Detector response linearity

The detector response linearity (peak area vs. concentration) was evaluated by preparing five calibration samples using a 1 1 1 mixture of ots-casein (CN), P-CN, and k-CN (each solution was injected three times).The cahbration range was 2-30mg/mL for ots- and p-CN and 2-lOmg/mL for k-CN. 

Figure 2 Sample-volume visualizations that would be expected to produce 95% of detector response. Linear attenuation coefficients for soil and air have been estimatedfor energy level 662 keV...

When an analyte is too concentrated, it is easy to overload the column, thereby seriously degrading the separation. In addition, the analyte may be present at a concentration level that exceeds the detector s linear response. Dissolving the sample in a volatile solvent, such as methylene chloride, makes its analysis feasible. 

The two complicating factors that are encountered most frequently are the linearity of detector response and stray light scattering at low signal levels. DTGS... 

Delta function response - Over most of the wavelengths of interest, optical and infrared detectors produce one photoelectron for every detected photon, which provides a one-to-one correspondence between detected photons and photoelectrons. This means that the detector response is exactly linear to the intensity incident on the detector - an attribute that allows astronomers to precisely remove sky background and electronic bias to accurately measure the intensity of the astronomical object. 

It is important for obtaining precise results that the signals from the samples to be determined should lie on the linear part of the calibration graph as elsewhere within the dynamic range a small change in detector response corresponds to a relatively large range of concentrations. 

Figure 2.6 Detector response curve showing (a) ideal behaviour, (b) real behaviour, (c) its linear range, (d) its dynamic range, (e) the noise level, and (f) the limit of detection at three times the noise level.

The buffer concentration also directly affects the size of droplets produced - the higher the buffer concentration, then the smaller they are, and this is desirable. The buffer concentration, however, has an effect on the ionization efficiency and at high buffer concentrations (>10 M) the relationship between detector response and analyte concentration is not linear. As indicated earlier in Figure 2.6, this situation must be avoided for precise quantitative measurements. 

Linearity verifies that sample solutions are in a concentration range in which the detector response is linearly proportional to analyte concentration. Current FDA guidelines call for establishing linearity. For regulatory methods, this is generally performed by preparing standard solutions at four or five concentrations, from 30 to 200% of the tolerance. 

Linearity is often assessed by examining the correlation coefficient (r) [or the coefficient of determination (r )] of the least-squares regression line of the detector response versus analyte concentration. A value of r = 0.995 (r = 0.99) is generally considered evidence of acceptable fit of the data to the regression line. Although the use of r or is a practical way of evaluating linearity, these parameters, by... 

A new nonweighted linear calibration curve is to be generated with every set of samples analyzed. The calibration standards are interspersed among the analytical samples, preferably with a standard between every two analytical samples, and injected into the HPLC/OECD system. The calibration curve is generated by plotting peak height of the detector response against the concentration for each calibration standard of EMA and methylated HEMA. 

Faraday collector, simultaneously with U, U and U during the first sequence. This shortens the analysis routine, consuming less sample. Ion beam intensities are typically larger in MC-ICPMS than in TIMS due to the ease with which signal size can be increased by introducing a more concentrated solution. While this yields more precise data, non-linearity of the low-level detector response and uncertainties in its dead-time correction become more important for larger beam intensities, and must be carefully monitored (Cheng et al. 2000 Richter et al. 2001). 

Detectors are usually conpued in terns of their operational characteristics defined by the nininvin detectable quantity of standards, the selectivity response ratio between standards of different conpositlon or structure, and the range of the linear portion of the detector-response calibration curve. These terns are wid. y used to neasure the perfomance of different chronatographic detectors and were fomally defined in section 1.8.1. 

A linear dependence between detector response and the amount of sample entering the detector is expected for phosphorus and is generally found. Deviations from the predicted detector response are more common with sulfur-containing than phosphorus-containing compounds (171,173). The detector response in the sulfur aK>de can be described by equation (3.17)... 

Validate routine methods, i.e., define the conditions under which the assay results are meaningful.115 To do that, one must select samples that are truly representative of the product stream. This may be a difficult task when the process is still under development and the product stream variable. The linearity of detector response should be defined over a range much broader than that expected to be encountered. Interference from the sample matrix and bias from analyte loss in preparation or separation often can be inferred from studies of linearity. Explicit detection or quantitation limits should be established. The precision (run-to-run repeatability) and accuracy (comparison with known standards) can be estimated with standards. Sample stability should be explored and storage conditions defined. 

The peak symmetry, resolution, and detector response are directly dependent on the concentration of the sample. As the concentration of a sample increases, the retention time, separation, and peak symmetry generally decrease. These phenomena are due to isotherm nonlinearity. The detector response may also be nonlinear above or below certain concentrations. In some cases, small amounts of a dilute component are irreversibly adsorbed to the column, leading to reduced recovery. Above some concentration, the response of any detector will cease to be linear. The UV-VIS is one of the most linear detectors, generally exhibiting at least three decades of linearity, while RI, electrochemical, and fluorimetric detectors have a markedly narrower range of linearity. 

Calibration of an internal standard method is done by preparing standard samples of varying concentration. The same amount of IS is added to each, and the standard samples are analyzed using a developed method. The detector response, area or height, of each standard is determined, and a ratio is calculated. The graph of concentration vs. area ratio is plotted. The method is considered linear if the correlation coefficient is 0.99 or better. The response factor RF is calculated as... 

ELSD Quasi-universal No dependence on eluent conditions Droplet size control Moderate sensitivity (low ng) Compound-dependent and non-linear detector response [31,51-53]... 

Figure 8.6 Positive ion LD TOF mass spectra of P. falciparum parasite sample (upper trace), and a control (uninfected blood) sample (lower trace). Protocol D is used for sample preparation. Both samples—in vitro cultured P. falciparum parasites in whole blood, and the whole blood control—are diluted to 5% hematocrit (10-fold) in PBS buffer. In the infected sample the estimated number of deposited parasites per sample well is approximately 100. A commercial LD TOF system is used, and both spectra are normalized to the same (40 mV) detector response value. Each trace represents the average of one hundred single laser shot spectra obtained from linear scanning of an individual well (no data smoothing). The characteristic fingerprint ions of detected heme in the upper trace are denoted.

Fluorescence detectors can be made much more sensitive than uv absorbance detectors for favourable solutes (such as anthracene) the noise equivalent concentration can be as low as 10 12 g cm-3. Because both the excitation wavelength and the detected wavelength can be varied, the detector can be made highly selective, which can be very useful in trace analysis. The response of the detector is linear provided that no more than about 10% of the incident radiation is absorbed by the sample. This results in a linear range of 103-104. 

Amarnth and Amamth [15] described a specific method for the determination of penicillamine and cysteine. Treatment with 1,1-thiocarbonyl diimidazole converts penicillamine to 5,5-dimethyl-2-thioxothiazolidine-4-carboxylic add. The detection limit is 2 pmol of the drug per injection, and the detector response is linear up to 1 nmol. 

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