A method for detecting and determining in a sample, by mass spectrometry using a single injection, the amount of five analytes selected from the group consisting of N-acetylthreonine, phenylacetylglutamine, tryptophan, creatinine, and pseudouridine, the method comprising: a) subjecting the sample to an ionization source under conditions suitable to fragment a parent ion to produce one or more daughter ions detectable by mass spectrometry from each of the five analytes, wherein the analytes are not derivatized prior to ionization and wherein the sample has been purified by liquid chromatography prior to being subjected to an ionization source; b) measuring, by mass spectrometry, the amount of the one or more daughter ions from each of the five analytes; and c) using the measured amount of the one or more daughter ions to determine the amount of each of the five analytes in the sample; wherein, when the mass spectrometer is operated in positive mode, the parent ion and the one or more daughter ions are selected from: Analyte Parent ion (m/z) Daughter ion for quantitation (m/z) Additional daughter ions (m/z) (all ±0.5) N-acetyl-DL-threonine 162.0±0.5 74.1 ±0.5 144.0, 126.1, 119.9, 116.1, 102.0, 97.9, 84.0, 70.0, 57.0, 56.0, 43.0, 28.1 phenylacetylglutamine 265.0±0.5 91.0±0.5 248.1, 219.1, 147.1, 136.0, 130.0, 129.1, 101.1, 84.0, 83.0, 65.0, 56.0, 50.9, 44.0, 40.9, 39.1, 28.0 creatinine 113.9±0.5 43.0±0.5 86.0, 72.0, 44.1, 42.0, 28.1 L-tryptophan 205.0±0.5 146.0±0.5 188.1, 170.0, 159.1, 144.0, 143.0, 142.0, 140.0, 132.0, 130.1, 128.1, 126.9, 117.9, 116.9, 114.9, 103.0, 91.0, 89.9, 89.0, 77.0, 74.9, 74.0, 64.9, 63.0, 62.0, 61.0, 50.9, 49.9, 39.2, 28.0 pseudouridine 244.9±0.5 191.0±0.5 209.0, 179.0, 167.0, 163.0, 154.8, 151.0, 148.0, 139.0, 125.0. 120.0, 111.8, 109.8, 107.8, 96.0, 92.0, 84.0, 82.0, 80,0, 68.0, 65.2, 55.0, 54.0, 43.0, 41.0, 39.0 or wherein, when the mass spectrometer is operated in negative mode, the parent ion and the one or more daughter ions are selected from: Analyte Parent ion (m/z) Daughter ion for quantitation (m/z) Additional daughter ions (m/z) (all ±0.5) pseudouridine 242.9±0.5 42.0±0.5 or 153.0±0.5 182.8, 151.9, 139.9, 138.9, 124.0, 110.8, 109.9, 96.0, 82.0, 55.0, 41.0 Acetyl-L-threonine 159.9±0.5 73.9±0.5 118.1, 115.8, 97.9, 71.9, 70.9, 70.1, 56.1, 54.0, 42.0, 40.9. 26.0 L-Tryptophan 202.9±0.5 115.9±0.5 185.9, 158.9, 141.9, 130.0, 74.1, 72.2, 59.0, 44.9 Phenylacetylglutamine 262.9±0.5 42±0.5 Creatinine 111.9±0.5 67.9±0.5 a) subjecting the sample to an ionization source under conditions suitable to fragment a parent ion to produce one or more daughter ions detectable by mass spectrometry from each of the five analytes, wherein the analytes are not derivatized prior to ionization and wherein the sample has been purified by liquid chromatography prior to being subjected to an ionization source; b) measuring, by mass spectrometry, the amount of the one or more daughter ions from each of the five analytes; and c) using the measured amount of the one or more daughter ions to determine the amount of each of the five analytes in the sample; wherein, when the mass spectrometer is operated in positive mode, the parent ion and the one or more daughter ions are selected from: Analyte Parent ion (m/z) Daughter ion for quantitation (m/z) Additional daughter ions (m/z) (all ±0.5) N-acetyl-DL-threonine 162.0±0.5 74.1 ±0.5 144.0, 126.1, 119.9, 116.1, 102.0, 97.9, 84.0, 70.0, 57.0, 56.0, 43.0, 28.1 phenylacetylglutamine 265.0±0.5 91.0±0.5 248.1, 219.1, 147.1, 136.0, 130.0, 129.1, 101.1, 84.0, 83.0, 65.0, 56.0, 50.9, 44.0, 40.9, 39.1, 28.0 creatinine 113.9±0.5 43.0±0.5 86.0, 72.0, 44.1, 42.0, 28.1 L-tryptophan 205.0±0.5 146.0±0.5 188.1, 170.0, 159.1, 144.0, 143.0, 142.0, 140.0, 132.0, 130.1, 128.1, 126.9, 117.9, 116.9, 114.9, 103.0, 91.0, 89.9, 89.0, 77.0, 74.9, 74.0, 64.9, 63.0, 62.0, 61.0, 50.9, 49.9, 39.2, 28.0 pseudouridine 244.9±0.5 191.0±0.5 209.0, 179.0, 167.0, 163.0, 154.8, 151.0, 148.0, 139.0, 125.0. 120.0, 111.8, 109.8, 107.8, 96.0, 92.0, 84.0, 82.0, 80,0, 68.0, 65.2, 55.0, 54.0, 43.0, 41.0, 39.0 or wherein, when the mass spectrometer is operated in negative mode, the parent ion and the one or more daughter ions are selected from: Analyte Parent ion (m/z) Daughter ion for quantitation (m/z) Additional daughter ions (m/z) (all ±0.5) pseudouridine 242.9±0.5 42.0±0.5 or 153.0±0.5 182.8, 151.9, 139.9, 138.9, 124.0, 110.8, 109.9, 96.0, 82.0, 55.0, 41.0 Acetyl-L-threonine 159.9±0.5 73.9±0.5 118.1, 115.8, 97.9, 71.9, 70.9, 70.1, 56.1, 54.0, 42.0, 40.9. 26.0 L-Tryptophan 202.9±0.5 115.9±0.5 185.9, 158.9, 141.9, 130.0, 74.1, 72.2, 59.0, 44.9 Phenylacetylglutamine 262.9±0.5 42±0.5 Creatinine 111.9±0.5 67.9±0.5