used was of type 1 (>18 MΩ cm), obtained from a MilliQ ultrapure
water purification system (Merck Millipore, Darmstadt, Germany). Methanol
was obtained from Rathburn Chemicals (Walkerburn, Scotland). Formic
acid (98%) was obtained from Merck.
Tobramycin, acylcarnitines
C2, C12, and C16, D2 glycolic acid, D6 glucose, and acylcarnitines
D3 C2, D3 C12, and D3 C16 were obtained from Larodan (Solna, Sweden).
D4 succinic acid, 13C creatine, and uric acid were purchased
from Sigma (Darmstadt, Germany). Vancomycin (1000 mg powder) was obtained
from MIP Pharma GmbH (Blieskastel, Germany). 13C2 guanidinoacetate was obtained from Dr. H Ten Brink (VU University
Medical Center, Amsterdam, The Netherlands). Creatinine was obtained
from Merck. Creatine was obtained from Nutritional Biochemical Corporation
(Cleveland, OH, USA).