Detector For Supercritical Fluid Chromatography Research Articles

Evaluation of a condensation nucleation light scattering detector for the analysis of synthetic polymer by supercritical fluid chromatography

A condensation nucleation light scattering detector (CNLSD) was adapted for use as a detector for supercritical fluid chromatography. The performance of the CNLSD was evaluated and compared to evaporative light-scattering detector (ELSD) using a well-defined equimass mixture of uniform poly(ethylene glycol) oligomers and a certified reference material of poly(ethylene glycol) 1000. The CNLSD was able to detect a 10 times less concentrated solution of uniform oligomers compared to the ELSD. The quantitativeness of CNLSD was high enough to obtain the molecular mass distribution of poly(ethylene glycol) 1000 without any calibrations; on the other hand, the original data measured by ELSD was about 4% smaller than the certified value of poly(ethylene glycol) 1000. The CNLSD was suitable for supercritical fluid chromatography as a mass concentration detector.

Quantitative comparison of a corona-charged aerosol detector and an evaporative light-scattering detector for the analysis of a synthetic polymer by supercritical fluid chromatography

A corona-charged aerosol detector (CAD) was developed to improve the sensitivity, reproducibility and quantitativeness of detection as compared to evaporative light-scattering detector (ELSD) for liquid chromatography. Our laboratory used the corona CAD as a detector for supercritical fluid chromatography (SFC) and evaluated its performance compared to the ELSD by using a certified reference material of poly(ethylene glycol) (PEG) and a well-defined equimass mixture of uniform PEG oligomers. The corona CAD was able to detect a 10 times more dilute solution of uniform oligomers compared to the ELSD. Although the original data of molecular mass by ELSD was 4.6% smaller than the certified value of PEG 1000, molecular mass distribution obtained by corona CAD was virtually almost the same as the certified value without any calibrations.

Calibration of an evaporative light-scattering detector as a mass detector for supercritical fluid chromatography by using uniform Poly(ethylene glycol) oligomers

The quantitativeness of an evaporative light-scattering detector (ELSD) for supercritical fluid chromatography (SFC) was evaluated by using an equimass mixture of uniform poly(ethylene glycol) (PEG) oligomers. Uniform oligomers, in which all molecules have an identical molecular mass, are useful for the accurate calibration of detectors. We calibrated the SFC-ELSD system for various concentrations and molecular masses by using an equimass mixture of PEG oligomers. ELSD not only showed a good linear response to the injected concentration over a wide concentration range, from 10 −4 to 10 −1 g/mL, but also showed a strong dependence on the molecular mass of the solute. By using chromatograms of the equimass mixture of uniform oligomers to calibrate SFC-ELSD, it was possible to determine exact values of not only the average mass but also the molecular-mass distribution for a PEG 1540 sample. The average molecular mass was shifted to a higher value by several percentage points after calibration of the ELSD.

The effect of two gases forming supercritical fluids (Xe and CO 2) on the spectral characteristics and analytical capabilities of microwave induced plasmas

A comparative study of the effect of CO 2 and Xe added along with the plasma gas to He and Ar microwave induced plasmas (MIPs), simulating possible conditions to be used when a MIP is employed as specific detector for supercritical fluid chromatography (SFC), has been carried out. The proportions of CO 2 and Xe to the plasma gas investigated are comparable to the typical percentages used for SFC-MIP couplings. The study has been performed with two different MIP systems: an atmospheric pressure discharge held in a Beenakker cavity TM 010 and a reduced pressure surfatron-MIP. The influence of CO 2 and Xe addition on the spectrochemical properties of the discharge has been studied by using the atomic emission of mercury and some typical non-metals (chlorine, carbon and sulfur) at different wavelengths (atomic and ionic lines). Results showed that ion line emission intensities are always reduced more significantly than atom line emissions by both dopant gases on study, whatever the pressure. In general terms, however, the effect of adding Xe is less severe, both for atom and ion lines, than that of CO 2; in most cases the detection limits (DLs) observed are better for Xe than for CO 2 as dopant gas. In fact, the DLs obtained for the selected lines of mercury measured were practically unaltered by the addition of 0.2% Xe to atmospheric pressure Ar or He MIPs. CO 2 addition (0.2%) produced about 1.5 times worsening of the observed DLs for mercury. For non-metal analyses better DLs were also obtained, in general terms, with Xe than with CO 2 as dopant gas.

Supercritical Fluid Chromatography with Electrochemical Detection of Phenols and Polyaromatic Hydrocarbons

A self-contained electrochemical cell consisting of a working and a counter electrode coated with a thin poly(ethylene oxide) film containing lithium triflate has been evalulated as an on-line detector for supercritical fluid chromatography. Electrochemical detection of 11 priority phenols and 13 polyaromatic hydrocarbons separated on a packed diol column with neat and methanol-modified CO2 mobile phases is described. The detector is operated voltammetrically, which permits the simultaneous detection of both oxidizable and reducible components of individual mixtures. Quantitative aspects of the detector performace have been evaluated and compared to those of a downstream flame ionization detector. The electrochemical detector provides low-nanogram detection limits and responds linearly over two decades of injected quantities. An advantage of voltammetric detection is the selectivity derived from the range of applied potentials used. Overlapping elution profiles of chloro-, methyl-, and nitro-substituted p...

