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Tyge Greibrokk

Publications and source records attributed to Tyge Greibrokk.

28 records · Page 2Linked to original sources
PubMed2004

Determination of perfluorooctane sulfonate and perfluorooctanoic acid in human plasma by large volume injection capillary column switching liquid chromatography coupled to electrospray ionization mass spectrometry.

Rapid, selective, and sensitive methodology for the quantification of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in human plasma using packed capillary liquid chromatography coupled to electrospray ionization ion-trap mass spectrometry has been developed. Plasma proteins were precipitated using acetonitrile and the resulting supernatant was diluted 1+1 with water containing 10 mM ammonium acetate (NH4Ac) prior to injection. Sample volumes of 250 microL were loaded onto a 30 mm x 0.32 mm ID 10 microm Kromasil C18 precolumn by a carrier solution consisting of 10 mM NH4Ac in ACN/H2O (5/95, v/v) at a flow rate of 100 microL/min, providing on-line analyte enrichment and sample clean-up. Backflushed elution onto a 100 mm x 0.32 mm ID 3.5 microm Kromasil C18 analytical column was conducted using an ACN/H2O solvent gradient containing 10 mM NH4Ac. In order to improve the robustness and performance of the method, perfluoroheptanoic acid (PFHA) was used as internal standard. Separation and detection of PFOA, PFHA, and PFOS were achieved within 10 minutes. Ionization was performed in the negative mode in the m/z range 250-550. The method was validated over the concentration range 1-200 ng/mL for PFOA and over the range 5-200 ng/mL untreated plasma for PFOS, yielding correlation coefficients of 0.997 (PFOA) and 0.996 (PFOS), respectively. The within-assay (n = 6) and between-assay (n = 6) precisions were in the range 2.1-9.2 and 5.6-12%, respectively. The concentration limits of detection (cLOD) of PFOA was 0.5 ng/mL while the cLOD of PFOS was estimated to be 0.2 ng/mL in untreated plasma.

Alkanesulfonic Acids↗
PubMed2004

Capillary columns in liquid chromatography: between conventional columns and microchips.

Liquid chromatography on columns with small internal diameters has been reviewed as the intermediate technique between conventional liquid chromatography and microchip separations. The development of micro column separations in the early years has been described, starting with the papers of Horváth and co-workers and Ishii and co-workers, continuing into the first part of the eighties, then making a leap in time to recent innovations with small-bore columns. Based on internal diameters a classification of the different analytical HPLC columns has been suggested. The advantages of small-bore columns have been discussed, with particular emphasis on the advantage of coupling to concentration sensitive detectors when the sample amount is limited. Open tubular columns are treated as a part of the historic background. The recent developments include a brief look into the current status of monolithic columns, the use of packed nano columns and micro columns with electrospray mass spectrometry, and the potential of two-dimensional comprehensive liquid chromatography. Finally, the coupling of sample preparation to analytical columns and the future applications of the novel technological improvements to the microchip separation methods have been discussed.

Journal Article↗
PubMed2004

The contributions of Csaba Horváth to liquid chromatography.

This article is not a biographic description of the life of Csaba Horváth, but an attempt to describe his most important contributions to liquid chromatography, as viewed by an author who himself started with HPLC in 1973. With the introduction of columns packed with rigid pellicular particles, which could withstand high pressures, the combination of fast separations with high efficiency was designated high pressure liquid chromatography about 35 years ago. The contribution of Horváth to the birth of modern LC was to imagine the potential for high-speed separations in LC by transferring ideas and technology from gas chromatography. From this time, his strong participation in understanding and describing the processes of separation science made him a leading scientist in fundamental studies of separation principles until his passing away in April 2004. In addition to being one of the forefathers of modern liquid chromatography, Csaba Horváth described both the ionic interactions and the hydrophobic interactions on ion exchangers as well as on reversed phase materials and developed a theoretical basis for understanding these processes. If one person should be mentioned as the inventor of ion-pair chromatography of organic compounds, of hydrophobic interaction chromatography, and of the theoretical basis for reversed phase chromatography, this person is Csaba Horváth. Throughout the last 30 years he also had a strong interest in studying proteins in separation processes, and in the last decade he made valuable contributions to capillary electrochromatography, particularly for separation of proteins on monolithic columns. For this author is difficult to find another person who has had a greater impact on liquid chromatography than Csaba Horváth.

