Multicapillary Column Research Articles

Spiral multicapillary columns

It was shown in a theoretical study and confirmed by experiment that a spiral multicapillary column had maximum efficiency if the bunch of capillaries was additionally coiled around its longitudinal axis to produce an integral number of coils. This technique made it possible to manufacture gas-chromatographic columns with performance as high as 12 to 16 thousand theoretical plates. These columns can find various applications, especially if quick separation is required.

Comparison of negative and positive modes of ion-mobility increment spectrometry in the detection of heroin vapors

Some analytical characteristics of ion-mobility increment spectrometry (IMIS) in the negative and positive modes were compared in detecting diacetylmorphine vapors. It was shown experimentally that the sensitivity of IMIS in the negative mode to diacetylmorphine depends on the concentration of the water vapors in the drift gas: the lower the concentration, the higher the sensitivity. Data for cocaine are presented for comparison. Sampling diacetylmorphine and cocaine in the ionization chamber of the ion-mobility increment spectrometer was performed using a chromatograph with a multicapillary gas-chromatographic column.

Exemplar application of multi-capillary column ion mobility spectrometry for biological and medical purpose

In recent years, ion mobility spectrometry is increasingly in demand for new applications especially on biological samples (cells, bacteria, fungi), in medicine (diagnosis, therapy and medication control e.g. from breath analyses), for food quality control, safety monitoring and characterisation or process control in chemical and pharmaceutical industry. For this purpose instruments based on gas phase separation of ions in weak electric fields were developed at ISAS–Institute for Analytical Sciences, focussing on the particular challenges such as humid and rather complex samples, specific sampling procedures adapted to the application, fast pre-separation techniques like multi-capillary columns and suitable data processing including data bases for relevant analytes and automatic characterisation of IMS-chromatograms. Feasibility studies were carried out successfully for biological and medical purpose at ISAS, including the detection of bacteria, fungi and metabolites of cells and in human breath. For all those samples characteristic pattern of analytes were found and could be used for the identification of cell lines, fungi and bacteria as well as of numerous diseases. Furthermore, the quantification of those analytes could be used to obtain information about the state of the process or person (e.g. growth of cultures, development of diseases, level of medication, grade of cancer). Those examples shall demonstrate the potential of ion mobility spectrometry for the selected applications. However, a general and reliable data bases of reference analytes is required in the near future to enable an exploitation of the metabolic pathways and to confirm the relevance of the detected signals for the investigated topic.

A multicapillary gas chromatographic column with a Sol-Gel sorbent based on aluminum oxide

A multicapillary gas chromatographic column with an adsorption layer based on alumina was prepared. The column allowed the high-speed separation of C1-C4 light hydrocarbons to be performed in 8–12 s. The possibility of creating columns with various selectivities was demonstrated.

Efficiency of multicapillary columns

A multicapillary column model capable of qualitatively and quantitatively describing the dependence of the efficiency of the column on the mode and conditions of coating it with the stationary phase, the carrier gas flow direction, the pressure drop across the column, and the nature of the analytes.

Detection of emissions from surfaces using ion mobility spectrometry

Emissions from surfaces (from furniture, wall paintings or floor coverings for instance) significantly influence indoor air quality and therefore the wellbeing or even the health of the occupants. Together with metabolites from mold they are responsible for the well-known "sick building syndrome". Therefore, it is in the interest of the manufacturer as well as of the occupants to have a fast and accurate method for the detection of substances relevant to this syndrome in order to be able to monitor and control product quality and indoor air quality. The use of small and easy-to-transport ion mobility spectrometers that use UV light as the ionization source enables rapid in situ detection of such substances with high selectivity and sensitivity (detection limits in the lower ppb range). If a multicapillary column is used for preseparation as well, the selectivity is increased and the unwanted influence of humidity on the spectra can be eliminated, thus enabling the use of the instruments under normal ambient conditions. Furthermore, the use of air as carrier gas avoids the need for other sources of high-purity gas. An emission cell with a homogeneous and constant air flow over the surface to be investigated was developed in order to ensure reproducible results. Investigations of emissions from wooden surfaces with and without additional contamination as well as from complex mixtures are presented. The results demonstrate that relevant emissions can be identified and quantified with high sensitivity and selectivity in under five minutes. Therefore, the method is useful for indoor air quality monitoring, especially when miniaturized instruments are applied.

