Amino acid analyser versus HPLC – a direct comparison

Sooner or later, many laboratories face the question of whether amino acids are better determined using a dedicated amino acid analyser or a universal HPLC system. Both approaches are technically established, but differ significantly in terms of methodology, suitability for everyday use and result stability.

Why this question is asked regularly

Modern HPLC systems are flexible, widely used and suitable for a variety of analytical tasks. At the same time, there are dedicated amino acid analysers that have been developed exclusively for this one analysis.

In practice, this often raises the following questions:

• Is an existing HPLC system sufficient?
• Or is a specialised system the better solution in the long term?

There is no blanket answer – but there are clear decision-making criteria.

Methodological comparison of both approaches

Separation principles

In amino acid analysers, separation is typically performed using ion exchange chromatography. This method is specifically tailored to the properties of amino acids and has been methodologically established for decades.

HPLC systems usually work with:

• Reversed-phase columns
• alternative stationary phases
• individually adapted eluent systems

This offers flexibility, but usually requires methodological adjustments to the respective sample matrix.

Derivatisation – pre-column versus post-column

A significant difference lies in derivatisation:
 

Amino acid analyser

• Post-column derivatisation
• Reaction occurs only after separation
• Chromatography remains unaffected

HPLC

• Mostly pre-column derivatisation
• Reaction occurs before separation
• Possible influence on retention times and separation behaviour

What this means for routine analysis

Post-column methods are methodologically more stable, while pre-column methods are more flexible but more susceptible to interference.

Detection methods

Amino acid analysers generally use photometric detection of ninhydrin reaction products, but fluorescence is also used as a method.

Depending on their design, HPLC systems work with:

• UV/Vis detection
• Fluorescence
• or coupled systems

While modern detectors can be very sensitive, the quality of the results depends heavily on derivatisation, calibration and matrix effects.

Comparison in everyday laboratory use

Robustness and long-term stability

Dedicated amino acid analysers are designed for continuous operation. Methods, columns and reagents are coordinated and remain comparable over many years.

HPLC systems offer more degrees of freedom, but are more sensitive to:

• Changes in the sample matrix
• Column changes
• Reagent batches
• Small methodological deviations

This difference is relevant for long-term studies or routine measurements.

Method development and validation

For amino acid analysers:

• Predefined, established methods
• Low validation effort
• High comparability between measurement series

For HPLC methods:

• Greater flexibility
• However, regular method adaptation
• Additional validation effort in the event of changes

The effort thus shifts from the device level to the method level.

Operation and training effort

Amino acid analysers are generally:

• clearly structured
• focused on one type of analysis
• can be operated safely even by changing personnel

HPLC systems require more:

• methodological understanding
• experience in troubleshooting
• intervention in case of deviations
• trained, permanent personnel

Result quality and reproducibility 

A key point is the comparability of results.

Amino acid analysers deliver:

• very good reproducibility
• high matrix independence
• stable retention times

HPLC-based methods can achieve ‘comparable accuracy’, but are more dependent on:

• derivatisation conditions
• sample matrix
• instrument configuration

This difference is particularly evident with changing samples or long measurement series.

Which method is suitable for which laboratory?

The decision depends less on the ‘better technology’ and more on the specific application.

An amino acid analyser is useful if:

• Amino acids are determined regularly
• Reproducible results are required over long periods of time
• Different sample matrices are present
• Methodological reliability is a priority

Amino acid analyser versus HPLC – a direct comparison

An HPLC system is useful if:

• Amino acids are only analysed occasionally
• High methodological flexibility is required
• Existing infrastructure is to be used

Typical mistakes

In practice, similar problems arise time and again:

• Underestimation of the validation effort required for HPLC methods
• Overestimation of time savings
• Lack of comparability of results over longer periods of time

These aspects should be taken into account before making an investment decision.

Summary

Amino acid analysers and HPLC pursue different concepts.

While HPLC systems offer flexibility, dedicated amino acid analysers provide methodological stability, reproducibility and long-term comparability.

The right choice is based on the requirements of everyday laboratory work – not on maximum technical versatility.