Automatic pressure-assisted dual-headspace gas-liquid microextraction. Lab-in-syringe platform for membraneless gas separation of ammonia coupled with fluorimetric sequential injection analysis

Automated Determination of Ammonium at Nanomolar Levels in Seawater by Coupling Lab-in-Syringe with Highly Sensitive Light-Emitting-Diode-Induced Fluorescence Detection

Ammonium concentrations in marine environments are typically found at the nanomolar level, and due to the transformation tendencies of ammonium species, there is a growing demand for a simple, convenient, and highly sensitive automated method for seawater ammonium quantification. Such a method should be suitable for in situ applications without the need for additional enrichment or extraction steps. To meet this need, we developed a highly sensitive automated flow system that integrates a portable LED-induced fluorescence detector, incorporating the novel AccuOpt 2000 photodetector and lab-in-syringe technology, enabling direct fluorescence measurement of trace ammonium in seawater. Key system parameters were optimized, and the seawater matrix effects were assessed. The system achieved a detection limit of 0.90 nmol/L, with a linear range up to 400 nmol/L and relative standard deviations of 0.94% (100 nmol/L, n = 21). The sensitivity was nearly ten-fold higher than those of conventional approaches. Seawater matrix effects, including carryover, were negligible. The system's measurements correlated well with the indophenol blue spectrophotometric method. These results underscore the system's strong potential for in situ/on-site monitoring of trace ammonium levels in marine environments.

Development and Characterization of a Sol-Gel-Functionalized Glass Carbon Electrode Probe for Sensing Ultra-Trace Amounts of NH3 and NH4+ in Water

This study centers on the development and characterization of an innovative electrochemical sensing probe composed of a sensing mesoporous functional sol-gel coating integrated onto a glassy carbon electrode (sol-gel/GCE) for the detection of NH3 and/or NH4+ in water. The main interest for integrating a functional sol-gel coating onto a GCE is to increase the selective and sensing properties of the GCE probe towards NH3 and/or NH4+ ions. The structure and surface morphology of the newly developed sol-gel/GCE probe were characterized employing scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and Fourier-transform infrared (FTIR), while the electrochemical sensing properties were evaluated by Berthelot's reaction, cyclic voltammetry (CV), and adsorptive square wave-anodic striping voltammetry (Ads SW-ASV). It is shown that the newly developed sol-gel coating is homogeneously deposited on the GCE with a sub-micron and uniform thickness close to 630 nm and a surface roughness of 25 nm. The sensing testing of the sol-gel/GCE probe showed limits of detection and limits of quantitation of 1.7 and 5.56 nM of NH4+, respectively, as well as a probe sensitivity of 5.74 × 10-1 μA/μM cm-2. The developed probe was fruitfully validated for the selective detection of NH3/NH4+ in fresh and sea water samples. Computed Student texp (0.45-1.25) and Fexp (1.69-1.78) (n = 5) tests were less than the theoretical ttab (2.78) and Ftab (6.39) at 95% probability.

Headspace Microextraction. A Comprehensive Review on Method Application to the Analysis of Real Samples (from 2018 till Present)

This work describes current trends in the development of headspace microextraction methods. The main trends in the selection of detection techniques used in combination with microextraction and preferences in the selection of headspace liquid-phase microextraction (HS-LPME) or headspace solid-phase microextraction (HS-SPME) methods, depending on the analytes and their quantity, are also briefly presented. In the main part of the work, on the basis of current journal literature, headspace microextraction analytical methods used for the determination of various inorganic and organic analytes are classified and compared over the last five years. The work also reflects the current modifications of techniques and approaches proposed for these microextraction methods.

An integrated automatic lab-in-syringe sol-gel coated foam microextraction platform as a front-end to high performance liquid chromatography for the migration studies of bisphenol A

The proof-of-concept of an integrated automatic foam microextraction lab-in-syringe (FME-LIS) platform coupled to high performance liquid chromatography is presented. Three different sol-gel coated foams were synthesized, characterized, and conveniently packed inside the glass barrel of the LIS syringe pump, as an alternative approach for sample preparation, preconcentration and separation. The proposed system efficiently combines the inherent benefits of lab-in-syringe technique, the good features of sol-gel sorbents, the versatile nature of foams/sponges, as well as the advantages of automatic systems. Bisphenol A (BPA) was used as model analyte, due to the increasing concern for the migration of this compound from household containers. The main parameters that affect the extraction performance of the system were optimized and the proposed method was validated. The limit of detection for BPA were 0.5 and 2.9 μg L^-1, for a sample volume of 50 mL and 10 mL, respectively. The intra-day precision was <4.7% and the inter-day precision was <5.1% in all cases. The performance of the proposed methodology was evaluated for the migration studies of BPA using different food simulants, as well as for the analysis of drinking water. Good method applicability was observed based on the relative recovery studies (93-103%).

