Stopped-flow Mode Research Articles

Stilbenes in Carex acuta and Carex lepidocarpa.

Stilbenes in the roots of Carex acuta and Carex lepidocarpa were studied. Root samples were extracted with 100% methanol and analyzed by HPLC and LC-MS. In this way, trans-resveratrol dimers (m/z 455 Da [M + H]+), trimers (m/z 681 Da [M + H]+) and tetramers (m/z 907 Da [M + H]+) were identified in the extracts. Using LC-NMR in stop-flow mode, pallidol and trans-ε-viniferin as dimers were identified. After the separation of individual peaks and their measurement by 1H NMR, cis and trans-miyabenol A as a tetramer and cis-miyabenol C as a trimer were identified. In the case of miyabenol A, it is a chromatographically inseparable mixture of cis and trans isomers in the ratio of 2:3 according to 1H NMR measurement. In the case of cis-miyabenol C, the Z-trans-trans-miyabenol C configuration was confirmed. The remaining unidentified peak with a practically identical UV-VIS spectrum to that of cis-miyabenol C is most likely another isomer of miyabenol C.

Microphysiological system with integrated sensors to study the effect of pulsed electric field

This study focuses on the use of pulsed electric fields (PEF) in microfluidics for controlled cell studies. The commonly used material for soft lithography, polydimethylsiloxane (PDMS), does not fully ensure the necessary chemical and mechanical resistance in these systems. Integration of specific analytical measurement setups into microphysiological systems (MPS) are also challenging. We present an off-stoichiometry thiol-ene (OSTE)-based microchip, containing integrated electrodes for PEF and transepithelial electrical resistance (TEER) measurement and the equipment to monitor pH and oxygen concentration in situ. The effectiveness of the MPS was empirically demonstrated through PEF treatment of the C6 cells. The effects of PEF treatment on cell viability and permeability to the fluorescent dye DapI were tested in two modes: stop flow and continuous flow. The maximum permeability was achieved at 1.8 kV/cm with 16 pulses in stop flow mode and 64 pulses per cell in continuous flow mode, without compromising cell viability. Two integrated sensors detected changes in oxygen concentration before and after the PEF treatment, and the pH shifted towards alkalinity following PEF treatment. Therefore, our proof-of-concept technology serves as an MPS for PEF treatment of mammalian cells, enabling in situ physiological monitoring.

A cyclometalated N-heterocyclic carbene and acetylacetonate ligands in a phosphorescent Pt(II) dye for sensing glucose

New β-diketonate platinum (II) complexes, containing a cyclometalated N-heterocyclic carbene [Pt(Naph^C*iPr)(acac)] (3A) (HNaph^C*-κC* = 3-isopropyl-1-(naphthalen-2-yl)-1H-imidazole-2-ylidene), or a cyclometalated pyrazole, [Pt(Naph^Npz)(acac)] (3B) (HC^Npz = 1-(naphthalen-2-yl)-1H-pyrazole) and [Pt(Naph^Ndmpz)(acac)] (3B') (HC^Ndmpz = 1-(naphthalen-2-yl)-1H-3,5-dimethylpyrazole) have been prepared and characterized. Their absorption and emission properties in films of ethyl cellulose (EC) were determined along with those of the already reported for complex [Pt(Naph^C*Me)(acac)] (3A'). They showed that all four β-diketonate complexes display a bright phosphorescent emission with maxima in the blue region (λmax ∼ 480 nm for 3A and 3A'; 490 nm 3B and 3B'). The higher quantum yield (QY), longer decay times and greater oxygen sensitivity were exhibited by the Naph^C* derivatives, compared to the Naph^N ones. Polyacrylamide membranes with entrapped 3A' as dye, and glucose oxidase (GOx) enzyme were used for monitoring glucose level. The RSD is about 5% and the detection limit is at ∼5·10−4 M, with a response time usually of 10–15 min working in stop-flow mode. These platinum-based membranes respond reversibly to glucose for, at least, 20 measures. 3A’ is the first Pt(II) complex bearing a cyclometalated N-heterocyclic carbene ever used as dye for sensing glucose.

