Volume Of Liquid Sample Research Articles

Calibration of an automatic instrument for bicarbonate monitoring

Abstract The performance of an automatic instrument which allows one to measure discontinously (every 20 minutes) bicarbonate alkalinity (BA) in complex organic solutions is evaluated. Bicarbonate concentration is determined from overpressure measurements in a sealed vessel where inorganic carbon is completely converted to carbon dioxide after acidification of the sample. The accuracy of the instrument has been tested as a function of various operating parameters (ratio of overhead gas volume in the vessel over the liquid sample volume, concentration of bicarbonates and temperature). Error sources were evaluated and operating conditions which yield satisfactory performance identified.

Use of the 1294 keV photopeak of41Ar to correct for variations in liquid sample volume

A measurement of the41Ar content in the vial containing a liquid sample can be used to correct for variations in sample geometry due to changes in liquid sample volume. This technique makes use of the residual argon in the atmosphere when performing INAA of relatively short-lived radionuclides. The correction factor requires somea priori knowledge of the argon content of the solvent. Application of this correction technique requires the use of sample vials with consistent internal volumes. The need for correction is most evident with samples contained in vials of small cross section when using a vertically facing detector.

On-line coupled reversed-phase high-performance liquid chromatography—gas chromatography—mass spectrometry: A powerful tool for the identification of unknown impurities in pharmaceutical products

An alternative approach to HPLC—MS involving direct coupling of reversed-phase HPLC to GC—MS is described for the identification of unknown impurities in pharmaceutical products. Conventional-sized reversed-phase HPLC (column of 4.6 mm I.D., flow-rate 2 ml/min) was coupled to GCMS. Liquid sample volumes of 500 μl were transferred. In contrast to LC—MS coupling techniques, the proposed method technique experiences no problems with low-molecular-mass solutes or any buffer salts in the reversed-phase LC eluent. An example illustrating the use of this technique in analytical research and development in the pharmaceutical industry is presented. As unknown impurity observed in the HPLC of a stressed sample of a pharmaceutical product was identified by directly transferring the LC fraction of interest to a GC—MS system. The transfer problems arising from the content of water and buffer salts in the LC eluent were circumvented by on-line coupling of liquidliquid extraction by means of a sandwich-type phase separator, which was coupled to a loop-type LC—GC interface. It is shown that this technique can be improved by lowering the extraction temperature below the freezing point.

Combined two‐dimensional GC/MS/matrix isolation FT‐IR with a versatile sample introduction system

AbstractA versatile sample introduction system or injector/trap (I/T), described in this paper, is a stand‐alone, computer‐controlled, cryogenic concentrator with provisions for solvent venting and inert sample transfer. The I/T is designed to provide a common interface between the column and a variety of sampling modules.Modules to perform thermal desorption and pyrolysis, as well as modules for remote sampling (pre‐traps) have been developed. Large volumes of either gaseous or liquid samples can be introduced by means of pre‐traps packed with suitable substrates. Pretraps packed with Tenax TA allowed quantitative recovery of compounds as volatile as n‐decane (n‐C10) when contained in a 1‐mL volume of pentane. The introduction of a 1–mL sample makes it possible to reach a detection limit of ca. 100 ppt,ppt, ppb, ppm refer to parts‐per‐trillion (1012), billion (109), and million (106), respectively. with an FID, for compounds with boiling points ≥n‐C9.The capability to do trace analyses with the I/T is enhanced by interfacing it to a twodimensional gas chromatograph (2D/GC) equipped with a mass‐selective detector (MSD) and a matrix isolation fourier transform infrared spectrometer (MI FT‐IR). The resulting instrumentation greatly facilitated the identification of organic compounds present at ppbconcentrations in perfume samples.

An electric birefringence cell with small intrinsic optical retardation

A sample cell for electric birefringence measurements which has a special adjustable low-strain attachment of suprasil windows to the cell body is described. Its intrinsic optical retardation is below a few minutes. The optical path length is 75 mm and the spacing of the plane parallel electrodes (oriented perpendicularly to the windows) is 1.77 mm. Only a small volume of liquid sample is needed (less than 2 cm3) and filling, flushing or cleaning of the cell is easily performed.

Discrete microsample injection into a gaseous carrier

Discrete injection (DI) of μl- volume liquid samples into a continuous flow of air as carrier is demonstrated. Atomic-absorption (AA) detection is used. Calibration graphs for zinc, obtained by using the DI-AA-air carrier method have a slope 1.8 times that of graphs obtained by the flow-injection analysis (FIA)-AA-air carrier method. The DI-AA-air carrier signals are higher and sharper than the FIA-AA-water carrier signals, and even exceed the AA steady-state signals for the same zinc solutions, owing to improved nebulization/atomization. The air-carrier method is more rapid than the liquid-carrier method. Measurement rates of 600/hr are possible. The signals show precision comparable to that attainable with water as carrier. The method is particularly useful for flame or plasma detectors and is potentially useful with different gases or vapours as carriers, and for gas-liquid reactions in FIA.

