Sampling Valve Research Articles

Optimisation of the rate of sample injection in high-performance liquid chromatography with microsyringes and with sampling valves

The rate of sample injection has been studied as a factor influencing the separating power of high-performance liquid chromatographic systems with syringe and valve curtain flow injection. Full practical details of the systems are presented.

Intra-column injection system for liquid chromatography

An intra-column injection system is described whereby the contents of a sampling valve are discharged into the packing of a column and carried through the column by an ancillary curtain flow of solvent. The device has two advantages. Firstly, it permits columns, deteriorated by the formation of a void between the top of the packing and the frit to provide a satisfactory performance and in some cases, to recover their original efficiency. Secondly, it reduces column deterioration resulting from pressure pulse effects and packing shrinkage. The advantages of the device have been demostrated by its use with poorly packed columns and columns that have seriously deteriorated over a period of time.

Chromatographic sampling valve for dynamic kinetic experiments

Chromatographic sampling valve for dynamic kinetic experiments

Automated simultaneous determination of nitrate and nitrite by pre-valve reduction of nitrate in a flow-injection system

Nitrate is reduced to nitrite by using the pre-valve in-valve reduction technique prior to the sampling system. One loop of a two-position sampling valve is replaced by a copperised cadmium column. Nitrite from the samples as well as nitrite formed in the reduction procedure is sampled by a second valve and introduced into the flow system. The two sampling valves are synchronised in such a way that two peaks are obtained, one corresponding to the nitrate plus nitrite and the other to the nitrite only. The method is suitable for the simultaneous determination of nitrate and nitrite at a sampling rate of up to 72 determinations per hour with coefficients of variation better than 1.96% for nitrate and 0.83% for nitrite.

Systematic errors occurring with the use of gas-sampling loop injectors in gas chromatography

Gas sampling valves, involving a fixed-volume loop, are widely used as injection devices in gas chromatography. It is shown that adsorption of the substance under consideration on the inner wall of the loop tube will cause a systematic error in the injected amount. This effect can in many practical cases be significant as is shown by experiments and theoretical calculations.

Automated turbidimetric determination of sulphate in surface, ground and domestic water by flow-injection analysis

A simple, modified, automated method for the turbidimetric determination of sulphate in surface, ground and domestic water, based on the principles of the flow-injection technique, is described. The one loop of a two-position sampling valve is used to sample an alkaline buffer-EDTA solution, alternated with water samples on the other loop. This ensures that the residual precipitate, coating the walls of the flowcell, is redissolved and the system kept clean. The method is suitable for the analysis of sulphate at a rate of up to 60 samples per hour with a coefficient of variation of better than 0.95 %.

Automated prevalve sample filtration in flow injection analysis: Determination of sulphate in water removing suspended solids and colour before sampling

Suspended solids and the presence of organic substances and colour are the main interferences in the turbidimetric spectrophotometric determination of sulphate at 420 nm in water. An automated flow-injection procedure is proposed in which these interferences are automatically removed by using an active carbon filter, which is incorporated in the flow system between the sampler and the sampling valve system. With this automated prevalve sample filter the proposed turbidimetric method gives the same results as a standard flow injection and an automated segmented method where the above mentioned interferences are manually removed prior to sampling. The method is applicable for the analysis of sulphate in surface, ground and domestic waters in the concentration range up to 200 mg/l at a sampling rate of up to 60 samples per hour with a coefficient of variation of better than 1%.

Rapid on‐line analysis of low molecular weight hydrocarbons using glass capillary gas chromatography

AbstractRapid analysis is important for on‐line chromatography. Gaseous or vaporized samples have been injected via heated gas sampling valves of less than 500 μl dead volume. The critical sampling and split problems could be solved by temperature programming. The general analysis described could be successfully used inter alia in scouting reactions.