Microsampling and enantioselective liquid chromatography coupled to mass spectrometry for chiral bioanalysis of novel psychoactive substances

In this paper, the development of efficient enantioselective HPLC methods for the analysis of five benzofuran-substituted phenethylamines, two substituted tryptamines, and three substituted cathinones is described. For the first time, reversed-phase (eluents made up with acidic water-methanol solutions) and polar-ionic (eluent made up with an acetonitrile-methanol solution incorporating both an acidic and a basic additive) conditions fully compatible with mass spectrometry (MS) detectors were applied with a chiral stationary phase (CSP) incorporating the (+)-(18-crown-6)–tetracarboxylic acid chiral selector. Enantioresolution was achieved for nine compounds with α and RS factors up to 1.32 and 5.12, respectively.Circular dichroism (CD) detection, CD spectroscopy in stopped-flow mode and quantum mechanical (QM) calculations were successfully employed to investigate the absolute stereochemistry of mephedrone, methylone and butylone and allowed to establish a (R)<(S) enantiomeric elution order for these compounds on the chosen CSP.Whole blood miniaturized samples collected by means of volumetric absorptive microsampling (VAMS) technology and fortified with the target analytes were extracted following an optimized protocol and effectively analysed by means of an ultra-high performance liquid chromatography-MS system. By this way a proof-of-concept procedure was applied, demonstrating the suitability of the method for quali-quantitative enantioselective assessment of the selected psychoactive substances in advanced biological microsamples. VAMS microsamplers including a polypropylene handle topped with a small tip of a polymeric porous material were used and allowed to volumetrically collect small aliquots of whole blood (10 μL) independently from its density. Highly appreciable volumetric accuracy (bias, in the −8.7–8.1% range) and precision (% CV, in the 2.8–5.9% range) turned out.

A mixing microfluidic chip for real-time NMR monitoring of macromolecular reactions

NMR spectroscopy permits real-time monitoring of reactions that involve changes in the spectra of reactants. MICCS (MIcro Channelled Cell for Synthesis monitoring) is a microfluidic chip for such purposes, which is used to rapidly activate reactions by mixing the reactant solutions in the chip inserted into the typical NMR tube. Although it allows monitoring of chemical reactions of small compounds, its simple mixing system dependent on diffusion in the microchannel was not suitable for macromolecules such as proteins with low diffusion rates. Here, we developed a new microfluidic chip based on MICCS by incorporating a mixer of split-and-recombination type within the microchannel. We applied it to monitoring of the protein-folding reaction in a stopped-flow mode. A solution of denaturant-unfolded RNase A was injected from a syringe pump into the microchip set inside the NMR magnet and mixed with a buffer for dilution to reach the folding condition. Immediately after dilution, the reaction was initiated and detected by a series of NMR measurements that were synchronized with activation and inactivation of the pump. The process was repeated for accumulation of the data. By analysing the change of the spectra by factor analysis, a kinetic constant of 0.57 min-1 was obtained.

LC–NMR for Natural Product Analysis: A Journey from an Academic Curiosity to a Robust Analytical Tool

Liquid chromatography (LC)–nuclear magnetic resonance (NMR) combines the advantage of the outstanding separation power of liquid chromatography (LC) and the superior structural elucidating capability of nuclear magnetic resonance (NMR). NMR has proved that it is a standout detector for LC by providing maximum structural information about plant originated extracts, particularly on the isolating ability of isomeric (same molecular formula) and/or isobaric (same molecular weight) compounds as compared to other detectors. The present review provides an overview of the developmental trends and application of LC–NMR in natural product analysis. The different LC–NMR operational modes are described, and how technical improvements assist in establishing this powerful technique as an important analytical tool in the analysis of complex plant-derived compounds is also highlighted. On-flow, stop-flow and loop-storage modes, as well as the new offline mode LC–solid phase extraction (SPE)–NMR and capillary LC (capLC)–NMR configurations which avoid the ingestion of expensive deuterated solvents throughout the experiment, are mentioned. Utilization of cryogenic probe and microprobe technologies, which are the other important promising approaches for guaranteeing sensitivity, are also described. Concluding remarks and future outlooks are also discussed.

