contemporary chemical analysis.

Implementation of an automatic and miniature on-line multi-parameter water quality monitoring system and experimental determination of chemical oxygen demand and ammonia-nitrogen

An automatic, miniature and multi-parameter on-line water quality monitoring system based on a micro-spectrometer is designed and implemented. The system is integrated with the flow-batch analysis and spectrophotometric detection method. The effectiveness of the system is tested by measuring chemical oxygen demand (COD) and ammonia-nitrogen in water. The results show that the modified system provides a cost-effective, sensitive, reproducible and reliable way to measure COD and ammonia-nitrogen in water samples with automatic operation and low toxic chemical consumption. In addition, the experiment results show that the relative error of the system is less than 10%, the limit of detection is 2 mg/L COD and 0.032 mg/L ammonia-nitrogen, respectively, and the relative standard deviation was 6.6% at 15.0 mg/L COD (n = 7) and 5.0% at 0.300 mg/L ammonia-nitrogen (n = 7). Results from the newly designed system are consistent with the data collected through the Chinese national standard analysis methods.