Author
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WONG, WILLIAM - Children'S Nutrition Research Center (CNRC) |
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CLARKE, LUCINDA - Children'S Nutrition Research Center (CNRC) |
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Submitted to: Rapid Communications in Mass Spectrometry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/7/2015 Publication Date: 12/15/2015 Citation: Wong, W.W., Clarke, L.L. 2015. Accuracy of delta 18O isotope ratio measurements on the same sample by continuous-flow isotope-ratio mass spectrometry. Rapid Communications in Mass Spectrometry. 29: 2252-2256. Interpretive Summary: Stable hydrogen and oxygen isotopes have been used to measure caloric intake, breast milk volume production, water needs, and body fat in nutrition studies because the stable isotope method can be done almost anywhere. The method does not require blood draw and the isotopes are found in nature and in the foods and drinks that we eat and drink everyday. Therefore, the method can be used in studies with premature infants, newborns, toddlers, children, adolescents, and pregnant and lactating women. However, the traditional assays of these two isotopes require that each isotope be prepared and analyzed separately. Therefore, a larger volume of sample is needed and more laboratory supplies and equipment are required in addition to added labor. We tested a new method to analyze both isotopes on the same sample. Based on the stable hydrogen and oxygen isotope numbers measured on urine samples, the new method produced very accurate numbers when compared to the standard method. Since the same sample can be analyzed for both isotopes, sample volume is reduced. The new method reduced the cost of laboratory supplies, the cost of labor, and sample processing time. Any laboratories with the continuous-flow isotope-ratio mass spectrometers can easily adapt the new method. Technical Abstract: The doubly labeled water method is considered the reference method to measure energy expenditure. Conventional mass spectrometry requires a separate aliquot of the same sample to be prepared and analyzed separately. With continuous-flow isotope-ratio mass spectrometry, the same sample could be analyzed sequentially for both 2H and 18O content and thus minimize sample requirement, reduce analytical cost, and avoid memory effect. The 2H contents of 197 urine samples collected from 22 doubly labeled water studies were determined using a Thermo Delta V Advantage continuous-flow isotope-ratio mass spectrometer. The 18O content of these samples was measured either using a separate aliquot of the same sample using a VG Isogas gas-isotope-ratio mass spectrometer or using the same sample following the 2H measurements on a Thermo Delta V continuous-flow isotope-ratio instrument. The delta 18O values using the same aliquot of samples were accurate to 0.18 +/- 2.61 part per thousand (mean difference +/- standard deviation (SD); 95% CI, -0.18 to 0.55 part per thousand; P = 0.33) compared with the values based on the standard conventional method. Bland and Altman pair-wise comparison also yielded a bias of 0.18 part per thousand with a 95% limit of agreement between -4.94 and 5.30 part per thousand. The study demonstrated that continuous-flow isotope-ratio mass spectrometry is capable of producing accurate 18O measurements on the same sample after 2H measurements. The method greatly reduces the analytical cost and sample size requirement and could easily be adopted by any laboratories equipped with a continuous-flow isotope-ratio mass spectrometer. |