A Tunable High-Q Microwave Detector for On-Column Capillary Liquid Chromatography

We report a novel approach to ultrahigh quality factor ( $Q$ ) in the split-ring resonator with an active feedback loop, which utilizes a phase shifter to tune equivalent negative resistance for accurate loss compensation. Based on the proposed technique, a microwave detector is designed for on-column liquid chromatography. With lossy solvents loaded, the measured $Q$ is as high as $4.0\times 10^{6}$ at ~ 3.89 GHz. We demonstrate the highly sensitive and contactless measurement of glucose–water solution in a capillary tube under stop–flow and plug–unplug modes, respectively. With the stop–flow mode, different concentrations between 40 and 150 mg/dL are measured, which covers the normal blood-glucose levels. The minimum detectable quantity of glucose is ~18.8 ng with an effective sample volume of ~47 nL. The plug–unplug mode provides fast and flexible sampling and analysis. Further investigations are required for quantification of material-under-test permittivity and promotion of sensitivity.

Sensitive determination of bioaccessible mercury in complex matrix samples by combined photochemical vapor generation and solid phase microextraction coupled with microwave induced plasma optical emission spectrometry

The photochemical generation technique of mercury vapor (PCVG) coupled with headspace solid phase microextraction (SPME) and microwave induced plasma optical emission spectrometry (MIP-OES) has been developed and successfully applied for fast and sensitive determination of mercury in complex matrix samples. Mercury vapor was generated by UV photo-reduction of inorganic mercury and methylmercury to mercury vapor in 5% (v/v) formic acid with subsequent gas-liquid separation and preconcentration by solid phase microextraction. A stopped-flow mode of the PCVG-SPME unit was employed with the aim of increasing analyte preconcentration factor, thus improving both sensitivity of determination and detection limits for mercury. The calibration curves were linear up to 20 ng mL−1 with the limit of detection for inorganic mercury and methylmercury of 0.030 and 0.045 ng mL−1, respectively. This manifold allowed a repeatability, expressed as relative standard deviation, of below 5%. Due to differences in efficiency of Hg vapor generation for Hg2+ and CH3Hg+, the quantification was performed against external Hg2+ and CH3Hg+ aqueous standards, respectively. The method was validated by the analysis of two CRM materials of different matrix composition, i.e. estuarine sediment ERM CC580 for total mercury content and tuna fish ERM CE464 for methylmercury content, respectively. The results proved good accuracy of the method with recovery of 101% total mercury and 87.3% methylmercury and precision of 3.8% and 12.5%, respectively. Effect of concomitants in the stopped-flow generation of mercury vapor with the new manifold was also investigated. Next, the proposed method was successfully applied for monitoring of bioaccessible fraction of mercury during their incubation in simulated body fluid in the presence of selenium nanoparticles examined as a potential mercury detoxifying agent.

Fully Automated Electric-Field-Driven Liquid Phase Microextraction System with Renewable Organic Membrane As a Front End to High Performance Liquid Chromatography.

This article reports for the first time a programmable-flow-based mesofluidic platform that accommodates electric-field-driven liquid phase microextraction (μ-EME) in a fully automated mode. The miniaturized system is composed of a computer-controlled microsyringe pump and a multiposition rotary valve for handling aqueous and organic solutions at a low microliter volume and acts as a front-end to online liquid chromatographic separation. The organic membrane is automatically renewed and disposed of in every analytical cycle, thus minimizing analyte carry-over effects while avoiding analyst intervention. The proof-of-concept applicability of the automated mesofluidic device is demonstrated by the liquid chromatographic determination of nonsteriodal anti-inflammatory drugs in μ-EME processed complex samples (such as urine and influent wastewater) using online heart-cut approaches. Using 5 μL of 1-octanol, 7.5 μL of untreated sample and 7.5 μL of acceptor solution (25 mM NaOH), and 250 V for only 10 min in a stopped-flow mode, the extraction recoveries for the μ-EME of ibuprofen, ketoprofen, naproxen, and diclofenac exceed 40% in real samples. The flow-through system features moderately selective extraction regardless of the sample matrix constituents with repeatability values better than 13%.

LC-NMR for Natural Products Analysis: A Journey from an Academic Curiosity to a Robust Analytical Tool

LC–NMR combines the advantage of the outstanding separation power of liquid chromatography (LC) and the superior structural elucidating capability of nuclear magnetic resonance (NMR). NMR has proved that it is a standout detector for LC by providing maximum structural information about plant originated extracts particularly in its isolating ability of isomeric (same molecular formula) and/or isobaric (same molecular weight) compounds as compared to other detectors. The present review provides an overview of the LC–NMR developmental trends and its application in natural products analysis. The different LC–NMR operational modes are described, as well as how technical improvements assist in establishing this powerful technique as an important analytical tool in the analysis of complex plant-derived compounds. On-flow, stop-flow and loop-storage modes, as well as the new offline mode LC–SPE–NMR and capLC-NMR configurations that avoid the ingestion of expensive deuterated solvents throughout the experiment are mentioned. Utilization of cryogenic probe and microprobe technologies which are the other important promising approaches for guaranteeing the sensitivity issues are also described. Concluding remarks and future outlooks are also discussed.

