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New concepts and techniques for quantification and trace analysis by gas chromatography
KTH, Superseded Departments, Chemistry.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the first part of this thesis, strategies for avoiding systematic errors when quantifying the main components in mixtures of solvents has been developed (paper I). It is shown that variations in density caused by variations in sample composition and/or volume contraction need to be taken into account. In this way, quantification can be improved.

The second part (paper II-V) describes a number of new methods for the analysis of organic trace components present in gaseous or aqueous samples, after an overview of the most commonly applied sample enrichment techniques has been given.

For the enrichment of volatile trace compounds from gaseous samples, the concept of open tubular trapping has been further developed. A simplified procedure for preparing ultra-thick film, sorptive open tubular traps (OTTs) is described (paper III). The traps are coated with an irregular film of PDMS, and it is shown that the performance in terms of breakthrough volume is only marginally affected by the use of such traps. In paper IV, it is shown both experimentally and with a theoretical model that the enrichment capacity of OTTs can be significantly increased by increasing the inner diameter of the traps.

A fully automated procedure for high-capacity sorption enrichment of trace organic analytes present in water is also reported (paper II). Time-based non-equilibrium extractions are feasible, enabling fast extractions that still allow sub-ppt limits of detection. The high flexibility of the automated system makes it possible to sample from process streams or off-line sources.

Finally, the development of a new 2-dimensional precolumn-backflush method for the analysis of polar volatile trace analytes in water is described (paper V). This concept is based on the action of a hygroscopic salt which has a strong affinity for water, in a precolumn. Organic trace compounds, such as volatile alcohols or ketones show little retention on the precolumn and are eluted ahead of the bulk amount of the water onto a capillary column for subsequent high resolution separation. The residual water is removed from the system by backflushing the precolumn. The procedure allows the direct injection of aqueous sample volumes of at least 100 µl, and the pre-fractionation is accomplished within only a few minutes. Quantification limits for selected polar trace components were in the low ppb-region.

Place, publisher, year, edition, pages
Kemi , 2004. , x, 77 p.
Keyword [en]
Chemistry, quantitative accuracy, calibration, extenal standards, valume contraction, molar excess volume
Keyword [sv]
Kemi
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-44ISBN: 91-7283-827-2 (print)OAI: oai:DiVA.org:kth-44DiVA: diva2:12138
Public defence
2004-11-12, Kollegiesalen, KTH, Valhallavägen 79, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2008-10-10 Created: 2008-10-10 Last updated: 2012-03-21Bibliographically approved
List of papers
1. Quantitative accuracy in the gas chromatographic analysis of solvent mixtures
Open this publication in new window or tab >>Quantitative accuracy in the gas chromatographic analysis of solvent mixtures
2003 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 985, no 1-2, 21-27 p.Article in journal (Refereed) Published
Abstract [en]

Quantitative accuracy is of great importance in the analysis of bulk mixtures of solvents, particularly when the analysis is related to quality control of very large product volumes like in solvent recovery plants. Serious errors can be made if the effects of density differences between the pure solvents and volume contractions are not properly addressed. In earlier work, the use of an iterative process for correcting such errors has been suggested. However, in the case of volume contractions and mixtures of several solvents, this procedure is difficult to apply. In the present paper, we describe a simple procedure where calibration curves based on mass concentration are utilized. The densities of calibration mixtures of known compositions are determined with a density meter, in order to provide for correction factors caused by volume contractions. Model experiments with mixtures of water, ethanol, acetone and methanol showed a significant improvement in quantitative accuracy, when the suggested calibration strategy was applied.

Keyword
accuracy, calibration, external standards, volume contraction, molar excess volumes, gas chromatography, ethanol, water, methanol, acetone
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-4909 (URN)10.1016/S0021-9673(02)01830-7 (DOI)000180580400004 ()
Note
QC 20100928Available from: 2008-12-23 Created: 2008-12-23 Last updated: 2017-12-06Bibliographically approved
2. Automated high-capacity sorption probe for extraction of organic compounds in aqueous samples followed by gas chromatographic analysis
Open this publication in new window or tab >>Automated high-capacity sorption probe for extraction of organic compounds in aqueous samples followed by gas chromatographic analysis
2004 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1033, no 2, 339-347 p.Article in journal (Refereed) Published
Abstract [en]

An automated high-capacity sorption device for GC analysis of ultra trace components has been developed. The scope of the presented technique was to combine the simplicity of solid-phase microextraction (SPME) with the high extraction efficiency of the stir bar sorptive extraction technology. Sorptive extractions of water samples were performed using polydimethylsiloxane (PDMS) rubber tubing (120 μl) mounted onto a glass rod. The sampling procedure was carried out by a robotic autoinjector. Since the setup is fully automated, unattended and precise time-controlled extraction of samples is possible and makes quantitation with non-equilibrium extractions feasible. The sorption probes are easy to exchange, which facilitates off-line/in-field sampling. The system was evaluated with a test mixture of 44 environmentally hazardous compounds. Detection limits were found to be in the sub-ppt region. The performance of the system was demonstrated with the analysis of polycyclic aromatic hydrocarbons in urban snow.

