~(13)C固体核磁共振技术检测PM_(2.5)中的总有机碳质组分

建立了13C固体核磁共振技术检测PM2.5中总有机碳质组分的分析方法。针对大气气溶胶中有机质组分的复杂性,探索出较为快速检测PM2.5中总有机质组分的核磁共振分析方法,使样品无需进行繁琐的前处理即可获得可靠的化学结构信息。利用该方法获得了太原、新乡、广州冬季PM2.5样品中总有机物的化学结构信息。结果表明,该方法操作简单,检测较为快速,准确度较高,可以满足大气气溶胶总有机成分的检测要求。     

气相色谱-质谱-自动质谱解卷积技术在沉积物和污泥中有机污染物非靶标筛查中的应用

以沉积物和污泥中非极性和弱极性有机污染物的非靶标筛查为目的,建立了一种超声波辅助提取-气相色谱-质谱结合自动解卷积技术的筛查方法。以二氯甲烷为溶剂超声波辅助提取样品3次,每次20 min,提取液经凝胶渗透色谱(GPC)和硅胶层析柱净化,再用3 g铜粉超声10 min除硫。前处理方法的重复性(RSD, n=5)为5.8%~14.9%。采用自动质谱解卷积软件(AMDIS)和标准谱库定性鉴别出所含的有机物。在两类样品中共鉴别出290种有机污染物,其中沉积物样品中190种,污泥样品中153种。鉴别出的污染物包括美国环境保护署(EPA)优先控制污染物、药物和除草剂等新型污染物、抗氧化剂、中间体、有机溶剂及化工原料等。该方法灵敏度高,重复性好,可用于复杂基质样品中有机污染物的非靶标筛查。     

1H-吡唑-4-甲酸的合成改进

以氰乙酸乙酯和原甲酸三乙酯为原料,通过Claisen酯缩合、合环、脱氨和水解得到1H-吡唑-4-甲酸.用质谱(MS)、核磁共振氢谱(1HNMR)和核磁共振碳谱(13C NMR)表征了化合物的结构.实验结果表明,1H-吡唑-4-甲酸的收率由文献报道的70%提高到了97.1%.     

加速溶剂萃取法提取海洋沉积物中正构烷烃的方法研究

采用加速溶剂萃取法(ASE)提取了海洋沉积物中的正构烷烃,并对ASE的萃取剂比例、萃取温度、静态萃取时间以及循环次数等实验条件进行优化。结果表明,当样品长碳链正构烷烃含量较高或需要检测长碳链正构烷烃含量时,可使用甲醇-二氯甲烷(1∶3)作为萃取剂;而甲醇-二氯甲烷(1∶9)适用于短碳链正构烷烃含量较高或需要检测短碳链正构烷烃含量的样品。加速溶剂萃取提取沉积物中正构烷烃的最佳条件为:萃取温度150℃,静态提取时间15 min,循环3次。在优化条件下,测定沉积物样品中正构烷烃的精密度除C15为20%外,其余为3%~14%,替代物回收率为84%~114%。相比于传统的索氏提取法,该方法的工作效率高、回收率高、精密度良好,适用于沉积物样品中正构烷烃的定量分析。     

示差红外光谱在土壤有机质组成研究中的应用

采用红外透射光谱法,对不同管理方式下黑土有机质组成进行了红外光谱分析,并运用差谱的方法,降低土壤矿物对有机吸收峰的干扰。选择2920、2850、1630和1420 cm~(-1)作为代表有机质官能团的吸收峰,通过积分计算各吸收峰的相对面积,并对吸收峰面积与土壤有机质(SOM)的组分含量进行了相关分析。土壤在2920 cm~(-1)处脂族结构的吸收峰面积与土壤活性有机碳(水溶性有机碳、热水溶性有机碳、游离态轻组碳和闭蓄态轻组碳)含量呈正相关,可反映土壤活性有机碳含量;在1630 cm~(-1)处芳香结构的吸收峰面积与以上活性有机碳含量呈负相关,可反映土壤稳定性有机碳含量。土壤在1630和2920 cm~(-1)处吸收峰面积的比值(1630∶2920)与稳定性(重组)有机碳和活性(轻组)有机碳含量的比值呈显著正相关,可指示SOM的稳定程度。本方法所需样品量少、成本低、便捷,适用于对矿物组成一致的土壤进行有机质组成的测定。     

