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 (R2 = 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.
Abstract. Monoterpenes (C 10 H 16 ) are the products of metabolism found in many plants and are most notably emitted by conifers. Many abiotic and biotic factors are known to stimulate monoterpene emissions from conifers, including: temperature, wounding, herbivory, infestation, UV-radiation, O 3 exposure etc. Monoterpenes have been shown to contribute to aerosol and cloud formation, which have a net cooling effect on Earth's radiative balance. Thus, there is a need to explore all the factors that influence monoterpene emissions from forests. One as yet largely unexplored process is the effect of nutrient availability on monoterpene emission. In this study we treated young Scots pine seedlings with fertilizer (NPK and urea) largely and observed a large increase in monoterpene emission compared with unfertilized controls. Measurements at 26°C suggests an emission increase of 0.8 ng g -1 DW min -1 per addition of 1 kg N tot ha -1 year -1 . These results are important for understanding future trends in monoterpene emission, since nitrogen deposition, as consequence of industrial emissions and agricultural sources, is increasing in the soils of boreal and high altitude temperate forests.
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