Cell Culture Media Amino Acid Analysis

What we measure in cell culture media

In a fed-batch run, three groups of amino acids matter most: the ones that run out, the ones that turn into ammonia, and the ones cells push back into the medium. Glutamine often shows the highest demand of any amino acid in CHO cultures, especially during exponential growth ¹. In one GS-CHO line, asparagine was the most consumed amino acid during exponential growth ¹. Converting glutamine to glutamate and asparagine to aspartate releases ammonia ¹.

Ammonia matters because it inhibits growth, reduces viability, alters glycosylation and lowers recombinant protein productivity in CHO cells ². In one study, adding ammonium chloride at up to 15 mM slowed CHO growth and reduced IgG galactosylation ³. Lactate is the other main metabolic waste of CHO culture ⁴. In a GS-CHO antibody line, lowering both lactate and ammonia raised N-glycan galactosylation ⁴. Lactate accumulation, with sodium and potassium, also drives most of the osmolality rise during culture ⁵. AA-1 reports ammonia with the amino acids. Lactate is not on our panel, so read our results alongside your own metabolite data.

Analytes	Why they matter in culture	Panel
Glutamine, glutamate, ammonia	Highest-demand amino acid in many CHO runs; cells and plain chemistry both turn it into ammonia ^1,6	AA-1
Asparagine, aspartate	Major nitrogen donor; partly replacing asparagine and glutamine with aspartate and glutamate has been reported to cut ammonia by about 40% ¹	AA-1
Essential amino acids, tyrosine, proline	Depletion can cause misincorporation and sequence variants in the product ^1,7	AA-1
Alanine	In CHO-K1, excretion of alanine, glutamate and ammonia rose with glutamine supply ⁸	AA-1
Ornithine, citrulline, taurine, GABA, hydroxyproline	Across soy hydrolysate lots, ornithine and citrulline content correlated with antibody titer ⁹	AA-2
Cysteine, cystine	Redox-active and unstable in media ⁷; needs its own workup	AA-3, on request

We derivatize free amino acids with AQC, separate them by reversed-phase HPLC on a C18 column and detect at 260 nm. See how AQC derivatization works. The same chemistry has been used to follow cell culture media, showing glutamine falling and alanine rising over a culture ¹⁰. Results come in µM and mg/L. Every sample carries an internal standard, and every run includes a QC standard of known concentration. Our work supports research, development and process monitoring; the lab does not operate under GLP or GMP.

Questions this answers

"Is glutamine gone before the next feed, and is the ammonia coming from my cells or from the medium itself?"
"Which essential amino acids are close to zero at the end of the run, so we can rebalance the feed?"
"Did switching to a glutamate-based feed or a GS cell line actually lower ammonia, and where did the nitrogen go?"
"Is asparagine running out faster than we assumed?"
"Are these two lots of basal medium, feed or hydrolysate the same in free amino acids?"
"What did the cells take up between inoculation and harvest?"

Caveats for this matrix

Glutamine degrades without any cells

In culture media at 37 °C, about 10% of glutamine decomposes per day to pyrrolidone carboxylic acid and ammonia; at 4 °C, the same 10% loss takes about nine days ⁶. The reaction speeds up at higher pH and with phosphate or bicarbonate present ¹¹. It produces ammonia but no matching rise in glutamate ⁶. We report glutamine, glutamate and ammonia from the same derivatized sample, so you can read them against each other. A cell-free medium control run alongside your culture separates chemistry from uptake.

Glutamine dipeptides are not free glutamine

Large-scale processes often supply glutamine as a stable dipeptide such as alanyl-glutamine ^7,12. In CHO culture, intact dipeptides including alanyl-glutamine were found inside cells, evidence that they are imported and then cleaved ¹². Extracellular alanine rose as the dipeptide was consumed ¹². AA-1 reports free glutamine and free alanine. The intact dipeptide is not counted as glutamine, so low free glutamine in a dipeptide-fed culture does not by itself mean the glutamine source is used up.

Cysteine and cystine need their own workup

Cysteine is redox-active and unstable in media, which is why some formulations replace it with more stable derivatives ⁷. Cysteine and cystine are not part of AA-1. We measure them on request (AA-3) using a reduction–alkylation workup.

Protein, salt and pH

AQC reacts with primary and secondary amines. Complete derivatization needs a 4–6-fold molar excess of reagent and a buffered pH of about 8.2–10.1 ¹³. Serum, albumin, hydrolysate peptides and product protein also carry amine groups, so we remove protein before derivatization. We dilute high-salt or strongly buffered samples to keep the reaction in range; see sample preparation. The first time we see a new matrix type, we run a spike-recovery qualification (PREP-2). Results below the quantitation limit are flagged, not reported as numbers. The analyte reference lists what each panel covers.

Application notes

Application note · Cell culture media

Glutamine, Glutamate and Ammonia Across a Fed-Batch Run

A literature review of glutamine use, ammonia build-up and glutamine-free strategies in fed-batch CHO culture, and how to sample for them.

Read the note →

Literature watch

New publications on cell culture media analysis are reviewed monthly; relevant findings and what they change for sampling or interpretation are added to this page.

Key references

Amino acid metabolism, demand and supply in Chinese Hamster ovary cell culture – A comprehensive literature review — Yatipanthalawa BS, Lee YY, Gras SL, Martin GJO, Biotechnology Advances, 2026.
Valine feeding reduces ammonia production through rearrangement of metabolic fluxes in central carbon metabolism of CHO cells — Shahidi Pour Savizi I, Maghsoudi N, Motamedian E, Lewis NE, Shojaosadati SA, Applied Microbiology and Biotechnology, 2022.
Substitution of glutamine by glutamate enhances production and galactosylation of recombinant IgG in Chinese hamster ovary cells — Hong JK, Cho SM, Yoon SK, Applied Microbiology and Biotechnology, 2010.
Reduction of ammonia and lactate through the coupling of glutamine synthetase selection and downregulation of lactate dehydrogenase-A in CHO cells — Noh SM, Park JH, Lim MS, Kim JW, Lee GM, Applied Microbiology and Biotechnology, 2017.
Osmolality Effects on CHO Cell Growth, Cell Volume, Antibody Productivity and Glycosylation — Alhuthali S, Kotidis P, Kontoravdi C, International Journal of Molecular Sciences, 2021.
Spontaneous decomposition of glutamine in cell culture media — Tritsch GL, Moore GE, Experimental Cell Research, 1962.
Amino acids in the cultivation of mammalian cells — Salazar A, Keusgen M, von Hagen J, Amino Acids, 2016.
Investigation of glutamine metabolism in CHO cells by dynamic metabolic flux analysis — Wahrheit J, Nicolae A, Heinzle E, BMC Proceedings, 2013.
Applications and analysis of hydrolysates in animal cell culture — Ho YY, Lu HK, Lim ZFS, Lim HW, Ho YS, Ng SK, Bioresources and Bioprocessing, 2021.
Monitoring Cell Culture Media with the Waters Amino Acid Analysis Solution — Hong P, Wheat TE, Mazzeo JR, Diehl DM, Waters Corporation application note, 2007.
L-Glutamine in Cell Culture — MilliporeSigma, technical article, 2024.
Tracking dipeptides at work: uptake and intracellular fate in CHO culture — Sánchez-Kopper A, Becker M, Pfizenmaier J, et al., AMB Express, 2016.
Derivatization of Amino Acids Using Waters AccQ•Tag Chemistry — Waters Corporation, educational primer, n.d.

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

Amino Acid Analysis of Cell Culture Media