Keyword
Automation, Environmental analysis, Extraction methods, Polynuclear aromatic hydrocarbons, Sorption, Water analysis
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-4910 (URN)10.1016/j.chroma.2004.01.056 (DOI)000220398900018 ()2-s2.0-1542298904 (Scopus ID)
Note
QC 20100831Available from: 2008-12-23 Created: 2008-12-23 Last updated: 2017-12-06Bibliographically approved
3. Thick film traps with an irregular film: Preparation and evaluation
Open this publication in new window or tab >>Thick film traps with an irregular film: Preparation and evaluation
2004 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1035, no 2, 159-165 p.Article in journal (Refereed) Published
Abstract [en]

A new method for preparation of sorbent-based ultra-thick film traps for concentration of trace volatile components from gaseous matrices is described. The procedure is based on blowing a prepolymer (polydimethylsiloxane) through a capillary tube, forming an irregular film of stationary phase. Subsequently, the prepolymer is immobilized in a few seconds by heating to 200 °C. Evaluation of the performance of the new traps showed that the loss of efficiency, compared to regular smooth film traps is only on the order of 20–30%. In terms of breakthrough volume, this loss in performance is rather insignificant. The technology is extremely simple and allows a rapid and cheap production of a large number of ultra-thick film traps, even in non-specialized laboratories. The method can be applied to any type of cross-linkable stationary phase, thereby expanding the scope of sorbent-based trapping and preconcentration concept. Many applications are anticipated in trace and ultra-trace analysis in a wide range of fields, such as environmental chemistry, polymers, food and process analysis.

Keyword
Instrumentation, Open tubular traps, Sample handling, Sorbent trapping, Volatile organic compounds
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9793 (URN)10.1016/j.chroma.2004.02.062 (DOI)000220783100001 ()2-s2.0-1842533047 (Scopus ID)
Note
QC 20101004Available from: 2008-12-23 Created: 2008-12-23 Last updated: 2017-12-14Bibliographically approved
4. Ultra thick film open tubular traps with an increased inner diameter
Open this publication in new window or tab >>Ultra thick film open tubular traps with an increased inner diameter
2004 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1047, no 1, 93-99 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, the concept of open tubular traps, coated with a very thick film of polydimethyldisiloxane for enrichment of trace volatile components has been further explored. From theoretical calculations as well as practical experiments it is demonstrated that it can be advantageous to increase the inner diameter of such traps. For a given sampling flow rate and phase ratio, the plate number of the traps is not dependent on the inner diameter, provided that the linear flow velocity remains sufficiently high to offset the effect of axial diffusion. It is shown that this is due to the basic fact that for a given sampling flow rate, the average linear flow velocity in the trap is inversely proportional to the square of the inner diameter of the trap. However, in contrast to chromatographic separations, the linear flow velocity is not important. Under conditions of a constant phase ratio, an increased inner diameter also increases the amount of sorbent in the trap, which is a key parameter for obtaining high breakthrough volumes. Open tubular traps with an expanded inner diameter have very low pressure drop characteristics, which provides the possibility to construct new, simplified sampling systems.

Keyword
Open tubular traps, Preconcentration, Sorbent trapping, Ultratrace analysis, Volatile organic compounds
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-4912 (URN)10.1016/j.chroma.2004.06.072 (DOI)000223560700010 ()2-s2.0-4143051273 (Scopus ID)
Note
QC 20101005. Uppdaterad från Accepted till Published (20101005).Available from: 2008-12-23 Created: 2008-12-23 Last updated: 2017-12-06Bibliographically approved
5. Method for analysis of polar volatile trace components in aqueous samples by gas chromatography
Open this publication in new window or tab >>Method for analysis of polar volatile trace components in aqueous samples by gas chromatography
2005 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 77, no 10, 3365-3371 p.Article in journal (Refereed) Published
Abstract [en]

A new method has been developed for direct analysis of volatile polar trace compounds in aqueous samples by gas chromatography. Water samples are injected onto a short packed precolumn containing anhydrous lithium chloride. A capillary column is coupled in series with the prefractionation column for final separation of the analytes. The enrichment principle of the salt precolumn is reverse to the principles employed in conventional methods such as SPE or SPME in which a sorbent or adsorbent is utilized to trap or concentrate the analytes. Such methods are not efficient for highly polar compounds. In the LiCl pre-column concept, the water matrix is strongly retained on the hygroscopic salt, whereas polar as well as nonpolar volatile organic compounds show very low retention and are eluted ahead of the water. After transfer of the analytes to the capillary column, the retained bulk water is removed by backflushing the precolumn at elevated temperature. For direct injections of 120 μL of aqueous samples, the combined time for injection and preseparation is only 3.5 min. With this procedure, direct repetitive automated analyses of highly volatile polar compounds such as methanol or tetrahydrofuran can be performed, and a limit of quantification in the low parts-per-billion region utilizing a flame ionization detector is demonstrated.

Keyword
Capillarity, Distillation columns, Gas chromatography, Ionization
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-4913 (URN)10.1021/ac040170k (DOI)000229206800042 ()2-s2.0-18844442547 (Scopus ID)
Note
QC 20100922. Uppdaterad från Submitted till Published (20100922). Tidigare Titel "A new method for analysis of polar volatile trace components in aqueous samples by gas chromatography". Available from: 2008-12-23 Created: 2008-12-23 Last updated: 2017-12-06Bibliographically approved

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