APPLICATIONS

 Liquid chromatography                          Capillary Electrophoresis

Figure 1 Inorganic Anions in Urine with Capillary Electrophoresis/TraceDec^®.

Condictions: Capillary: 50 µm ID, L = 50 cm, l_eff = 37 cm; Buffer: 7 mM Sorbic Acid, 15 mM Arginin, 0,001% Hexadimethrin Hydroxide (HDB), pH 9.0; Injection: hydrodynamic 20 sec/ 10 mbar; Separation: U = 30 kV;

Figure 1 depicts the separation of inorganic anions in urine compared with a 100 ppb standard mixture. The advantages of capillary electrophoresis lie in the short separation times (usually only a few minutes) and mostly short and simple method development strategies. In addition, contactless conductivity detection now adds to these advantages by contributing an extremely sensitive detection technique. Even with capillary diameters below 50 µm the limits of detection for inorganic anions are in the ppb and ppt range.

Figure 2 Capillary Electrophoresis of Inorganic Cations in Capillaries with Very Small Inner Diameters (10 µm) with TraceDec^® Direct Contactless Conductivity Detection.Conditions: Capillary: 10 µm ID, L = 50 cm, l_eff = 46 cm; Buffer: 25 mM MES, 25 mM Histidin, 1 mM 18-K-6, pH 6.1; hydrodynamic 30 sec/ 280 mbar; Separation: U = 30 kV

To demonstrate the use of truly miniaturized separation channels, Figure 2 shows a series of separations of inorganic cations in real samples using a 10 µm i.d. capillary. Whereas optical detection schemes would be quite useless, contactless conductivity detection still enables a sensitive detection with limits of detection below 50 ppb.

Figure 3 Trace Analysis of Perchlorate in Water with CE/TraceDec^® Conductivity Detection.Conditions: Capillary: 25 µm ID, L = 52 cm, l_eff = 45 cm; Buffer: 7 mM Sorbic Acid, 15 mM Arginin, 0.001% HDB, pH 9.0; Injection: hydrodynamic 30 sec/ 250 mbar; Separation: U = 30 kV

As an example for environmental trace analysis, Figure 3 shows the determination of perchlorate in an aqueous matrix. Currently, this application is of great interest in the area around San Jose (California, USA) where ground water contamination is of public concern. Capillary electrophoresis in combination with the TraceDec^® contactless conductivity detector enables the rapid (1 minute) and sensitive (below 1 ppb) determination of perchlorate. Furthermore, it is remarkable that this separation is obtained in a 25 µm separation capillary which demonstrates the capabilities of the detection technique also for miniaturized separation schemes.

Figure 4 Determination of Amino Acids in Beer with Capillary Electrophoresis/TraceDec^® Conductivity Detection.Conditions: Capillary: 25 µm ID, L = 52 cm, l_eff = 40 cm; Buffer: Fluka Buffer Solution pH 2.5, Dilution 1:10 (5 mM Sodium Phosphate), 0.001% Sodium Polyanethol Sulfonate (SPAS); Injection: hydrodynamic 30 sec/ 30 mbar; Separation: U = 30 kV

Contactless conductivity detection is not limited to inorganic ions. Organic ions usually exhibit a lower inherent conductivity compared with inorganic ions, however, they can be detected using indirect conductivity detection. In order to limit the baseline noise of background electrolytes with a higher conductivity, capillaries with small I.D.s, e.g. 25 µm, are used.

Figure 4 shows an electropherogram of amino acids in beer. A diluted pH buffer (Fluka Buffer Solution pH 2.5, 1:5) was employed as the separation electrolyte. In order to establish a strongly electroosmotic flow even at strongly acidic conditions, an anionic electroosmotic flow modifier (sodium polyanethol sulfonate, SPAS) is added to the background electrolyte. Despite the reduced detection sensitivity compared to direct detection methods, limits of detection in the sub ppm range are obtained even in 25 µm capillaries.

Figure 5 Separation of Protease and Reverse Transcriptase Inhibitors with Capillary Electrophoresis/TraceDec^® Conductivity Detection.Conditions: Capillary: 25 µm ID, L = 52 cm, l_eff = 40 cm; standard mixture 10ppm (3TC, DDC), 20ppm (ABC), 50ppm (NFV);Buffer: Fluka Buffer Solution pH 2.5, Dilution 1:5 (10 mM Sodium Phosphate), 0.001% SPAS; Injection: hydrodynamic 30 sec/ 30 mbar; Separation: U = 30 kV

Figure 5 demonstrates the use of contactless conductivity detection for a clinical application. A mixture of  3 reverse transcriptase inhibitors and one protease inhibitor (nelfinavir) as used for anti-retroviral HIV therapy can be separated and detected in a 25 µm capillary.

Inorganic-Cations Standards

Samples (cations, anions,etc.)

IC Application

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