Isocratic Separation of Basic, Neutral, and Acidic Molecules on a Thermo Scientific™ Acclaim™ Mixed-Mode WAX-1 Column

Importance of the topic

Efficiently separating basic, neutral and acidic compounds in a single isocratic run addresses a common challenge in pharmaceutical, environmental and clinical laboratories. Mixed-mode chromatography combines multiple interaction mechanisms within a single column, offering baseline resolution of chemically diverse analytes without gradient complexity.

Objectives and Study Overview

This application note demonstrates the isocratic separation of eleven model compounds spanning basic, neutral and acidic chemistries using the Thermo Scientific™ Acclaim™ Mixed-Mode WAX-1 column. The study aims to showcase the column’s multi-mode retention behavior, method simplicity and robustness under routine analytical conditions.

Methodology and Used Instrumentation

The separation was performed under the following conditions:

• Column: Acclaim Mixed-Mode WAX-1, 4.6 × 150 mm, 5 μm particle size
• Column temperature: 30 °C
• Mobile phase: 50/50 v/v acetonitrile and 20 mM phosphate/pyrophosphate buffer (pH 6.0)
• Buffer composition: 6.8 g KH₂PO₄ and 0.5 g Na₂P₂O₇·10H₂O per 1 L deionized water, adjusted to pH 6.0 with NaOH
• Flow rate: 1.0 mL/min
• Injection volume: 5 µL
• Detection: UV at 220 nm

The pyrophosphate additive suppresses metal ion interference, preserving column lifetime and peak shape.

Main Results and Discussion

Baseline separation of all eleven analytes was achieved in a total run time of 20 minutes. Retention and elution order reflected combined hydrophobic, anion-exchange and cation-exclusion interactions:

• Early eluters (neutral species): caffeine, acetaminophen, phenanthrene
• Intermediate retention (basic molecules): amitriptyline
• Late eluters (acidic species): benzoic acid, salicylic acid, ketoprofen, naproxen
• Steroidal compounds (hydrocortisone, dexamethasone) eluted between basic and acidic regions
• An inorganic anion (iodide) was resolved among organics, illustrating mixed-mode selectivity

The chromatogram demonstrated sharp, symmetrical peaks and consistent retention times, indicating robust performance and minimal matrix effects.

Benefits and Practical Applications

Mixed-mode isocratic separation offers several advantages:

• Single-method workflow for complex mixtures, reducing analysis time and solvent consumption
• Enhanced selectivity for analytes with overlapping polarities
• Reduced need for column switching or gradient programming
• Compatibility with routine UV detection and potential coupling to mass spectrometry

This method suits quality control of pharmaceutical formulations, impurity profiling and environmental monitoring of acidic and basic contaminants.

Future Trends and Potential Applications

Advancements in mixed-mode stationary phases will focus on tailored selectivity for challenging analytes such as zwitterions and highly polar metabolites. Integration with automated sample preparation and hyphenation to high-resolution mass spectrometry will expand applications in metabolomics and proteomics. Development of green mobile phases and miniaturized column formats may further improve sustainability and throughput.

Conclusion

The Acclaim Mixed-Mode WAX-1 column delivers reliable isocratic separation of basic, neutral and acidic compounds in a single run. Its unique combination of hydrophobic, anion-exchange and cation-exclusion interactions simplifies method development and enhances laboratory productivity.

References

No external literature cited in the source document.