Variable-volume sample valve for high-performance liquid chromatography

Variable-volume sample valve for high-performance liquid chromatography

A rapid sampling valve with minimal dead space for laboratory scale fermenters

Biotechnology and BioengineeringVolume 23, Issue 2 p. 437-440 Communications To The EditorFree Access A rapid sampling valve with minimal dead space for laboratory scale fermenters J. J. Lønsmann Iversen, J. J. Lønsmann Iversen Institute of Biochemistry, Odense University, Campusvej 55, 5230 Odense M, DenmarkSearch for more papers by this author J. J. Lønsmann Iversen, J. J. Lønsmann Iversen Institute of Biochemistry, Odense University, Campusvej 55, 5230 Odense M, DenmarkSearch for more papers by this author First published: February 1981 https://doi.org/10.1002/bit.260230218Citations: 10AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume23, Issue2February 1981Pages 437-440 ReferencesRelatedInformation

Quench Layer Contribution to Exhaust Hydrocarbons from a Spark-Ignited Engine

INTRODUCTION Hydrocarbons remaining in a wall quench layer have been proposed as a major source of hydrocarbon emissions in spark-ignited internal combustion engines (Daniel and Wentworth, 1962). Additional experiments using wall mounted sampling valves were subsequently carried out by Daniel (1967), Muller and von Watzdorf (1968), Weiss et al. (1979), and Henningsen and Qvale (1980). Our paper presents the results of an experimental study of the quench layer also using a wall mounted sampling valve. The valve was electrohydraulically actuated and had uniquely small leakage and crevice characteristics. Our results do not support the contention that the wall quench layer is a major source of exhaust emissions. Hydrocarbons from other sources, as yet not quantified, such as those emitted from ring crevices, deposits or oil films appear to be likely contributors to exhaust hydrocarbons (Wentworth, 1971; Haskell and Legate, 1972; and Kaiser et al., 1980).

Volatile phase profiling of mainstream smoke by glass capillary gas‐chromatographic techniques

AbstractA heated injection system for a microprocessor‐controlled GC has been developed for the (GC)2 analysis of the volatile phase of whole smoke of a cigarette. Effects of injection port temperature and the presence of a Cambridge filter pad are demonstrated. Chromatograms are shown for smoke samples with and without a Cambridge Filter with the sample valve oven at 25°, 165° and 205°C. The use of a flame ionization and a nitrogen‐phosphorous detector is illustrated.

Graphite furnace atomic absorption spectrophotometers as automated element-specific detectors for high-pressure liquid chromatography : The determination of arsenite, arsenate, methylarsonic acid and dimethylarsinic acid

Techniques for the determination of trace element compounds at ppb 1 1 Throughout this article, the American billion (10 9) is meant. and ppm levels (in contrast to the determination of the total element concentration) are a prerequisite for the study of the transformations of trace elements in biological systems and the interactions of trace element compounds with biologically important molecules. Two automated high-pressure liquid chromatography (HPLC) systems with element-specific detectors, capable of detecting, identifying and quantitating trace element compounds were developed independently in our laboratories. One of the detectors consists of a Perkin-Elmer graphite furnace atomic absorption spectrometer (GFAA) and a specially adapted autosampler, whereas a Hitachi-Zeeman GFAA, a sample valve, an injector and associated electronics to control the analysis sequence comprise the components of the other detector. The capability of these systems to speciate trace element compounds is demonstrated using arsenite, arsenate, methylarsonic acid (MAA) and dimethylarsinic acid (DMAA) as examples. Arsenite, MAA and DMAA were successfully separated and quantitatively determined on a strong anion-exchange column with an aqueous acetate buffer as mobile phase. Arsenite, DMAA and arsenate can be speciated with a strong cation-exchange column using an aqueous solution of ammonium acetate as mobile phase. All four arsenic compounds can be separated on a C 18 reversed-phase column with methanol-water mixtures saturated with tetraheptylammonium nitrate. These compounds can be identified and quantified in solutions containing 10–20 ppb arsenic. Sample sizes required for GFAA analysis vary between 20 and 100 μl. The separation schemes developed for the four arsenic compounds were used to speciate these compounds in 5 ppb even in rather complex matrices employing a SAX column. Arsenate and arsenite can be determined using a SCX column provided methylarsonate is not present. All four compounds can be separated and quantitated on a C 18 reversed-phase column. These separation schemes are applicable to the determination of arsenic compounds in soil extracts and drinking water samples. The separations reported in this paper very likely can be improved by application of columns tailored to arsenic compounds. As an example of column materials development the preparation of reversed-phase cation- and anion-exchange resins is mentioned. These columns were used to separate heterocyclic nitrogen bases and ribonucleoside phosphates 12 and should be applicable to the separation of arsenic compounds. Recently the use of a proprietary special anion-exchange column for the separation of arsenic compounds was reported 13. Improved column design will make the HPLC-GFAA technique even better suited for the speciation of trace element compounds in a variety of matrices. The work with arsenic compounds clearly shows the great potential of these systems in the area of environmental trace element chemistry, in the field of physiological chemistry and in trace-element related nutritional studies.

