Francis I. Onuska

Preparation of surface-modified wide-bore wall-coated open-tubular columns

Abstract A new procedure for modifying the inner surface of glass open-tubular capillary columns is presented. At elevated temperatures ammonium hydrogen difluoride dissociates to produce gaseous hydrogen fluoride which results in silica whisker formation. In comparison with similar procedures, greater uniformity and controlled whisker length can be achieved. The method can be applied to both wide-bore and analytical column preparation yielding high-performance capillary columns. Examples of wide-bore open-tubular columns prepared in this manner are given.

Narrow-bore wall-coated open-tubular columns for fast high-resolution gas chromatographic separations of toxicants of environmental concern

Abstract High-resolution gas chromatographic columns with 100 μm I.D. can achieve better separations than presently used 250-μm I.D. wall-coated open-tubular (WCOT) columns in about half the total time. However, these columns also produce narrower solute peaks that require low dead volume gas chromatographic systems. This paper describes a new technique for static coating of such columns and their adoption for cold on-column injections and interfacing with mass spectrometer and electron-capture detectors. They can be used with present gas chromatographic equipment, usually without any system modifications. A number of questions relating to the use of these new columns were examined experimentally. The results show no compromise in GC performance. A number of applications of narrow bore WCOT columns are presented, including comparisons of separations with corresponding 250 or 320-μm I.D. columns. It is shown that many difficult environmental separations can be resolved using narrow bore WCOT columns.

Determination of nitrophenols by capillary zone electrophoresis in a hydrodynamically closed separation compartment

The use of β-cyclodextrin (β-CD) and polyvinylpyrrolidone (PVP) as complexing agents to capillary zone electrophoretic (CZE) separations of a group of ten nitrophenols was investigated. The analytes were baseline resolved in one CZE run when PVP was present in the carrier electrolyte at a 2.5% (w/v) concentration. β-CD was less effective as it did not baseline resolve a complete group of the studied nitrophenols within an applicable concentration range (0–10 mmol/l). The separations were carried out in a 300-μm I.D. capillary tube made of fluorinated ethylene–propylene copolymer to enhance the load capacity of the separation system. Under these working conditions, a 100-nl sample injection volume resulted in 20–80 ppb concentration limits of detection for nitrophenols, using a photometric absorbance detector operating at a wavelength of 254 nm. The separation efficiencies for the analytes spanned from 1.6–2·105 theoretical plates per meter. Their migration times were reproducible not only in a within day but also in a day-to-day time frame (1% or less for a period of several weeks). This was achieved for a hydrodynamically closed separation compartment while minimizing fluctuations in the concentration of CO2 in the carrier electrolyte. Reproducibility in the determination of nitrophenols was in the range of 1–5% for 1–6 ppm concentrations. Rain, drinking and process water samples served as matrices to assess the practical applicability of the elaborated CZE procedure. This procedure can be combined with isotachophoretic sample pretreatment to make its use possible in situations when nitrophenols are present in the samples at low ppb concentrations.

Open Tubular Column Gas Chromatography in Environmental Sciences

Download PDF Ebook and Read OnlineOpen Tubular Column Gas Chromatography In Environmental Sciences%0D. Get Open Tubular Column Gas Chromatography In Environmental Sciences%0D It is not secret when connecting the writing skills to reading. Reviewing open tubular column gas chromatography in environmental sciences%0D will make you get more sources as well as sources. It is a way that could enhance just how you neglect and also comprehend the life. By reading this open tubular column gas chromatography in environmental sciences%0D, you can greater than what you get from other book open tubular column gas chromatography in environmental sciences%0D This is a popular publication that is released from renowned author. Seen form the author, it can be trusted that this book open tubular column gas chromatography in environmental sciences%0D will certainly provide many inspirations, about the life and encounter and also every little thing inside. open tubular column gas chromatography in environmental sciences%0D. Is this your leisure? Just what will you do then? Having extra or downtime is extremely remarkable. You can do everything without force. Well, we suppose you to save you couple of time to read this e-book open tubular column gas chromatography in environmental sciences%0D This is a god book to accompany you in this leisure time. You will not be so difficult to understand something from this book open tubular column gas chromatography in environmental sciences%0D A lot more, it will certainly assist you to obtain better information and encounter. Even you are having the great tasks, reviewing this e-book open tubular column gas chromatography in environmental sciences%0D will not include your thoughts. You could not should be doubt concerning this open tubular column gas chromatography in environmental sciences%0D It is not difficult way to get this book open tubular column gas chromatography in environmental sciences%0D You can merely visit the distinguished with the link that we give. Right here, you could purchase the book open tubular column gas chromatography in environmental sciences%0D by on-line. By downloading and install open tubular column gas chromatography in environmental sciences%0D, you could locate the soft documents of this publication. This is the exact time for you to begin reading. Even this is not published publication open tubular column gas chromatography in environmental sciences%0D; it will exactly provide even more perks. Why? You could not bring the published book open tubular column gas chromatography in environmental sciences%0D or only stack

