Profiles of volatile metabolites in biological fluids using capillary columns

Nickel capillary columns coated with moderately polarstationary phases such as Witconol can be used for the separation of the organic volatile fraction from biological fluids. A “transevaporator” sampling technique for the collection of the organic volatiles on glass beads from as little as 5 to 500 μl of biological fluids (e.g. urine, serum, amniotic fluid, breast milk, saliva, etc.) is described. The organic volatiles are thermally desorbed from the glass beads into a short precolumn cooled in liquid nitrogen, which overcomes the problems associated with sample introduction onto narrow-bore capillary columns. The application of the full analytical technique to problems associated with the early detection of disease is illustrated.     

A novel method of preparing of glass capillary columns: Low-temperature plasma etching and polymerization

A novel method is described for the preparation of stable glass capillary columns (glass open tubular columns), including the etching and formation of a polymer film on the inner glass capillary surfaces. The approach used here is based on low-temperature plasma etching and polymerization. Under the influence of a field of radio frequency discharge, low pressure gases of fluoric compounds, introduced into the glass capillary tube, generate excited fluorine radicals which etch the inner surface. The plasma of organosilicone monomer in the glass capillary yields a uniform polymerized film on the inner surface. The resultant material functions as a good stationary phase for glass capillary gas chromatography (GC²). The inner surfaces treated with such a plasma, can be studied by means of a scanning electron microscope (SEM). The flexibility of this method permits the use of various stationary phases and surface modification.     

Variation of tube diameter and film thickness of capillary columns

This paper briefly surveys three important considerations related to the tube diameter and film thickness. These are the interrelationship of these two parameters through the phase ratio, the different meanings of the term “efficiency”, and the influence of film thickness and tube diameter on sample capacity. Comparative examples are given for columns having different diameters and film thicknesses.     

Gas-liquid chromatography of amino acids: Columns and methodology as a basis for routine amino acid analysis using glass capillary gas chromatography

A carefully Standardized technique is described for the preparation of glass capillary columns which can be used successfully for routine quantitative amino acid analysis. Comparison is made between two different modes of sample injection. Preliminary quantitative results from “split” injection and “on-column” injection techniques are evaluated statistically and it is concluded that the “on-column” system is a prerequisite for quantitative amino acid analysis by glass capillary gas chromatography. An analysis of fish muscle protein hydrolyzate illustrates an application of this technique and results are compared with those from a packed column analysis.     

Extra-column effects in multi-dimensional switching systems (MDSS) — GC

In order to permit valveless MDSS operation and easy column change, the hardware designed contains several connections. These can give rise to extra-column band broadening effects. In order to quantitate such effects, the packed-capillary column configuration (without trap) was used. The band broadening caused by the connections was found to be small: 120 ms². A more practical approach was used to check the performance of the trap (re-injection) in the capillary-trap-capillary column configuration. Here the results obtained with re-injection from the trap were compared with results obtained in transfer and heart-cutting modes while the trap was heated. Re-injection was tested with n-alkanes ranging from n-C₆ to n-C₂₈. A starting peak width of 1.6 s was found.     

Gas chromatography of amino acids: Use of a fused-silica capillary column in the determination of plasma amino acids

A capillary chromatographic procedure using a fused silica column is described which can be used to quantitatively determine amino acids in plasma following the pre-chromatographic “clean-up” described in a recent paper [1]. In substituting this procedure for that involving a packed column, advantage has been taken of the greater resolving power to separate amino acids from background component peaks. In order to extend this advantage and provide a sound basis for quantitative analysis, the technique of cold on-column injection was employed. As a result, good precision of standard analysis was obtained with relative standard deviation (RSD) values for all amino acids of less than 4%. Application of the entire procedure to plasma samples yields RSD values of better than 10% for all amino acids with recoveries ranging from 72% to 104%. Simultaneous determination of plasma amino acid levels by gas chromatography (GC) using capillary columns and by classical ion exchange (CIE) showed reasonable agreement. Statistical evaluation showed no significant difference between twelve amino acids. Values for the remaining two, namely, phenylalanine and histidine are significantly different (p < 0.005). Comparison of the values obtained from GC capillary and packed columns reveals no significant difference between fourteen amino acids. Significant differences exist between results for phenylalanine and tyrosine (p < 0.001). It is concluded that there is good agreement between data obtained by GC capillary and CIE techniques and that differences between results for phenylalanine and histidine are method related.     

Preparation of inert glass capillary columns coated with UCON 50 HB-5100. An attempt to rediscover industrially produced α, ω-polyethylene/polypropyleneglycol ethers as stationary phases in capillary gas chromatography

Using UCON 50 HB-5100, one of the most successful stationary phases in capillary gas chromatography during the past decade, as an example, we wish to redirect attention to the excellent properties of the polyethylene/polypropyleneglycol ether copolymer coatings. Based on experience gained in work with OH-terminated polysiloxanes, a method is described for preparing inert and relatively temperature stable chemically bonded and crosslinked coatings in a single working step. Methyltrimethoxysilane was used as coupling agent, and trifluoroacetic acid was introduced as an acidic catalyst. The reaction mechanisms involved as well as the influence of additional crosslinking on the column behavior are discussed, particularly with respect of the inertness of the coatings.     

Synthesis,Structures, Fluorescence Properties,and Natural Bond Orbital (NBO) Analysis of Two Metal [EuIII,CoII] Coordination Polymers Containing 1, 3‐Benzenedicarboxylate and 2‐(4‐methoxyphenyl)‐1H‐imidazo[4, 5‐f][1, 10]phenanthroline Ligands

Two new metal‐organic coordination polymers[Eu(m‐BDC)_1.5(MOPIP) · 1/2H₂O]_n ( 1 ) and [Co(m‐BDC)(MOPIP)₂ · 2H₂O]_n ( 2 ) [m‐H₂BDC = benzene‐1, 3‐dicarboxylic acid, MOPIP = 2‐(4‐methoxyphenyl)‐1H‐imidazo[4, 5‐f] 1 , 10 phenanthroline] were hydrothermally synthesized and structurally characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. The coordination polymers crystallize in monoclinic space group P2₁/m for 1 ( 2 : P2₁/n), with a = 9.779(2), b = 18.242(4), c = 17.146(3) Å, β = 106.41(3)° for 1 , and with a = 8.2153(16), b = 27.974(6), c = 17.974(4) Å, β = 100.40(3)° for 2 . The crystal structure of complex 1 is a zipper‐like chain of octacoordinate Eu³⁺ ions, in which Eu³⁺ ions are bridged in two coordination modes by m‐BDC²⁺ ligands and decorated by MOPIP ligands. The molecular structure of complex 2 consists of a hexacoordinte Co²⁺ atom, which generates a slightly distorted octahedral arrangement, and assembles into three‐dimensional supramolecular nets by π ··· π stacking interactions. Additionally, these two compounds show strong fluorescence in the solid state at room temperature. Natural bond orbital (NBO) analysis is performed by using the NBO method built in Gaussian 03 Program. The calculation results show a weak covalent interaction between the coordinated atoms and metal ions.