Mobile phase solvents, handling

Early work involving high-temperature GPC of polyesters utilized solvents such as meta-cresol and or-tho-chlorophenol as mobile-phase solvents. These solvents are very viscous and require system temperatures of between 140°C and 150°C. Both solvents are also very dangerous and difficult to handle [8,9]. 

As a general rule, the following practices should be considered when handling mobile phase solvents ... 

Developing solvents should be composed of as few solvents as possible however, they mostly consist of 2 to 4 solvent components. It is recommended that developing solvents be prepared fresh every time and to use them only once. Some clues for handling of mobile phase rnixmres are as follows ... 

As the mobile phase in this system is normally a sodium hydroxide solution there is no need to handle or dispose of organic solvents. This is a particular bonus to some smaller sites that are not set up to use organic solvents. 

The major amount of HPLC separations is performed with re versed-phase columns employing binary or tertiary solvent mixtures with isocratic or gradient elution. The protons of the solvents of the mobile phase cause severe problems for an adequate NMR registration. The receiver of the NMR instrument (either a 12-bit or a 16-bit analog-digital converter (ADC)) is unable to handle the intense solvent signals and the weak substance signals at the same time. 

The sample, dissolved in mobile phase or a similar solvent, is first loaded into the sample loop and then injected by turning a handle swinging the sample loop into the pressurized mobile phase stream. Fresh solvent pumped through the injector sample loop washes the sample onto the column head and down the column. 

Basically, no special devices have been developed to handle mobile phases in nano-HPLC. However, our experience dictates that reservoirs small in volume and of high quality glass are preferred for this purpose. Solvent containers should be air tight and free from any contamination. The use of helium gas, through a sparging device, may be beneficial for degasification of solvents in nano-HPLC, which can improve check valve reliabilities, especially at nano flow, and diminish baseline noise in UV detection. Besides, each reservoir should be equipped with a shutoff valve for efficient helium consumption [9]. 

The liquid from an LC is compatible with normal IR sampling and is less of a problem. However, LC mobile phases may not be transparent in the IR, and water is a particularly difficult solvent to handle. For volatile organic solvents, evaporation is possible, and the remaining nonvolatile analytes can be deposited in KBr and pressed into pellets. Further discussion can be found in reference 20. 

A column consisting of a deactivated silica-based stationary phase is used for the packed-column mode. A packed column allows larger volumes of sample solvent to be injected, thus improving sensitivity. Generally, the column dimensions are 1 x 100-250 mm and the particle size is 5 / m. Commercial SFC instruments are also available that will handle the classical 4.6 x 150-mm or 250-mm columns. With the introduction of electronically controlled variable restrictors to control the back pressure, the packed columns are becoming increasingly more popular. This feature allows the independent flow and pressure control of mobile phases, thus helping in rapid optimization of selectivities. Some of the commonly used packed columns are as follows ... 

The mobile phase plays a crucial role in the separation process for at least three main reasons. The selectivity of the separation, retention time, and solubility of the racemate are directly affected by the mobile phase composition. Other parameters such as viscosity, solvent recovery, cost, and solvent handling properties also play a prominent role. This brief introduction is also applicable to the criteria for CSP selection for SMB. 

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