Real-time underway measurement of ammonium in coastal and estuarine waters using an automated flow analyzer with hollow fiber membrane contactor

Ammonium (NH₄⁺) is an important parameter for aquatic ecosystems. To date, continuous and underway acquisition of NH₄⁺ in coastal and estuarine waters has been challenged by the strongly varying salinity and complex matrices in these waters. To address these issues, a hollow fiber membrane contactor (HFMC) was constructed and incorporated in flow injection analysis (FIA) to achieve online separation/preconcentration of NH₄⁺ in water. In the FIA-HFMC system, NH₄⁺ in the water sample was converted into NH₃ under alkaline conditions in the donor channel. The generated NH₃ diffused across the membrane and was absorbed in an acid solution in the acceptor channel. The resultant NH₄⁺ in the acceptor was then quantified based on a modified indophenol blue (IPB) method. Parameters affecting the performance of the FIA-HFMC-IPB system were evaluated and optimized. Under the optimized conditions, the proposed system exhibited a limit of detection of 0.11 μmol L^-1, with relative standard deviations of 1.0-1.9 % (n = 7), and a good linear response (R² = 0.9989) for the calibration in the field with NH₄⁺ standards in the range of 0.40-80 μmol L^-1. The proposed system was applied to a shipboard underway measurement of NH₄⁺ in a two-day cruise in the Jiulong River Estuary-Xiamen Bay, China. A good agreement was observed between measurements from the proposed system and those from manual sampling and laboratory analysis. Both laboratory and field results demonstrated that the system was free of salinity effect and interference from organic nitrogen compounds. The system also showed excellent stability and reliability during a 16-day observation. This work suggests that the proposed FIA-HFMC-IPB system is applicable for the underway measurement of NH₄⁺ in water, especially for estuarine and coastal waters with varying salinity and complex matrices.

Ammonium determination by merging-zone flow injection analysis and a naphthalene-based fluorescent probe

This paper discusses the first-time study of a naphthalene-based fluorescent probe-naphthalene-2,3-dicarboxaldehyde (NDA), in combination with merging-zone flow injection analysis for the automated fluorescence determination of ammonium. The determination was contingent on detecting the fluorescent product of NDA-SO₃^2--NH₄⁺, which has maximum excitation and emission wavelengths of 508 nm and 564 nm, respectively. And the possible sensing mechanism of NDA-NH₄⁺ was proposed. The effects of the reaction parameters, including reagent concentrations, reaction flow rate, coil length, reaction temperature, and pH were optimized. Under optimal conditions, this method afforded a sampling rate of 8 h^-1, a limit of detection of 0.045 μmol L^-1, and RSD of 3.68% (n = 14) with 1.50 μmol L^-1 ammonium, and the calibration range was 0.045-6.00 μmol L^-1. Examination of the organic nitrogen interference confirmed that the method attracts minimal interference from organic nitrogen, and the stability of the NDA reagent facilitates its field application. Other exhibited advantages include low reagent consumption and high automation; the method has been utilized in the successful determination of ammonium in freshwater and rainwater. The development of NDA applications for ammonium determination also provides more options for fluorometric determination of ammonium.

A novel automatic flow-batch extraction induced by emulsion breaking platform for on-line copper determination in edible oil samples by atomic absorption spectrometry

A novel automatic flow-batch platform coupled with atomic spectrometry for on-line acidic extraction induced by emulsion breaking with heating (FB-EIEBH) for metal determination in edible oils (corn, sunflower and olive oil), was developed for the first time. The proposed system was demonstrated for copper determination in conjunction with flame atomic absorption spectrometry. The extraction of metal is accomplished after the oil emulsification with an aqueous solution consisted of Triton X-114 and nitric acid, in an on-line programmed manner. All the main parameters affecting the extraction procedure, such as oil dilution, type and concentration of surfactant and nitric acid as well as temperature and time for the emulsion breaking and phase separation, have been investigated and optimized. A mixture of oil/xylene at 10:2 proportion was found to be appropriate to use in the flow manifold. Optimum conditions were verified employing 8.0 mL of oil sample, 990 μL of extractant solution containing 10.0% m/v Triton X-114 and 10.0% v/v HNO₃. Emulsion breaking and phases separation were completed at temperature 90 °C, and time 300 s. The detection and quantification limit for copper determination was found to be 5.8 μg L^-1 and 19.3 μg L^-1, employing aqueous standards, which are proved to produce similar performance characteristics with oil-based standards. Recovery tests were executed by appropriate additions of oil-based standard solution of copper and the recoveries ranged between 94.2 and 102.4%.

