General Applicability of High-Resolution Continuum-Source Graphite Furnace Molecular Absorption Spectrometry to the Quantification of Oligopeptides Using the Example of Glutathione

This communication introduces the first-time application of high-resolution continuum-source molecular absorption spectrometry (HR CS MAS) for the quantification of a peptide. The graphite furnace technique was employed and the tripeptide glutathione (GSH) served as a model compound. Based on measuring sulfur in terms of carbon monosulfide (CS), a method was elaborated to analyze aqueous solutions of GSH. The most prominent wavelength of the CS molecule occurred at 258.0560 nm and was adduced for monitoring. The methodological development covered the optimization of the pyrolysis and vaporization temperatures. These were found optimally to be 250 °C and 2250 °C, respectively. Moreover, the effect of modifiers (zirconium, calcium, magnesium, palladium) on the absorption signals was investigated. The best results were obtained after permanent coating of the graphite tube with zirconium (total amount of 400 μg) and adding a combination of palladium (10 µL, 10 g L−1) and calcium (2 µL, 1 g L−1) as a chemical modifier to the probes (10 µL). Aqueous standard samples of GSH were used for the calibration. It showed a linear range of 2.5–100 µg mL−1 sulfur contained in GSH with a correlation coefficient R2 > 0.997. The developed method exhibited a limit of detection (LOD) and quantification (LOQ) of 2.1 µg mL−1 and 4.3 µg mL−1 sulfur, respectively. The characteristic mass accounted for 5.9 ng sulfur. The method confirmed the general suitability of MAS for the analysis of an oligopeptide. Thus, this study serves as groundwork for further development in order to extend the application of classical atomic absorption spectrometry (AAS).

Synthesis of Fullerenes from a Nonaromatic Chloroform through a Newly Developed Ultrahigh-Temperature Flash Vacuum Pyrolysis Apparatus

The flash vacuum pyrolysis (FVP) technique is useful for preparing curved polycyclic aromatic compounds (PAHs) and caged nanocarbon molecules, such as the well-known corannulene and fullerene C60. However, the operating temperature of the traditional FVP apparatus is limited to ~1250 °C, which is not sufficient to overcome the high energy barriers of some reactions. Herein, we report an ultrahigh-temperature FVP (UT-FVP) apparatus with a controllable operating temperature of up to 2500 °C to synthesize fullerene C60 from a nonaromatic single carbon reactant, i.e., chloroform, at 1350 °C or above. Fullerene C60 cannot be obtained from CHCl3 using the traditional FVP apparatus because of the limitation of the reaction temperature. The significant improvements in the UT-FVP apparatus, compared to the traditional FVP apparatus, were the replacement of the quartz tube with a graphite tube and the direct heating of the graphite tube by impedance heating instead of indirect heating of the quartz tube using an electric furnace. Because of the higher temperature range, UT-FVP can not only synthesize fullerene C60 from single carbon nonaromatic reactants but sublimate some high-molecular-weight compounds to synthesize larger curved PAHs in the future.

METHODS FOR HEATING CONTROL OF GRAPHITE TUBE IN ELECTROTHERMAL ATOMIZER OF ATOMIC-ABSORPTION SPECTROMETER

The research is devoted to the assessment of changes in the degree of blackness (emittance) and electrical resistance of graphite tubes in the electrothermal atomizer of an atomic absorption spectrometer as they wear out. A joint change of these parameters effects on the heating of the atomizer, and, consequently, on the absorption signals of the elements of the periodic table. The heating of the atomizer is controlled by feedback on the temperature, measured using a brightness pyrometer, the measurements of which depend on degree of blackness of the graphite cuvette. Evaluation of the change in the emissivity was carried out by measuring the temperature of the cuvette with a spectral pyrometer, the measurements of which are independent of the emissivity of the controlled object. The electrical resistance, which effects on the heating rate of the cuvette, was calculated after measuring the current and voltage between the contacts of the atomizer. According to the results of the research, we can say that the main contribution to the change in the heating parameters of graphite tubes as they wear out is made by the varying emissivity.

Transformation of β-SiC from Charcoal, Coal, and Petroleum Coke to α-SiC at Higher Temperatures

SiC is one of the main intermediate compounds formed during the industrial production of silicon (Si). In the Si process, SiC is produced when carbon added to the raw materials reacts with the silicon monoxide gas (SiO(g)) formed in the furnace. Carbon materials used are either biomass-based (charcoal and wood chips) or based on fossil sources (coal, coke, petroleum coke). The most common forms of SiC prevailing at atmospheric pressure are the polytypes of α-SiC and β-SiC. β-SiC is formed at low temperatures and transforms to α-SiC at higher temperatures (> 2000 °C). In this study, β-SiC with elemental Si of varying amounts, formed from industrial carbon materials (charcoal, coal, and petroleum coke), were utilized to study the transformation of β-SiC to α-SiC. A graphite tube furnace efficient for high-temperature experiments was utilized for the heat treatment of β-SiC particles at temperatures ranging from 2100 °C to 2450 °C. The transformation to α-SiC was greatly influenced by the original carbon source. Charcoal-converted β-SiC particles easily transformed to α-SiC at 2100 °C, compared with β-SiC produced from coal and petroleum coke. Moreover, the amount of elemental Si in SiC particles enhanced the transformation to α-SiC at 2100 °C.

Effects of K2CO3 Addition on Inclusions in High-Carbon Steel for Saw Wire

In order to avoid the formation of crack initiation sites, inclusions in high-carbon steel for saw wire are strictly required to have excellent deformability. However, it is hard to achieve this goal with only conventional inclusion softening art, such as Si-Mn deoxidation and low basicity top slag refining. Therefore, a new method should be put forward to enhance the deformability of inclusions. Low melting temperature inclusions are widely considered to have good deformability, hence, adding K (potassium) into inclusions may become a potential new method to better enhance the deformability of inclusions due to the pronounced effect of K2O on lowering the melting temperature of inclusions. In the present study, the influences of Fe/K2CO3 (weight ratio), K2CO3 addition amount and reaction time on inclusions were investigated by using a graphite tube resistance furnace. Through this study, a solution to adding K into inclusions effectively by K2CO3 addition was developed and the melting temperature of inclusions was significantly reduced. In addition, the reaction mechanism between K2CO3/slag/steel/inclusion was deduced and the relation between deformability and crystallinity of inclusions was also briefly discussed.