Instrumentation temperature effects

The nOe difference spectrum is highly demanding, since even the slightest variation in the spectra recorded with and without preirradiations will show up as artifacts in the difference spectrum (Fig. 4.8). The errors can be random, due to phase instability caused by temperature effects on the Rf circuits, variations in spinner speed, etc. The problem of phase instability is reduced in the latest generation of instruments with digital... 

Post-processing, n - performing a mathematical operation on an intermediate analysis result to produce the final result, including correcting for temperature effects, adding a mean property value of the calibration model, or converting the instrument results into appropriate units for reporting purposes. 

Instrument/Equipment Effects Examples include the calibration and precision of an analytical balance, the specified tolerance for volumetric glassware and a temperature controller that maintains a mean temperature which is different (within specification) from its indicated value. 

Viscosity differences-. Different sample vial temperatures create different viscosities, and thus different amounts injected. To reduce the effect, use the instrument temperature control (see Section IV). However, often the sample and buffer vials reside outside the temperature-controlled area. The effect of this might vary depending on the climate system in your lab and how the lab temperature varies over the year. Besides temperature control, it is important to match samples and standards in terms of viscosity and conductivity. 

As previously discussed, the density of the fluid whose flow is to be measured can have a large effect on flow sensing instrumentation. The effect of density is most important when the flow sensing instrumentation is measuring gas flows, such as steam. Since the density of a gas is directly affected by temperature and pressure, any changes in either of these parameters will have a direct effect on the measured flow. Therefore, any changes in fluid temperature or pressure must be compensated for to achieve an accurate measurement of flow. 

The steady movement of the baseline either up or down the scale is referred to as drift. Drift is often indicative of variations in chromatographic conditions, such as temperature or solvent programming. It can also be indicative of instrument instability owing to temperature effects on the detector. 

So far, the separation efficiencies reported with the submicron packed beds have not offered a significant improvement over those obtained with particle diameters in the 1 pm range [66,119-121]. Fig. 4.17 depicts the separation of a test mixture obtained in a packed bed with particles of about 0.5 pm in diameter. As reported by Luedtke, et al. [121], plate heights of about three times the particle diameter (H = 3dp) are achieved. This has been attributed to band dispersion due to temperature effects and instrumental limitations, such as the maximum electric field that can be applied with existing units and detection systems [121], Plots of plate height versus linear... 

Most chromatographic systems employ process control of operating parameters. These may well be built into the instrument. Temperature control is particularly important, especially for contemporary techniques such as chiral recognition and protein interaction.23 In liquid chromatography, for instance, temperature directly effects retention, separation efficiency, and selectivity. Stability of temperature is thus extremely important, since variations of more than 1°C can lead to noticeable effects.24... 

The laser temperature jump instrument can effectively be used to initiate and observe the fast events in protein/peptide folding and unfolding as well as those events that extend out to several milliseconds. In the present study, the unfolding of a helical peptide was determined to occur within tens of nanoseconds, supporting the need for nanosecond or faster initiation techniques. Promising results obtained by the laser temperature jump method will continue to stimulate the development of additional monitoring techniques such as UV absorption and circular dichroism. 

The thermogravimetric analyser is a SDT-DTA from TA Instruments, supported by an HP PC and software for control and data handling. The system consists of a dual beam horizontal balance. Each arm holds one cup and there is one thermocouple under and in contact with each cup. One cup contains the char sample and the other cup is empty, used as a reference for temperature effects. Detailed description of the instrument can be found somewhere else. Ceramic cups were used for most of the experiments. The apparatus has been recently upgraded and it was possible to operate in a TGA-DSC mode. Therefore, not only the temperature and the weight have been registered but also the heat demand of the process. Table 2 and Table 3 show the experimental matrix for this work. 

Calorimetry Another category of laboratory systems that can be used for kinetics includes calorimeters. These are primarily used to establish temperature effects and thermal runaway conditions, but can also be employed to determine reaction kinetics. Types of calorimeters are summarized in Table 7-12 for more details see Reid, Differential Microcalorimeters, /. Physics E Scientific Instruments, 9 (1976). 

Regarding the influence of the Schlieren effect on analytical procedures, the effect of differences between the temperature of the ambient environment and the sample on the absorbance was originally reported in relation to stopped-flow procedures [84]. The systematic deviation in absorbance was proportional to the temperature difference and was also dependent on the optical properties of the instrument. The effect also manifested itself when identical solutions at different temperatures were mixed [85] a linear dependence of the measurement on the temperature... 

Plate 5. Ozone anomalies (ppmv) versus altitude (km) and time (years) in the equatorial region (4°N-4°S) derived from observations made by the HALOE instrument on board the Upper Altitude Research Satellite (UARS). Superimposed on ozone values are the zonal winds measured by the HRDI instrument on the same satellite. Full lines are eastward winds and dashed lines westward winds with intervals corresponding to 10 m/s. In the 20-30 km altitude range, the positive ozone anomalies are associated with the westerly shear in the quasi-biennal oscillation (QBO), while the negative anomalies are indicative of easterly shears. Above 30 km, ozone variability is associated with temperature variability, which affects the photochemical source terms. Above 35 km, the observed variations are due to temperature effects associated with the QBO and to the semi-annual oscillation. Courtesy of Paul Newman, NASA/GSFC. 

Instrumental Errors. Instrumental errors are caused by nonideal instrument behavior, by faulty calibrations, or by use under inappropriate conditions. Typical sources of instrumental errors include drift in electronic circuits leakage in vacuum systems temperature effects on detectors currents induced in circuits from llO- power lines decreases in voltages of batteries with use and calibration errors in meters, weights, and volumetric equipment. 

Often the physical state of the sample (gas, liquid, or solid) is dictated by the physical principle upon which the measurement is based, and a phase conversion may be required. Some instruments (for example, gas chromatographs and infrared analyzers) utilize either gas or liquid samples the appropriate phase may be chosen to optimize any of the instrumental parameters discussed earlier. If the measurement is temperature sensitive and the sample temperature may vary, temperature compensation or temperature control must be provided. Temperature compensation is usually supplied as part of the measuring system the sample temperature is continuously monitored and the measurement signal electrically corrected to offset the temperature effects. When temperature control is required, a batch sample or a sample side-stream is used, and the sample temperature is adjusted prior to measurement. This procedure adds dead-time to the measurement because the sample has to be in the temperature converter long enough to come to thermal equilibrium. 

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