A Flow Injection Analyzer for Chemical Oxygen Demand Using Potassium Permanganate

ABSTRACT An apparatus for measuring chemical oxygen demand (COD) based on the principle of flow injection analysis (FIA) is described. The apparatus is simple and inexpensive, and constructed by components such as a double plangent pump, sampling valve, flow cell, spectrophotometer and recorder, commercially available for high performance liquid chromatography. Polytetrafluoroethylene (Teflon) tubing is used for mixing coils and transmission lines. The operating conditions are determined by using glucose, as the standard COD substance. The peak heights obtained for various concentrations of aqueous glucose solutions correspond to their manual COD values obtained by JIS method.

Gas Chromatographic Measurement of Nitrous Oxide Dissolved in Water Using a Headspace Analysis Technique

A method is described for measuring the concentration of nitrous oxide dissolved in soil water. An aliquot of the sample of water is equilibrated with nitrogen in a closed pressurised vial, and the excess pressure is used to inject the sample via a gas sampling valve. Nitrous oxide is separated from other gases on a column packed with Carbosieve ‘B’ and detected using an electron capture detector. One analysis takes eight minutes and the coefficient of variation for 121 ng ml−1 nitrous oxide contained in water was 3.1%.

Preparative liquid chromatography: sample volume overload

The maximal injection volume equation has been developed from the well-known expression for the output profile resulting from large sample input volume in elution chromatography. The validity of this equation is examined experimentally. In order to quantify the maximal sample load under volume overload conditions, the maximal injection concentration in the maximal injection volume is studied in terms of column dimensions and chromatographic parameters. A sampling valve connected with a solute sprinkler is used with a split-stream technique and is compared with other injection modes with respect to band spreading and column loadability

Determination of the volume of the gas sampling valve for chromatographs

Determination of the volume of the gas sampling valve for chromatographs

Mode of operation and performance characteristics of microbore columns for use in liquid chromatography

The production and operating characteristics of microbore columns are described and details of the modification of the LDC UV monitor to give the necessary low dead volume detection cell for use with such columns are given. A method of connecting the Valco high-pressure sampling valve to microbore columns to provide the necessary small sample volume is described and a system given that permits the operation of the Waters Assoc. 6000 pump over the flow-rate range of 2 to I00 ,ul/min. The effect on column performance of column radius and particle diameter of the packing is examined in detail and height equivalent to a theoretical plate curves and reduced plate height curves are included; the effect of coiling the column on efficiency is also reported. Examples of the use of microbore columns for high-speed and high- efficiency separations are given and include results obtained from reversed-phase columns. The construction and performance of a column having 750,000 plates is described.

A system for turbulent concentration measurements

A system is described for measuring instantaneous concentration values in turbulent flow, when the levels of concentration are too low for conventional laboratory techniques to be used. The system is designed for use in the wind tunnel modelling of atmospheric dispersion. It consists of a small sampling valve, placed in the wind tunnel at the required measuring position, which injects samples of tunnel air into a carrier line of gas flowing to a flame ionisation detector. The low dispersive properties of laminar pipe flow are utilised in passing the sample to the flame ionisation detector. Tests show the system to be capable of measuring down to 1 ppm by volume of trace gas (propane) in air, with a 2 mm diameter sample volume and a 10 m carrier line, at a sampling rate of 2 s-1.

Fischer-Tropsch reaction studies with supported ruthenium catalysts: I. Product distributions at moderate pressures and catalyst deactivation

Hydrocarbon synthesis especially in the range C 5Ci 12 using 0.5% ruthenium-on-alumina pellets at elevated pressures (8 to 16 bar) was undertaken. For this purpose a stirred gas-solid reactor was used together with a gas Chromatograph fitted with an on-line hot sampling valve for a complete product analysis up to C 12. Product spectra consisting mainly of saturated hydrocarbons and with C 5Ci 12 fractions of the order of 23.3–26.9 mol% (of total hydrocarbons) or 54.0–59.5 wt% (assuming saturated hydrocarbons only) were obtained at temperatures close to 500 K. At 550 K and higher, there appears to be a critical space velocity for an optimum yield of C 5C 12. The selectivity of the hydrocarbons leaving the reactor was found to be influenced by the partial pressure of the carbon monoxide inside the reactor. Some catalyst characterizations are also presented, such as carbon burn-off and BET areas, obtained from samples taken at instants when product analyses were performed.