NMR spectroscopic method for studying homogenous liquid phase reaction kinetics in systems used in reactive gas absorption and application to monoethanolamine–water–carbon dioxide

An NMR spectroscopic method for measuring homogenous liquid phase reaction kinetics in systems that are used in reactive gas absorption processes is presented. In the kinetic experiment, carbon dioxide loaded and unloaded aqueous amine solutions are mixed such that no gas phase is involved. This procedure enables studying liquid phase reaction kinetics without the influence of the kinetics of the physical absorption process. A rapid-mixing NMR flow cell is used for the measurements, which are carried out in stopped-flow mode. 1H NMR spectra are taken at short intervals to monitor the kinetic process. The cell is liquid thermostatted and pressure resistant, such that a wide range of conditions can be studied. The new method was used for studying reaction kinetics in the system monoethanolamine (MEA)–water (H2O)–carbon dioxide (CO2) at temperatures between 293 and 333 K. From the data, information on the kinetics of the reaction of MEA with bicarbonate (HCO3-) to form MEA carbamate was obtained. That reaction was investigated for the first time in the present work without using bicarbonate salts. An Arrhenius model was fitted to the new data. The formation of MEA carbamate from MEA and HCO3- is often neglected in models for describing the reactive absorption of CO2 with aqueous MEA solutions. A process simulation study carried out in the present work reveals that it should be taken into account in predictions of reactive absorption processes that are operated under elevated pressure with a high mole fraction of CO2 in the gaseous phase.

Myeloperoxidase-catalyzed oxidation of cyanide to cyanate: A potential carbamylation route involved in the formation of atherosclerotic plaques?

Protein carbamylation by cyanate is a post-translational modification associated with several (patho)physiological conditions, including cardiovascular disorders. However, the biochemical pathways leading to protein carbamylation are incompletely characterized. This work demonstrates that the heme protein myeloperoxidase (MPO), which is secreted at high concentrations at inflammatory sites from stimulated neutrophils and monocytes, is able to catalyze the two-electron oxidation of cyanide to cyanate and promote the carbamylation of taurine, lysine, and low-density lipoproteins. We probed the role of cyanide as both electron donor and low-spin ligand by pre-steady-state and steady-state kinetic analyses and analyzed reaction products by MS. Moreover, we present two further pathways of carbamylation that involve reaction products of MPO, namely oxidation of cyanide by hypochlorous acid and reaction of thiocyanate with chloramines. Finally, using an in vivo approach with mice on a high-fat diet and carrying the human MPO gene, we found that during chronic exposure to cyanide, mimicking exposure to pollution and smoking, MPO promotes protein-bound accumulation of carbamyllysine (homocitrulline) in atheroma plaque, demonstrating a link between cyanide exposure and atheroma. In summary, our findings indicate that cyanide is a substrate for MPO and suggest an additional pathway for in vivo cyanate formation and protein carbamylation that involves MPO either directly or via its reaction products hypochlorous acid or chloramines. They also suggest that chronic cyanide exposure could promote the accumulation of carbamylated proteins in atherosclerotic plaques.

Low-temperature atomic layer deposition of SiO2/Al2O3 multilayer structures constructed on self-standing films of cellulose nanofibrils.

In this paper, we have optimized a low-temperature atomic layer deposition (ALD) of SiO2 using AP-LTO® 330 and ozone (O3) as precursors, and demonstrated its suitability to surface-modify temperature-sensitive bio-based films of cellulose nanofibrils (CNFs). The lowest temperature for the thermal ALD process was 80°C when the silicon precursor residence time was increased by the stop-flow mode. The SiO2 film deposition rate was dependent on the temperature varying within 1.5-2.2 Å cycle-1 in the temperature range of 80-350°C, respectively. The low-temperature SiO2 process that resulted was combined with the conventional trimethyl aluminium + H2O process in order to prepare thin multilayer nanolaminates on self-standing CNF films. One to six stacks of SiO2/Al2O3 were deposited on the CNF films, with individual layer thicknesses of 3.7 nm and 2.6 nm, respectively, combined with a 5 nm protective SiO2 layer as the top layer. The performance of the multilayer hybrid nanolaminate structures was evaluated with respect to the oxygen and water vapour transmission rates. Six stacks of SiO2/Al2O with a total thickness of approximately 35 nm efficiently prevented oxygen and water molecules from interacting with the CNF film. The oxygen transmission rates analysed at 80% RH decreased from the value for plain CNF film of 130 ml m-2 d-1 to 0.15 ml m-2 d-1, whereas the water transmission rates lowered from 630 ± 50 g m-2 d-1 down to 90 ± 40 g m-2 d-1This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