Home-Made Membraneless Vaporization Gas-Liquid Separator for Colorimetric Determination of Ethanol in Alcoholic Beverages

This work utilized the simplicity of a so-called membraneless vaporization (MBL-VP) unit as a gas separator for the colorimetric determination of ethanol in alcoholic beverages. A beverage sample with a volume of 1 mL was directly injected into a small container which was hung from a lid inside a closed 40 mL reused glass bottle without pretreatment such as distillation. An acidified potassium dichromate (Cr₂O₇ ^2-) acceptor solution, preadded to the glass bottle, was reduced to Chromium (III) ion by the diffusion of vaporized ethanol from the sample. After 5 min, the absorbing solution was collected for colorimetric detection at 590 nm. The unit manually quantifies ethanol in the range 1.0-90% (v/v) with satisfactory interday precision but without matrix effect (recovery 89-109%). The method was validated with the conventional distillation/pycnometer method which showed no significant difference of ethanol contents between those two methods and the declared values of 12 alcoholic beverages, indicating sufficient accuracy. Analyses of alcoholic beverages using this method were successful with benefits of simplicity, cheapness, and less energy consumption.

Flow-Injection Methods in Water Analysis-Recent Developments

Widespread demand for the analysis and control of water quality and supply for human activity and ecosystem sustainability has necessitated the continuous improvement of water analysis methods in terms of their reliability, efficiency, and costs. To satisfy these requirements, flow-injection analysis using different detection methods has successfully been developed in recent decades. This review, based on about 100 original research papers, presents the achievements in this field over the past ten years. Various methodologies for establishing flow-injection measurements are reviewed, together with microfluidics and portable systems. The developed applications mostly concern not only the determination of inorganic analytes but also the speciation analysis of different elements, and the determination of several total indices of water quality. Examples of the determination of organic residues (e.g., pesticides, phenolic compounds, and surfactants) in natural surface waters, seawater, groundwater, and drinking water have also been identified. Usually, changes in the format of manual procedures for flow-injection determination results in the improvement of various operational parameters, such as the limits of detection, the sampling rate, or selectivity in different matrices.

Direct immersion single-drop microextraction of semi-volatile organic compounds in environmental samples: A review

Single-drop microextraction (SDME) techniques are efficient approaches to pretreatment of aqueous samples. The main advantage of SDME lies in the miniaturization of the solvent extraction process, minimizing the hazards associated with the use of toxic organic solvents. Thus, SDME techniques are cost-effective, and represent less harm to the environment, subscribing to green analytical chemistry principles. In practice, two main approaches can be used to perform SDME - direct immersion (DI)-SDME and headspace (HS)-SDME. Even though the DI-SDME has been shown to be quite effective for extraction and enrichment of various organic compounds, applications of DI-SDME are normally more suitable for moderately polar and non-polar semi-volatile organic compounds (SVOCs) using organic solvents which are immiscible with water. In this review, we present a historical overview and current advances in DI-SDME, including the common analytical tools which are usually coupled with DI-SDME. The review also focuses on applications concerning SVOCs in environmental samples. Currents trends in DI-SDME and possible future direction of the procedure are discussed.

Dual-Purpose Photometric-Conductivity Detector for Simultaneous and Sequential Measurements in Flow Analysis

This work presents a new dual-purpose detector for photometric and conductivity measurements in flow-based analysis. The photometric detector is a paired emitter-detector diode (PEDD) device, whilst the conductivity detection employs a capacitively coupled contactless conductivity detector (C4D). The flow-through detection cell is a rectangular acrylic block (ca. 2 × 2 × 1.5 cm) with cylindrical channels in Z-configuration. For the PEDD detector, the LED light source and detector are installed inside the acrylic block. The two electrodes of the C4D are silver conducting ink painted on the PEEK inlet and outlet tubing of the Z-flow cell. The dual-purpose detector is coupled with a sequential injection analysis (SIA) system for simultaneous detection of the absorbance of the orange dye and conductivity of the dissolved oral rehydration salt powder. The detector was also used for sequential measurements of creatinine and the conductivity of human urine samples. The creatinine analysis is based on colorimetric detection of the Jaffé reaction using the PEDD detector, and the conductivity of the urine, as measured by the C4D detector, is expressed in millisiemens (mS cm-1).

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.

Automatic On-Line Purge-and-Trap Sequential Injection Analysis for Trace Ammonium Determination in Untreated Estuarine and Seawater Samples

An innovative automatic purge-and-trap (P&T) system coupled with fluorimetric sequential injection (SI), for the on-line separation and preconcentration of volatile compounds, is presented. The truth of concept is demonstrated for the ammonium fluorimetric determination in environmental water samples with complex matrices without any pretreatment. The P&T flow system comprises a thermostated purge-vessel where ammonium is converted into gaseous ammonia and a trap-vessel for ammonia collection. This configuration results in matrix removal as well as analyte preconcentration, avoiding membrane-associated problems. All the main parameters affecting the efficiency of a P&T system were studied and optimized. The proposed method is characterized by a working range of 2.7–150.0 μg L⁻¹ of NH₄⁺, with a detection and quantification limit of 0.80 and 2.66 μg L⁻¹, respectively, for a 10-mL sample consumption. The accuracy of the method was assessed by recovery assays in seawater, estuarine, and lake water samples as well as by the analysis of standard reference material.