Common to all these methods is that they require relatively high amounts of sample material, the conversion takes place in vacuo, and the reactions do not always lead to a single oxygen-bearing product, necessitating a second reaction step to convert other oxygen-containing products to CO 2 .A prerequisite for an on-line technique for d 18 O measurement is a fast and quantitative conversion of the sample oxygen to a single gaseous product. To produce CO or CO 2 as a measuring gas for the isotope ratio mass spectrometer (IRMS) during a carbon reduction reaction, a reagent providing carbon and reduction equivalents is needed. Although the ratio between CO and CO 2 in a static system is according to the Boudouard equilibrium 99:1 in the presence of carbon at temperatures above 1000°C, even higher temperatures are necessary in dynamic systems. 29In a previously described on-line system for d18 O and d 15 N measurement of nitrate, 30,31 samples were converted at 1200°C with graphite, but the main product was still CO 2 , accompanied by small amounts of CO, probably due to the construction of the heating device.
A method for the automated sample conversion and on-line oxygen isotope ratio (delta(18)O) determination for organic and inorganic substances is presented. The samples are pyrolytically decomposed at 1400 degrees C in the presence of nickelized graphite. With the system presented organic as well as inorganic samples such as nitrates, sulphates and phosphates of 50-100 &mgr;g O can be analyzed for their delta(18)O values with a standard deviation usually better than 0.5 per thousand. Additionally, carbon isotope ratios of organic substances and nitrogen isotope ratios of inorganic nitrogenous compounds are available in the same sample run. Data for international and some inter-laboratory reference materials are presented to show the accuracy and reliability of the method. The effect of some additives on the CO yield was checked for substances which do not pyrolyze completely. Copyright 1999 John Wiley & Sons, Ltd.
A new technique for the sample preparation and direct coupling to an Isotope Ratio Mass Spectrometer (IRMS) for the D/H-determination is described. 1 μl size samples of water are injected and reduced with chromium metal in a novel reaction furnace. The hydrogen gas flows directly into the IRMS and is analysed (standard/sample comparison). The reproducibility is about 1 %. The accuracy of the technique was proven by means of the IAEA-standard waters V-SMOW, GISP, SLAP.
The purpose of the present study was to validate the 13C bicarbonate method (13C-M) and the doubly labeled water method (DLWM) for the estimation of the CO2 production R(CO2) in goats as a ruminant model. Indirect calorimetry was chosen as the reference method. Studies were carried out in 2 male African dwarf goats at 3 different developing stages (age: 5, 10, and 14 months, body mass: 14.6, 20.3, and 21.7 kg). Animals were fed a balanced feed 14 days before and during the studies. The isotope tracers (4 mg/kg NaH13CO3, 120 mg/kg 2H2O, and 75 mg/kg H218O; 99 AT.-%) were simultaneously given as a single pulse injection into the jugular vein. Thereafter, the animals were kept for 8 days in two respiration chambers (volume of chamber: 2.85 m3, air flow rate: 25 1/min) for the estimation of CO2 production and O2 consumption. For the determination of R(CO2) using the 13C-M samples of exhaled breath were drawn from the respiration chambers. The 13C enrichment and CO2 concentration of breath samples were measured by means of an infrared isotope analyzer. In order to determine R(CO2) by means of the DLWM, blood serum was used. The 2H and 18O enrichments were measured by an isotope ratio mass spectrometer. Urine samples were collected over 24 h to quantify renal water losses. The R(CO2) was calculated by means of the 13C-M using the area under the 13C enrichment-time curve. The determination of R(CO2) by means of the DLWM was based on the slopes of the 2H and 18O disappearance curves and the body water pool obtained from the zero time intercept of the isotope curves. The values of R(CO2) resulting from the 13C-M were found to be comparable with those from the calorimetric measurement. Smaller (not statistically significant) values of R(CO2)--92% from 13C-M and 87% from DLWM--compared to the indirect calorimetry could indicate the incorporation of 13C and 2H into metabolites other than CO2 and H2O, respectively. The body water contents calculated from the zero time intercepts of the 2H and 18O disappearance curves amounted to 66% and 63%, respectively. The body water content was found to be not related to the age of animals. The renal water loss was calculated to be 35% of the total water loss (0.76 l/d.
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