Some applications of capillary gas chromatography in clinical chemistry

Profile analysis using capillary gas chromatography is applied in clinical chemistry to detect metabolic abnormalities. Examples are the increase of the urinary excretion of aromatic acids carrying a 4-hydroxyl group and the decrease of hippuric acid in liver cirrhosis, and the elevated concentrations and excretions of dicarboxylic, oxocarboxylic, and hydroxycarboxylic acids in diabetes mellitus. Gas chromatographic quantitations, in some instances using mass selective detection, are performed on clinically relevant constituents. An example is the investigation of plasma and urinary hippuric acid and 3-carboxy-4-methyl-5-pro-pyl-2-furanpropionic acid in different stages of renal diseases.     

GC-MS separation and quantitation of 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid and hippuric acid from plasma of patients with renal failure: Application to blood purification methods

Solid-phase extraction, capillary GC, and mass selective detection have been used to determine 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (furanpropionic acid) and hippuric acid in the plasma of patients with chronic renal failure. The concentrations of furanpropionic acid and hippuric acid were found to be highly elevated and reached levels of 4.56 ± 2.37 mg/dl (10 to 20-fold higher than normal) and 12.90 ± 14.06 mg/dl (40 to 60-fold), respectively. Treatment by hemodialysis and hemofiltration effectively eliminated hippuric acid (on average by 66 and 56%, respectively) but had little effect on furanpropionic acid. Intermittent peritoneal dialysis gave the best long-term results. Both components were maintained at a lower level than by hemodialysis and hemofiltration.     

Characterization of the chemical homogeneity of solid-state materials by chemometric methods. Multivariate aspects and general recommendations

Summary Data from milliprobe analysis of a copper standard material by spark source mass spectrometry have been investigated using multivariate methods in addition to earlier — predominantly univariate — treatment in order to derive some general recommendations for characterizing the chemical homogeneity of solids. A disarmed MANOVA test with the locations as effect variables and the normalized concentration data of the diverse chemical elements as replicates provided a highly rigorous Yes-No decision on homogeneity from an overall point of view. For more detailed information, data visualization by raster graphics combined with cluster analysis, principal components analysis, and non-linear mapping proved a useful explorative tool, particularly in the (here assumed) case without any preinformation. Dependent on how these methods are used, information on locations of inhomogeneities or on correlations between the analytes results. It has been shown that seeking for correlations should be the first explorative step. Employing the further steps to correlating elements increases the rigour of detecting element-specific inhomogeneities. On the other hand, including all the determined elements enables a more critical judgment of collective homogeneity. To confirm multivariate results on inhomogeneity by statistical means, the revealed groups of sub-samples should be tested by linear discriminant analysis. Deviations from a homogeneous distribution can be detected and/or characterized for any single element (or correlating elements) individually by univariate methods based on models of the spatial distributions, if these can be presumed a-priori or after preliminary investigations.     

Applications of fuzzy theory to spatially resolved analysis of solids

Fuzzy theory is applied to compare response profiles and surfaces in spatially resolved materials analysis. Different options are proposed for the type of membership function, the definition of spreads, and specially defined similarity values. These similarity values are expressed analytically, thus permitting the development of a fast computer program. A special normalization in the calculation of the similarity values allows a set of distributions to be arranged hierarchically by clustering; the distributions are displayed as a dendrogram. The fuzzy techniques are also used to judge the homogeneity of a solid with respect to the distribution of chemical elements on its surface. Depth profiles from Rutherford back-scattering spectrometry and results of surface analysis by spark-source mass spectrometry are investigated as practical examples.     

