Hardware and Detector Operation

Conventional conductivity detector cells where the electrolyte is in contact with the electrodes are likely to use electrodes made from 316 stainless steel. A new cell should be treated with 1 N nitric add for about 60 min to deactivate or passivate the cell and stabilize the signal. In fact, such nitric acid treatment is a good idea for all parts of a stainless steel IC system. 

The mobility of ions in solution varies with the solution temperature. Ionic solutions will increase conductivity about 2 % for every degree increase in temperature. Conductivity detectors usually compensate automatically for temperature change by 

The flow path may also include a compartment containing the thermistor probe for electronic feedback. Even though conductance cells tend to be low dead volume, the total dead volume in a conductance detector can be quite large and considerable mixing of the eluent stream may take place after the peak has been measured. If two detectors are used, it may be best to place the conductivity detector cell last to avoid peak broadening. 

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From the practical point of view, dual-channel phase detectors operated in quadrature appear to be the best hardware-detection choice. Unlike other techniques, phase detection is sensitive to RF frequency offset from resonance and to the RF phase which, on the one hand, makes the signals more complex to use (as well as and more sensitive to instrument instabilities) but, on the other hand, leads to a number of important advantages, such as ... 

A gas chromatograph can have a mass spectrometer as a detector, or a gas chromatograph can be used as in injection system for a mass spectrometer. In this book the former case is true. In any event, GC/MS is one of the most powerful techniques available and concomittantly one of the most technically sophisticated. The high specificity and sensitivity for thermally stable volatiles enable unambiguous qualitative and quantitative information. It is expensive in terms of hardware and the expertise necessary for reliable operation. It is recommended that interested parties consider the system in its entirety. McFadden s (53) book is well suited for such a purpose. 

Once the appropriate detector is chosen and the hardware system is operating correctly, the next ingredient for a successful chromatogram is retention of the components in the mixture. The measure of the retention of a compound on a column is referred to as the capacity factor and is a measure of retardation of the compound in terms of the number of column void volumes it takes to elute the apex (center) of the peak. This measure is called k (pronounced kay prime) and is simply the ratio of the elution volume of the component (V/) to the void volume of the column (Vo), which is expressed as... 

A peristaltic pump delivers the eluent and sample to the low-pressure column. Because a peristaltic pump is a flow-through device, the integrity of the sample is maintained as it is passed through the pump. However, because peristaltic pumps can only pump at a maximum of 100 psi, the columns must operate at a low backpressure. Development of a low backpressure column depends on several factors. First, the ion exchange resin must be small, uniform and efficient. The column hardware and fluid connections must be well designed and not contain flow paths that broaden the sample peaks. The column should be short so that the eluent backpressure is low. Finally, the detector must be able to operate at low (eluent) flow rates. The low eluent flow rates (approximately less than 100 pL/min) generate lower backpressures than standard flow rates. 

The transient signals provided by the detectors were formerly registered with a strip-chart recorder, which required human participation in the final stage of the analytical process the operator had to measure signals, contrast samples with standards and match samples and results. The later use of microcomputers for data acquisition and treatment allows the easy delivery of results, expressed in the preselected units, through a printer. Technicon market hardware and software suited to their simpler AutoAnalyzers, which can also be adapted for this purpose with the interesting innovations reported recently [22-25]. Multi-channel models (e.g. SMAC) feature a built-in central computer which, in addition to serving this function, controls the analyser operation. 

The hardware of an automated solid-phase synthesizer consists of all the electromechanical components of the system (reaction vessel, tubing, valves, pumps, detectors, power supplies, circuit boards, sensors, etc.). It is imperative that all these components are reliable and can operate without failure for many synthesis cycles before repair or replacement. Before using any component in an automated system, it should undergo compatibility and lifetime testing with the reagents that would be in contact during the synthesis. 

The control trailer houses the remote systems for the MMD-1 operations. Inside the control trailer is the monitoring room that contains the NRT (MINICAMS) racks and then-respective support equipment. The control trailer also houses the remote system for the process trailer VIKING Gas Chromatograph/Mass Selective Detector (GC/MSD). The remote VIKING GC/MSD system includes the associated computer hardware and software to perform remote operations. 

Contractor Support. Availability ofcontractor support services for both gas detectors and upstream system hardware and software must be assessed. Service advice via an toll-free 800 phone number, operation and maintenance training of user personnel, and quick response on-site field service assistance are all desirable support features. 

The testing of the hardware should cover the functionality of the instrument expected during normal operation. For example, the testing for an HPLC system would include the operation of the pump, the injector, and the detector [15]. 

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