Online Electrochemical Detectors for Supercritical Fluid Chromatography

A self-contained electrochemical cell consisting of a working and a quasi-reference electrode coated with a thin film of a conductive polymer was used as a postcolumn detector for supercritical fluid chromatography (SFC-EC). Cyclic voltammetry was used to obtain chromatograms of ferrocene, anthracene, p-benzoquinone, and hydroquinone after they elution from a C 18 packed column with unmodified, acetonitrile-modified, or methanol-modified CO 2 . In unmodified CO 2 , the quantitative performance of the SFC-EC detection of ferrocene was similar to that obtained with a downstream FID with respect to detection limit, response linearity, and peak shape. The baseline signal of the EC detector remained flat during density gradient elution while a noticeable drift occurred in the baseline signal of the FID. Futhermore, whereas the FID was totally inoperable in a mobile phase containing ∼3% (v/v) of either acetonitrile or methanol, the EC detector functioned well in the modified fluids. Thus, the EC detector is compatible with both unmodified and modified CO 2 mobile phases. A valuable feature of these newly developed SFC detectors is they compatibility with a very large fraction of the rye of separation conditions that are important to SFC

The plasma emission detector (PED) as an element-selective detector for supercritical fluid chromatography

The plasma emission detector (PED) has been shown to be an element specific detector for supercritical fluid chromatography (SFC). The commonly used eluents (CO2 and N2O) tend to disturb the He plasma; two different discharge tubes were tested in an attempt to overcome this problem. Promising results were obtained with a concentric dual flow torch design for the element specific detection of Cl, H, and C containing analytes using N2O as SFC mobile phase.

Optimization of a flame photometric detector for supercritical fluid chromatography of organotin compounds

A single flame photometric detector has been optimized for capillary supercritical fluid chromatography (cSFC) of trialkyltin chlorides for the first time. Detection variables (temperature, hydrogen and air flow-rates) were optimized by a combination of factorial experimental design and simplex. Furthermore, the position of the restrictor in the flame and injection volumes were also considered. Optimum sensitivity was achieved using high hydrogen-air ratios (1.8). Using the optimum conditions, baseline was stable during pressure programming. The detection limit of tributyltin chloride ( S/N = 3) was around 40 pg (as tin). Reproducibility was high (R.S.D. = 3.8%, n = 5) and dynamic range was measured over two orders of magnitude. Furthermore, dibutyl-, diphenyl- and triphenyltin chlorides were also successfully eluted for the first time using linear density programming (carbon dioxide, 50°C).

Determination of halogenated compounds with supercritical fluid chromatography–microwave-induced plasma mass spectrometry

Helium microwave-induced plasma mass spectrometry (MIP-MS) has been evaluated as an element selective detector for supercritical fluid chromatography (SFC). In this study the determination of halogenated hydrocarbons at trace levels is demonstrated by using two test compounds, 1-chloronaphthalene and 1-bromo-2-methylnaphthalene. The SFC–MIP-MS interface was developed and optimized. Chromatograms obtained for the two halogenated compounds show detection levels in the low picogram range with absolute minimum detectable quantities of 100 and 25 pg for Cl and Br, respectively. Absolute detection limits were found to be 15 pg for Cl and 0.75 pg for Br. The linear ranges are over 3 orders of magnitude (50 pg–50 ng) and reproducibilities for the sample injections are of the order of 5% relative standard deviation. A preliminary chromatogram for a standard pesticide mixture is also presented.

Evaluation of inductively coupled plasma mass spectrometry as an elemental detector for supercritical fluid chromatography

Supercritical fluid chromatography coupled with inductively coupled plasma mass spectrometry shows high potential for the determination at ultratrace levels of organometallic compounds of environmental interest. In this study the determination of organotin compounds at ultratrace levels is demonstrated. In this work a supercritical fluid chromatography/inductively coupled plasma mass spectrometry (SFC/ICPMS) interface was developed. Separation of tetraalkyltin compounds shows detection levels in the subpicogram range (0.034 pg for tetrabutyltin; 0.047 pg for tetraphenyltin). The linear ranges are over 3 orders magnitude (1-1000 pg). The reproducibility of sample injections are better than 5% RSD.