The determination of sulphur and phosphorus by cool-flame chemiluminescence emission spectrometry with an electrothermal atomiser for sample introduction

The technique described allows simple and rapid determination of sulphur and phosphorus in solutions of samples and sample digests. A graphite-tube atomisation device is employed for the introduction of microlitre volumes of liquid samples, after desolvation, into a cool argon—hydrogen entrained air flame in which the chemiluminescent emission from S 2 and HPO species is monitored by using a wide band-pass monochromator system.

Optical emission spectrometry with an inductively coupled radiofrequency argon plasma source and direct sample introduction from a graphite rod

Preliminary studies of analytical performance are described for an instrumental assembly in which microlitre volumes of liquid samples are applied to a graphite rod, desolvated and the rod is inserted axially directly into a continuously operating low-power inductively coupled argon plasma. Simplex optimisation of operating parameters has been undertaken for manganese to determine the most favourable signal to background intensity ratios and detection limits are reported for manganese, cadmium, cobalt, copper, iron, nickel and lead.

A “spiral test” applied to bacterial mutagenesis assays

A new procedure (the spiral test) has been set up and validated for the distribution of chemicals in bacterial multagenesis asssays. This metzhod involves the use of a special instrument (spiral plater), which dispenses, along a spiral track, decreasing volumes of liquid samples, from the near centre to the periphery of a rotating agar plate. A gradient of concentration of a compound up to about 1500:1 is thus formed on a single plate. The activity of 18 mutagens of various potencies and chemical classes was checked in the Salmonella/microsome test by dispensing their solutions either on the surface of top agar (method A) or of the minimal-glucose agar medium, before the addition of molten top agar incorporating bacteria and eventually S9 mix (method B). Compared with the spot test, the gradient of concentration of a compound produced by the spiral diluter was much wider and more gradual. Even non-diffusible chemicals (e.g. benzo[ a]pyrene and benz[ a]anthracene) were efficiently detected in the spiral test, as well as very weak (e.g. mebanazine and trimethylphosphate) or borderline (e.g. perylene, 1,1-dimethylhydrazine and procarbazine) mutagens, which were negative in the spot test. Method B was at least as sensitive as the plate-incorporation test, such a goal being achieved in a single plate instead of in serial plates. Technical problems made method A less sensitive, but it was more efficient in detecting unstable mutagens (e.g. β-propiolactone). Like the plate test, the spiral test appeared to be suitable for a semi-quantitative assessment of mutagenicity data, and was efficient in demonstrating both the activation of promutagens and the deactivation of some directly acting mutagens. Preliminary assays were also carried out with repair-proficient (WP2) or -deficient (TM1080: lex A −/ polA −/R391 and CM871: lexA −/ uvrA −/ recA −) trp − strains of E. coli.

A novel device for the accurate dispensing of small volumes of liquid samples

A sample dispenser with electronic control of delivered volume has been designed and evaluated. With this device, liquid samples are dispensed in the form of uniform droplets less than 4 nl in volume; total volumes as small as 40 nl can be delivered with 1.5% precision. Important features of the microdroplet formation process have been studied and the effect of sample solution concentration and viscosity have been examined. The dispenser is expected to find application in several areas, including electrothermal atomization atomic absorption spectrometry, automated titrimetry, and high-precision, low-volume solution sampling.

Techniques for High-Performance Liquid-Liquid and Ion Exchange Chromatography with Controlled Surface Porosity Column Packings

The speed of liquid-liquid and ion exchange chromatographic separations can be significantly increased with columns of controlled surface porosity (CSP) packings. Electron micrographs show that these CSP materials provide a relatively large surface area on which a thin film of sorbent may be uniformly dispersed; the open-structured surface is readily accessible to the mobile phase. The high speed capabilities of these packings are primarily due to the low level of peak broadening resulting from mass transfer effects. Important parameters for providing highly efficient liquid chromatographic separations include: the type of column tubing used, column configuration, and the volume of liquid sample injected into the column. Liquid chromatographic analyses are carried out with CSP packings in a manner analogous to gas chromatography with regard to time and column efficiency. Liquid-liquid chromatographic columns containing CSP support have been routinely used for the precise assay of materials which cannot be analyzed by other means. Separations of test systems show that the CSP cation and anion columns provide separations at least an order of magnitude faster than conventional gel ion exchange chromatography.

Vacuum line buret for measuring liquid sample volumes

Vacuum line buret for measuring liquid sample volumes