Total Amount Of Sample Research Articles

Optimization in headspace GC/FTIR

In recent years GC/FTIR has developed into a valuable complementary technique to GC/MS, yielding additional information especially with respect to the identification of isomeric compounds. A disadvantage of GC/FTIR is its inherent inability to attain the low detection levels of GC/MS. Sensitivity is known to be enhanced when employing headspace GC for the trace analysis of volatile components in a non-volatile matrix. Thus, lower detection limits may be expected in GC/FTIR when using the headspace sampling technique. Nevertheless, very little work on headspace GC/FTIR has been done in the past [1]. Generally speaking, optimization in GC/FTIR means increasing the amount of sample and modifying the chromatographic operating parameters in order to obtain the best compromise between maximum chromatographic resolution and highest S/N ratio of the infrared spectra. Using the equilibrium headspace technique, the chromatographic resolution is influenced most strongly by the volume of gas injected onto the column. In balanced pressure sampling with a long injection period, the total amount of sample may be so large that peak distortion will occur. Therefore, in order to optimize headspace GC/FTIR, information is needed on how the sampling time will influence the chromatographic resolution and the S/N ratio of the spectra. The best possible approach to optimized headspace GC/FTIR utilizes the cryogenic capillary head trapping technique, which allows high preconcentration during long sampling periods without any loss in chromatographic resolution [2].

Visman equations in the design of sampling plans for chemical analysis of segregated bulk materials

From preliminary measurements, guidelines are given for determining whether a bulk population is well-mixed or segregated and for the design of experiments to estimate sample size and number. For well-mixed populations, the total amount of sample collected determines the degree to which the population is represented. For segregated populations, sampling uncertainty is reduced primarily by increasing the number of sample increments collected. Methods for estimating Visman's sampling constants for segregated populations are discussed, along with a way of calculating a theoretical average particle mass for nonparticulate materials. An average theoretical particle mass of 20 g was calculated for unmixed samples of Athabasca oil sand. This large value, confirmed by using the Benedetti-Pichler equation, explains the extensive sampling required to estimate reliably the bitumen and water in oil sand.

Sampling in capillary gas chromatography: A comparison between the split and the PTV-split procedures

Parallel studies on split-sampling and PTV-sampling procedures have been made to highlight the difficulties in quantitative analysis for capillary columns. Parameters such as total sample amount, carrier gas and packing material used for the injector glass insert were studied. The results clearly demonstrate the importance of optimizing all experimental parameters which give rise to discrimination effects during injection.

Quantitative investigations on the diaplacental transfer of thallium by field desorption mass spectrometry.

The placental transfer of thallium cations in pregnant mice was investigated by determining the thallium concentrations in fetal and maternal tissue 0.5 to 24 h after application of thallium. The maternal dose of thallium was 8 mg/kg body weight throughout. Uterus and fetus were found not to differ from other organs like heart and liver in time course and magnitude of thallium uptake with an initial surge during the first few hours of exposure to thallium and a rapid decrease to steady 12 and 24 h values somewhat lower than those found in the kidney. Diaplacental transfer is therefore assumed comparatively rapid and a specific placental barrier for thallium does not seem to exist. For the determination of thallium concentrations Field Desorption Mass Spectrometry was utilized as a reliable, fast and sensitive method for the analysis of metal cations in biological material. This method does not require extensive pretreatment of the tissue and total sample amounts in the range of milligrams and less are sufficient for quantitative analysis.

On-Line Identification of Gas Chromatographic Fractions by a Raman Multichannel Spectrometer

A Raman multichannel system is described which is feasible for the on-line identification of fractions separated by gas chromatographic columns. In Raman multichannel systems, the sensor, i.e., the laser focus, is small enough and the possible recording times are short enough to avoid any affliction of the separation process, even with capillary columns in use. At the measurements described, capillary columns with a length of 15 m and an inner diameter of 0.25 mm were employed. The detection limit was at about 1 to 10 nl of one fraction corresponding to about 1 to 10% of the total amount of sample suited for capillary columns.

