Sensitivity drift

The TRAACS 800+ is controlled by a personal computer and the features provided include complete interactive control via keyboard or mouse calculation of results as necessary taking into account baseline or sensitivity drift, graphical output of calibration curves for all calibration types—either Hnear or non-hnear, input facility for sample identification data allowing storage on disc and real-time results together with chart traces on a computer printer. The programs allow easy access to input or data files and connection to other computers, and gives system performance verification to CLP standards and built-in QC charts. 

Once a valid calibration has been established, the calibration curve is stored in computer memory for ongoing usage. Modern NIR instmments are highly stable with respect to sensitivity drift, and extensive calibration and diagnostic test procedures have been developed which may be routinely applied to ensure this... 

The accuracy of a Pirani gauge is typically +20%, although an individual (clean) gauge properly used over a two-year period may show a sensitivity drift of only 2%.53... 

Detectors. A detector capable of continuously monitoring effluent from the column is essential for efficient HPLC analyses. Considerations in connection with detector performance include absolute and relative sensitivity, drift characteristics, noise, linearity, specificity, and band spreading resulting from detector design. The selection of a proper detector is essential for successful analysis, both from the standpoint of sensitivity and elimination of effects of interfering compounds (specificity). 

An intermediate concentration standard is reanalyzed after approximately every 20 injections, to calibrate sensitivity drift. 

Tanimoto, H., Hirokawa, J., Kajii, Y., and Akimoto, H., Characterization of gas chromatography/ negative ion chemical ionization mass spectrometry for ambient measurements of PAN potential interferences and long-term sensitivity drift, Geophys. Res. Lett., 27, 2089-2092, 2000. 

Response time (sensor) T,g.9o Response time (monitor) Cross sensitivity Drift... 

The temperature dependence of the calibration error (temperature drift) is tested in new balances at the factory. Test weighings are made in an environmental test chamber at various temperatures (e.g., 10, 20, and 30 °C). A typical tolerance for the span drift (sensitivity drift) as a function of temperature for an analytical balance is 1 ppm/ °C, also expressed as I0 /°C. With a test weight of lOOg, this means that a correct reading of 100.0000 g at 20 °C could change to 99.9999 g or 100.0001 g (or anywhere in between) if the temperature were to change to either 19 or 21 °C. 

The on-line calibration procedure of flow-analyses (baseline and sensitivity drift compensation) is described in Section 10.3.6. 

Fig. 10-27. Compensation of baseline and sensitivity drift (lower and upper line) in steady-state flow analysis Z1 to Z7 and SI to S2 are the zero and standard plateaus, respectively XI to XIO are samples.

The start and end of baseline and sensitivity drift are assumed at the beginning of the first and the end of the last sample. The zero line (lower) and the sensitivity line (upper) in Fig. 10-27 at the time of the respective peak-end represent the terms Al and Ah in the concentration calculation formula. 

The final formula to calculate concentrations from absorbances or equivalent signals including baseline and sensitivity drift correction, therefore, is ... 

Since neither ASTM method makes specific recommendations regarding the gas chromatographic column, any column can be used that meets the method s specifications for separation in order of boiling point and certain column performance requirements regarding resolution, system noise and sensitivity, drift, and so on. Consequently, high-resolution GC has been increasingly applied to... 

A comparison of the low-frequency sensitivity drift is also difficult to do directly, but a reasonable analogy can be drawn. A variation in sensitivity over a series of sample spots is a situation similar to infusion and observation of baseline drift with ESI. Using ideal conditions of sample deposition and crystallization with pure standards and solvents establishes some idea of reproducibility limits. An example is shown in Figure 13.12, where a series of spots from a sample of the dmg Propanolol were created with an electrostatic deposition device." The spots were rastered at a speed such that each spot was traversed in 600 ms. Absolute area reproducibility of approximately 6% was achieved— that is, worse than the infusion data of NanoESI and the high flow techniques, but still reasonable, particularly if referencing the signal to an internal standard (not done here) in the same spot that is ionized at the same time as the analyte. Suffice it to say that good quantitation is possible when an internal standard is cocrystallized with the analyte. ESI or APCI do not require coelution of the internal standard and analyte. 

