Typical Instrument Parameters

Capillary electrophoresis of PCR-amplified products is usually performed in the reverse polarity mode (negative potential at the injection end of the capillary). A coated capillary (100 mm i.d., 37-57 cm total length) is filled with a gel buffer system. PCR samples are introduced hydrodynamically or, after desalting, electrokinetically. The PCR sample and a DNA marker of known size may be injected sequentially and allowed to comigrate in the capillary. With a capillary temperature set at 20 to 30°C, separation of PCR products is accomplished at field strengths of 200 to 500 V/cm. Detection is on-line, measuring either UV absorbance at 260 nm, or LIF. 

Since DNA fragments from the PCR typically are contained in a high salt matrix, their mobility will vary depending on sample salt concentration. Thus, proper identification of these DNA fragments requires the use of an internal standard to normalize analyte velocity. This practice corrects for variance in fragment mobility due to sample matrix differences (i.e., salt content). These internal standards are included for size determination (in bp) as well as a reference for migration time. Candidates for such internal standards include the primer or primer-dimer peaks, since both components are already present in the PCR mixture alternatively, one or more coinjected standard DNA peak s may be chosen. If any of these fragments are to serve as the internal standard, they must be separated from one another and any PCR product, a precondition that is not easily met when the size of the PCR product is below 60 bp. 

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Table 1 Approximate values for r (Rayleigh criterion) estimated for three characteristic wavenumbers typical instrument parameters for transmission and ATR experiments assumed...

Atomic absorption measurements were made using standard conditions. Nearly stoichiometric flames were used for all metals but chromium, for which a reducing flame was used. The air-acetylene flame was used for all metals but vanadium, for which a nitrous oxide-acetylene flame was used. A single slot titanium burner was used for all of the metals investigated. Water saturated MIBK was used as the blank. Table I presents typical instrument parameters. 

Christman et al. [72] gave details of procedures for extraction, clean-up, and concentration of samples of soil prior to the determination of their content of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans by gas chromatography and by gas chromatography-mass spectrometry. Instrumental parameters are also included. Some typical results are tabulated. 

Performing an operational qualification ensures that the individual components of the instrument and the instrument as a whole are functioning correctly to certain defined specifications. The testing of individual instrument parameters and comparing the results to those specifications require the isolation of the parameters. Each identified parameter is related to a specific function within the instrument. Typical functions that should he subject to the qualification process and their associated parameters are described below. 

Performing an operational qualification procedure ensures that the specific parts of an instrument are functioning according to defined specifications for precision, linearity, and accuracy. For operational qualification, testing individual instrument parameters and comparing them to accepted values requires isolating each parameter. Each parameter is related to a specific CE function. Typical CE functions that are subjected to qualification and their associated parameters are shown in Figure 12.2. 

Other outputs from a typical instrument include complex modulus, creep compliance, relaxation modulus, sample stiffness, and all the basic data including instrument parameters. 

Static headspace extraction is also known as equilibrium headspace extraction or simply as headspace. It is one of the most common techniques for the quantitative and qualitative analysis of volatile organic compounds from a variety of matrices. This technique has been available for over 30 years [9], so the instrumentation is both mature and reliable. With the current availability of computer-controlled instrumentation, automated analysis with accurate control of all instrument parameters has become routine. The method of extraction is straightforward A sample, either solid or liquid, is placed in a headspace autosampler (HSAS) vial, typically 10 or 20 mL, and the volatile analytes diffuse into the headspace of the vial as shown in Figure 4.1. Once the concentration of the analyte in the headspace of the vial reaches equilibrium with the concentration in the sample matrix, a portion of the headspace is swept into a gas chromatograph for analysis. This can be done by either manual injection as shown in Figure 4.1 or by use of an autosampler. 

Modern chemical instrumentation is capable of generating enormous amounts of data in very short periods of time. It is clear that a major task of scientists for the near future is to develop techniques to utilize more effectively this capability, in order to avoid the typical dilemma of being buried in data with little or no perspective of the information content. Thus, there are three key developments that must be pursued definition of "information content" identification of methods to correlate instrumental parameters with information content and development of tools for the instrumental enhancement of information content and the efficient extraction of information from data. 

All detection limits are given in micrograms per liter and were determined using elemental standards in dilute aqueous solution. All detection limits are based on a 98% confidence level (3 S.D.). All atomic absorption (Model 5100) detection limits were determined using instrumental parameters optimized for the individual element, including the use of system 2 electrodeless discharge lamps where available. ICP emission (Optima 3000) detection limits were obtained under simultaneous multielement conditions with a radial plasma. Detection limits using an axial plasma (Optima 3000 XL) are typically improved by 5-10 times. 

Typical solid samples representing a partition system include polymers heated above their glass transition point. These samples are amenable to application of the usual HS modes (e.g. the standard-addition technique). The standard can be added to the gas phase in the closed vial by injection through the septum, equilibrium being established by diffusion from both sides. If the regression analysis reveals the absence of linearity, then either some instrumental parameter (e.g. the sample temperature or equilibration time) will have to be adjusted or the system is not a partition but rather an adsorption system. 

These equations use only two peaks computer algorithms use all identified peaks to obtain more precise MW values. The number and relative abundance of different molecular ions depend on the protein medium (buffer, salt concentration) and instrumental parameters (i.e., voltage, vacuum). Typical MW determination results are shown in Figure 15.9. 

Figure 6. Typical instrument operating parameters for GLC and LC analysis for...

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