Solenoid Micro‐pumps: A New Tool for Sample Introduction in Batch Injection Analysis Systems with Electrochemical Detection

AbstractThis work presents the use of solenoid micro‐pumps as a new strategy for sample introduction in batch‐injection analysis (BIA). The volume of solution dispensed on each pulse of the solenoid micro‐pump (μL) is used as fixed and reproducible injection volume for BIA. In this system, the injection steps are possible in stopped flow mode resulting in low background noise levels, which would not be possible under continuous flow conditions and using solenoid micro‐pumps. As a proof‐of‐concept, amperometric and square‐wave voltammetric (SWV) determination of dopamine was demonstrated as well as anodic‐stripping voltammetry (ASV) of metals. The micro‐pump provided injections of 14 μL of solution per pulse at 512 μL s−1 over the electrode during electrochemical measurement. Moreover, fast injections of analyte or electrolyte were programmed during deposition or conditioning steps of ASV for analyte preconcentration or electrode cleaning. The proposed system improved limits of detection and sensitivity (2‐fold), precision and sample throughput in comparison with traditional BIA due to enhanced mass transfer and consequent reduced dispersion of analyte, and possible control of injections without analyst intervention. This work opens new possibilities of applications of the BIA system, including on‐line sample treatment (derivatization or dilution steps).

A flow microslot NMR probe coupled with a capillary isotachophoresis system exhibits improved properties compared to solenoid designs.

We report on the hyphenation of capillary isotachophoresis (cITP) separations with online nuclear magnetic resonance (NMR) detection using a planar microslot waveguide probe design. While cITP is commonly coupled with a solenoidal microcoil NMR probe, the structural information provided is limited by broad resonances and poor spectral resolution due to the magnetic field created by the separation current. The microslot probe design described herein allows the separation capillary to be oriented parallel to the static magnetic field, B 0, eliminating the spectral broadening produced by the secondary magnetic field induced by the separation current. This allows high-resolution nuclear magnetic resonance spectra of the charged analytes to be obtained in online mode, whereas conventional solenoidal capillary NMR designs must resort to the stopped flow mode. The potential of the microslot probe for hyphenated electrophoretic separations is demonstrated by performing cITP focusing and online NMR detection of the 1H NMR spectrum of a system containing spermine and aniline. Graphical Abstract High resolution NMR spectra in flow capillarelectrophoretic separations with microslot NMR probe.

Quantum dots as chemiluminescence enhancers tested by sequential injection technique: Comparison of flow and flow-batch conditions

The effect of 0.01–100µmol L−1 Quantum Dots (QDs) with different emission wavelengths (520–640nm) and different surface modifications (mercaptopropionic, mercaptoundecanoic, thioglycolic acids and mercaptoethylamine) on permanganate-induced and luminol–hydrogen peroxide chemiluminescence (CL) was studied in detail by a sequential injection technique using a spiral detection flow cell and a flow-batch detection cell operated in flow and stop-flow modes.In permanganate CL system no significant enhancement of the CL signal was observed while for the luminol–hydrogen peroxide CL substantial increase (>100% and >90% with the spiral detection cell in flow and stop-flow modes, respectively) was attained for CdTe QDs. Enhancement exceeding 120% was observed for QDs with emissions at 520, 575 and 603nm (sizes of 2.8nm, 3.3nm and 3.6nm) using the flow-batch detection cell in the stop-flow mode. Pronounced effect was noted for surface modifications while mercaptoethylamine was the most efficient in CL enhancement compared to mercaptopropionic acid the most commonly applied coating. Significant difference between results obtained in flow and flow-batch conditions based on the entire kinetics of the extremely fast CL reaction was discussed. The increase of the CL signal was always accompanied by reduced lifetime of the CL emission thus application of QDs in flow techniques should be always coupled with the study of the CL lifetime.

