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Besides a gradient HPLC system for the analysis of the compounds of interest on a LiChrosorb RP\u201018 (7 \u03bcm) column with mobile phase containing 0.05% aq. solution of trifluoroacetic acid and acetonitrile has been elaborated. The procedure has been successfully applied to the analysis of methylxanthines and methyluric acids in urine of patients with chronic asthma treated with theophylline and in urine of healthy subjects.<\/jats:p>","DOI":"10.1002\/jssc.200401841","type":"journal-article","created":{"date-parts":[[2004,9,16]],"date-time":"2004-09-16T07:01:00Z","timestamp":1095318060000},"page":"1166-1172","source":"Crossref","is-referenced-by-count":27,"title":["Separation, pre\u2010concentration, and HPLC analysis of methylxanthines in urine samples"],"prefix":"10.1002","volume":"27","author":[{"given":"Miros\u0142awa","family":"Zydro\u0144","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jacek","family":"Baranowski","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Irena","family":"Baranowska","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2004,10,6]]},"reference":[{"key":"e_1_2_1_2_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0899-9007(00)00369-5"},{"key":"e_1_2_1_3_2","doi-asserted-by":"publisher","DOI":"10.1016\/0278-6915(88)90007-5"},{"key":"e_1_2_1_4_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0003-2670(99)00061-6"},{"key":"e_1_2_1_5_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0378-4347(99)00040-7"},{"key":"e_1_2_1_6_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0378-4347(00)00325-X"},{"key":"e_1_2_1_7_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0378-4347(96)00275-7"},{"key":"e_1_2_1_8_2","doi-asserted-by":"publisher","DOI":"10.1016\/S1570-0232(03)00557-9"},{"key":"e_1_2_1_9_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0378-4347(98)00016-4"},{"key":"e_1_2_1_10_2","doi-asserted-by":"publisher","DOI":"10.1016\/0378-4347(93)80083-G"},{"key":"e_1_2_1_11_2","doi-asserted-by":"publisher","DOI":"10.1016\/0378-4347(95)00374-6"},{"key":"e_1_2_1_12_2","doi-asserted-by":"publisher","DOI":"10.1016\/0378-4347(92)80163-K"},{"key":"e_1_2_1_13_2","doi-asserted-by":"publisher","DOI":"10.1159\/000457700"},{"key":"e_1_2_1_14_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0378-4347(97)00590-2"},{"key":"e_1_2_1_15_2","doi-asserted-by":"publisher","DOI":"10.1093\/jat\/17.4.225"},{"key":"e_1_2_1_16_2","doi-asserted-by":"publisher","DOI":"10.1081\/JLC-100102072"},{"key":"e_1_2_1_17_2","doi-asserted-by":"publisher","DOI":"10.1081\/JLC-100100432"},{"key":"e_1_2_1_18_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0378-4347(01)00251-1"},{"key":"e_1_2_1_19_2","unstructured":"Merck Application Guide ChromCircle 2.0 Merck\u2010Hitachi Darmstadt Germany 2000."},{"key":"e_1_2_1_20_2","unstructured":"Baker Application Notes Mallinckrodt Baker Inc. 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