Effect of the interface on separation in multicapillary gas chromatography-based hyphenated techniques for speciation analysis of organometallic compounds

This paper reports the effect of transfer line (TL) internal diameter (i.d.) on gas chromatographic separation characteristics such as efficiency and speed, when a multicapillary (MC) column is used for speciation analysis of mercury. Five different TL consisting of fused-silica capillaries with 0.15, 0.20, 0.25, 0.32, and 0.53 mm i.d. are compared. The separation efficiency and total chromatographic run time are critically affected by the i.d. of the TL. Narrow capillaries (i.d.< or =0.20 mm) produce minimum peak dispersion whereas wide capillaries result in narrow peaks and shorter chromatographic analysis times. A thermodynamic approach is proposed to describe the motion of the analytes through the separation column and TL. The model provides good agreement with the experimental data for high pressures (> or =35 psig) and wide TL (> or =0.25 mm i.d.).

Volatile organoselenium monitoring in production and gastric digestion processes of selenized yeast by solid‐phase microextraction‐multicapillary gas chromatography coupled microwave‐induced plasma atomic emission spectrometry

AbstractEvolution of volatile organoselenium compounds in the production and gastric digestion of selenized yeast has been monitored. The industrial production of these kinds of material, employed as food supplements, has been simulated in a process of yeast enrichment with inorganic selenium selenium (IV) in different growth media, with variation of the pH value. The in vitro gastric digestion process was carried out with pepsin in an acid and salt mixture. Determination of volatile species of selenium was achieved coupling solid‐phase microextraction (SPME) for preconcentration and sample–matrix separation and microwave‐induced plasma atomic emission spectrometry, in combination with multicapillary (MC) gas chromatography for separation and detection of the selenium species. The MC column was operated at low temperatures (∼30 °C). The method was optimized, using a chemometric approach, with respect to the detection of organoselenium species such as dimethylselenide, diethylselenide and dimethyldiselenide. SPME sampling was carried out in the headspace above the corresponding solutions. Separation is fast, with a chromatogram being obtained in less than 5 min, and the detection limits were at the low parts per billion level for all species investigated. The results of the yeast enrichment process demonstrate inorganic selenium transformation into volatile organic species. The presence of inorganic selenium gave rise to at least five different volatile species after metabolization by yeast, with dimethylselenide and dimethyldiselenide being the predominant species. Commercial pasteurized yeast, containing mainly selenomethionine for use as a food supplement, and tablets were found to be still active under conditions of the simulation of the digestion process, even though producing relatively low amounts of organoselenium compounds. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Determination of terpenes in humid ambient air using ultraviolet ion mobility spectrometry

Atmospheric humidity causes the major problem using ion mobility spectrometers (IMS) under ambient conditions. Significant changes of the spectra are decreasing sensitivity as well as selectivity. Therefore, the influence of humidity on the IMS signal was investigated in case of direct introduction of the analyte into the ionisation chamber and in case of pre-separation by help of a multi-capillary column (MCC). For direct analyte introduction, a significant decrease of the total number of ions in the range of 28–42% with increasing relative humidity was found. Simultaneously additional peaks in the spectra were formed, thus complicating the identification of the analytes. In case of pre-separation of the analyte, the spectra do not change with increasing relative humidity, due to the successive appearance of the analyte and the water molecules in the ionisation chamber. Detection limits were found in the range of 5 μg/m 3 (about 1 ppbv) for selected terpenes and—with pre-separation—independent on relative humidity of the analyte. Without pre-separation, detection limits are in the same range for dry air as carrier gas but in the range of 200–600 μg/m 3 when relative humidity reaches 100%. Thus, MCC-UV ion mobility spectrometry is optimally capable for the detection of trace substances in ambient air (e.g. indoor air quality control, process control, odour detection) without further elaborate treatment of the carrier gas containing the analyte and independent on relative humidity.

Express analysis of explosives, chemical warfare agents and drugs with multicapillary column gas chromatography and ion mobility increment spectrometry

Description of a gas chromatograph designed for express analysis of explosives (2,4-dinitrotoluene, 2,4,6-trinitrotoluene, pentaerythritol tetranitrate), chemical warfare agents (mustard gas, lewisite, sarin) and drugs (heroin, cocaine hydrochloride, crack) is given. The devices comprises a multicapillary chromatographic column and an ion mobility increment spectrometer (MCC–IMIS). The main analytical characteristics of an IMIS (estimated detection limit (DL), linear dynamic range (LDR), speed of response) and a chromatographic column (separation power, degree of separation, a number of possible peaks at a chromatogram section, divided by analysis time) are determined. The maximum value of DL equal to 5 pg/ml was registered for cis-α-LW, and the lowest one of 0.001 pg/ml was for cocaine. The maximum value of LDR equal to 1000 was registered for sarin and the lowest one of 150 was for the ions of lewisite. Speed of response of one compound detection with the IMIS was 0.7 s.

