Another metabolic profiling study of urine was conducted using HS-SPME-GC-MS in combination with NMR spectroscopy to investigate gender differences [45]. The authors identified 51 volatiles metabolites using HS-SPME-GC-MS and 18 metabolites using NMR spectroscopy. They found that gender differences were related to changes in the metabolism of lipids and amino acids, and in the tricarboxylic acid cycle.