Modeling indirectly detected analyte peaks in ion-pair reversed-phase chromatography

Area of Science:

• Analytical Chemistry
• Chromatography
• Chemical Modeling

Background:

• Indirect detection quantifies analytes lacking inherent properties by using a detectable probe.
• Two distinct interaction models (co-ion and counter-ion) are crucial for accurate indirect detection analysis.
• Existing models may not fully capture the complexities of probe-analyte interactions in chromatography.

Purpose of the Study:

• To develop and validate models for indirect detection in chromatography.
• To investigate the behavior of analytes as co-ions and counter-ions with a detectable probe.
• To assess the predictive accuracy of adsorption isotherm models for elution profiles and method sensitivity.

Main Methods:

• Modeling indirect detection for co-ion (alkyl sulfonates) and counter-ion (amines) analytes.
• Utilizing competitive bi-Langmuir and modified bi-Langmuir isotherm models.
• Employing an XBridge Phenyl column with a sodium 2-naphthalenesulfonate probe in an acetonitrile/phosphate buffer eluent.

Main Results:

• Adsorption isotherm models accurately predicted system peaks for both co-ion and counter-ion cases.
• Calculated relative errors in retention times were consistently low, often below 1%.
• Models demonstrated excellent agreement between experimental and calculated analytical method sensitivities.

Conclusions:

• The developed adsorption isotherm models are valid and effective for simulating indirect detection in chromatography.
• The study confirms the utility of these models for predicting elution behavior and optimizing analytical methods.
• This work advances the understanding and application of indirect detection techniques in chemical analysis.