Volatile organo-selenium speciation in biological matter by solid phase microextraction–moderate temperature multicapillary gas chromatography with microwave induced plasma atomic emission spectrometry detection

Microwave induced plasma atomic emission spectrometry (MIP-AES) in combination with multicapillary (MC) gas chromatography could be proven to be useful for element specific detection of volatile species. Solid phase microextraction (SPME) was used for preconcentration and sample-matrix separation. The fiber desorption unit as well as the heating control for the MC column were in-house developed and multicapillary column was operated at moderate temperatures (30–100 °C). The method was optimized for organo-selenium species (dimethylselenide (DMSe), diethylselenide (DEtSe) and dimethyldiselenide (DMDSe)), using a chemometric approach. Stationary phases for the separation column were optimized using a conventional GC and contrasted with the results obtained with the MC. Application was focussed on selenium accumulating biological matter, such as lupine, yeast, Indian mustard and garlic. These samples were grown in hydroponic solution containing inorganic selenium (Na 2SeO 3 and Na 2SeO 4). SPME sampling was carried out in fixed volume flow boxes in headspace above the living plants and in vials using treated samples. Results demonstrate inorganic selenium transformation into volatile organic species during metabolism. Separation is fast, a chromatogram can be obtained in less than 3 min and detection limits were at sub-ppb level for all investigated species. The system is independent from the use of a conventional gas chromatographic oven and can be used as a versatile alternative to highly cost intensive methods such as GC–ICP-MS.

Miniaturized mass-selective detector with atmospheric pressure chemical ionization

The miniaturized mass-spectrometric detector with atmospheric pressure chemical ionization (APCI) is described. The analyzer employed in this instrument is the monopole with rod 54 mm in length and 2 mm in radius, which retains its efficiency up to 0.13 Pa (≈10 −3 Torr). Together with the ion source, channeltron ion detector, radio frequency power supply and preamplifier, it is packed into a case with dimension of 185 mm×100 mm×70 mm. Mass spectrometer with the whole vacuum system weighs about 20 kg. In spite of low power of the vacuum system, the limit of detection at ppt level is achieved. The “strong” fragmentation mode is suggested for high-specific detection of phosphor-containing substances. The detector conforms to multicapillary column attachment.

Development of a fixed-bed continuous-flow high-throughput reactor for long-chain n-alkane hydroconversion

A high-throughput vapor-phase catalytic experimentation unit with 15 parallel microreactors and fast, on-line GC product analysis was built. The 15 open tubular microreactors were mounted in a single furnace and fed with a common gas stream. Decane hydroisomerization experiments were conducted on 35 mg quantities of reference platinum-loaded ultrastable Y zeolite particles at 200 °C, 4.5 bar, using a hydrogen/hydrocarbon molar ratio of 375/1 and contact times of 100–800 kg s/mol. The microreactor outlets were sampled sequentially. GC analysis of the C 1C 10 alkane product mixtures was achieved in 3.2 min with a multi-capillary column. The actual gas flow rates and contact times in the individual microreactors were derived from the GC FID signals after dilution of the reaction product stream with a calibrated hydrogen gas flow. The maximum temperature difference among the microreactors, measured in an empty reactor unit was ca. 6 °C at 200 °C. The conversion data were in excellent agreement with a kinetic model established for a conventional reactor. Fitting of the kinetic data obtained in the individual microreactors to the model confirmed the small temperature variations depending on the location of each microreactor in the catalyst furnace.

Rapid Determination of Explosives and Narcotics Using a Multicapillary-Column Gas Chromatograph and an Ion-Mobility Spectrometer

A gas chromatograph for the rapid determination of explosives (2,4-dinitrotoluene, 2,4,6-trinitrotoluene, and pentaerythritol tetranitrate) and narcotics (heroin, cocaine hydrochloride, and crack) is described, and its analytical characteristics are presented. The instrument was equipped with a multicapillary column and an ion-mobility spectrometer as a detector.

Rapid determination of butyltin species in water samples by multicapillary gas chromatography with atomic emission detection following headspace solid-phase microextraction

A procedure for the rapid determination of mono-, di- and tributyltin in water samples is described. The analytes are simultaneously ethylated and concentrated on a solid-phase microextraction fibre placed in the headspace over the sample for 2 min. The ethylated species are then separated and selectively quantified in only 90 s using a multicapillary gas chromatography column combined with atomic emission detection. The influence of blank signals and sampling conditions on the sensitivity of the method is described. Detection limits of 1–5 ng/l and relative standard deviations of 6–10% at concentrations of 20 ng/l were obtained.

