title: Direct determination of urinary creatinine by reactive-thermal desorption-extractive electrospray-ion mobility-tandem mass spectrometry.
abstract: A direct, ambient ionization method has been developed for the determination of creatinine in urine that combines derivatization and thermal desorption with extractive electrospray ionization and ion mobility-mass spectrometry. The volatility of creatinine was enhanced by a rapid on-probe aqueous acylation reaction, using a custom-made thermal desorption probe, allowing thermal desorption and ionization of the monoacylated derivative. The monoacyl creatinine [M + H](+) ion (m/z 156) was subjected to mass-to-charge selection and collision induced dissociation to remove the acyl group, generating the protonated creatinine [M + H](+) product ion at m/z 114 before an ion mobility separation was applied to reduce chemical noise. Stable isotope dilution using creatinine-d3 as internal standard was used for quantitative measurements. The direct on-probe derivatization allows high sample throughput with a typical cycle time of 1 min per sample. The method shows good linearity (R(2) = 0.986) and repeatability (%RSD 8-10%) in the range of 0.25-2.0 mg/mL. The creatinine concentrations in diluted urine samples from a healthy individual were determined to contain a mean concentration of 1.44 mg/mL creatinine with a precision (%RSD) of 9.9%. The reactive ambient ionization approach demonstrated here has potential for the determination of involatile analytes in urine and other biofluids.
authors.affiliation: Centre for Analytical Science, Department of Chemistry, Loughborough University , Loughborough, Leicestershire LE11 3TU, United Kingdom.
authors.forename: Neil A
authors.initials: NA
authors.lastname: Devenport
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Blenkhorn
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Weston
authors.forename: James C
authors.initials: JC
authors.lastname: Reynolds
authors.forename: Colin S
authors.initials: CS
authors.lastname: Creaser
mesh_terms: D003124:Colorimetry / Q000379:methods; D003404:Creatinine / Q000652:urine*; D006801:Humans; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D003404:Creatinine