Determination of the 2H/1H, 17O/16O,and 18O/16O isotope ratios in water by means of tunable diode laser spectroscopy at 1.39 microm

We demonstrate the feasibility of the accurate and simultaneous measurement of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water vapor by means of tunable diode laser spectroscopy. The absorptions are due to the v1 + v3 combination band, observed using a room temperature, distributed feedback (DFB) diode laser at 1.39 microm. The precision of the instrument is approximately 3, 1, and 0.5/1000 for the 2H, 17O, and 18O isotope ratios, respectively, and is at present limited by residual optical feedback to the laser. The signal-to-noise, however, is superior to that obtained in a similar experiment using a color center laser at 2.7 microm. Replacing the current laser with a better unit, we are confident that a precision well below 1/1000 is attainable for all three isotope ratios. The diode laser apparatus is ideally suited for applications demanding a reliable, cheap, and/or portable instrument, such as the biomedical doubly labeled water method and atmospheric sensing.     

Diode laser absorption spectrometry for 13CO2/12CO2 isotope ratio analysis: Investigation on precision and accuracy levels

Near-infrared laser spectroscopy is used to measure the ¹³C/¹²C isotope abundance ratio in gas phase carbon dioxide. The spectrometer, developed expressly for field applications, is based on a 2 μm distributed feedback diode laser in combination with sensitive wavelength modulation detection. It is characterized by a simplified optical layout, in which a single detector and associated electronics are used to probe absorptions of a pair of ¹³CO₂ and ¹²CO₂ lines, simultaneously in a sample, as well as a reference gas. For a careful investigation of the achievable precision and accuracy levels, we carried out a variety of laboratory tests on CO₂ samples with different isotopic compositions, calibrated with respect to the international standard material by means of isotope ratio mass spectrometry. The 1-σ accuracy of the ¹³CO₂/¹²CO₂ determinations, reported in the so-called δ notation, is about 0.5‰ (including both statistical and systematic errors), for δ-values in the range from -30‰ to +20‰. We show that the major source of systematic errors is a consequence of the non-linearity of the Lambert–Beer absorption law, and can be corrected for to a very high degree of accuracy. PACS 42.62.Fi; 42.55.Px; 33.20.Ea     

First real-time measurement of the evolving 2H/1H ratio during water evaporation from plant leaves

We have studied the temporal behaviour of the deuterium isotope ratio of water vapour emerging from a freshly cut plant leaf placed in a dry nitrogen atmosphere. The leaf material was placed directly inside the sample gas cell of the stable isotope ratio infrared spectrometer. At the reduced pressure ( approximately 40 mbar) inside the cell, the appearance of water evaporating from the leaf is easily probed by the spectrometer, as well as the evolving isotope ratios, with a precision of about 1 per thousand. The demonstration experiment we describe measures the 2H/1H isotope ratio only, but the experiment can be easily extended to include the 18O/16O and 17O/16O isotope ratios. Plant leaf water isotope ratios provide important information towards quantification of the different components in the ecosystem water and carbon dioxide exchange.     

高分离度快速液相色谱法测定牛黄解毒片中黄芩苷的含量

采用高分离度快速液相色谱(RRLC)测定牛黄解毒片中黄芩苷的含量。色谱柱为Zorbax XDB-C18(4.6×50mm,1.8μm),流动相为甲醇-水-磷酸(45∶55∶0.2),检测波长315nm,流速0.5mL.min-1,柱温为30℃。黄芩苷在0.15—1.35μg(r=0.9999)范围内峰面积与浓度呈良好的线性关系,加样回收率为100.41%,RSD=1.42%。采用高分离度快速液相色谱(RRLC)测定复方牛黄解毒片中黄芩苷的含量,缩短了保留时间,提高了效率,降低了成本。本方法简便、准确,结果稳定。