Gas chromatography for in situ analysis of a cometary nucleus: III. Multi-capillary column system for the cometary sampling and composition experiment of the Rosetta lander probe

The cometary sampling and composition (COSAC) experiment is one of the principal experiments of the surface lander probe of the European Space Agency Rosetta mission to be launched in January 2003. The instrument is designed for the in situ chemical analysis of a cometary nucleus as the details of the nucleus composition are of primary importance for understanding both the formation of the solar system, and the origin of life on Earth. The COSAC experiment consists of an evaporation/pyrolysis device and two analytical systems: a multi-column gas chromatograph and a high-resolution time-of-flight mass spectrometer which may either be operated alone or in a coupled mode. The gas chromatograph includes five general purpose chromatographic columns and three chiral ones, all mounted in parallel. Taking into account the chemical species potentially present in the cometary nucleus as well as the space constraints, a set of five complementary columns was selected to perform the separation and identification of the compounds present in the cometary nucleus. This set of columns includes a carbon molecular sieve porous-layer open tubular (PLOT) column used for the separation of both the noble and other permanent gases, and the C 1–C 2 hydrocarbons. A second PLOT column uses a divinylbenzene–ethylene glycol–dimethylacrylate porous polymer as stationary phase for the analysis of a wide range of C 1–C 2 organic molecules. Two complementary wall-coated open tubular (WCOT) columns with polydimethylsiloxane (PDMS) liquid stationary phases, one containing cyanopropyl–phenylsiloxane and the other diphenylsiloxane groups, are designed to target the same range of organic compounds (C 3–C 7) which could be representative of the widest range of cometary compounds. A third WCOT column with an apolar stationary phase made of non-substituted PDMS is used for the separation and identification of higher-molecular-mass compounds (up to C 10) and aromatic species (monoaromatic and polyaromatic). This paper describes these five general-purpose capillary PLOT and WCOT columns, selected to be used in the COSAC GC system. The analytical capabilities are examined with a special emphasis on the exobiological and planetological implications.

Fast and simultaneous determination of tin and mercury species using SPME, multicapillary gas chromatography and MIP-AES detection

A procedure for the simultaneous and fast determination of methylmercury (MeHg+), inorganic mercury (Hg2+) and mono-, di- and tributyltin species (MBT, DBT, TBT) in water samples, as ethylated derivatives using a multicapillary GC column and MIP-AES detection, has been developed. The influences of the auxiliary gas pressure and the helium cavity vent flow in the MIP-AES response to mercury and tin species were evaluated and adjusted to obtain optimal detection conditions for both groups of organometallic compounds in the same chromatographic run. The proposed method was applied to the fast and simultaneous determination of mercury and tin species in water samples after a concentration step using solid-phase microextraction fibres.

AN AUTOMATED SPECIATION ANALYSER OF ORGANOMETALLIC COMPOUND CONTENT

This paper presents the design of an automated measurement device developed for speciation studies of organometallic compounds in samples of a complex and varying composition matrix. The instrument automates three essential steps in a typical speciation analysis procedure: isolation of analytes, their enrichment, and time-resolved introduction into a detector. Analytes are extracted by purging from post-sample dissolution/digestion mixture, in the form of volatile derivatives, with their simultaneous enrichment on a capillary cryotrap. Before introduction into a detector, they are rapidly (ca. 0.5 min.) separated on a multi-capillary gas chromatographic column operating in isothermal mode. The construction of the automated speciation analyser (ASA) makes it practically independent of a kind of the detector used (it was tested with MIP-AED,[1] ICP—MS,[2] and AAS detectors) and gives the freedom of choice of sample preparation procedure. The only requirement to the latter is that analytes should be in a form of volatile compound in an aqueous matrix.

Dependence of the efficiency of a multicapillary column on the liquid phase loading method

One of the main approaches employed to reach fast chromatographic separation is based on using columns containing up to 1000 capillaries with the diameter size down to 10–100 μm. The efficiency of such columns depends on the dispersion of the capillary radius and on the way of the liquid-film loading. We present general equations describing these effects. Specifically, we show theoretically and experimentally that the separation efficiency can be improved by using the loading methods specially designed in order to take into account correlation between the film thickness and capillary radius.

RADIOLOGICAL QUIZ

Current challenges of clinical breath analysis include large data size and non-clinically relevant variations observed in exhaled breath measurements, which should be urgently addressed with competent scientific data tools. In this study, three different baseline correction methods are evaluated within a previously developed data size reduction strategy for multi capillary column – ion mobility spectrometry (MCC-IMS) datasets. Introduced for the first time in breath data analysis, the Top-hat method is presented as the optimum baseline correction method. A refined data size reduction strategy is employed in the analysis of a large breathomic dataset on a healthy and respiratory disease population. New insights into MCC-IMS spectra differences associated with respiratory diseases are provided, demonstrating the additional value of the refined data analysis strategy in clinical breath analysis.