Rapid sequential separation of essential oil compounds using continuous heart-cut multi-dimensional gas chromatography-mass spectrometry

A method for separation and identification of peaks in essential oil samples based on rapid repetitive heart-cutting using multidimensional gas chromatography (MDGC)-mass spectrometry (MS) coupled with a cryotrapping interface is described. Lavender essential oil is analyzed by employing repetitive heart-cut intervals of 1.00 and 1.50 min, achieved in a parallel MDGC-MS/GC-FID experiment. The number of peaks that were detected in 1D GC operation above a given response threshold more than tripled when MDGC-MS employing the cryotrapping module method was used. In addition, MDGC-MS enabled detection of peaks that were not individually evident in 1D GC-MS, owing to effective deconvolution in time of previously overlapped peaks in 1D GC. Thus separation using the cryomodulation approach, without recourse to using deconvolution software, was possible. Peaks widths decreased by about 5-7-fold with the described method, peak capacity increased from about 9 per min to 60 per min, and greater sensitivity results. Repeatability of retention times for replicate analyses in the multidimensional mode was better than 0.02% RSD. The present study suggests that the described heart-cutting technique using MDGC-MS can be used for general improvement in separation and identification of volatile compounds.     

Application of Pyrolysis Cryogenic Trap Gas Chromatography/Atomic Emission Detection (Py-CryT-GC/AED) for the Study of Nitrogen Forms and Dynamics in a Grassland Soil

Soil organic nitrogen (N) was characterized for its chemical species and chemical transformations in a grassland soil profile by using a combination of cryogenic pyrolysis gas chromatography atomic emission detection method with soil physical size fractionation. The soils taken from 0–12, 12–25, and 25–38 cm depth layers were separated into five fractions, <2, 2–38, 38–53, 53–105, and 105–250 µm and each of which was analyzed for total organic C and N, and different N forms. Our results showed that (1) total organic carbon has a positive correlation with the total organic nitrogen (TON) with correlation coefficient increased with soil depth; (2) deep and small particle-size fraction soils yielded more volatile pyrolysate N than the surface and large particle-size fractions and the amount of volatile pyrolysate N has a linear positive correlation with TON and correlation coefficient increased with soil depth; (3) the major components of the volatile pyrolysate N include ammonia, acetonitrile, hydrogen cyanide, pyridine, and pyrrole; (4) of the total volatile pyrolysate N, ammonia accounted for more than 40%, and the sum of acetonitrile and hydrogen cyanide accounted for approximately 30–50%; and (5) the amounts of acetonitrile, hydrogen cyanide, and pyridine had increased positive correlations with TON with increasing soil depth, but the correlation between the amount of pyrrole and depth decreased in the opposite direction. Our research result sheds some light into soil organic nitrogen forms and its transformations in the processes of soil organic C aging and stabilization.     

低温容器高真空多层绝热性能分析

高真空多层绝热性能对于低温容器的应用与安全至关重要。文中依据逐层导热计算模型,对高真空多层绝热低温容器的气体导热、间隔材料的固体导热和反射屏的辐射换热进行了分析计算,给出了多层绝热层中每一层的温度分布情况,气体导热、固体导热及辐射换热所占的比例,换热系数随层数的变化情况,以及真空度对绝热性能的影响,为提高高真空多层绝热性能提供了理论依据。     

真空丧失条件下液氦容器安全性试验

真空丧失对液氦容器的安全性是一大威胁,可能会造成十分严重的后果。通过试验,利用氦气及空气作为介质,对低温液氦容器在真空层发生泄漏情况下的漏热进行了研究。结果表明,多层绝热结构对于真空遭到破坏后的液氦容器能够起到一定的保护作用,而渗入到真空绝热层中气体的性质对于最终漏热情况也有影响,发现空气的“破坏力”明显小于氦气。     

Irreversible structural changes in cryogenic mechanically milled isotactic polypropylene

The influence of cryogenic mechanical milling on the structure and the thermal behavior of isotactic polypropylene was investigated by means of wide-angle X-ray scattering, differential scanning calorimetry and transmission electron microscopy. The results presented show that structural changes caused by mechanical milling at cryogenic temperatures are only partly reversible. The decrease in the degree of crystallinity as determined by differential scanning calorimetry with increasing milling time is attributed to a reversible transformation of the initial morphology into a nanostructured morphology, consisting of small fragments of the original isotactic polypropylene lamellae. During recrystallization from the molten state, there still exists an influence of the previous milling treatment, leading to significantly changed crystallization behavior. The reason for this behavior might be a decrease in the molecular weight or a change in the molecular weight distribution or the formation of long-chain branched polypropylene molecules induced by cryogenic mechanical milling.

Photolysis of water/dicyanoacetylene complexes: an infrared matrix isolation and theoretical study

The structure and energy of the 1:1 complexes formed between dicyanoacetylene and water (D₂O) in argon matrix are investigated using FTIR spectroscopy and ab initio calculations at the B3LYP/6-31g** level of theory. Two types of 1:1 complexes are observed. The first one corresponds to the NH structure characterized by a hydrogen bond between H₂O and one of the nitrogen of dicyanoacetylene. The second corresponds to the CO form which involves a van der Waals interaction between the Cβ of dicyanoacetylene and the oxygen of water.

These complexes were irradiated with an Hg–Xe lamp at 10 K. Two products were observed by FTIR spectroscopy. The first one corresponds to the Isonitrile:H₂O complexes formation. The second one, resulting from the reaction of water on the photolyzed dicyanoacetylene, corresponds to the cyanoketene:HCN complex formation.     

Cryogenic studies, site selectivity and discrete fluorescence in salicylic acid dimer

Cryogenic effects (10–293 K) on the photophysics of salicylic acid (SA) dimer have been using steady state and time-resolved spectroscopic techniques. SA dimer shows two emissions at approximately 390 nm (dimer, D) and approximately 430 nm (tautomer, T), formed by cyclic double proton transfer plus fast excited state intramolecular proton transfer (ESIPT), at low temperatures; a vibrational structure also develops which is due to C = O and OH stretches. On red edge excitation (REE), only the dimer-type (UV) emission is observed, which shifts with excitation energy resembling emission due to site selectivity. Due to the asymmetry of the double potential energy curves of D and T, all dimers can be trapped in the D minimum. The UV emission of the dimer is accompanied by the Stokes' shifted tautomer emission on excitation at 1050 cm⁻¹ higher than the (0,0) band of D, which is interpreted as the barrier height of the double potential energy curves of D and T. Time-resolved studies at various temperatures have helped to clarify the photophysics of crystalline SA.     

溯源至低温辐射计的硅陷阱探测器紫外波段绝对光谱响应度测量

介绍了溯源至低温辐射计的紫外绝对光谱响应度测量装置,对硅陷阱探测器在三个激光波长点进行了绝对光谱响应度校准实验.测量了硅陷阱探测器的空间均匀性和非线性系数,分析了影响测量准确度的各不确定度分量.实验表明:硅陷阱探测器在紫外波段266、325、379 nm三个激光波长点处的绝对光谱响应度测量扩展不确定度分别为0.19％、0.14％、0.11％,可作为紫外波段光辐射功率基准保持和传递的标准探测器,用于提高紫外波段光谱辐射度的校准能力.