On-line hyphenation of quantum cascade laser and capillary electrophoresis.

We report the first successful hyphenation of a Fabry Pérot quantum cascade (QC) laser to a capillary electrophoresis system. This involved use of a dedicated IR-transparent flow cell, made of CaF2, constructed by means of SU-8 based lithography and low temperature wafer bonding techniques. Adenosine, guanosine, xanthosine and adenosine-5'-monophosphate were separated in a borate-containing separation electrolyte (10 mM, pH 9.3). Functional group (carbohydrate) detection was accomplished by use of the 1080 cm(-1) emission line of the available QC-laser. The assessable optical path length could be increased, from the normally available 10-15 microm in CE-FTIR analyses, to 60 microm using this powerful mid-infrared laser and aqueous solutions.

Capillary electrophoretic separation of sugars in fruit juices using on-line mid infrared Fourier transform detection.

Fourier Transform infrared spectroscopy has been coupled to on-line capillary electrophoresis (CE) for the separation and detection of natural sugars in orange fruit juices. The CE separation electrolyte comprised 50 mM sodium carbonate buffer adjusted to pH 12.3 with NaOH. Galactose was selected as an internal standard. To ensure tight connections between the custom-made IR-transparent flow cell (optical path length was 15 [micro sign]m) and the fused silica capillaries, commercially available O-rings were used. The scanner of the spectrometer was operated at a HeNe laser modulation frequency of 320 kHz, recording interferograms in a double-sided, forward-backward mode with 8 cm(-1) spectral resolution. For each spectrum 64 interferograms (512 for the background) were co-added and a Blackman-Harris 3-term apodization function was performed. A low-pass filter at 1828 cm(-1) was inserted in the IR beam to increase the light throughput in the spectral region of interest (1800 cm(-1)-900 cm(-1)). Using these features a new spectrum could be obtained every two seconds. Sucrose, glucose and fructose were structurally identified and quantified in orange juice samples. The limits of detection (3S/N) for all analytes were in the low millimolar range (0.7-1.9 mM) or, in absolute amounts, the low nanogram range (1.5-3.2 ng). The resolution ranged between 1.14 to 3.15 and the RSD of the proposed method was 1.8-4.4%.

Micellar electrokinetic chromatography with on-line Fourier transform infrared detection.

Micellar electrokinetic chromatography (MEKC) was successfully coupled to Fourier transform infrared (FTIR) detection, using a micromachined IR-transparent flow cell with an optical path length of 15 micro m for the on-line detection of five neutral analytes. Tight connections between the flow cell and the capillaries were achieved by creating a small O-ring of UV-curing epoxy adhesive on the sharply cut capillary ends. The background electrolyte consisted of 15 mM phosphate buffer at pH 7 and 40 mM sodium dodecyl sulfate (SDS). Five analytes (paracetamol, caffeine, p-nitro benzyl alcohol, m-nitrophenol and p-nitrophenol) were successfully separated, yielding detailed IR stack plots that could be used for quantification and identification. Linear calibration graphs were obtained for each individual analyte present in mixtures at concentrations up to 10 mM. The limit of detection (3 S/N) ranged between 1.1 and 1.5 mM (1.2-1.8 ng). Analytes were identified by comparing spectra obtained during the MEKC separation with those resulting from completely filling the capillary with each individual analyte dissolved in the micelle-containing electrolyte. Information on the specific functional groups of all analytes could be elucidated from the spectra. Since FTIR is a nondestructive detection technique, a conventional on-line UV detector was introduced directly after the developed IR flow cell to test the system's performance and to demonstrate that tandem FTIR and UV detection is feasible.

On-line infrared detection in aqueous micro-volume systems.

Mid infrared spectroscopy is a non-destructive technique that can provide detailed information on important, molecule-specific features such as the conformation and functional groups of a large range of compounds. Infrared spectroscopy is now an established and frequently used technique for qualitative analysis, i.e. the identification of chemical constituents in a sample. In addition, its use for quantitative purposes has grown dramatically in recent years. It is important to realise that the analytical problem defines the mode of operation and implementation of the FTIR technique. This Highlight article focuses on the advantages and scope of on-line FTIR detection strategies. However, in common with all techniques, on-line FTIR detection has a number of potential shortcomings, which are also discussed.

On-line fourier transform infrared detection in capillary electrophoresis.

The coupling of Fourier transform infrared (FT-IR) spectroscopy as a new on-line detection principle in capillary electrophoresis (CE) is presented. To overcome the problem of total IR absorption by the fused-silica capillaries that are normally employed in CE separations, a micromachined IR-transparent flow cell was constructed. The cell consists of two IR-transparent CaF2 plates separated by a polymer coating and a titanium layer producing an IR detection window, 150 microm wide and 2 mm long, with a path length of 15 microm. The IR beam was focused on the detection window using an off-axis parabolic mirror in an optical device (made in-house) attached to an external optical port of the spectrometer. The connections between the fused-silica capillaries and the flow cell were made by a small O-ring of UV-curing epoxy adhesive on the sharply cut ends of the capillaries, allowing the capillaries to be easily replaced. Aqueous solutions comprising mixtures of adenosine, guanosine, and adenosine monophosphate were used to test the system's performance. Conventional on-line UV detection was employed to obtain reference measurements of analytes after the IR detection flow cell. The limit of FT-IR detection for all analytes (in absolute amounts) was in the nano- to picogram range corresponding to concentrations in the low-millimolar range.