Solvent pump

This component draws solvent from the reservoir and delivers it to the column at a constant flow rate. The flow rate should be accurate, reproducible and 

Pumps are usually constructed from stainless steel, check valves and pistons from ruby or sapphire, and the seals from PTFE. These are the only materials which come into contact with the solvent and are inert to most of the common solvents. Unstabilized chloroform can present problems when used with inferior grades of stainless steel due to attack by hydrogen chloride generated from decomposition of the chloroform. In some types of chromatography, low concentrations of metal ions extracted from the pump components by the solvent can cause interference with the analyses. For these applications it is possible to obtain pumps constructed with ceramic or titanium heads. However, these problems do not normally arise in size exclusion chromatography. 

There is a great variety of pumping systems on the market and it is impractical here to attempt to discuss them all in detail. I shall briefly describe two designs which are commonly used in SEC applications, and would refer the reader to manufacturers literature for detailed descriptions of others. 

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The maximum and minimum flow rate available from the solvent pump may also, under certain circumstances, determine the minimum or maximum column diameter that can be employed. As a consequence, limits will be placed on the mass sensitivity of the chromatographic system as well as the solvent consumption. Almost all commercially available LC solvent pumps, however, have a flow rate range that will include all optimum flow rates that are likely to be required in analytical chromatography... 

One day, the lead operator gave verbal and written instructions, via a second worker, to the top floor man to pump solvent to 12A blender. The top floor man actually pumped the solvent to 21A blender, as a result of connecting the hose to the 21A blender pipe and not the 12A blender pipe. Consequently the solvent pumped to 21A blender was charged on top of another batch already in 21A blender. The contaririnated batch had to be pumped back into a reactor where the mischarged solvent was removed by the application of vacuum. 

Solvent pumped to wrong blender— contaminated batch Reduce noise levels. Reschedule operator tasks to reduce overload. Incorporate use of procedures in training scheme. 

V1 = Sample Valve V2 = Backup Valve V3 = LC Valve Pump 1 = Transfer Solvent Pump 2 = LC Solvent... 

A simple system is comprised of an isocratic pump, a manual injector, a UV detector, and a strip-chart recorder. A schematic diagram of an HPLC instrument is shown in Fig. 15.4. This simple configuration is rarely used in most modern laboratories. A typical HPLC system is likely to consist of a multi-solvent pump, an autosampler, an on-line degasser, a column oven, and a UV/Vis or photodiode array detector all connected to and controlled by a data-handling workstation. Examples of modular and integrated systems are shown in Fig. 15.5. Some of the important instrumental requirements are summarized in Table 15.2. 

The solvent pump was turned on at t 0 sec. It takes ca. 20 sec for the solvent to reach the flow cell containing the PMMA-Phe sample. A significant reduction in fluorescence intensity signals the arrival of solvent at the PMMA-Phe surface. 

The amount of solvent needed for the purification of a unit amount of target compound is conveniently described by the term specific production. Thus, the minimum solvent consumption can be determined for a given purification. The amount of solvent pumped through the column during one cycle is proportional to the mobile phase flow rate and the cycle time. The amount of purified product made in one cycle is the product of the amount injected and the recovery yield. Thus, the specific production can be written as [43]... 

However, it has been mentioned before, and must be bourne in mind, that it is not the pressure capability of the solvent pump that normally determines the maximum pressure that can be employed, but the maximum pressure the whole chromatographic system can tolerate. Although valves have been designed to operate at 10,000 p.s.i., or even higher, their useful lifetime at that pressure is often relatively short, usually as a result of sample contamination scoring the valve seats. For long-term continuous operation the maximum inlet pressure a valve can tolerate is often only about 3000 p.s.i.. 

Flow rate control of the solvent pump was difficult because 0.2 L/h is near the low end of the solvent pump s capacity. 

High-performance liquid chromatograph (HPLC e.g., Waters Chromatography) equipped with column heater, solvent pump, UV detector (set at 210 nm), integrator, autosampler, and (for manual injection) a 10-pl sample loop 15 x 0.46-cm YMC-ODS-AQ analytical column (AQ12S031546WT, Waters Chromatography)... 

The ChromSpher Lipids column (250 mm X 4.6-mm ID stainless steel 5 /Am) was purchased from Chrompack (Middelburg, Netherlands) and used as received. Solvent flow was standardized at 1.0 ml/min and run temperatures at 22-23°C. A small cooling fan was used to minimize temperature fluctuations and bubble formation at the solvent pump mixing solenoid. 