氯化亚铬脱除黄铁矿对桦甸油页岩有机质结构的影响

采用元素分析、~(13)C NMR、XPS和TG-MS技术考察了氯化亚铬(CrCl_2)脱除黄铁矿对桦甸油页岩有机质结构的影响。结果表明,CrCl_2可有效脱除有机质中的黄铁矿,脱除率为96.19%。CrCl_2对有机质的碳骨架结构影响较小,脱除黄铁矿前后有机质中脂碳、芳碳和羧基/羰基碳的相对含量以及有机质的热解特征温度基本保持不变,但CrCl_2可破坏有机质中的C-O键,使C-O/C-OH和O=C-O的含量减少,造成0.98%的有机碳损失和12.54%的有机质损失。CrCl_2处理后,有机质的C含量显著增加,H含量稍有增加,O含量显著降低,使得H/C略微降低,O/C明显降低。另外,CrCl_2处理后,单位质量有机质中脂碳的含量增加了5.28%,使其热解过程中产生了更多的挥发分,残留的氧化铬对有机质的热分解可能也具有促进作用。     

固相萃取-色谱测定水、沉积物及土壤中氯霉素和3种四环素类抗生素

建立了固相萃取-高效液相色谱(UV)检测水、沉积物和土壤中的氯霉素、土霉素、四环素和金霉素4种抗生素的方法。水样、土壤和沉积物样品的前处理采用EDTA-McIlvaine缓冲溶液提取,用SAX-HLB串联小柱纯化和富集,用丙酮(含10%甲醇)洗脱进一步减小天然有机质的影响。采用乙腈和0.01mol/L草酸溶液作为流动相,8min内分离4种抗生素。测定了贵阳市阿哈湖、南明河和乌江渡水库的水样及沉积物,均有抗生素检出。     

胡敏酸的结构特征及其吸附行为

使用0.5mol/L NaOH和0.1mol/L Na_4P_2O_7溶液分别从土壤中提取胡敏酸,并且对其进行了元素分析、红外光谱、固态13C核磁共振的定性、定量研究。结果表明,两种胡敏酸的性质很相似,但也存在一些微小差异,Na_4P_2O_7提取的胡敏酸比NaOH提取的具有芳香度较大、聚合度较高、极性官能团含量较多的特点。测定了菲在6个胡敏酸上的吸附等温线,Freundlich模型很好的拟合了所有吸附等温线,相关系数r均在0.992以上。有机碳分配系数K_(oc)与胡敏酸中极性碳(POC)之间存在明显的线性相关关系,并受到提取剂类型的影响。     

气相色谱/质谱法检测灰尘、土壤和沉积物中有机磷酸酯

本研究对实验过程中可能存在的污染源进行了定性筛查,采用不同的质控措施以降低实验过程中的背景污染。在严格的质控措施下研究了不同净化方法对样品中有机磷酸酯(OPEs)的净化效果,建立了气相色谱/质谱联用(GC/MS)检测灰尘、土壤和沉积物中7种主要OPEs的分析方法。以正己烷-二氯甲烷(1∶1,V/V)混合溶剂超声提取灰尘样品,以正己烷-丙酮(1∶1,V/V)索氏抽提土壤和沉积物样品中的待测组分,灰尘样品经一步固相萃取柱净化,土壤和沉积物样品经两步串联固相萃取柱联合净化后采用气相色谱/质谱进行定量。结果表明:采用上述净化手段,实验过程省时省力,基质去除率高,7种OPEs的回收率可稳定在67%以上。在高、低2个添加浓度水平下,不同基质样品(灰尘、土壤)中平均回收率为67.9%~117.4%;仪器检出限(LOD)为2.5~25.8μg/L,方法定量限(LOQ)分别为1.4~15.7 ng/g(灰尘)和0.3~2.9 ng/g(土壤)。采用此方法检测6份实际样品(包括2份灰尘样品、2份土壤样品、2份沉积物样品),OPEs在所有样品中均有检出,其浓度范围分别在1313~1988 ng/g、29.9~32.0 ng/g和682~739 ng/g之间。     

快速加热容量法测定土壤中有机质含量

建立快速容量法测定土壤中有机质的分析方法。采用恒温电热板控温加热替代油浴加热溶解样品,使用硫酸银作为催化剂,重铬酸钾–硫酸标准溶液作为氧化剂,使用硫酸亚铁铵溶液为滴定剂,测定土壤中有机质含量。优化后的分析条件:溶样温度为220℃,溶样时间为(5.5±0.5) min,催化剂用量为0.08 g。对3个国家一级标准物质进行分析,测定结果与推荐值相符,相对误差为–4.0%～0.0%,相对标准偏差为1.17%～3.66%(n=6)。该法可用于大批量土壤样品中有机碳含量的快速测定。     

Advances of sensitive techniques in laser spectroscopy

Different techniques are used for the sensitive detection of overtone transitions of small molecules, such as H₂S, C₂H₂, OCS, O₃ in the visible and near infrared region. The techniques include: phase-modulated or wavelength-modulation absorption spectroscopy with a widely tunable single mode diode laser, opto-acoustic spectroscopy in resonance cells with a color center laser or a Ti:Sapphire laser, and sub-Doppler opto-thermal spectroscopy in cold collimated molecular beams, using a low temperature bolometer as detector. The three techniques are compared with regard to sensitivity and spectral resolution. The mass selective sensitive detection of small metal clusters Li₃ and Na₃ and their high resolution sub-Doppler spectroscopy, using resonant two-photon ionization with cw lasers, is briefly discussed.     