Chromatography, Liquid↗
PubMed2003

Trace determination of peptides in water samples using packed capillary liquid chromatography with UV and MS detection and characterization of peptide oxidation products by MS.

A capillary liquid chromatographic column switching method has been developed for fast and sensitive determination of peptides in water samples. Sample volumes of 1 mL were loaded onto a (320 microm I.D. x30 mm) 10 microm Kromasil C(18) pre-column, providing on-line analyte enrichment, prior to back-flushed elution onto a (320 microm I.D. x150 mm) 3.5 microm Kromasil C(18) analytical column. Loading flow rates of 250 microL/min and a mobile phase composition of acetonitrile/water/trifluoroacetic acid (22/77.9/0.1, v/v) provided a total analysis time of less than 25 minutes for the test peptides angiotensin II, bombesin, bradykinin, corazonin, neurotensin and substance P, using temperature programmed elution. In addition, solvent gradient elution and combined solvent gradient elution and temperature programming were explored. Using on-capillary UV detection at 210 nm resulted in a concentration limit of detection (cLOD) of about 1 ng/mL. The method was validated over the concentration range 1-100 ng/mL, yielding a coefficient of correlation of 0.997 or better. The within-assay ( n=6) and between-assay ( n=6) precisions of peak areas were on average 6% RSD and 5% RSD, respectively. When the method was applied to spiked chlorinated tap water samples, it was found that peptides containing methionine, tryptophan and cystine were oxidized. Identification of the oxidation products of the peptides in hypochlorite-treated water was done with positive electrospray ionization time-of-flight mass spectrometric detection.

Capillary Action↗
PubMed2003

Mesoporous polybutadiene-modified zirconia for high-temperature packed capillary liquid chromatography: column preparation and temperature programming stability.

In the present study, three different methods for packing of 3 microm PBD-ZrO2 particles in 0.5 mm i.d. glass-lined stainless steel columns have been examined. The two first methods were based on a traditional downstream high-pressure technique using tetrachloromethane (Method I) or aqueous Triton X-100 (Method II) as slurry solvents, while Method III was an upstream high-pressure flocculating method with stirring, using isopropanol both as the slurry and packing solvent. Method I was found to be superior in terms of efficiency, producing 0.5 mm i.d. x 10 cm columns with almost 90,000 plates m(-1) for toluene (R.S.D. = 8.7%, n = 3), using a slurry concentration of 600 mg ml(-1), ACN-water (50:50 (v/v)) as the packing solvent and a packing pressure of 650 bars. For Method I, the slurry concentration, column i.d., column length and initial packing pressure were found to have a significant effect on column efficiency. Finally, the long-term temperature stability of the prepared columns was investigated. In isothermal mode, using ACN-20 mM phosphate buffer, pH 7 (50:50 (v/v)) as the mobile phase, the columns were found to be stable for at least 3,000 void volumes at 100 degrees C. At this temperature, the solute efficiencies changed about 5-18% and the retention factors changed about 6-8%. In temperature programming mode (not exceeding 100 degrees C), on the other hand, a rapid decrease in both column efficiency and retention factors was observed. However, when the columns were packed as initially described, ramped up and down from 50 to 100 degrees C for 48 h and refilled, fairly stable columns with acceptable efficiencies were obtained. Although not fully regaining their initial efficiency after refilling, the solute efficiencies changed about 19-28% (32-37%) and the retention factors changed about 4-5% (13-17%) after running 3,000 (25,000) void volumes or 500 (3,900) temperature programs.

Butadienes↗
PubMed2003

Fast and sensitive determination of urinary 1-hydroxypyrene by packed capillary column switching liquid chromatography coupled to micro-electrospray time-of-flight mass spectrometry.

