Giancarlo Goretti

Evaluation of small diameter capillary columns for gas chromatography

Abstract Glass and fused silica capillary columns of inner diameter 50–200 μm were compared for their chromatographic characteristics and their application to the analysis of complex mixtures. The results show that columns of small diameter can be usefully employed in gas chromatography despite some instrumental difficulties.

A General Procedure For Preparing High Resolution Glass Capillary Columns

SummaryThe critical factor in the preparation of glass capillary columns is the coating of the inner wall with stationary phase. Difficulty is usually met when a very polar compound has to be coated and statisfactory results are obtained only when the inside surface is roughened. Though a number of devices have been suggested, reproducible results are seldom obtained. The outstanding properties of graphitized carbon black (GCB) permit the formation of an ideal precoating of a glass capillary upon which any stationary phase can be applied. The precoating is carried out by flowing through the capillary a colloidal solution of GCB obtained by exposing a 1% solution in methylene chloride to an ultrasonic generator. A colloidal solution is obtained by means of this treatment, which after introduction into the capillary and evaporation of the solvent leaves a layer, which strongly adheres to the surface and is not even removed by washing with polar and non polar solvents. After washing the graphite surface a new stationary phase can be coated on it. A great variety of columns of different polarity can be prepared such as SP 1000, apiezon, carbowax, SE 30 and SE 52, and their characteristics are evaluated. The use of a colloidal solution prepared by ultrasonic means can be extended also to the preparation of gas solid columns.

Evaluation of capillary gas chromatographic columns in series : Analytical application to lemon oil

Abstract The advantages of capillary columns connected in series for solving analytical probles are discussed. Two columns of the same length and very different polarity (SE-54 and PEG 20M) were used. Under isothermal conditions, owing to the carrier gas compressibility a noticeable increase in polarity is observed when the sequence of columns SE-54—PEG 20M is reversed. With temperature programming, an increase in the programming rate decreases the influence of the second column. By changing the programming rate during the analysis it is possible to optimize the column polarity to obtain the best separations. An application to the analysis of lemon oil is reported; complete separation of the most important components was achieved.

Rapid determination of chlorinated pesticides using CN-bonded cartridges followed by GC-ECD

SummaryGas chromatography of chlorinated pesticides in water is carried out after adsorption of a 50 mL sample using a cartridge containing 100 mg CN-bonded porous silica and extraction with 500 μL pentane. The average recovery for eight organochloride pesticides at 1 ppb was >95%. The procedure described is simple, selective and reproducible.

The coupling of the flame photometric detector and the free fatty acid phase (FFAP) capillary column in the trace analysis of sulphur compounds

Abstract Trace amounts of sulphur compounds in gaseous mixtures, in organic liquids and in particulate matter were detected by means of a photometric detector coupled with a FFAP capillary column. This system permitted the detection of some sulphur compounds in citrus oils and confirmed that the odour of diesel exhausts is not due to the presence of sulphur compounds.

Short open tubular columns to trap organic micro-pollutants from aqueous samples

SummaryIn two previous articles some of the present authors had assessed and proposed the direct use of an analytical capillary column with a bonded phase for both trapping and later GC analyzing organic compounds. A few factors influencing band dispersion of the solute had been investigated and a mathematical relationship developed to calculate the degree of retained-substance dispersion starting from GC peak widths.This paper presents the effects of other variables (such as stationary-phase polarity, percentage of methanol added to samples, class of tested compounds, pH of some solutions and ionic strength of the aqueous medium) on the trapping efficiency. A new approach is also proposed for the determination of the constants necessary to use the above-mentioned relationship. The possibility of applying this sampling technique to “real”-samples analysis was assessed after evaluating the effects of a washing treatment of the stationary phase on the retained solutes. The suggested technique allows direct preconcentration and GC determination of organic compounds that are not very soluble in water.

Trapping efficiency of aqueous micropollutants sampled and analysed using the same capillary column. Theoretical aspects and experimental results

SummaryThe possibility of using capillary columns for both sampling and gas chromatographic analysis of aqueous micropollutants has been studied. Factors influencing gas chromatographic band dispersion of the solute were investigated and a mathematical relationship developed correlating the properties (ID, df) of the capillary columns to the degree of dispersion of adsorbed substances has been derived. The experimental results obtained with aqueous samples are in good agreement with the theoretically forecast data. The method developed allows gas chromatographic dosing of traces of organic substances, reducing inconvenience deriving from excessive sample handling to a minimum. Non-refocusing of the analyte does not, in any significant way, compromise column efficiency for substances that are not very soluble in water.

Gas—liquid microcapillary columns precoated with graphitized carbon black

Abstract Glass and fused-silica capillary columns (100 μm I.D.) were precoated with a very thin layer of graphitized carbon black and then coated with polar liquid phases. The layer of graphitized carbon black and then coated with polar liquid phases. The layer of carbon black in the inner walls increased the wettability of the capillary columns and, consequently, a very uniform coating was obtained. The polymeric polar liquid phases were also more strongly retained on the carbon black, and these microcapillary columns showed a much higher temperature stability. Columns coated with free fatty acid phase, Carbowax 20M, 40M and 600M were prepared. The columns were tested with a mixture of polar compounds.

Development of porous-layer capillary columns

Abstract Procedures for preparing porous-layer capillary columns have been improved and their preparation with kaolin and graphitized carbon black coated with a variety of stationary phases is described. It is shown that an almost theoretical coverage can be achieved and that short columns with high efficiency can be realized. A number of separations (terpenes, essential oils, anilines, chlorocarbons, amines, alkylbenzenes isomers) are reported.

Hydrophobic-phase-modified fused-silica columns for capillary electrophoresis

Coated capillaries modified with a hydrophobic layer were developed. Linear hydrocarbons and ethylbenzene modified surfaces greatly improved the electrophoretic performance of the capillaries. The column efficiency for organic compounds reached as high as 327 000 theoretical plate numbers per meter on a 50 microm I.D. linear hydrocarbon (C6) surface treated fused-silica capillary column. This value did not change during 50 repeated analyses and the columns showed strong stability against 0.1 M NaOH and 0.1 M HCl. The relative standard deviation of the run-to-run, day-to-day, and capillary-to-capillary coating with hydrophobic layer showed values of < or =2.5%, and good reproducibility. The separations of four aromatic amines and six pharmacological amines at pH 2.5 is reported.