title: Quantitative analysis of colistin A and colistin B in plasma and culture medium using a simple precipitation step followed by LC/MS/MS.
abstract: An analytical method for quantitation of colistin A and colistin B in plasma and culture medium is described. After protein precipitation with acetonitrile (ACN) containing 0.1% trifluoroacetic acid (TFA), the supernatants were diluted with 0.03% TFA. The compounds were separated on an Ultrasphere C18 column, 4.6 mm x 250 mm, 5 microm particle size with a mobile phase consisting of 25% ACN in 0.03% TFA and detected with tandem mass spectrometry. The instrument was operating in ESI negative ion mode and the precursor-product ion pairs were m/z 1167.7-->1079.6 for colistin A and m/z 1153.7-->1065.6 for colistin B. The lower limit of quantification (LLOQ) for 100 microL plasma was 19.4 and 10.5 ng/mL for colistin A and B, respectively, with CV <6.2% and accuracy <+/-12.6%. For culture medium (50 microL+50 microL plasma), LLOQ was 24.2 and 13.2 ng/mL for colistin A and B, respectively, with CV <11.4% and accuracy <+/-8.1%. The quick sample work-up method allows for determination of colistin A and B in clinical samples without causing hydrolysis of the prodrug colistin methanesulfonate (CMS).
authors.affiliation: Division of Pharmacokinetics and Drug Therapy, Department of Biopharmaceutical Sciences, Biomedicum, Box 591, SE-75124 Uppsala, Sweden. britt.jansson@farmbio.uu.se
authors.forename: Britt
authors.initials: B
authors.lastname: Jansson
authors.forename: Matti
authors.initials: M
authors.lastname: Karvanen
authors.forename: Otto
authors.initials: O
authors.lastname: Cars
authors.forename: Diamantis
authors.initials: D
authors.lastname: Plachouras
authors.forename: Lena E
authors.initials: LE
authors.lastname: Friberg
mesh_terms: D000900:Anti-Bacterial Agents / Q000032:analysis* / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D003091:Colistin / Q000032:analysis* / Q000097:blood; D003470:Culture Media / Q000032:analysis; D005615:Freezing; D006801:Humans; D006868:Hydrolysis; D013058:Mass Spectrometry; D010316:Particle Size; D011786:Quality Control; D012015:Reference Standards; D015203:Reproducibility of Results; D012996:Solutions; D013048:Specimen Handling; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D012996:Solutions; D003091:Colistin