Quantitative high-resolution gas chromatography and mass spectrometry of toxaphene residues in fish samples

This report describes an analytical method which permits the determination of ppb (1 microgram/kg) level of toxaphene in fish tissues. Interferences both from biogenic and from xenobiotic substances are reduced even with low-resolution mass spectrometry. The methodology has a low susceptibility to false positive determinations, which could result from the presence of a wide variety of co-contaminants. The method is based on the measurement of a signal representative of the toxaphene residue (m/z 158.9) relative to a known amount of an internal standard 37Cl-labelled compound. A modular approach to toxaphene enrichment has permitted a moderately simple procedure, significantly reducing analytical time requirements and the number of sample manipulations, and making the procedure amenable to automation. The reliability and accuracy of the procedure are demonstrated by the results of intra- and interlaboratory studies. The methodology has been validated and the presented data indicate that the detection limit is 1 microgra/kg of total toxaphene. Toxaphene recovery from fish at concentration levels between 0.1 and 10 micrograms/g is 84 +/- 12%.

Identification and determination of polychlorinated biphenyls by high-resolution gas chromatography

Abstract We have developed an integrated analytical procedure for polychlorinated biphenyl (PCB) multiresidues in sediment samples that enables quantitation of PCB residues at levels as low as 0.1 μg/kg in sediments. PCB residues are characterized and quantified by wall-coated open-tubular column gas chromatography with electron-capture detection. An automated data system, based on a Spectra Physics SP-4100 computing integrator, is used to select and quantitate peaks of individual isomers and homologous groups of PCBs. This procedure consistently yields results with a reproducibility within 3%.

Separation of nitrophenols by capillary zone electrophoresis

Separation conditions suitable to a rapid resolution of a group of eight nitrophenols by capillary zone electrophoresis (CZE) were found. Required differences in their effective mobilities were achieved via host-guest complexation of β-cyclodextrin combined with intermolecular interactions involved by polyvinylpyrrolidone. When both additives were present in the carrier electrolyte at pH=9.1 nitrophenols could be separated in the column of a, 300 μm I.D. and 180 mm in the length within 8–9 minutes. It is shown that the column of such an I.D. providing enhanced sample load capacity, can operate with high separation efficiencies as maintaining zone dispersions due to Joule heating on a tolerable level. CZE on-line coupled with isotachophoretic sample pretreatment is shown to provide the concentration limits of detection at low ppb concentrations by using an on-column photometric detector operating at 254 and 405 nm detection wavelengths.

The Retention Index System

The retention behavior of a compound contains the qualitative information available from gas chromatography. This has long been recognized and stimulated many efforts to establish useful concepts for developing systematic data broadly applicable to analytical problems. The concept of specific retention volume was suggested to make retention data essentially independent of the variable chromatographic parameters.1 Its calculation of the volume of carrier gas reduced to 0 °C required to elute a compound takes into account the column temperature, carrier gas flow rate, column pressure drop, and the amount of liquid phase present. Although it is theoretically correct, specific retention volume is not used in practice because it is awkward to calculate, does not allow for retention changes with temperature, and calls for values that may change. The use of relative retention data is at present the most accepted method. In the determination of relative retention, the retention of both a reference compound and the sample components are determined under identical chromatographic conditions. Since it is almost impossible to establish only one compound to be a reference, a more universal method is needed for wide usage. It is known that under isothermal conditions a plot of the logarithm of the adjusted retention time t′ R versus molecular weight of a homologous series is linear.

Adsorption Study of RDX and TNT Explosives in Soils by HPLC

Abstract The environmental contamination by explosives has concerned the scientific community, due to their toxicity, mainly in those areas where the explosives are manufactured, stored, or still demilitarized. This paper describes the RDX and TNT interaction in different matrices. The Freundlich isotherms were used for the data mathematical treatment. The results indicated that the largest adsorption and the smallest desorption of the RDX and TNT explosives occurred in the peat in natura, with adsorption coefficient (Kd) of 24.88 and Freundlich dessorption value 37.56 of RDX explosive, and adsorption coefficient (Kd) 78.11 and Freundlich desorption value 110,31 of TNT explosive.

Poly(a-olefins)—novel non-polar stationary phases for gas chromatography

Abstract Several special poly( a -olefinic) type polymers were characterized and evaluated as non-polar liquid phases for gas chromatography. In addition, a new non-polar stationary phase, produced by the catalytic hydrogenation of an Apiezon L grease is also described. These new phases have the advantage over squalane of a maximum operating temperature of 225° allowing preparation of non-polar well-coated open-tubular columns exhibiting a much wider temperature range. These polymers have desirable physical and chemical properties. Because of their structural configuration, they have the ability to coat glass surfaces with a uniform thin film. A limited number of applications indicate that capillary columns prepared with new phases provide very good separation of different functional group compoundds and can separate structurally similar compounds such as Mirex and its metabolites.