Detector characteristics linearity

Table 30.8, provides a comprehensive comparison of various typical detector characteristics invariably used in HPLC, such as response, concentration expressed in g ml 1 and the linear range. However, the linear range usually refers to the range over which the response is essentially linear. It is mostly expressed as the factor by which the lowest factor (i.e., Cn) should be multiplied in order to obtain the highest concentration. 

Ge(Li) Detector Characteristics. Resolution measurements for the 18-cm.8 Ge(Li) detector were made with the anticoincidence shield in the inoperative mode, with a normal operating bias of 1700 volts, and with a preamplifier designed in our Laboratory (3, 4), and operated in conjunction with a Tennelec TC-200 linear amplifier. Resolution at 1.33 M.e.v. was 2.62 k.e.v., FWHM (Figure 4). The electronic pulser resolution for the amplifier system at a slightly lower energy was 1.86 k.e.v., the total capacitance of the detector was 28 pF, the noise slope was 0.035 k.e.v./pF, and the leakage current at 1700 volts was 0.5 X 10"9 amp. 

The methods of quantitation and the criteria for precise and accurate determination for LC are similar to those used in GC, though there are a number of important differences. External standard calibration—i.e. where the detector response to a solution of known concentration is measured and then a calibration curve is constructed—is the recommended method for quantitation in LC. It is imperative that the linearity of detector response is confirmed over the concentration range of interest with standards prepared in a matrix similar to the sample. Table 6.2 details detector characteristics. The increased precision obtained compared to GC is attributable to the... 

Here is described the verification of one particular characteristic parameter of one flaw detector, i.e. vertical linearity. The system of verification VERAPUS is connected to peripheral equipment as indicated in figure 2. The dialogue boxes show the operator how to adjust the R.F. signals that are sent by the arbitrary generator to the flaw detector. 

Basic Interferometer Properties (1.6-9) Although the relationship between element aperture diameter, baseline, and wavelength is quite simple, it is instructive to visualise the influence of each of these characteristics. To this end, we consider a Young s interferometer with element diameters D = Im, a baseline B = 10m at a wavelength A = 1/nm in the animations. The intensity profile across the fringe pattern on the detector (screen) is shown with linear and logarithmic intensity scales in the lower two panels. The blue line represents the intensity pattern produced without interference by a single element. 

The requirements for an instrumental method of specifying reflected color include a light source, the colored object and a detector. What this means is that all we need is a source, an object and a detector. However, since the response characteristics of these optical components are not linear, nor flat, we need an analogue system in order to be able to measure color. 

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. 

Solute property detectors, such as spectroscopic andj electrochemical detectors, respond to a physical or chemical] property characteristic of the solute which, ideally, is] independent of the mobile phase. Althou this criterion is rarely met in practice, the signal discrimination is usually sufficient to permit operation with solvent changes (e.g., flow programming, gradient elution, etc.) and to provide high sensitivity with aj wide linear response range. Table 5.4. Solute-specific detectors complement ulk property detectors as they provide high ... 

Principles and Characteristics As mentioned already (Section 3.5.2) solid-phase microextraction involves the use of a micro-fibre which is exposed to the analyte(s) for a prespecified time. GC-MS is an ideal detector after SPME extraction/injection for both qualitative and quantitative analysis. For SPME-GC analysis, the fibre is forced into the chromatography capillary injector, where the entire extraction is desorbed. A high linear flow-rate of the carrier gas along the fibre is essential to ensure complete desorption of the analytes. Because no solvent is injected, and the analytes are rapidly desorbed on to the column, minimum detection limits are improved and resolution is maintained. Online coupling of conventional fibre-based SPME coupled with GC is now becoming routine. Automated SPME takes the sample directly from bottle to gas chromatograph. Split/splitless, on-column and PTV injection are compatible with SPME. SPME can also be used very effectively for sample introduction to fast GC systems, provided that a dedicated injector is used for this purpose [69,70],... 

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.

The purpose of a detector is to monitor the carrier gas as it emerges from the column and respond to changes in its composition as solutes are eluted. Ideally a detector should have the following characteristics rapid response to the presence of a solute a wide range of linear response high sensitivity stability of operation. 

The ideal HPLC detector should have the same characteristics as those required for GC detectors, i.e. rapid and reproducible response to solutes, a wide range of linear response, high sensitivity and stability of operation. No truly universal HPLC detector has yet been developed but the two most widely applicable types are those based on the absorption of UV or visible radiation by the solute species and those which monitor refractive index differences between solutes dissolved in the mobile phase and the pure mobile phase. Other detectors which are more selective in their response rely on such solute properties as fluorescence, electrical conductivity, diffusion currents (amperometric) and radioactivity. The characteristics of the various types of detector are summarized in Table 4.14. 

Important performance characteristics of UV/Vis detectors are sensitivity, linearity, and band dispersion. These are controlled by design of the optics and the flow cell—more specifically by spectral bandpass, stray light characteristics, and the volume and path length of the flow cell. 

The main characteristics of these applications are good linearity, with squared correlation coefficient above 0.999, and repeatability with RSD below 2% when no internal standard is used and below 1% with an internal standard. Depending on the buffer and injection optimization, the different authors found an POD and limit of quantitation (LOQ) close or below 1 pg/mL. Using a conductivity detector, the POD and POQ decreased by a factor 100. Many authors also report the accuracy and recovery of the method. 

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