The present work reports capillary liquid chromatographic column switching methodology tailored for fast, sensitive and selective determination of 1-hydroxypyrene (1-OHP) in human urine using micro-electrospray ionization time-of-flight mass spectrometric detection. Samples (100 microl) of deconjugated, water diluted and filtered urine samples were loaded onto a 150 microm I.D.x 30 mm 10 microm Kromasil C(18) pre-column, providing on-line sample clean-up and analyte enrichment, prior to back flushed elution onto a 150 microm I.D.x 100 mm 3.5 microm Kromasil C(18) analytical column. Loading flow rates up to 100 microl/min in addition to the use of isocratic elution by a mobile phase composition of acetonitrile/water (70/30, v/v) containing 5 mM ammonium acetate provided elution of 1-OHP within 5.5 min and a total analysis time of less than 15 min with manual operation. Ionization was performed in the negative mode and 1-OHP was observed as [M-H](-) at m/z 217.08. The method was validated over the concentration range 0.2-40 ng/ml 1-OHP in pre-treated urine, yielding a coefficient of correlation of 0.997. The within-assay (n=6) and between-assay (n=6) precisions were in the range 6.4-7.3 and 7.0-8.1%, respectively, and the recoveries were in the range 96.2-97.5 within the investigated concentration range. The method mass limit of detection was 2 pg, corresponding to a 1-OHP concentration limit of detection of 20 pg/ml (0.09 nmol/l) diluted urine or 0.3 ng/ml (1.35 nmol/l) urine.

Pyrenes↗
PubMed2003

High-temperature liquid chromatography.

The present state of the active use of elevated temperatures in liquid chromatography is reviewed, including the effects on retention, selectivity and efficiency. Separations in aqueous mobile phases as well as non-aqueous media are discussed, with particular emphasis on narrow-bore columns.

Chromatography, Liquid↗
PubMed2003

The impact of column inner diameter on chromatographic performance in temperature gradient liquid chromatography.

The impact of column inner diameter on chromatographic performance in temperature gradient liquid chromatography has been investigated in the present study. Columns with inner diameters of 0.32, 0.53, 3.2 and 4.6 mm were compared with respect to retention and efficiency characteristics using temperature gradients from 30 to 90 degrees C with temperature ramps of 1, 5, 10 and 20 degrees C min(-1). The columns were all of 15 cm length and were packed with 3 microm Hypersil ODS particles. Alkylbenzenes served as model compounds, and the mobile phase consisted of acetonitrile-water (50:50, v/v). The study revealed that the column ID is not a critical limiting factor when performing temperature programming in LC, at least for columns narrower than 4.6 mm inner diameter in the temperature interval 30-90 degrees C. The retention times for all components on all columns were highly comparable, with similar peak profiles without any signs of peak splitting. The use of mobile phase pre-heating when using the larger bore columns was avoided by starting the temperature gradients close to ambient. However, the relative apparent efficiency was inversely proportional to column inner diameter, making the capillary columns generally more functional towards temperature gradients than the larger bore columns with respect to chromatographic efficiency. In addition, the capillary columns possessed higher robustness towards temperature programming than the conventional columns.

Benzene Derivatives↗
PubMed2002

Temperature-promoted large-volume solute enrichment in column-switching miniaturized liquid chromatography: determination of an antioxidant.

A two-valve sub-ambient temperature-promoted reversed-phase packed-capillary liquid-chromatography column-switching system has been tailored for sensitive determination of hydrophobic compounds. Such compounds are not easily dissolved in solvent mixtures of non-eluting properties that traditionally are used for solute enrichment in reversed-phase liquid chromatography. Enrichment-column solute focusing of large sample volumes was promoted by use of sub-ambient temperatures only, allowing the use of sample solvents that were stronger or equal to the mobile phase solvent strength. Subsequent column switching and enrichment-column temperature increment provided efficient low-dispersion back-flushed enrichment-column solute desorption onto the analytical column, where the solute was subjected to temperature-programmed gradient action. The antioxidant, Irganox 1076 (octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) extracted from low density polyethylene with 100% acetonitrile served as a hydrophobic model compound. The mobile phase consisted of acetonitrile containing 10 mM triethylamine and formic acid, and the 0.25 mm id enrichment-column and analytical column in lengths of 27 and 250 mm, respectively, were packed with 3.5 microm Kromasil C18 particles. Sample volumes of up to 500 microL were successfully focused on the enrichment column at 5 degrees C using loading flow rates of up to 40 microL min(-1) prior to temperature programming to 90 degrees C. The concentration limit of detection of Irganox 1076 was 6 ng mL(-1) when using an injection volume of 500 microL. The within-assay precision was in the range 3.5-6.8% (n = 6) while the between-day precision was 7.5% (n = 3) relative standard deviation. The method was linear within the investigated mass range 3-100 ng (R2 = 0.9993).

Antioxidants↗