Graphite columns

A technique for the determination of methylmercury in aqueous samples (natural and seawater) involved the conversion of methylmercury to gaseous methyl-ethylmercury by reaction with sodium tetraethylborate (Bloom, 1989 Bloom and Watras, 1989). The volatile derivative was purged from the solution and concentrated on a graphitic column at room temperature. The derivative was thermally desorbed from the column, and then analysed by cryogenic gas chromatography with cold vapour atomic fluorescence detection. In addition to methylmercury, labile Hg11 species could be determined (as diethylmercury) as well as dimethylmercury (which is not ethylated). The detection limit for... 

Problems with contamination and losses of volatile boron compounds during sample preparation have limited the reliable documentation of boron concentrations in human tissue and body fluids. A complex technique involving a porous graphite column—inductively coupled plasma-atomic emission spectrophotometry (ICP-AES)— and an ICP time of flight mass spectrometer (TOF-MS) has been developed for investigations of boron neutron capture in cancer therapy. Adaptation of this method to nutritional studies of boron should be possible. 

Note that we add the initial value to the change to obtain the equilibrium value in each column. Note also that we include data only for those substances whose concentrations change thus, in this case, the C(graphite) column is blank. We use reaction tables in many of the equilibrium problems in this and later chapters. 

Nisel son (394, 395) has concluded that any separation process based on differences in volatility should be carried out within the temperature range 440°-475°C. Vapor pressure measurements at the triple point only lead to a separation coefficient of 1.7 (415). On the other hand, small quantities of zirconium-free hafnium have been prepared by gas chromatographic techniques on a synthetic, highly purified graphite column at 295°C (543). 

The AHTR 500 is a further development of the HTR-MODUL design with 500 MW(th). The helium coolant is heated up from 330 to 950 °C. The system pressure is 2 MPa. The new feature of this reactor design is a central graphite column to provide an additional heat sink. It contains a passive decay heat removal system on the basis of natural convection which runs also during normal operation. No intermediate circuit is foreseen for the connection with a coal gasification system [41]. 

Another interesting example of extractive distillation is the separation of HCl from azeotropic hydrochloric acid with H2SO4 as described by Grewer [63]. He used a graphite column. Fig. 230 shows the isoharic boiling equilibrium for his system. 

The fission chamber was first placed in a graphite column containing an Sh-Be source at a position where the thermal-neutron flux and t he Cd ratio were known from standard indium foil measurements. By exposing the chamber... 

Gross fission heat, MW Active core diameter m Active core height, m Diameter over reflector m Height over reflector, m No. of graphite columns Duct diameter mm Mass of graphite stack, t Number of fuel channels Fuel channel pitch (square lattice), mm... 

In order to investigate more accurately the possible process optimization of an industrial column, a laboratory scale graphite column was constructed. The laboratory scale cadmium colunm is assembled from 13 graphite trays. The column can be divided into four main sections ... 

Most eluents for the separation of creatine and creatinine on a reversed-phase column are based on a phosphate buffer (Table 2). The addition of a quaternary ammonium ion-pairing agent such as tetra-butyl ammonium sulfate increases the hold-up of interfering species to help separate them from creatine. This method is one of the most popular for simultaneous determination of creatine and creatinine. Porous graphitic columns can also be used. 

A 100% methanol mobile phase was used in the study of the retention characteristics for over 50 alkyl-substituted benzenes on a porous graphite column [109]. Retention times varied from 1.8 min k = 0.2) for benzene (just slightly more than the void volume) to 58 min (k = 3 7) for pentamethylbenzene. A distinct advantage of this system over a normal Cjg system was the enhanced selectivity of the graphite column towards both isomeric forms as well as methyl and methylene homo logs. The k values and retention times for all analytes are tabulated. The retention differences between polymethylbenzenes and alkyl-substituted benzenes of the same carbon number (e.g., trimethylbenzenes vs. n-propylbenzene) were studied in detail on Cjg and phenyl columns using an 80/20 methanol/water mobile phase. 

PFPWR50 Japan IX PWR with TRISO fuel -/50 7.3 UO2 based TRISO within graphite column in fuel rods <5 Forced circulation H2O -240/260 Heating reactor -5 years ... 

The PFPWR50 is a small PWR with proposed mild variant of the use of HTGR type TRISO fuel within graphite columns packed in Zr-alloy claddings of conventional LWR type fuel elements. It uses a hexagonal lattice that is tighter than the square lattice of conventional... 

Fig. 3. Maximum bending of graphite columns during AV-3 reactor operation.

A porous graphite column has shown promise for separations of polar metabolites, such as glucuronides of AZT. Micellar electrokinetic capillary chromatographic analysis of forty desulfoglucosinolates produced enzymolitically has been reported,and a further study examined the liminoid glucosides in citrus seeds. ... 

The core consisted of 37 fuel elements in a hexagonal array with an effective diameter of 1.08 m. This array was surrounded by 30 prismatic graphite columns of the inner reflector, machined on one side to match the profile of the adjacent fuel element and on the other to form a circle of 1.5 m diameter. The 24 control rods operated in holes in the inner reflector. The relatively small size of the DRAGON core meant that its neutron efficiency was not very high the hot core, just critical, with control rods withdrawn, lost 32% of the neutrons by leakage, whereas it was calculated that in large power reactors of about 1,000 MW (Th), the leakage would be around 2%. ... 

---