The HPLC column operates in a similar fashion. The principle of like attracting like still holds. In this case, our nonpolar layer happens to be a moist, very fine, bonded-phase solid packing material tightly packed in the column. Polar solvent pumped through the column, our mobile phase, serves as the second immiscible phase. If we dissolve our purple dye in the mobile phase, then inject the solution into the flow from the pump to the column, our two compounds will again partition between the two phases. The more non-... 

The simplest HPLC system is made up of a high-pressure solvent pump, an injector, a column, a detector, and a data recorder (Fig. 1.4). 

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. 

The simplest HPLC system is made up of a high-pressure solvent pump, an injector, a column, a detector, and a data recorder (Fig. 9.1). The high pressures referred to in the system name are of the order of 2,000-6,000psi. Since we are working with liquids instead of gases, high pressures do not pose an explosion hazard. Leaks occur with too much pressure. The worst problems to be expected are drips, streams, and puddles. 

Xie et al. [9] reported on-chip generation of gradient elution by using electrochemical pumping in LC-ESI, which contains two 3 p-L on-chip solvent reservoirs, two electrochemical pumps, and an ESI nozzle. Solvent pumping was controlled galvanostatically at a flow rate of 200 nL/min. The authors reported a higher electrical current was used to increase flow rate or to achieve... 

A schematic diagram of an ASE system is shown in Figure 3.7. It consists of solvent tank(s), a solvent pump, an extraction cell, a heating oven, a collec-... 

Beside column dimension the size of stationary phase particles is a matter of recent progress. More traditional columns are packed with 3.0-5 pm particles enabling satisfying resolution and reasonable column back pressure of solvent suitable to be processed by conventional HPLC pumps. In contrast, sub 2-pm particles (e.g. 1.7 and 1.8 pm) as applied in rapid or fast LC or ultra high-performance LC (UHPLC) allow better resolved separations in shorter run times. Column back pressure (>12,000 psi) is remarkably high demanding more robust solvent pumps. 

Solvents pumped into containers to avoid vapors and droppage. 

Basic equipment and components An HPLC system comprises four key components, namely (1) solvent pump(s) (delivery of mobile phase) (2) sample injector (3) HPLC column (stationary phase) and (4) detector linked to recording device. The basic components comprising an HPLC system are illustrated in Figure 7.8. 

Solvent pump(s) The primary purpose of a solvent pump is to draw mobile phase (solvent) from a reservoir, through a filter, and sufficiently pressurize the solvent to overcome resistance and allow passage through the column into the sample injector. Prior to use, solvents must have all dissolved gases removed (i.e. degassed and purged) after which they may be drawn into the... 

Sample injector The sample injector is located between the solvent pump and the HPLC column, and serves to deliver or inject the sample dissolved in solvent onto the column. The most common form of sample injector is the so-called loop-and-valve injector. Sample is injected from a specialized syringe (manually) or delivered by means of an autosampler (automatically) into a small diameter loop. The loop-and-valve injector allows switching by means of a valve between initial delivery of solvent alone to the column (so-called column equilibration), to subsequent delivery of the sample onto the column. 

Question 21 Solvent pump (delivery of mobile phase) sample injector HPLC column (stationary phase) and detector linked to recording device. 

Thus, the response index can be easily determined. However the accuracy of the measurement will depend on the flow rate remaining constant throughout the calibration, and consequently for a GC detector a precision flow controller must be employed and for an LC detector, a good quality solvent pump. Manufacturers do not usually provide the response indices for their detectors and so it is left to the analysts to measure it for themselves. 

The noise level of detectors that are particularly susceptible to variations in column pressure or flow rate (e.g. the katherometer and the refractive index detector) are often measured under static conditions (i.e. no flow of mobile phase). Such specifications are not really useful, as the analyst can never use the detector without a column flow. It could be argued that the manufacturer of the detector should not be held responsible for the precise control of the mobile phase, beitmay a gas flow controller or a solvent pump. However, all mobile phase delivery systems show some variation in flow rates (and consequently pressure) and it is the responsibility of the detector manufacturer to design devices that are as insensitive to pressure and flow changes as possible. 

It is also necessary to monitor the volume of solvent which has passed through the GPC column set from the time of injection of the sample (this is called the elution volume or the retention volume). Solvent flow is conveniently measured by means of elapsed time since sample injection, relying implicitly on a con.stant solvent pumping rate. As an added check on this assumption, flow times may be ratioed to those of a low-molecular-weight marker that provides a sharp elution peak at long flow times. 

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