A Simple injection valve for flow injection analysis

A novel sample introduction valve, based on a modified glass syringe, is described for flow injection analysis. Sample volumes of 1.4 μl or more can be injected manually or automatically, by driving with a 12-V solenoid. The valve has advantages of freedom from maintenance and long lifetime.     

New injection valves and their application in flow injection analysis

Summary Two variable volume injection valves, equipped with bypass loops, have been developed, primarily to circumvent problems with matrix effects in high sensitivity FIA.The application of a dual channel valve for simultaneous analysis, zone sampling and merging zones techniques is discussed.Examples for on-line dilutions up to several thousand-fold and the direct determination of calcium in Kjeldahl digests using the zone sampling approach and a study of the interference of ascorbic acid on the Griess reaction for nitrite are presented. The application of chasing zones techniques by coupling a simple single channel valve in a new way is proposed.

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Neue Injektionsventile und ihre Anwendung in der Fließinjektionsanalyse

     

Programmed-temperture split-splitless injection of triglycerides: Comparison to cold on-column injection

The performance of split and splitless programmed-temperature (PTV) injection is compared to cold on-column and hot (classical) split injection for the analysis of triglycerides on an apolar capillary gas chromatographic column. Quantitative accuracy and precision of PTV injection are determined for a synthetic mixture of triglycerides relative to cold on-column injection.     

Dual-purpose gas chromatographic injection device for pressurized liquid and gas injection

A dual-purpose gas chromatographic injection device, capable of injecting pressurized liquid sample of up to 5000 psig and gas sample with a volume as high as 5000 μL, has been successfully developed and implemented. The injection device is synergized by the effectiveness of a classical flash vaporization of a syringe injection and the reliability of a proven rotary valve. Depending on the matrix involved, this injection device employs either a commercially available four-port internal valve for liquid sampling or a six-port external valve for gas sampling, a modified removable needle used in standard liquid syringe, and an auxiliary flow stream that can be either mechanical or electronic flow controlled for solute transfer. For pressurized liquid, the device was found suitable of up to nC₁₆ hydrocarbon with no observable carry-over despite the injection device was operating at ambient temperature. A relative standard deviation of less than 2% (n = 20) was obtained for hydrocarbon compounds ranging from nC₈ to nC₁₆. For gas injection, the device performed well even under difficult chromatographic conditions such as with a low column inlet pressure of less than 1 psig. A relative standard deviation of less than 0.5% (n = 10) was obtained for reactive sulfur compounds such as alkyl mercaptans. The device can be operated manually or automated with pneumatic or electrical actuator, is platform neutral, and can be moved amongst instruments without hardware modification as well as implemented for on-line or in situ applications. In this paper, the utility of the device was also demonstrated with selected GC applications of industrial significance.     

On-line sulphate monitoring by reversed flow injection analysis and alternating reagent injection

Summary An on-line automated system for the determination of sulphate in effluent water streams based on the concept of reversed flow injection analysis and alternating reagent injection is described (turbidimetric determination of barium sulphate). The rate of determination is 60 actual analyses/h. The method is suitable for the on-site monitoring of sulphate in the concentration range up to 200 mg/l with a coefficient of variation of better than 2.0%.

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On-line Sulfatbestimmung durch umgekehrte Fließinjektionsanalyse und alternierende Reagensinjektion

Zusammenfassung Es wird ein automatisiertes on-line System für die Sulfatbestimmung in Abwasserausflüssen beschrieben, das auf umgekehrter Fließinjektion beruht (turbidimetrische Bestimmung von Bariumsulfat). Je Stunde können 60 Analysen ausgeführt werden. Das Verfahren ist zur Überwachung vor Ort geeignet für einen Konzentrationsbereich bis zu 200 mg/l mit einem Variationskoeffizient besser als 2,0%.

     

A simple flow injection system with bead injection for trace iron determination

A simple and low cost flow injection (FI) system with bead injection (BI) was developed for determination of low concentration (mumol l(-1)) of iron in water samples. Chelex-100 chelating resin beads, trapped in a jet ring cell, were employed. The intensity of red complex of 1,10-phenanthroline with Fe(2+) was monitored using colorimetric detector with a LED green light source. Amount of total Fe (Fe(2+) and Fe(3+)) and Fe(2+) can be evaluated by with and without reduction of Fe(3+) using ascorbic acid. Lowest detectable levels of Fe(2+) were 0.90 and 0.45 mumol l(-1) for sample loading time of 3 and 5 min, respectively. Working range was up to 3.90 mumol l(-1) using 0.3% w/v 1, 10-phenanthroline. Percent recoveries of spiked water samples (0.90-2.33 mumol l(-1) of Fe(2+)) were 100-110%.     

Study of injection bias in a simple hydrodynamic injection in microchip CE

The electrokinetically pinched method is the most commonly used mode for sample injection in microchip capillary electrophoresis (microCE) due to its simplicity and well-defined sample volume. However, the limited injection volume and the electrophoretic bias of the pinched injection may limit its universal usage to specific applications. Several hydrodynamic injection methods in microCE have been reported; however, almost all claimed that their methods are bias-free without considering the dispensing bias. To investigate the dispensing bias, a simple hydrodynamic injection was developed in single-T and double-T glass microchips. The sample flow was produced by hydrostatic pressure generated by the liquid level difference between the sample reservoir and the other reservoirs. The reproducibility of peak area and peak area ratio was improved to a significant extent using large-surface reservoirs for the buffer reservoir and the sample waste reservoir to reduce the Laplace pressure effect. Without a voltage applied on the sample solution, the voltage-related sample bias was eliminated. The dispensing bias was analyzed theoretically and studied experimentally. It was demonstrated that the dispensing bias existed and could be reduced significantly by appropriately setting up the voltage configuration and by controlling the appropriate liquid level difference.     