Application of a new micro-reactor 1H NMR probe head for quantitative analysis of fast esterification reactions

A fully liquid-thermostatted micro-reactor probe head for 1H NMR spectroscopic studies of fast reaction kinetics, which was recently developed, is tested in the present work by studying fast esterification kinetics in the stopped flow mode. It is shown that reliable kinetic data can be obtained using this set-up for reactions with time constants down to a few seconds. The two test systems are the formation of methyl acetate (MA) and methyl formate (MF). Both are homogeneously catalyzed by sulfuric acid, which is added to the educts in different amounts. The temperatures of the kinetic studies are chosen between 303 and 333K. The reaction kinetic data for both systems is correlated by activity-based kinetic models. For the MA formation, reference data from the literature is available, however only for regimes with time constants of minutes to hours. That data fits well to the results of the present study. The MF formation was studied here at conditions in which the time constants are of the order of seconds and therefore no reference data is available. The new probe head substantially extends the range in which NMR spectroscopy can be used for studies of fast reaction kinetics.

Array-Based Online Two Dimensional Liquid Chromatography System Applied to Effective Depletion of High-Abundance Proteins in Human Plasma.

In this work, an array-based online two-dimensional liquid chromatography (2D-LC) system was constructed for protein separation and effective depletion of high-abundance proteins in human plasma. This system employed a strong anion exchange column in the first dimension and eight reversed-phase liquid chromatographic columns in the second dimension. All the protein components in the first dimension were enriched on the trapping columns, simultaneously back-flushed and concurrently separated in the second dimension. LC eluents were then collected on 96-well plates for further analysis. Compared with common 2D-LC system, this system showed an 8-fold increase in throughput and convenient utilization of stop-flow mode for sample separation. The RSD of retention time and peak area were separately below 0.51% and 8%. Recovery rates of four standard proteins were all above 95%. This array-based 2D-LC system was subsequently applied to the analysis of proteins in human plasma. The eluents containing high-abundance proteins were rapidly located according to the results of bicinchoninic acid assay. In all, with the effective depletion of 84 high-abundance proteins, a total of 1332 proteins were identified through our system. The dynamic range of the identified protein concentrations covered 9 orders of magnitude, ranging from 41 g/L level for HSA down to 0.01 ng/mL level for the low-abundance proteins.

Axial, Helical, and Planar Chirality in Directly Linked Basket-Handle Porphyrin Arrays.

The single-electron oxidative dimerization of basket-handle porphyrins (BHPs) with different coordinated metal ions [Cu(II), Ni(II), Pd(II), Zn(II)] yielded directly meso-meso linked dimers in excellent yields. The synthetic protocol is suited for coupling substrates with different meso-substituents (H, Br, aryl, alkyl) opposite to the coupling site. Experimental findings concerning reactivities and selectivities were in good agreement with theoretical investigations using ALIE calculations. The dimers, which all are axially chiral, were resolved into their enantiomers by HPLC on a chiral phase. ECD spectra were measured in the stopped-flow mode and compared with results from quantum-chemical ECD calculations to assign the absolute configuration. One directly linked dimer was further oxidized to a fused system, which possessed a stable helical chirality. Its absolute configuration was again assigned by ECD investigations. Furthermore, functionalized BHPs and tetraarylporphyrins were coupled under Suzuki conditions to give dimers and trimers with either β-meso or β-β linkages. Because of the steric shielding of one of the BHP hemispheres, the products were formed with full diastereoselectivity regarding all porphyrin-porphyrin axes. The stereostructures of these arrays were investigated by quantum-chemical calculations (DFT-D3, TD DFT, and sTD DFT), and the absolute configurations were assigned for all chiral representatives.

Argentometric Titration Apparatus with a Light Emitting Diode‐based Nephelometric Detection System

A newly revised apparatus for argentometric precipitate titrations was fabricated and evaluated. A light emitting diode was adapted as a solid‐state light source and a syringe pump was used for manipulating titrant both in stopped flow mode and continuous mode. The performance of the two modes was compared in terms of accuracy and precision. The continuous flow mode is much faster and shows generally higher accuracy under given experimental conditions. The patterns of precipitate titration curves were changed with different coagulant concentrations and addition flow rates of titrant. However, end point volumes were not affected by these experimental factors tested here.