DRIFT drawback

Drawbacks of ion-selective electrodes ° Selectivity not always sufficient ° Direct read-out is less accurate with higher valent ions EMF-Drift may require frequent standardization... 

Both H2SO4 and HF catalysts suffer from substantial drawbacks. Anhydrous HF is a corrosive and highly toxic liquid with a boiling point close to room temperature. Tests in the Nevada desert showed that, if released into the atmosphere, HF forms stable aerosols, which drift downwind at ground level for several kilometers. In 1987, the accidental release of gaseous HF in Texas City resulted in emergency treatment for several hundred people (9). Therefore,... 

When assaying tissue, growth stimulation by unknown factors is always a drawback. In the assay of rat liver with L. pJantarum such stimulation was noted the drift was overcome by the addition of enzymatically hydrolyzed casein (FI). When assaying human liver, we also noted growth enhancement for O. danica by unknown factors the 1 2 dilution, as described above, obviated any drift. Biotin recoveries ranged from 96 to 103%. 

As with transmission analysis, DRIFTS test samples are generally ground and mixed with an IR transparent salt, such as potassium bromide (KBr), prior to sampling. However, to ensure that there is no catalytic effect, most systems use CaF2 or powdered crystalline carbon (diamond). One drawback is the presence of reststrahlen bands whose contrast can be reduced by... 

First the responses Rq are measured for the sample. Thereafter K is determined by fitting the changes in the concentrations of the analytes in the sample, brought about by the standard additions, to the changes in the responses. Once all elements in the calibration matrix, K, have been determined, the concentration vector of the analytes in the sample is calculated. The method has been successfully applied to absorption spectrophotometry , anodic stripping voltametry and ICP-atomic emission spectrophotometry Attractive features of the method are that automation is very easy and automatic drift compensation is possible . A drawback is that all interferents should be known and be corrected for. 

In the beginning, the refractive index detector was the most used detection system, although it has two important drawbacks (1) solvent gradients cannot be used, and (2) it has low sensitivity and different responses to saturated and highly unsaturated TGs (112). Moreover, use of the ultraviolet (UV) detector is difficult, because the most adequate solvents also absorb in the same range and therefore cause an important baseline drift with gradient elution systems (106). 

Both Zeeman and frequency modulation are used for line observation but each has its drawbacks frequency modulation is often accompanied by a steady drift of the recorder base line, while Zeeman modulation becomes inefficient when the electric field gradient is highly asymmetric, especially for the v lines. 

Monoclonal antibodies generated by fusing mouse spleen cells to myeloma cells can be considered as a pure single reagent that is available in unlimited quantity. Drawbacks are high costs, clonal drift and often low affinity. 

Gradient elution does have several drawbacks. The extra equipment is usually very costly and the technique can be very time-consuming as the column must be reconditioned with the initial eluent between runs. In addition, drifting of the detector response and the appearance of spurious peaks arising from solvent impurities may occur. Although gradient elution should be avoided wherever possible it may be necessary for the analysis of complex mixtures where the components have wide-ranging polarities. 

The acquisition of solid-state FTIR spectra suitable for use in the characterization of polymorphic impurities is performed using either the Nujol mull technique, diffuse reflectance (DRIFT), or attenuated total reflectance (ATR). One should avoid the use of pelleting techniques to eliminate any spurious effects associated with compaction of the KBr pellet. The simplest approach is to prepare a mull of the sample in mineral oil, sandwich this between salt plates, and measure the spectrum using ordinary transmission techniques. The main drawback of the mull technique is that regions in the IR spectrum overlapping with carbon-hydrogen vibrational modes will be obliterated because of absorbance from the oil. 

The other type of design relies on linear piezoelectric translational stages, which either move the sample or the scanner tube, while the other remains fixed. These designs do not suffer from the drawback mentioned above and can reproducibly position the scanner tube and thus the tip in x-y-direction. However, concerning stability/drift upon cooling, the beetle design is superior, because it is a very well balanced system. 

A wide variety of anisotropy measurement setups are used. The simplest solution is the L configuration", i.e. a standard fluorescence setup with 90° exeita-tion. A polariser is placed in the detection path and the components Ip (t) and Is (t) are measured consecutively with the polariser in 0° and 90° orientation (Fig. 5.16). Instruments of this type were used in [338] and [272]. The advantage of this setup is that the instrament response function is the same for both measurements. The drawback is that two measurements are required. Drifts in the deteetor effieieney, photobleaching, or temperature changes in the sample ean therefore impair the results. Moreover, about 50% of the photons are not used, whieh ean be a drawback if the photostability of the sample is an issue. 

However, there is also an important drawback of DRIFT Quantitative measurements are hardly possible since, different from the situation in UV-Vis DRS, no general standard sample is available. However, some researchers reported successful quantitative DRS measurements in the IR region (cf. [166-169]) of adsorbates on silica-alumina. 

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