Time-based flow injection analysis

Time-based flow-injection systems are novel measurement systems which use induced dispersion of the sample in the system and measurement of time to evaluate the concentration of the analyte in the sample. There are two types of time-based system. In the standard systems, assays are based on the chemistries of the classical intensity assays; in the pseudo-titration systems, the assays are based on classical titration chemistries. These systems are discussed in terms of basic theory, classification of the systems and their advantages.     

Flow injection calibration techniques

Summary The role of calibration in the overall analytical procedure is discussed and the potential role of flow injection techniques are assessed. The factors affecting the dispersion obtained in a flow injection system are described and examples given of how control of the various factors can be exploited to produce manifolds for calibration purposes. Most of these examples concern atomic spectrometry methods for which there is considerable interest at present in developing extended range calibrations and flow injection versions of the standard additions method. Several examples of the latter are given.

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Anwendung der Fließinjektions-Technik für Eichmethoden

     

Novel three-dimensional in-cavity transient temperature measurements in injection molding and fluid-assisted injection molding

This report presents novel experimental set-ups which allow the measurement of three-dimensional temperature fields in the depths of injection molding cavities throughout molding cycles. Two specific molds equipped with two types of temperature measuring devices, i.e., a mesh type device consisting of thermocouples mounted on metal wires and a tubular type device consisting of tubular needles guiding embedded micro-thermocouples inside the cavities, have been designed and built. Temperature distributions in both injection molding and fluid assisted injection molding processes, including gas and water assisted injection molding, were measured and recorded by a data acquisition system on a personal computer. It was found that the tubular type device induced much less flow disturbance and provided accurate temperature profiles. Among the processes, the water assisted injection molding process required the least time to cool the parts, followed by gas assisted injection molding and conventional injection molding. In addition, the experimental results also suggested that the shear heating by viscous dissipation in the runners leads to a significant increase in melt temperature. A precise measurement of the in-depth temperature profile can be helpful to better understand the molding phenomena, to validate numerical simulation results, as well as to optimize the parameters for the molding processes.     

Bead injection for biomolecular assays: Affinity chromatography enhanced by bead injection spectroscopy

Selective capture of target biomolecules by ligands immobilized on a solid support is a cornerstone of two seemingly unrelated techniques: micro-Affinity Chromatography (microAC) and micro-Bead Injection Spectroscopy (microBIS). This work shows, for the first time, how these techniques can be carried out using the same instrument and how the data obtained this way complement each other, yielding complete information on retention and elution of target biomolecules. Biomolecular association and dissociation were investigated by microAC and microBIS, using computer-controlled programmable flow and the same instrument for automated bead transport, packing of a micro-column, assay of the analyte, and bead disposal. The absorbance of the analyte was monitored within the fiber optic flow cell configured either for monitoring directly on the beads or post-column after elution. The separation, binding, and elution of immunoglobulins (human IgG, rabbit IgG, and horse IgG) on protein G-coated Sepharose beads were studied as model systems. The limit of detection of the microAC technique was determined to be 5 ng microL(-1) IgG, and that of the microBIS technique was 50 ng microL(-1) IgG.     

Spectrophotometric simultaneous determination of creatinine and creatine by flow injection with reagent injection

The reactions of creatinine with picric acid and of creatine with 1-naphthol and biacetyl, both in an alkaline medium, have been used to develop a flow injection method for the simultaneous determination of creatinine and creatine, respectively. The sample containing both analytes is continuously merged with a picrate stream and mixed through the reactors; the coloured stream passes through a flow cell in a spectrophotometer set at 520 nm, recording a continuous signal proportional to the creatinine concentration. The mixture of the reagents 1-naphthol and biacetyl is inserted into the stream by use of the injection valve, which results in a peak (superimposed on the continuous signal), proportional to the creatine concentration. Linear calibration graphs for both analytes were obtained up to 30 mg l^–1 with relative standard deviations <2%, and a sampling rate of 42 measurements h^–1. The method was applied to the determination of creatinine and creatine in broth cube samples.     

New injection technique for flow injection atomic absorption spectrometry using tubing clamp valves

Flow injection devices for atomic absorption spectrometry usually are equipped with a sixport-valve consisting of two PTFE-cylinders. This kind of valve can be substituted by an arrangement of tubing clamp valves. The advantages and limits of this new injection technique for flow injection atomic absorption spectrometry are discussed.     

New injection technique for flow injection atomic absorption spectrometry using tubing clamp valves

Flow injection devices for atomic absorption spectrometry usually are equipped with a sixport-valve consisting of two PTFE-cylinders. This kind of valve can be substituted by an arrangement of tubing clamp valves. The advantages and limits of this new injection technique for flow injection atomic absorption spectrometry are discussed.