Of key importance is the sensitivity of the sensor current or voltage output, expressed as nA/ppmv or mV/ppmv of target gas, and any cross-sensitivity to nontarget gases, as mentioned above. These sensitivities are usually quantified by pre- and/or post-fieldwork laboratory calibrations where the sensor is exposed to a fixed concentration of gas. Such point calibrations assume linearity of the sensor responses to the target gases, which is generally a valid assumption see, e.g., reference In order to reduce adverse effects from possible sensitivity drift, calibrations should be performed immediately prior to or after the fieldwork. Further, the laboratory calibrations performed at room temperature ( 20-25 °Q and ambient pressure ( 1 atm) do not necessarily reflect sensor properties at the... 

Germanium metal is also used in specially prepared Ge single crystals for y-ray detectors (54). Both the older hthium-drifted detectors and the newer intrinsic detectors, which do not have to be stored in hquid nitrogen, do an exceUent job of spectral analysis of y-radiation and are important analytical tools. Even more sensitive Ge detectors have been made using isotopicahy enriched Ge crystals. Most of these have been made from enriched Ge and have been used in neutrino studies (55—57). 

The immersion of glass electrodes in strongly dehydrating media should be avoided. If the electrode is used in solvents of low water activity, frequent conditioning in water is advisable, as dehydration of the gel layer of the surface causes a progressive alteration in the electrode potential with a consequent drift of the measured pH. Slow dissolution of the pH-sensitive membrane is unavoidable, and it eventually leads to mechanical failure. Standardization of the electrode with two buffer solutions is the best means of early detection of incipient electrode failure. 

When the temperature of a solar cell rises, cell conversion efficiency decreases because the additional thermal energy increases the thermally generated minority (dark-drift) current. This increase in dark-drift current is balanced in the cell by lowering the built-in barrier potential, lU, to boost the majority diffusion current. The drop in F causes a decrease in and F. Therefore, a cell s output, ie, the product of F and decreases with increasing cell temperature. is less sensitive to temperature changes than F and actually increases with temperature. 

The main chemico-analytical properties of the designed ionoselective electrodes have been determined. The work pH range of the electrodes is 1 to 5. The steepness of the electrode function is close to the idealized one calculated for two-charged ions (26-29 mV/pC). The electrode function have been established in the concentration range from 0.1 to 0.00001 mole/1. The principal advantage of such electrodes is the fact that thiocyanate ions are simultaneously both complexing ligands and the ionic power. The sensitivity (the discovery limits), selectivity (coefficient of selectivity) and the influence of the main temporal factors (drift of a potential, time of the response, lifetime of the membranes) were determined for these electrodes. 

Sensing heads should be located in draft-free areas where possible, as air flowing past the sensors normally increases drift of calibration, shortens head life, and decreases sensitivity. Air deflectors are available from sensor manufacturers and should be utilized in any areas where significant air flow is anticipated (such as air conditioner plenum applicaiion.s). Additionally, sensors should be located, whenever possible, in loca[ion.s which are relatively free from vibration and easily accessed for calibration and maintenance. Obviously, this carmot always be accomplished. It usually is difficult, for example, to locate sensors in the tops of compressor buildings at locations which are accessible and which do not vibrate. 

Other situations may also occur that allow a simple determination of the sensitivity factor. When, for example, a sufficiently negative electrode potential forces all minority carriers to drift into the interior of the semiconductor electrode, where they recombine subject to the bulk lifetime Tfr we will see a limiting PMC signal (given a sufficiently thick electrode). Knowing the photonflux /0 (corrected for reflection), we may expect the following formula to hold ... 

Both the sensing device of the LC detector and the associated electronics can be temperature sensitive and cause the detector output to drift as the ambient temperature changes. Consequently, the detecting system should be designed to reduce this drift to a minimum. In practice the drift should be less than 1% of FSD at the maximum sensitivity for 1°C change in ambient temperature. 

During the development of these criteria the Semenov analysis was extended to systems with heat-exchanger reservoir temperatures different from feed temperatures (Tr < Tq) and with delayed runaway (larger value of e), which resulted In significant concentration drift prior to runaway. Since values of e for chain-addition polymerizations are not nearly as small as those for the gaseous explosions Investigated by Semenov, R-A Is not as sensitive nor Is It as early In terms of extent of reaction. 

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