{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,2]],"date-time":"2026-06-02T21:09:41Z","timestamp":1780434581677,"version":"3.54.1"},"reference-count":27,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,5,3]],"date-time":"2026-05-03T00:00:00Z","timestamp":1777766400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"European Regional Development Fund under the \u201cResearch, Innovation and Digitization for Smart Transformation\u201d","award":["Program 2021\u20132027 (Project BG16RFPR002-1.014-0006 \u201cNational Center of Excellence Mecha-tronics and Clean Technologies\u201d"],"award-info":[{"award-number":["Program 2021\u20132027 (Project BG16RFPR002-1.014-0006 \u201cNational Center of Excellence Mecha-tronics and Clean Technologies\u201d"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>In the present study, a rapid method based on total reflection X-ray fluorescence (TXRF) was developed to determine chromium in feed and fecal samples, containing chromic oxide. The method uses suspension sample preparation with gallium as an internal standard and does not require chemical reagents or complete sample digestion. Key parameters affecting performance, such as particle size, sample concentration, and acquisition time, were optimized to ensure stable signals and reliable quantification. The method showed a limit of quantification of 24 \u00b5g g\u22121 for Cr2O3 and good precision (relative standard deviations of 3\u20137% for both feed and fecal samples), at Cr2O3 concentrations in the range of 20\u201350 mg kg\u22121. These performance characteristics meets the requirements for digestibility studies. It requires only small sample quantities with minimal preparation. The developed method is suitable for routine analysis, particularly in studies generating large numbers of samples. The accuracy of the method was confirmed through agreement with results obtained using an independent method based on inductively coupled plasma optical emission spectrometry (ICP-OES) after acid digestion. The scatter plot analysis of the results obtained by both methods showed a linear regression line with a slope of 0.978 and a correlation coefficient (R2) of 0.9559, indicating good agreement. The p-value from the paired t-test performed was greater than 0.05, suggesting that the observed differences between paired measurements are not statistically significant at the 95% confidence level. The Bland\u2013Altman analysis demonstrated negligible systematic deviation between the two methods.<\/jats:p>","DOI":"10.3390\/molecules31091522","type":"journal-article","created":{"date-parts":[[2026,5,4]],"date-time":"2026-05-04T00:15:02Z","timestamp":1777853702000},"page":"1522","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Development and Verification of a Suspension-Based TXRF Method for Chromium Determination in Feed and Fecal Samples Containing Chromic Oxide as an External Digestibility Marker"],"prefix":"10.3390","volume":"31","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7586-6795","authenticated-orcid":false,"given":"Christina","family":"Tzvetkova","sequence":"first","affiliation":[{"name":"Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bontchev Str. Bl. 11, 1113 Sofia, Bulgaria"},{"name":"National Centre of Excellence Mechatronics and Clean Technologies, 8 bul. Kliment Ohridski, 1756 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lidia","family":"Ivanova","sequence":"additional","affiliation":[{"name":"Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bontchev Str. Bl. 11, 1113 Sofia, Bulgaria"},{"name":"National Centre of Excellence Mechatronics and Clean Technologies, 8 bul. Kliment Ohridski, 1756 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Albena","family":"Detcheva","sequence":"additional","affiliation":[{"name":"Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bontchev Str. Bl. 11, 1113 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Antonina","family":"Kovacheva","sequence":"additional","affiliation":[{"name":"Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bontchev Str. Bl. 11, 1113 Sofia, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5476-4802","authenticated-orcid":false,"given":"Miroslav","family":"Simeonov","sequence":"additional","affiliation":[{"name":"Agricultural Institute, Agricultural Academy, 6000 Stara Zagora, Bulgaria"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Irina","family":"Karadjova","sequence":"additional","affiliation":[{"name":"Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bontchev Str. 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