Relative molar responses of some compounds containing oxygen and nitrogen in GC–MS

Relative molar responses (RMRs) of some straight-chain aliphatic alkanes, ketones, aldehydes, alcohols, carboxylic acids, primary amines, aniline, and nitrobenzene derivatives were investigated related to naphthalene. Most of the respective compounds have not been investigated yet due to their high polarity or high boiling point. The earlier cross section data for oxygenated compounds were changed to RMRs which are more utilizable from an analytical aspect. A linear correlation was found between the RMRs and the carbon atom numbers in primary amines. In the cases of aniline and nitrobenzene derivatives the RMRs were also determined; however, no functional relationship was found. The measurement conditions, i.e., the type of column affect the apparent RMRs of aliphatic primary amines. A midpolar column having a higher maximum operating temperature provides a more sensitive apparent RMR (Rtx-1701) than the basic polar column having a lower maximum temperature (Stabilwax-DB), because a high temperature allows setting a higher injector temperature and a higher amount of compound can reach the ion source. Knowing correlations the quantitative analysis passes into easier and fewer reference materials are needed to investigate a sample having many components, because the sensitivities can be determined from the correlations studied in this paper. This is also valid for aromatic compounds, even though no functional relationship exists.     

Comparison of IFCC and NGSP methods for determination of glycated haemoglobin using advanced regression techniques

The objective of this work was a correct statistical comparison of two assay methods for determination of glycated haemoglobin HbA1c. The immunoturbidimetric determination of HbA1c was performed in two ways: using an automatic analyser Hitachi 912, calibrated according to the IFCC reference system (International Federation of Clinical Chemistry and Laboratory Medicine) and using an analyser Advia 1200 and the NGSP reference system (National Glycohaemoglobin Standardization Program). For statistical comparison of these two analytical methods several advanced regression methods were used, which respect random errors of both compared methods. Specifically, Deming regression with and without weights, orthogonal regression, and Passing-Bablok regression were employed. The results demonstrate that the investigated analytical assay methods do not correspond to each other. The summarized results indicate usefulness of better harmonisation of two existing reference systems.     

Improved sensitivity of headspace gas chromatography for organic aromatic compounds

Summary The effect of adding an electrolyte and increasing the temperature on the preconcentration of volatile compounds in headspace analysis has been investigated. Quantification of the interactive effects of temperature and addition of salt on the vapor concentration is of interest for the determination of trace organic impurities in pharmaceutical base materials. This study was undertaken to investigate the quantitative effects of the addition of salts alcohols, and acetone, and of increasing the temperature on the vapor concentrations and distribution coefficients of volatile aromatic compounds (benzene, toluene, ando-xylene). It was found that the concentration of aromatic compound residues in the headspace could be increased by adding an inert salt to the water, but this effect was not very significant because of the low orginal solubility of the aromatic compounds in water. The reverse effect can be achieved by use of polar organic additives; this can be explained by the high polarizability of aromatic compounds and their greater solubility in the presence of these solvents. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999.     

Modelling and measuring the thermal conductivity of multi-metallic Zn/Cu nanofluid

A metallic nanofluid is a suspension of metallic nanoparticles in a base fluid. Multi-metallic nanoparticles are a combination of two or more types of metallic particles. Such multi-metallic nanoparticles were suspended in water using an ultrasonic vibrator for different total volume fractions and different ratios of metallic/metallic nanoparticles. A transient hot wire setup was built to measure the thermal conductivity of the nanofluid at different temperatures. The experimental results were in good agreement with the results in the literature. Then, the experimental results were used as input data for an adaptive neural fuzzy inference system (ANFIS) to predict the thermal conductivity of the multi-metallic nanofluid. The maximum deviation between the ANFIS results and experimental measurements was 1 %. The predicted results and the experimental data were compared with other models. The ANFIS model was found to have good ability to predict the thermal conductivity of the multi-metallic nanofluid over the range of the experimental results.     

Response of flame ionization detectors to different homologous series

Summary Hydrogen flame-ionization detectors (FIDs) are the most widely used type of detector in gas chromatography. The FID signals is proportional to the number of carbon atoms in a hydrocarbon molecule; the presence of heteroatoms usually reduces the signal. If the extent of the signal-reducing effect of heteroatoms were known, it would be possible to measure compounds which are not available as pure standards, or cannot be prepared, or their preparation is very expensive. The sensitivity of a detector to an organic molecule containing heteroatoms is referred to normal hydrocarbons by means of the effective carbon-atom number (ECN) value. By use of the values of increments inECN for heteroatoms and functional groups, theECN can be calculated for any organic molecule. For this, exact values of theECN increments are needed, and the effects of different factors on the increments must be known. In this study a wide range of homologues of normal paraffins, alcohols, amines, and esters was investigated, with emphasis on differences between the behaviour of lower and higher homologues. Studies were extended to theECN values of ketones, and aromatic and halogenated compounds. For all types of compound investigated the difference between the actual carbon number and the calculated effective carbon number (dECN) was compared with literature data, and an attempt was made to interpret the differences.     

GC analysis of gas in halogen lamps using a new sampling device

Summary A new type of gas sampling device was constructed to improve the analysis of the gas in halogen lamps. Low levels of gases such as O₂, CH₄, C₂H₄ and CH₃Br could be determined by the techniques worked out.