Quantitative Analysis

In ITP, the concentration of ions in the steady-state zone is determined by their effective mobilities and by the concentration of the leading ion. Therefore, dilute components in a sample are concentrated according

Figure 2 Isotachopherograms and experimental definition of RE values. L, leading zone; A, B, C, sample zone(s); T, terminating zone; h, step height; Sh, step height corresponding to an asymmetric potential of a potential gradient detector, which can be determined using theoretical RE value of internal standard; RE, corrected RE value of sample. The subscript S denotes component A, B or C.

Figure 2 Isotachopherograms and experimental definition of RE values. L, leading zone; A, B, C, sample zone(s); T, terminating zone; h, step height; Sh, step height corresponding to an asymmetric potential of a potential gradient detector, which can be determined using theoretical RE value of internal standard; RE, corrected RE value of sample. The subscript S denotes component A, B or C.

to Kohlrausch's regulating function and conversely the concentrated components are diluted during migration. The following relation is valid among the total equivalent concentrations of the samples (Cl):

The quantitative index is the time-based zone length as shown in Figure 2. The absolute zone length of the sample A (lA in cm) can be defined as:

where n is the amount of applied sample (moles) and r the radius (cm) of the separation tube at a detector.

The zone passing time, t (s) is equal to the actual zone length divided by the ITP velocity, v (cm s"1). When both the sample ion and the buffer ion are monovalent, tA can be expressed as follows:

where F is the Faraday constant, Pq the mobility of the buffer ion, pA that of sample A, and i the migration current.

Isotachopherograms

Figure 3 ITP apparatus with potential gradient detection (PGD), high-frequency contactless conductivity detection (HFCCD), and ultraviolet detection (UVD). HV, high-voltage power supply (constant current); V/F, voltage-frequency converter; F/V, frequency-voltage converter.

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