{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T01:26:43Z","timestamp":1760059603392,"version":"build-2065373602"},"reference-count":33,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2025,6,26]],"date-time":"2025-06-26T00:00:00Z","timestamp":1750896000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Center for Research and Development in Poland","award":["V4-KOREA\/2\/9\/ATBG\/2024"],"award-info":[{"award-number":["V4-KOREA\/2\/9\/ATBG\/2024"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>To enhance the signal intensity of kynurenines, which are present at trace concentrations in biological fluids, a novel analytical approach was developed, combining pressure-assisted electrokinetic injection (PAEKI) with a mixed micelle system based on sodium dodecyl sulfate (SDS) and Brij-35. The method was applied to key compounds of the kynurenine pathway, including L-tryptophan, kynurenine, 3-hydroxykynurenine, and kynurenic acid, as well as to the aromatic amino acids (AAs) L-tyrosine and L-phenylalanine. PAEKI was performed by electrokinetic injection for 2 min at \u22126.5 kV (reversed polarity) and 0.5 psi (3.45 kPa) using a fused silica capillary (50 cm in length, 50 \u00b5m inner diameter). The background electrolyte (BGE) consisted of 20 mM Na2B4O7 (pH 9.2), 2 mM Brij-35, 20 mM SDS, and 20% (v\/v) methanol (MeOH). The limit of detection (LOD) using a diode array detector (DAD) was 1.2 ng\/mL for kynurenine and ranged from 1.5 to 3.0 ng\/mL for the other analytes. The application of PAEKI in conjunction with micellar electrokinetic capillary chromatography (MEKC) and solid-phase extraction (SPE) of artificial urine samples resulted in a 146-fold increase in signal intensity for kynurenines compared to that observed using the hydrodynamic injection (HDI) mode. The developed method demonstrates strong potential for determining kynurenine pathway metabolites in complex biological matrices.<\/jats:p>","DOI":"10.3390\/ijms26136125","type":"journal-article","created":{"date-parts":[[2025,6,26]],"date-time":"2025-06-26T06:55:13Z","timestamp":1750920913000},"page":"6125","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["On-Line Preconcentration of Selected Kynurenine Pathway Metabolites and Amino Acids in Urine via Pressure-Assisted Electrokinetic Injection in a Mixed Micelle System"],"prefix":"10.3390","volume":"26","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0467-1560","authenticated-orcid":false,"given":"Micha\u0142","family":"Pieckowski","sequence":"first","affiliation":[{"name":"Department of Pharmaceutical Chemistry, Medical University of Gda\u0144sk, Hallera 107, 80-416 Gda\u0144sk, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8898-6991","authenticated-orcid":false,"given":"Ilona","family":"Ol\u0119dzka","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, Medical University of Gda\u0144sk, Hallera 107, 80-416 Gda\u0144sk, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6468-1974","authenticated-orcid":false,"given":"Tomasz","family":"B\u0105czek","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, Medical University of Gda\u0144sk, Hallera 107, 80-416 Gda\u0144sk, Poland"},{"name":"Department of Nursing and Medical Rescue, Institute of Health Sciences, Pomeranian University in S\u0142upsk, 76-200 S\u0142upsk, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8446-8238","authenticated-orcid":false,"given":"Piotr","family":"Kowalski","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, Medical University of Gda\u0144sk, Hallera 107, 80-416 Gda\u0144sk, Poland"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,26]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"6608","DOI":"10.1021\/ac0608568","article-title":"On-line enhancement technique for the analysis of nucleotides using capillary zone electrophoresis\/mass spectrometry","volume":"78","author":"Feng","year":"2006","journal-title":"Anal. 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