Tom Visser

Identification of herbicides in river water using on-line trace enrichment combined with column liquid chromatography-Fourier-transform infrared spectrometry

Trace enrichment of herbicides on a 10×2.0 mm I.D. precolumn packed with Polygosil C18 material, was combined on-line with column liquid chromatography-Fourier-transform infrared spectrometry (LC-FT-IR). The isocratic LC separation was carried out on a 200×2.1 mm I.D Rosil C18 column using acetonitrile-phosphate buffer as eluent. The LC-FT-IR coupling was based on post-column on-line liquid-liquid extraction and solvent elimination, followed by FT-IR microscopy. The feasibility of the complete system was demonstrated by analysing river water spiked with triazines and phenylureas at the low-μg/l level. Identifiable spectra were obtained for all analytes, which included several isomers. Using 50–100 ml water samples, the identification limit for the herbicides typically was 1 μg/l. The usefulness of six spectral library search algorithms to correctly identify the recorded spectra was tested. A Peak-Search routine which is based on the matching of peak frequencies alone was found to be the most suitable to identify the analytes at the trace level.

On-Line Solid Phase Extraction–Gas Chromatography–Cryotrapping–Infrared Spectrometry for the Trace-Level Determination of Microcontaminants in Aqueous Samples

A large-volume on-column GC-cryotrapping-IR system was developed for injections of up to 100 μl of organic extracts. Considerable reduction of the solvent-and-water background and enhanced analyte detectability was achieved by using an open-split interface between the GC column and the IR detector and improving the leak-tightness of the system. The system was combined with solid-phase extraction to yield on-line SPE-GC-IR. With this set-up, sample volumes of only 20 ml sufficed to detect, and identify, microcontaminants in tap and surface water at the 0.1-1 μg/L level. Detection limits were on the order of 15 ng/L for tap water when using appropriate functional-group chromatograms. Or, in other words, SPE-GC-IR is a suitable technique for the screening of environmental water samples for functional groups, i.e. classes of compounds, of interest.

Spray jet assembly interface for the coupling of reversed-phase narrow-bore liquid chromatography and Fourier transform infrared spectrometry

Abstract Liquid chromatography was coupled to Fourier transform infrared spectrometry via solvent elimination prior to infrared detection. The method allows the immobilization of analytes separated by reversed-phase liquid chromatography. Using a spray jet assembly, the effluent from a narrow-bore reversed-phase liquid chromatography column was continuously sprayed onto a linearly moving substrate suitable for infrared detection. The deposited compounds were analyzed Fourier transform infrared microscopy. Transmission measurement using zinc selenide as substrate appears to be preferable to measurement in the reflection mode on an aluminum surface. With polycyclic hydrocarbons and quinones as model compounds, it was shown that the chromatographic separation is hardly effected during the immobilization process. The identification limits for these compounds were 10–20 ng. Aqueous methanol liquid chromatography eluents containing up to about 20% water cn be handled.

Isomer and congener identification of chlorinated pyrenes by narrow-bore liquid chromatography—Fourier transform infrared spectrometry

Abstract Liquid chromatography (LC) was coupled semi on-line to Fourier transform infrared spectrometry (FT-IR) using a spray-jet assembly interface to eliminate the LC eluent prior to IR detection. The usefulness of the LC-FT-IR system in the identification of closely related compounds in complex mixtures is demonstrated by the analysis of a chlorinated pyrene sample which contains a number of chloropyrene isomers and congeners. Characteristic FT-IR transmission spectra of all constituents could be recorded. Since most of these compounds have not been analysed by IR before, spectral assignment was mainly based on the empirical Hansen—Berg rules for substituted pyrenes. The identification limits for the chloropyrenes typically were 5–10 ng injected.

COUPLING OF LC AND FT-IR - IMPURITY PROFILING OF TESTOSTERONE UNDECANOATE

Reversed-phase liquid chromatography (RP-LC) was coupled to Fourier transform infrared spectrometry (FT-IR) with the use of a spray jet assembly to eliminate the solvent and to deposit the effluent on zinc selenide. The usefulness of the LC/FT-IR system in impurity profiling is demonstrated for the steroid drug testosterone undecanoate (TU). FT-IR transmission spectra of components of the steroid sample separated by LC are identified directly by library search or are interpreted to yield structural information. The study also shows the occasional similarity of the spectra of testosterone enanthate (TE) and testosterone decanoate (TD), two possible impurities of TU. This phenomenon, which can hinder identification, is attributed to the fact that TE and TD can both be either in a crystalline or in an amorphous state.

Improvements in environmental trace analysis by GC-IR and LC-IR

Abstract Research has been carried out to enlarge the potential of infrared (IR) spectrometry as a detector in gas and liquid chromatography (GC and LC). The study has been directed to applications in environmental analysis. Examples of recently obtained results are presented. The analyte detectability of GC-IR has been improved by incorporation of an on-column interface for the introduction of large sample volumes. The feasibility of the technique is demonstrated by the identification of pesticides in water at a level of 0.5 μg 1 −1 using on-line desorption of pre-sampled solid-phase extracted cartridges. The detectability of LC-IR, based on solvent elimination interfacing, has been enhanced by on-line trace enrichment. The applicability has been extended to buffered aqueous mobile phases by on-line post-column liquid-liquid extraction into a volatile solvent, and to gradient separations by reduction of the analytical flow using capillary LC combined with post-column addition of a make-up liquid. With both techniques, herbicides have been identified in water samples in the low μg 1 −1 range.

Trace Analysis GC-IR by Injection of Large Sample Volumes

The analyte-detection power of gas chromatography combined with cryotrapping infrared spectrometry (GC-IR) is improved by a factor of 30–100 by injection of large sample volumes by use of a loop-type interface with concurrent solvent evaporation. The usefulness of this of the analysis of real-life samples is illustrated by the identification of polyaromatic hydrocarbons (PAHs) in river Rhine water at a level of 0.5 μg/1.

Isomer differentiation of poly aromatic hydrocarbons by means of cryotrapping GC-FTIR

The usefulness of cryotrapping GC-FTIR to detect and identify polycyclic aromatic hydrocarbons (PAHs) in soil extracts has been studied. Specific attention was given to the differentiation and identification of molecular isomers in order to confirm and complement the results of HPLC/fluorescence analysis of these samples. The technique was found to be very useful for this purpose. Detection limits in the range 0.25 - 1 ng/(mu) l injected have been determined.

Comparison of light pipe, matrix isolation, and cryotrapping GC-FTIR

An inter-laboratory comparison has been carried out of three types of GC-FTIR interfacing: light-pipe, matrix isolation, and cryotrapping. Representative samples of industrial and environmental origin have been analyzed in parallel. Instruments utilizing sample storage of the GC-eluent are found to yield considerably better sensitivity than the light-pipe system. The chromatographic resolution was hardly degraded. Spectra obtained often show features characteristic to the interface used. Synchronous use of an FID or MS detector was found to allow better location and identification of the separated components.

Reversed phase HPLC-FTIR by on-line extraction and solvent elimination

A reversed phase LC-FTIR interface is described using on-line extraction of the aqueous effluent with a volatile organic solvent in conjunction with a solvent eliminating spray-jet device. Results are shown of the analysis of a 2. 10-4 M solution of acenaphthenequinone, phenanthrenequinone and two polar pesticides linuron and diuron. The mixture was separated with a mobile phase of acetonitrile-phosphate buffer and post-column extracted with dichloro-methane. Detection was carried out by FTIR transmission microscopy. The characteristics of the on-line extraction system are discussed in relation to results obtained from a direct deposition method.