QUANTITATIVE DETERMINATION OF AIRBORNE ASBESTOS DUST IN OCCUPATIONAL ENVIRONMENT BY X-RAY DIFFRACTION USING CONVENTIONAL AND ROTATING ANODE X-RAY TUBE

X-ray diffraction is used as an analytical tool for crystalline substances which are hazards in an occupational and natural environments. This paper describes a method for qualitative and quantitative determination of asbestos in airborne dust in the occupational environment. Airborne asbestos collected on glass fiber filter by means of high volume air sampler can be analyzed without removal of the dust from the filter and also without addition of internal standard material. For determination of amounts of total dust, the filter is weighed before and after the collection of the sample. For estimation of mass per unit volume of air, the total volume of air that passed through the filter is recorded. In order to obtain asbestos content in airborne particulates, two types of X-ray generators are used in this study. One is equipped with conventional sealed anode X-ray tube. It is applicable to determine quantita-tively 1 to 5 mg of asbestos with this method. The other is equipped with rotating anode X-ray tube in order to generate high power X-ray. This procedure can be carried out routinely in a laboratory and in occupational environment when the total amount of sample is of the order of 0.01 mg of glass fiber filter of 3.8 cm2 in area.The results of field survey indicate very high concentration of both asbestos and total dust in working area of asbestos industry, especially of sprayed mineral fiber containing asbestos.

Diffusional titration errors in coulometry Part I. Analytical solutions for non-stationary diffusion through non-interacting membranes

Analytical solutions are given for non-steady state diffusion in a membrane and a semi-infinite connecting chamber. The one-dimensional macroscopic diffusion inside the membrane is assumed to be governed by Fick's law using an empirical proportionality constant. The solutions apply to membranes without dead-end pores. The concentration distributions in the membrane and connecting chamber and the total sample amount inside these are calculated for linearly and exponentially decreasing types of titration. Analytical solutions under the simplified assumption of linear concentration distribution inside the membrane are also given.

Diffusional titration errors in coulometry: Part I. Analytical solutions for non-stationary diffusion through non-interacting membranes

Analytical solutions are given for non-steady state diffusion in a membrane and a semi-infinite connecting chamber. The one-dimensional macroscopic diffusion inside the membrane is assumed to be governed by Fick's law using an empirical proportionality constant. The solutions apply to membranes without dead-end pores. The concentration distributions in the membrane and connecting chamber and the total sample amount inside these are calculated for linearly and exponentially decreasing types of titration. Analytical solutions under the simplified assumption of linear concentration distribution inside the membrane are also given.

Search for biogenic structures and viable organisms in lunar samples: A review

A review of the work on searches for biogenic structures and viable life forms in Apollo 11 and 12 samples shows no evidence for biology in these samples. The total amount of samples examined and the negative results from the variety of systems conducive to growth and metabolic activity make it highly improbable that life will be found in surface samples yet to be tested.

Predictable Low Enrichment of Methane Isotopes by Clusius-Dickel Thermal-Diffusion Columns for Use in Radiocarbon Dating Technique

By means of the Clusius-Dickel thermal-diffusion column the range of the radiocarbon dating method may be extended by 20 000 years. It is shown in this work that the total sample amount required is reasonably low, if column dimensions are suitably chosen. The enrichment run time and the length of the thermal-diffusion column will allow sample enrichment in routine operation. Optimal values of column dimensions and operation conditions are calculated. With an all metal thermal-diffusion column that has been carefully constructed, a high reproducibility is found. The stationary as well as the non-stationary state operation are in agreement with column theory within 1%, concerning the enrichment both of C13H4 and C14H4 in methane. The theory has been evaluated by numerical methods

X-ray diffraction analysis of industrial dust.

Abstract Procedures used routinely in the laboratories of the Division of Occupational Health for the x-ray diffraction analysis of industrial dust are presented with particular reference to new techniques for the collection and analysis of air-borne dust when the total amount of sample is of the order of 1 milligram. The composition is given of a photographic developer for x-ray diffraction films which has low fogging properties and which provides a wide-range, linear intensity-density relationship. The use of beryl as an internal standard for the quantitative determination of quartz in industrial dust is discussed and results obtained by chemical methods are compared with results obtained by x-ray diffraction methods.