Capillary Electrophoresis and Contactless Conductivity Detection of Ions in Narrow Inner Diameter Capillaries

Abstract

Capillary electrophoresis and conductometry represent a combination of a high-resolution separation method with a sensitive detection principle for the analysis of ionic species. In this paper, results are reported that are obtained with a contactless conductivity detector. This device works without a galvanic contact of the electrolyte and the electrodes. The conductivity sensor is based on two metal tubes that act as cylindrical capacitors. These electrodes are both placed around a fused-silica capillary with a detection gap of 1 mm left in between. When a high audio or low ultrasonic oscillation frequency between 40 and 100 kHz is applied to one of the electrodes, a signal is produced as soon as an analyte zone with a different conductivity compared to the background electrolyte passes the detection gap. An amplifier and rectifier is connected to the other electrode where the signal is further processed. Limits of detection for lithium and fluoride are 4 and 13 ppb, respectively, with a linear range over 4 orders of magnitude from 90 ppb up to more than 1000 ppm for both anions and cations. Furthermore, it is demonstrated that for species with lower equivalent conductivities, such as organic ions, indirect conductivity detection is a sensitive alternative to indirect optical detection methods. Limits of detection of 50 ppb and below are obtained for organic acids.

Identification of inorganic ions in post‐blast explosive residues using portable CE instrumentation and capacitively coupled contactless conductivity detection

“…Of the CE separations of inorganic and small organic ions in the literature using C 4 D detection, the work presented by Mayrhofer et al [28] shows the separation of eight anions in 2.8 min using a sorbic acid/arginine BGE. Furthermore, contactless conductivity detection provided LODs for anions and cations as low as 30 mg/L.…”

Polyelectrolyte‐modified short microchannel for cation separation

“…The separation of small ions is routinely carried out by traditional CE in silica capillaries [11][12][13][14][15][16][17][18][19], the ions being typically separated in minutes when the capillary length ranges from 10 to 80 cm. Analysis of small inorganic/ organic charged species has also been performed on microchip platforms by capillary zone electrophoresis.…”

Determinação simultânea de cátions empregando eletroforese capilar com detecção condutométrica sem contato em equipamento construído em laboratório

“…5,7,[9][10][11][12] Na grande maioria destes trabalhos, soluções tampão contendo uma mistura de ácido 2-N-morfolinoetanossulfônico (MES) e histidina (His) em meio ácido são empregados como eletrólitos de trabalho, que mantêm a condutividade de fundo em níveis relativamente baixos. Geralmente, são adicionados ao eletrólito de trabalho agentes complexantes como éter coroa, ácido α-hidroxi-isobutírico (HIBA), ácido lático (Hlac), ácido málico e ácido tartárico para alterar as mobilidades eletroforéticas dos íons metálicos, 1,4,6,[12][13][14][15][16][17][18] além de solventes orgânicos como metanol para melhorar a resolução dos sinais no eletroferograma. 1,4,5,9,14 Este trabalho descreve a construção de um sistema CE-C …”