Detectors operating parameters

Reproducibility Controls various operational parameters Controls precisely mobile-phase composition temperature flow rate detector response... 

The second stage is data acquisition. This stage is entered when the operator starts the instrument. The instrument makes the first injection and signals the microcomputer via Intelink. After a delay proportional to the void volume of the column set, data are collected on a time basis (constant flow rate assumed) at the predetermined rate from each of the detectors selected, up to a maximum of three simultaneous detectors. VHien the sample run is complete, the instrument again signals the microcomputer which places the instrument in a hold state while it reads the operational parameters from the instrument for that sample and... 

Like chromatography, the FFF instrument consists of a pump to deliver the carrier fluid, a separation medium (FFF channel), a detector responding to the eluting species, and a computer to control the operative parameters (e.g., field, flow) and to acquire the digitized fractogram (see Figure 12.1). 

The major concern is that the character of the sample is not changed in the injection port, the column, or the detector prior to its actual detection. Thermal decomposition, catalyzed or thermal reaction, and adsorption of part or all of the sample will contribute to error in the analysis. Problems such as these may be determined by using the chromatograph itself first to detect possible problems by unexpected results and then confirmation of the problem by variation of the actual operating parameters of the chromatograph. 

Most HPLC instruments are on line with an integrator and a computer for data handling. For quantitative analysis of HPLC data, operating parameters such as rate of solvent flow must be controlled. In modern instruments, the whole system (including the pump, injector, detector, and data system) is under the control of a computer. 

P. Kuban and P.C. Hauser, Effects of the cell geometry and operating parameters on the performance of an external contactless conductivity detector for microchip electrophoresis, Lab Chip, 5 (2005) 407-415. J.G.A. Brito-Neto, J.A.F. da Silva, L. Blanes and C.L. do Lago, Understanding capacitively coupled contactless conductivity detection in capillary and microchip electrophoresis. Part 2. Peak shape, stray capacitance, noise, and actual electronics, Electroanalysis, 17 (2005) 1207-1214. 

The following table provides some comparative data for the selection and operation of the more common detectors applied to high-performance liquid chromatography.15 In general, the operational parameters provided are for optimized systems and represent the maximum obtainable in terms of sensitivity and linearity. In this table, the molar extinction coefficient is represented by s. 

Lichtenberg, J., Verpoorte, E., De Rooij, N.F., Operating parameters for an inplane, contactless conductivity detector for microchip-based separation methods. Micro Total Analysis Systems, Proceedings 5th i7AS Symposium, Monterey, CA, Oct. 21-25, 2001, 323-324. 

Gas Chromatography-Mass Spectrometry. A Hewlett-Packard Model 5890 Gas Chromatograph equipped with a hydrogen flame ionization detector was used in the study. A bonded phase DB-5 fused silica capillary column (30 m x 0.25 imi, 1 um film thickness) was used in all analyses (J W Scientific, Rancho Cordoba, CA). Operating parameters were as follows ... 

The main components of an LC-MS are the HPLC apparatus, an optional UV or photodiode array detector, the interface, the mass spectrometer and a computer system for data management and evaluation. The interface is the key component of the LC-MS system. All other components must be adapted to the particular interface that is used. Most commercially available systems work with thermospray, electrospray, or particle beam interfaces. Each interface has a distinct mode of action and its own operational parameters. 

Infrared spectra were recorded on a Nicolet model 598 IR spectrophotometer using the thin film method. Liquid samples were analysed using a Hewlett Packard 5880A series gas chromatograph (GC) equipped with a flame ionisation detector and a DB17 (30 m x 0.53 mm i.d.) fitsed silica capillary column. The operating parameters were as follows detector tenq>eraturc 22S°C injector temperature 22S°C temperature program, 5 min at 50 C heated at a rate of 5 C/min to 210 C held for 23... 

The latest production model of the microcoulometric detection system has a minimum detectable limit of about 1 ng of chlorine but, in the writer s opinion, the minimum for practical use is about 3 ng. This estimate is based upon responses obtained by Dohrmann Instruments personnel with standard solutions of pure lindane. These results were obtained in mode I operation (gas flow into the cell between the electrodes) rather than mode II operation (gas flow impinging directly on the sensor electrode), a more sensitive mode currently being used on last year s model detector in our laboratories. Mode I is preferred, for operating parameters are much less critical. 

The first step in the evaluation process is to define and document the current system use and user requirement specifications. If the system will be changed in the foreseeable future, any resulting changes in the intended use of the system should be described as well. The definition should include a list of system functions, operational parameters and performance limits. For chromatography software required functions may include instrument control, data acquisition, peak integration through quantitation, file storage and retrieval and print-out of methods and data. If the system also includes spectrophotometric detectors, the functions for spectral evaluation should be specified as well. Table 2 lists items that should be included in the system documentation. 

Most spectroscopic techniques quantitate results by comparison of sample values with standard values. In gas chromatography, the preferred quantitative technique makes use of an internal standard. For the assay of propoxyphene hydrochloride, pyrroliphene hydrochloride, is an excellent choice8. The multi-extraction of sample and standard is described, as well as the operating parameters of the gas chromatograph. Individual analysts usually have preferences on operating conditions. For this assay a flame ionization detector is desirable, because of its sensitivity. Detection of microgram quantities is practicable under the conditions described by... 

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