How We Control Quality in Amino Acid Analysis

Amino acid analysis quality control rests on six checks, and each answers a different question about a result. We add an internal standard to every sample and run a QC standard of known concentration with every run. We check detector sensitivity and run reagent blanks. Where the matrix calls for a recovery check, we spike amino acids into the sample. Results below the quantitation limit are flagged, not reported as numbers.

We are a research-use laboratory, not a GLP, GMP or ISO 17025 laboratory. Our services are for research, development and process monitoring. We cite regulatory guidance below because it explains the concepts clearly, not to claim compliance with it.

Internal standard in every sample

An internal standard is a compound added in a known amount to every sample, so that each result is calculated relative to it. The pharmacopeial chapter on amino acid analysis recommends one to monitor physical and chemical losses and variations during the analysis ². Its recovery indicates the general recovery of the amino acids through the procedure ². In amino acid work the internal standard is itself an amino acid ⁵. Added before derivatization, it goes through derivatization, injection and separation with your analytes.

An internal standard helps most when preparation has several steps whose volumetric recovery may vary; added early, it compensates for later losses ⁴. It cannot correct for anything that happened before it was added ⁴. It must never be found in the sample, and its peak must be well resolved ⁴. In pharmaceutical bioanalysis, the internal standard goes into every calibration standard, QC and study sample, and its responses are monitored for systematic variability ³.

Our example report uses α-aminobutyric acid. The United States Pharmacopeia names it, with norleucine and nitrotyrosine, among commonly used internal standards for amino acid analysis ². A manufacturer's AQC system guide lists it as the acceptable alternative to norvaline ⁵.

What this buys you: every sample carries its own monitor of losses and variations ², rather than relying on the run as a whole.

A QC standard with every run

A QC standard is an amino acid mixture of known concentration, derivatized and analyzed alongside your samples. It answers a run-level question: does the calibration still hold for this run? The pharmacopeial chapter describes testing the calibration by analyzing controls, and running standards with test material to show the integrity of the whole procedure ². In bioanalytical guidance, QC samples mimic study samples and are used to decide whether a run is accepted ³.

Because the QC standard is derivatized and separated like a sample, it tests the whole measurement, not just the detector ². The two checks work at different levels. The internal standard monitors each sample. The QC standard monitors the run as a whole.

Detector sensitivity checks

We check detector sensitivity because UV response depends on how much light reaches the detector. An aging lamp or contaminated flow-cell windows reduce that light and raise baseline noise ⁶. Because a quantitation limit can be estimated from signal-to-noise ⁷, extra noise matters most for the smallest peaks. The ICH guideline describes system suitability tests as regular checks that the measurement system is fit for its intended purpose ⁷.

Reagent blanks

A reagent blank goes through derivatization and analysis with no sample in it. Anything it shows came from reagents, water, glassware or the lab. The same system guide describes the reagent blank as a test of the derivatization reagent's quality ⁵. It lists glycine, serine, aspartate and glutamate as the most abundant contaminants, from sources such as dirty glassware, airborne dust and fingerprints ⁵. The pharmacopeial chapter adds glove powder and low-purity reagents, and notes that dust can raise glycine, serine and alanine ².

Blanks matter most for ammonia. An ammonia peak is always present in AQC derivatization, and its size varies with ammonia in the water and air ⁸. Excess reagent also hydrolyzes to 6-aminoquinoline, a by-product that does not interfere ^1,5. In bioanalytical practice, blanks reveal interference and carryover ³. The analyte reference covers where ammonia in samples comes from.

Spiked recovery where the matrix calls for it

A spike-recovery check adds known amounts of amino acids to a portion of the sample and measures how much comes back. It shows whether the matrix changes the response. The ICH guideline assesses accuracy this way, by spiking known amounts into the test matrix ⁷. Bioanalytical guidance calls the underlying problem a matrix effect: unidentified sample components alter the analyte response ³. One AQC study recommended preparing calibration in serum or tear matrix for exactly this reason ¹.

We run spiked recovery checks where the matrix calls for one. New-matrix qualification (PREP-2 on our pricing page) is a spike-recovery check the first time we see a matrix type. Sample preparation covers how matrices are handled before derivatization.

Results below the quantitation limit are flagged

The quantitation limit is the lowest amount that can be determined with suitable precision and accuracy ⁷. Below it, an analyte may be detectable but has no reliable value ⁷. We flag those results rather than report them as numbers. The detection limit sits lower still: the smallest amount that can be detected but not necessarily quantified ⁷. A flagged analyte may lie between the two limits, fall below the detection limit, or be absent; the flag does not distinguish these cases. Reading an amino acid profile explains how to handle a flagged value in your own calculations.

What you see on the report

Every report includes a QC summary, alongside concentrations in µM and mg/L and the chromatogram. Raw data are available as CSV on request. If your work requires data generated under GLP, GMP or ISO 17025, you need an accredited laboratory. For research, development and process monitoring, these are the checks behind our amino acid analysis service. For the derivatization chemistry itself, see AQC derivatization.

References

1. Fast and Sensitive Quantification of AccQ-Tag Derivatized Amino Acids and Biogenic Amines by UHPLC-UV Analysis from Complex Biological Samples — A. Guba et al., Metabolites, 2022.
2. 〈1052〉 Biotechnology-Derived Articles—Amino Acid Analysis — United States Pharmacopeia, harmonized text, official 2018.
3. M10 Bioanalytical Method Validation and Study Sample Analysis: Guidance for Industry — ICH / U.S. Food and Drug Administration, 2022.
4. When Should an Internal Standard be Used? — J.W. Dolan, LCGC North America, 2012.
5. UPLC Amino Acid Analysis Solution System Guide, Rev. B — Waters Corporation, 2007.
6. The LCGC Blog: HPLC Diagnostic Skills–Noisy Baselines — T. Taylor, LCGC, 2019.
7. Validation of Analytical Procedures Q2(R2) — International Council for Harmonisation, 2023.
8. What is the source of the NH3 peak in the AccQ•Tag derivatization reaction? — Waters Corporation, Knowledge Base.

OpenChemWorks Laboratory · Reviewed by the laboratory director, PhD chemist · Published September 23, 2026