Acidic Ion-bearing Group

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Acidic Ion-bearing Group

Zodiac provides several different columns with negatively charged functional groups due to the embedded anionic ion-bearing reagent. The Zodiac HST  – Acidic Cation Exchange Group  columns are designed with varying acid strengths, making them suitable for different basic compounds with varying pKa values.

  1. Zodiac HST A– pKa value: 0
    • Designed for weak bases, amino acids (AA), and metals. This column features the strongest acidic functional group,
  1. Zodiac HST OG– pKa value: 1
    • Suitable for weak to medium bases, amino acids (AA), and metals. This column offers a balance of acidic strength and can separate a broader range of basic compounds compared to the HST A column.
  1. Zodiac HST OG2– pKa value: 2
    • Ideal for strong bases and di-bases.
  1. Zodiac HST C– pKa value: 5
    • Intended for strong bases and di-bases. The weakest acidic functional group in this series makes it perfect for separating compounds that require minimal acidic conditions but still benefit from ion-exchange properties.

Functional Mechanism:

The embedded acidic functional group in these columns can exist in either an ionized or non-ionized form, depending on the pH of the mobile phase. For ion-exchange retention on Zodiac HST Series columns, the pH of the mobile phase should be selected close to or above the transition point of the embedded acidic groups. Below this transition pH, the column behaves similarly to a standard reverse-phase column, utilizing a non-ionized polar group for separation

Column Selection:

The column name correlates to the pH value at which the acid residue on the column transitions from its ionized form to its neutral form. The difference in the functional group acidity across the Zodiac HST Series columns allows for selecting the most appropriate column based on the pKa value of the compounds being analyzed.

This approach provides enhanced control over the retention and separation of compounds, particularly those with varying degrees of basicity, offering flexibility and precision in complex separations.

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