Selectivity tuning of serially coupled columns in high performance liquid chromatography

Abstract

The tuning of selectivity by changing the flow rate has been investigated in HPLC: two columns with different retention characteristics were coupled in series via a T-piece and the relative retention of components chromatographed on the system were changed by varying the individual flow rates in the coupled columns. The flow rate alteration was performed by adding a second flow after the first column.The flow rate ratio necessary for optimum resolution can be easily calculated on the basis of the capacity factors measured on the individual columns. The performance of this method for adjusting selectivity has been demonstrated by using different column combinations to separate several mixtures containing chlorophenols, nitroaromatic compounds, and aromatic hydrocarbons.

Two-dimensional high performance liquid chromatography for the separation of complex mixtures of explosives and their by-products

“…Safrole (3",4"-methylendioxyphenyl)propyl)-silica offers alternative selectivities compared to alkyl silica for most of the nitroaromatic compounds under investigation [5,38]. This characteristic is illustrated in Figure 1 where the retention factors k of some nitroaromatic substances are plotted for a C-18 column as well as for the safrole column.…”

“…The second column was a Merck cartridge (125 • 4 ram), packed in-house with safrole-silica which had been prepared from Kromasil-100 (5 pm) (Eka Nobel, Surte, Sweden) according to [5,38]. For the analyses of the field water sample, a Nucleosil C-18 guard column was used additionally.…”

“…Therefore, a careful optimization of selectivity and the retention window is necessary to separate simple mixtures of 10 to 20 components in one dimension. The possibilities of optimization include tailor made stationary phases, gradient elution and selectivity tuned serial column combinations [5]. An example is the HPLC separation of the 18 priority polyaromatic hydrocarbons (according to EPA) on a single column.…”

Selectivity Tuning in an HPLC Multicomponent Separation

“…Benická et al 1456 From Eqs. [2,15] Equation 11 can be written in the form: Thus, the overall polarity of two columns coupled in series can be tuned by adjusting the mobile phase flow in the individual columns, since weight factors (x A and x B ), often called relative retentivities (F A and F B ), determine the contributions of the individual column polarities to the overall polarity of the column series.…”

“…[1,2] Selectivity relates to the difference in physicochemical interactions between the solutes and the chromatographic system. Analysis of complex samples by HPLC requires relatively high selectivity in comparison to capillary GC since the HPLC columns commonly exhibit substantially lower efficiencies than capillary columns in GC.…”