Mass spectrometric identification of modified urinary nucleosides used as potential biomedical markers by LC–ITMS coupling

In diseases accompanied by strong metabolic disorders, like cancer and AIDS, modifying enzymes are up- or down-regulated. As a result, many different types of metabolic end-products, including abnormal amounts of modified nucleosides, are found in urine. These nucleosides are degradation products of an impaired ribonucleic acid (RNA) metabolism, which affects the nucleoside pattern in urine. In several basic experiments we elucidated the fragmentation pathways of 16 characteristic nucleosides and six corresponding nucleic bases that occur in urine using electrospray ionization ion trap MS⁵ (ESI-ITMS) experiments operated in positive ionization mode. For urinary nucleoside analysis, we developed an auto-LC–MS³ method based on prepurification via boronate gel affinity chromatography followed by reversed phase chromatography. For this purpose, an endcapped LiChroCART Superspher RP 18 column with a gradient of ammonium formate and a methanol–water mixture was used. This method gives a limit of detection of between 0.1 and 9.6 pmol for 15 standard nucleosides, depending on the basicity of the nucleoside. Overall, the detection of 36 nucleosides from urine was feasible. It was shown that this auto-LC–MS³ method is a valuable tool for assigning nucleosides from complex biological matrices, and it may be utilized in the diagnosis of diseases associated with disorders in RNA metabolism.     

N-Methylation and N,N-dimethylation of amino acids. An artifact production in the analysis of organic acids using diazomethane as derivatizing agent

In the fractions of the methyl esters of urinary organic acids seventeen N-methylated or N,N-dimethylated amino acid methyl esters are identified by gas chromatography-mass spectrometry. It is shown for twelve amino acids that their amino group reacts with diazomethane to form these derivatives. Using deuterated reagents, in particular deuterated diazomethane, in the sample preparation procedure during the organic acid analysis, it is shown that the N-methylated and N,N-dimethylated amino acids are artifacts from diazomethane and are not biochemical N-methylation products.     

Feasibility studies for the preparation and certification of reference materials Part II: mineral oil contaminated waste materials

The 2-year international joint project HYCREF (Contract-No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogenous and stable water-, soil- and waste reference materials contaminated with mineral oil hydrocarbons and to test certify the mineral oil content by gas chromatographic methods. As mineral oil products are important sources for environmental contaminations, appropriate reference materials certified by using the new gas chromatographic methods (soil: ISO/FDIS 16703, waste: prEN 14039 and KW/04, water: ISO 9377-2) are highly needed. Additional to the HYCREF-results presented in part I–mineral contaminated soils–this second paper gives an overview of the feasibility study for the preparation and test certification of three waste reference materials (offshore marine sediment, building material and industrial waste). The following specifications, which had been defined in the project work plan, were reached successfully: uncertainty of the mineral oil content resulting from the certification exercise ≤5% and a between-bottle inhomogeneity of ≤3%. All three materials have been evaluated for long- and short term stability. They contain different levels and types of mineral oil and cover the full application range of ISO/FDIS 16703 and prEN 14039 (100–10,000 mg/kg). The expanded uncertainties U _cert of the three materials are about 6%. In this way, they are comparable to ERM^®-CC015a (U _cert=7.1%, mineral oil in a river sediment) and are suited to close the present gap of commercially available CRM for mineral oil determination in waste.     

Interaction of Aluminum Metaphosphates in the Setting of Potassium Silicate Solutions in Terms of the Crystalline Phase Composition.

Aluminum phosphates are known as inorganic hardening agents for the setting of alkali silicate solutions, but only few studies have been published on the setting mechanism of potassium water glass. The solution behavior of two aluminum metaphosphates in alkaline environments were investigated photometrically determining the dissolved aluminum content. The crystalline phase composition of the hardened potassium silicate systems was determined by X-ray diffraction. New insights into the setting mechanism were obtained concerning the structure of the aluminum metaphosphate and the SiO₂/K₂O ratio of three different potassium silicate solutions. With increasing pH value aluminum tetrametaphosphate reacts rapidly and forms crystalline potassium tetrametaphosphate dihydrate by an ion-exchange-reaction. In parallel, a depolymerization of the cyclic metaphosphate structure occurs leading to potassium dihydrogen phosphate as final fragmentation product. With aluminum hexametaphosphate no ion-exchange reaction product was observed. Only potassium dihydrogen phosphate could be found in higher quantities compared to the reaction with aluminum tetrametaphosphate.