Evaluation of an ion mobility detector for supercritical fluid chromatography with solvent-modified carbon dioxide mobile phases

An ion mobility detector (IMD) was evaluated for open tubular column supercritical fluid chromatography (SFC) when organic solvent-modified supercritical CO2 was used as mobile phase. It was found that the SFC/IMD interface design in which the SFC capillaray restrictor was directly inserted into the ionization region of the IMD was not acceptable because of low sensitivity that resulted from the effect of the modifier on detector temperature and mechanism of detection. A new interface utilizing a heated nebulizer gas to provide heat to the restrictor and to minimize the formation of ion clusters, and a bent nozzle for enhancing the ionization efficiency of the solute in the IMD ion source are described. Using 5% acetonitrile in CO2, the minimum detectable quantity (S/N=3) for pyrene was improved from 25.2 ng to 2.1 ng with the new detector design. This compares to a minimum detectable quantity of 0.1 ng when using neat CO2 as mobile phase. The use of molecular connectivity calculations to predict the drift times of selected analytes is also successfully demonstrated.

Element-selective detection after supercritical fluid chromatography by means of a Surfatron plasma in the near-infrared spectral region

A microwave-induced plasma, known as the Surfatron, is evaluated as a detector for supercritical fluid chromatography. The spectral range that is investigated is the near-infrared region because of its relative freedom from many spectral interferences, compared to the UV and visible regions. A Novel method of heating the column restrictor is described, which is compatible with the very limited space and inaccessibility of the discharge tube configuration in the Surfatron cavity. Sensitivities and selectivities are determined for sulfur, chlorine, and bromine, using both a carbon dioxide and a nitrous oxide mobile phase. The detector is also evaluated in the “universal detection” mode by monitoring the carbon line when a nitrous oxide mobile phase is used. An application is demonstrated through the analysis of a mixture of sulfur-containing pesticides.

Evaluation of inductively coupled plasma emission spectrometry as an element-specific detector for supercritical fluid chromatography

A capillary supercritical fluid chromatograph (SFC) was interfaced to an inductively coupled plasma (ICP) atomic emission spectrometer (AES). The chromatographic system, interface, and plasma torch design are described. The argon plasma was optimized for Si I 251.6 nm emission to detect separated organosilicon compounds selectivity. The linear dynamic range for octamethylcyclotetrasiloxane was between 7.24 and 145.0 ng of Si injected, with a detection limit of 5.8 ng of Si injected (57.9 ppm Si). The precision of the measured peak heights of three replicate injections of 75 ng of Si was less than 5%. The effects of the mobile phase (CO{sub 2}) pressure on the plasma stability and sensitivity are presented.

Examination of a helium highly efficient microwave-induced plasma as an element-selective detector for supercritical fluid chromatography

The use of a highly efficient microwave-induced plasma as an element-selective detector for packed column supercritical fluid chromatography is discussed. The cavity is able to support an Ar or He discharge at powers of 150 W or less. The effects of the introduction of supercritical CO2 on the analytical parameters of the plasma are described and minimum detectable quantity values for S, P and Cl are presented.

Characterization of microwave-induced plasma as a detector for supercritical fluid chromatography

Abstract : A microwave induced plasma (MIP) sustained in helium is evaluated as an element selective detector for capillary supercritical fluid chromatography (SFC). The plasma source, a surface microwave induced plasma (surfatron), is described. Optimal plasma conditions including viewing position, helium flow rate, and applied microwave power are discussed for sulfur emission in the near-infrared spectral region. In addition, the effects of two common mobile phases (CO2 and N2O) on plasma stability, sensitivity, and spectral background from 200 nm to 1100 nm are assessed. Although the plasma was evaluated principally for use with SFC, much of the discussion is relevant to its application as a gas chromatographic detector. Keywords: Supercritical fluid chromatography; Nonmetal detection; Spectroscopic detector; Speciation; Sulfur detection.

Analytical applications of capillary supercritical fluid chromatography—mass spectrometry

Capillary chromatographic analyses of thermally labile, less volatile and higher molecular weight compounds can be accomplished using supercritical mobile phases due to the combination of solvating powers and attractive mass transport properties. Recent advances in the use of small bore (25–50μm) capillary columns, rapid pressure programming methods, and polar mobile phases have yielded high-sensitivity and high-speed analyses with chromatographic resolution approaching that of conventional capillary gas chromatography. Mass spectrometry (MS) provides a nearly universal detector for supercritical fluid chromatography (SFC), and the ease with which capillary SFC can be directly coupled with the mass spectrometer avoids the complications inherent in liquid chromatography (LC)—MS interfaces. Capillary SFC can be interfaced with both electron impact and chemical ionization (CI) modes of operation, and high selectivity and sensitivity as well as structural data can be obtained through appropriate choice of CI reagents. Recent developments in capillary SFC—MS and applications to several compound classes are described.

The Development and Characterization of a New Micro Adsorption Detector for Supercritical Fluid Chromatography

The Development and Characterization of a New Micro Adsorption Detector for Supercritical Fluid Chromatography