Decongestion of methylene spectra in biological and non-biological systems using picosecond 2DIR spectroscopy measuring electron-vibration–vibration coupling

Methylene is found in the repeat units of many polymers including proteins. In some cases it appears to be a useful reporter of variation in local environment whilst in other contexts average behaviour seems to dominate. In this paper we apply a particular 2DIR technique to a range of systems containing methylene groups, showing that mode frequencies, linewidths and splittings can be easily extracted even when the infrared absorption bands are too congested to allow reliable analysis. 2DIR spectra of polyethylene and several liquid alkanes are compared and it is shown for the case of l-arginine that the methylene scissor modes are split and that this can be resolved by tracking the 2DIR spectrum as a function of time. Calculations from first principles reveal that for most of the methylene modes studied, electrical anharmonicity is the dominant contributor to the 2DIR cross-peak intensity, with the mechanical anharmonicity making only a small contribution.     

Study of the thermal decomposition of a sepiolite by mid- and near-infrared spectroscopies

Near-infrared (NIR) and mid-infrared (MIR) spectroscopies were used to characterize the hydroxyl groups present in a sepiolite and its calcination products at 250, 500 and 800 °C. Calcining the sepiolite at 250 °C was found to result in its dehydration through the loss of coordination water. Raising the calcination temperature to 500 °C caused the sepiolite structure to fold and hydroxyl groups in octahedral layers to be removed. Finally, calcination at 800 °C resulted in a phase change leading to enstatite, as confirmed by XRD spectroscopy.     

Terahertz Time‐Domain Spectroscopy of Gases,Liquids, and Solids

The techniques and methods employed in the spectroscopic characterization of gases, liquids, and solids in the terahertz frequency range are reviewed. Terahertz time‐domain spectroscopy is applied to address a broadband frequency range between 100 GHz and 5 THz with a sub‐10 GHz frequency resolution. The unique spectral absorption features measured can be efficiently used in material identification and sensing. Possibilities and limitations of fundamental and industrial applications are discussed.     

Polarization Dependent Time-Resolved Infrared Spectroscopy and Its Applications

Polarization dependent time-resolved infrared (TRIR) spectroscopy has proven to be a useful technique to study the structural dynamics in a photochemical process. The angular information of transient species is obtainable in this measurement, which makes it a valuable technique for the investigation of electron distribution, molecular structure, and conformational dynamics. In this review, we briefly introduce the principles and applications of polarization dependent TRIR spectroscopy. We mainly focused on the following topics: (i) an overview of TRIR spectroscopy, (ii) principles of TRIR spectroscopy and its advantages compared to the other ultrafast techniques, (iii) examples that use polarization dependent TRIR spectroscopy to probe a variety of chemical and dynamical phenomena including protein conformational dynamics, excited state electron localization, and photoisomerization, (iv) the limitations and prospects of TRIR spectroscopy.     

The Kinetic and Mechanistic Evaluation of NMR Spectra. New analytical methods (18)

In addition to the static parameters of the chemical shifts and coupling constants, which serve as a source of knowledge for molecular structure and stereochemistry, an NMR spectrum can frequently furnish dynamic quantities characterizing relaxation and exchange phenomena. The information about nuclear switching processes has proved to be particularly useful in practice for the detection of internal molecular motions and for the estimation or determination of the corresponding energy barriers. A plethora of studies of this nature has in the past been performed on simple proton spectra. Methodological developments of recent years have led to a significant reduction of the effort required for the quantitative dynamic evaluation of NMR spectra arising from complex spin systems or involving other nuclei. In many cases it has, moreover, become possible to extract detailed mechanistic information inaccessible by other means. The practical execution of such analyses will be explained and illustrated by a selected number of applications.     

Isolation and Spectroscopic Characterization of New Endohedral Fullerenes in the Size Gap of C74 to C76

New alkaline earth metal endohedral fullerenes Sr@C₇₄, Sr@C₇₆‐I, II and Ca@C₇₄, prepared by means of the RF‐method, have been isolated using multistep HPLC. The purity was ascertained by anionic LDI TOF mass spectroscopy, considering the isotopic patterns of the compounds. The influence of the incorporated metal on the electronic structure has been studied by VIS‐NIR and Raman spectroscopy. Photoexcited triplet‐state EPR spectroscopy was used to investigate the structure of these otherwise EPR‐silent fullerenes. Displaying the frequency of the cage vs. encapsulated metal vibrational modes as a function of the square root of the reciprocal masses of the metals clearly separates the M³⁺@C_n^3— and the M²⁺@C_n^2— families. This seems to be a generally applicable tool for monitoring the metal to fullerene charge transfer.