Tryptophan is one of the standard amino acids that make up proteins, and it also occurs on its own, unattached, in foods, fermentation samples, and cell culture media. A lab reports tryptophan as part of a wider amino acid profile, not in isolation. Tryptophan carries the sharpest total-panel caution on this site: standard acid hydrolysis destroys tryptophan, so a total tryptophan result cannot be read off a standard acid-hydrolysed total panel. That distinction is stated first, before any panel detail, to prevent a wrong order.
Chemistry in plain terms
Standard biochemistry references classify tryptophan as an essential amino acid for humans, meaning it must come from food because the body cannot make it. Its side chain is an indole ring, which makes tryptophan one of the aromatic amino acids in standard classifications. PubChem lists L-tryptophan as a standard proteinogenic amino acid, built into protein chains as well as present free in solution. Bound and free forms are both real, and for tryptophan they are not interchangeable by the standard total method, for the reason below.
One method point also matters on a report: AABA, short for alpha-aminobutyric acid, is the internal standard the lab adds to help quantify the results. AABA is not tryptophan and is not a result for your sample.
Where it occurs
Tryptophan occurs as a building block in proteins across foods, feeds, and biological materials. Free tryptophan also occurs in cell culture and spent media, fermentation and process liquids, protein hydrolysates, and food and supplement products, where a free profile describes the sample as it is.
This page gives no typical level for any material. Levels vary with recipe, organism, process, and sampling point, and no verified figure is available. Measure your sample rather than borrowing a number from a different one.
Free vs total for tryptophan
A free tryptophan result measures the tryptophan already dissolved and unattached in the sample as received, with no hydrolysis step. That is the tryptophan measurement OpenChemWorks offers as part of AA-1, and it is the relevant number when the question is about the sample as used or as eaten: what is in the medium now, or what free profile a product presents.
A total tryptophan result would have to include tryptophan that was bound inside protein as well as the free fraction. Standard acid hydrolysis, the AA-T step that breaks protein chains apart, destroys tryptophan during that step. Tryptophan is therefore not reported from the standard AA-T acid hydrolysis. Any total tryptophan figure would need a different, tryptophan-appropriate hydrolysis approach, which is not part of AA-T here; ask before ordering if total tryptophan is your question, rather than assuming a total panel covers it.
That is different from the asparagine and glutamine case, where the amide groups are lost during acid hydrolysis and those amino acids are reported together with aspartic acid and glutamic acid respectively. For tryptophan, the point is destruction, not a combined reporting basis.
Method notes: how tryptophan is measured here
At OpenChemWorks, free tryptophan is measured as part of a panel using AQC pre-column derivatization, the Waters AccQ-Tag approach, with HPLC-UV detection. The amino acids are chemically tagged, separated on the HPLC column, and quantified against calibrated standards. AABA is added at a known amount as the internal standard, which is why its name appears in method paperwork. To restate the point: AABA is the standard, added by the lab; tryptophan is the analyte, measured from your sample. Different compounds, different roles.
No resolution, recovery, or detection-limit figure is quoted here, because no verified figure from this laboratory's validated method is available.
Which panel includes tryptophan
Tryptophan is included in AA-1, the free amino acid panel: 19 amino acids plus ammonia, measured by AQC HPLC-UV. Cysteine is excluded from AA-1 and needs a separate AA-3 workup. Tryptophan is not reported from AA-T: AA-T is total amino acid analysis by standard acid hydrolysis, and that hydrolysis destroys tryptophan, as stated above.
Prices are only these: AA-1 costs $150 per sample for liquids, $180 per sample for powders ($150 plus $30 powder preparation), and $150 flat for first-time customers, with $125 per sample at 25 or more samples per month. AA-T, total amino acid analysis, costs $230 per sample. The pilot is $250 for 5 samples, credited in full against a first contract signed within 90 days.
OpenChemWorks, in Davis, California, is validating now and reserving pilot slots. The lab is not GLP, GMP, or ISO/IEC 17025 accredited, and no turnaround is promised here. Email info@openchemworks.com with your sample description and whether your question is about free tryptophan in the sample as it is, or about total tryptophan, so the hydrolysis limit can be addressed before any order.
Frequently asked questions
Is AABA the same as tryptophan?
No. AABA, alpha-aminobutyric acid, is the internal standard added by the lab for quantification. Tryptophan is a different compound, and it is the analyte measured from your sample.
Do I get total tryptophan from the AA-T total panel?
No. Standard acid hydrolysis destroys tryptophan, so tryptophan is not reported from AA-T. Ask before ordering if total tryptophan is what you need.
Do I need free or total tryptophan?
Free, as part of AA-1, answers a question about the sample as received. Total tryptophan is a different question that the standard acid-hydrolysed total panel cannot answer, for the reason above.
Is tryptophan reported on its own?
At OpenChemWorks free tryptophan is reported as part of the AA-1 free panel, alongside the panel analytes.
References
- PubChem — L-Tryptophan (CID 6305) — Identity reference for the amino acid named on this page.
- Waters — Derivatization of Amino Acids Using Waters AccQ-Tag Chemistry — Method background for AQC derivatization and HPLC-UV amino acid analysis.
- British Journal of Nutrition (2023) — Asparagine and glutamine lose an amide residue during acid hydrolysis and are measured with aspartate and glutamate respectively.
- OpenChemWorks — Pricing — Published service and pricing copy (2026).
OpenChemWorks Laboratory · Reviewed by the laboratory director, PhD chemist · Published October 29, 2026