Jatisai Tanyanyiwa

Improved capacitively coupled conductivity detector for capillary electrophoresis

The new features of the capacitively coupled contactless conductivity detector for capillary electrophoresis described are higher peak-to-peak excitation voltages for the detector cell of up to 250 V, a pick-up amplifier in close proximity to the electrode and synchronous detection. The electrical performance of the cell was characterized and found to follow readily predictable patterns. The alterations led to a higher signal strength, a better signal-to-noise ratio (S/N) and improved stability. The 3 × S/N detection limits obtained for inorganic cations and anions are in the range 0.1–0.2 μM. For the indirect detection of model compounds of organic cations and anions (aliphatic amines and sulfonates), detection limits of typically 1 μM were achieved.

High-voltage contactless conductivity detection of metal ions in capillary electrophoresis.

The detection of alkali, alkaline earth and heavy metal ions with a high‐voltage capacitively coupled contactless conductivity detector (HV‐C4D) was investigated. Eight alkali, alkaline earth metal ions and ammonium could be separated in less than 4 min with detection limits in the order of 5×10‐8 M. The heavy metals Mn2+, Pb2+, Cd2+ Fe2+ , Zn2+, Co2+, Cu2+ and Ni2+ could also be successfully resolved with a 10 mM 2‐(N‐morpholino)ethanesulfonic acid/DL‐histidine (MES/His)‐buffer. Zn2+, Co2+, Cu2+ and Ni2+ showed an indirect response. The detection limits for the heavy metals were determined to range from about 1 to 5 νM.

Conductimetric and potentiometric detection in conventional and microchip capillary electrophoresis

Potentiometric detection is rarely used in separation methods but is promising for certain classes of analytes which can only with difficulty be quantified by more standard methods. Conductimetric detection of ions is very versatile and has recently received renewed interest spurned by the introduction of the capacitively coupled contactless configuration. Both are useful and complementary alternatives to the established optical detection methods, and to the more widely known electrochemical method of amperometry. The simplicity of the electrochemical methods makes them particularly attractive for microfabricated devices, but relatively little work has to date been carried out with regard to potentiometric and conductimetric detection.

High-voltage contactless conductivity-detection for lab-on-chip devices using external electrodes on the holder

The detection of ionic species in a polymeric planar electrophoresis device by contactless conductivity measurement is described. To our knowledge this is the first report of such measurements carried out with external electrodes which are part of the holder rather than the separation chip itself. The approach allows the use of bare devices as used for optical measurements, which greatly simplifies the method. The use of a sine wave of 100 kHz of a high amplitude of 500 V for cell excitation assures high sensitivity which is demonstrated with electropherograms for alkali and heavy metal ions as well as inorganic anions and carboxylates at concentrations between 10 and 50 µM. The determination of underivatized amino acids was also possible by using a buffer in the alkaline region where these species are present in anionic form. Detection limits were found to be in the order of 1–5 µM for the inorganic ions and between about 5 and 50 µM for the organic species.

Electrophoretic separations with polyether ether ketone capillaries and capacitively coupled contactless conductivity detection.

Polyether ether ketone (PEEK) capillaries were found to be compatible with capacitively-coupled contactless-conductivity detection (C4D). Detection limits in the order of 10(-7) M were obtained with C4D employing a high excitation voltage (HV-C4D) for inorganic cations and anions. The organic polymer capillary shows a relatively low electroosmotic flow of 2.6 x 10(-4) cm2 V(-1) s(-1). Thus inorganic anions and slower organic anions can be separated with a PEEK capillary in a single run without flow modifier. This feature also enables the analysis of both, cations and (fast and slow) anions, in a sample in two subsequent runs just by reversing the polarity or in a single run if dual opposite end injection is employed.