Baseline noise

How stringent is this model in terms of the necessary signal height relative to the baseline noise First, some redefinition of terms is necessary ... 

All techniques introduced so far rely on recognizable signals what happens if the signal more or less disappears in the baseline noise ... 

Sensitivity by itself is not sufficient to completely evaluate an LCEC system for analytical purposes. The minimum detectable quantity (detection limit) is of more practical importance. The detection limit takes into consideration the amount of baseline noise as well as the response to the analyte. The detection limit is then defined as the quantity of analyte which gives a signal-to-noise ratio of three (a S/N of 3 is the generally accepted criterion although other values have been used). For a complete description of an LCEC application, both the sensitivity and detection limit, along with the S/N criteria used, should be provided. 

EM affects the linewidth and is often also known as a line broadening function LB. A positive value of LB (here 0.8 and 1.9 Hz) broadens the lines, a negative value (here -0.3 Hz) sharpens them however, never forget that we are only modifying the information present, so that a decrease in the line-width is automatically accompanied by an increase in the baseline noise. This becomes clear immediately when we see the spectra of the OCH2 multiplet shown in Fig. 6. 

The sensitivity of this system is 430 pg/0.0044 absolute. The standard deviation of the baseline noise is about 0.0007 absolute, resulting in a noise-limited detection limit of 140 pg of germanium at the 95% confidence level. 

Substituent effects hae been observed in a series of substituted malonato complexes (167). The 9Be resonance frequencies move to higher field as the basicity of the ligand increases, as can be seen in Table XI. Quadrupolar broadening is considerable in complexes of the hydrolyzed trimer, so much so that unless a species of this sort is present in high concentration relative to the others, its signal may be buried in the baseline noise. The tetrahedron is significantly distorted from Td symmetry in these compounds. 

Obviously the optimum potential for detection of analyte X in this mobile phase is a compromise a higher potential will increase the peak height, but will also increase the baseline offset and thus the baseline noise and drift. Lower potentials will decrease the peak height, but also decrease the noise and drift. 

Electrochemical detectors are more sensitive to flow pulsation than UV-detectors and usually an efficient pulse dampener is required to minimize the contribution to baseline noise at high sensitivity. 

More research has to be done. One area is the influence of non-linearity which causes an extra baseline noise in the correlogram. Injection systems for other kinds of chromatography, in particular GC, have to be developed. The ability to detect very small differences between the solute concentrations in the background and the sample has to be investigated. 

Baseline noise, single wavelength < 0.35xl0 AU, dry cell, 254nm... 

With a modern variable-wavelength or PDA detector, it is safe to use a maximum absorbance of up to 1.0-1.5 absorbance units (AU). A typical UV detector today should have a baseline noise in the order of 10 micro absorbance units (10 AU). Therefore, modern UV detectors should have a dynamic range of 4-5 orders of magnitude. The sample concentration and injection volume can be adjusted to make it possible to quantify the major component and impurities at the 0.05% level in the same chromatographic run without changing detection wavelength, sample concentration, or injection volume. 

Narrow the peak shape (stacking effects, shorter separation time. Higher peaks, easier to be distinguished from baseline noise Influence on selectivity... 

From Equation (3), we learn that increasing the absorptivity of the probe and the detector pathlength will lower the LOD, while the noise should be as low as possible. However, some of these factors are interdependent lowering the concentration of the probe will decrease the dynamic reserve and increasing the detector pathlength will increase the baseline noise. 

The signaTto-noise ratio is determined by comparing measured signals of the analyte at low concentrations with the baseline noise of blank samples. In general, a signaTto-noise ratio between 3 1 or 2 1 is generally considered acceptable. 

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