Signal stability

Figure 26. Vibrations of the OFIP 1.52m telescope (tracking, dome open). The records at 23h35 (solid line)and at 23h50 (dotted line) show the signal stability. Amplitude is 66 mas rms (Tokovinin, 2000).

Additionally to meeting the requirement of high adsorption sensitivity the semiconductor sensors should be response-selective to a specific gas as well as exhibit high signal stability (i.e. reproducibility) over a long operation time. 

Time parameters of response curve may also contain important information concerning the behavior of the components of the gas-sensitive point-contact multistructure-analyte system. The time required for signal stabilization in the exposition phase is directly proportional to the concentration of molecules with higher adsorption energy. The relaxation time characterizes integral value of the adsorption energy of all ingredients of the gas medium under study. 

Most of these potential sources of error have actually been eliminated, or at least minimized, in commercial analyzers by proper hardware and software implementation, e.g., proper washing and cleansing procedures, signal stability criteria, corrections of the residual potential or simply by declaring limits , i.e., the types of sample, interfering substances, vial types to be avoided, by limiting the number of reports per hour, adjusting within-day and between-day imprecision and the lifetime of the electrodes. 

The above protocol provides a basic idea of a typical LAPS set-up. The number of measurement spots and the size of the sensor chip can vary for different applications. Electronic and software need to be adapted to the specific requirements and can be developed from the above description. Other light sources (e.g., laser) and different ways to modulate them might be investigated. The position of the light sources as well as the position of the amplifier stage is of great importance for the signal stability and should be as close as possible to the sensor chip. Furthermore, the conductivity of the electrolyte solution has to be... 

Monolithic nozzles have been fabricated to construct the ESI tips. They were fabricated on Si by DRIE. This approach has showed greater signal stability and intensity [790]. 

To solve these problems, the contaminated components in the mass spectrometer should be cleaned. Moreover, postcolumn switching or splitting should be considered to prevent or reduce the occurrence of contamination as well as to improve signal stability [39],... 

Figure 8. Microparticle Sensor Titration Curve. A sensor was place in a series of six buffers of different pHs. After the sensor signal stabilized, the intensity at the respective excitation and emission wavelengths was collected 405nm and 515nm 450nm and 515nm. The ratio at these intensities was plotted against pH.

The introduction of liquid samples into the LP-ICP-MS has been shown to be feasible [115]. A glass frit nebulizer may be used along with desolvation to improve analyte signal stability. To date, however, no speciation studies using such a system have been performed. 

The performance of hollow cathode lamps deteriorates slowly with use. After several months, or even a year or more, output tends to become progressively less stable and/or less intense. Because the loss in precision is gradual, it may well pass unnoticed. It is therefore useful to keep a recorder trace of signal stability after a new lamp has been in use for a few hours for comparison purposes. To be useful, however, it is important to have made a note of the slit width, photomultiplier gain setting, wavelength, and lamp current used, and the lamp position must of course have been carefully optimized. Some analysts prefer, on grounds of simplicity, to make a note of the absorbance attainable under optimized flame conditions from a specified determinant standard. However it must then be remembered that a decline in this parameter may be related to nebulizer deterioration rather than lamp deterioration. 

Use of Internal Standards The use of internal standards envisages different possibilities. The procedure described here is based on two internal standards. Once thawed, fish sample were dissolved in TMAH, ethylated with NaBEt4, extracted into iso-octane and subjected to GC-ICP-MS for the identification and quantification of Me-Hg and inorganic Hg2+. For the correction of procedural errors two internal standards were used. The sample pretreatment was corrected by the recovery factor of the spiked dibutyl-dipentyl-Sn (DBT-pe), while the GC-ICP-MS measurements were controlled by the signal stability of Xe added to the GC carrier gas [47], In another application propyl-Hg was used as an internal standard to correct for matrix-induced ion signal variation and instrumental drift [65]. 

If protease inhibitors should be identified and characterized, the assay should be tested for signal stability and endpoint linearity in the next step. The progress curves recorded for substrate concentrations near or below the KM value should be linear for up to 2 h. Such signal stability is a prerequisite to run the assay with a pre-incubation time of 1 h for enzyme and inhibitor. This long pre-incubation is recommended to ensure also that the IC50 values for slowly binding inhibitors are correctly determined. An additional hour for the incubation of enzyme, inhibitor and substrate after this pre-incubation is recommended. 

A two- or four-sprayer device to spray one solution through a number of needles was described to study the dynamic range and the flow-rate limitations of an API system [58]. The device allowed flow-rates up to 1 ml/min and provided improved signal stability at higher flow-rates. 

The NO analysis involved considerable problems. Eventually we used a Beckman NDIR (non-dispersive infrared) for NO measurements because of good signal stability and because the instrument read NO directly, not total NOj,. However all of the water had to be removed from the gas because moisture was recorded as NO. The NO-NO2-H2O interaction was eliminated in the water trap by removing the NO2 before the trap. After trying several approaches, we finally used a saturated solution of sodium sulfite at room temperature as the NO2 absorber... 

Firstly, the calibration of the individual chambers has been verified with muon runs. The charge yield obtained agrees well with the cosmic-ray muon calibrations performed several years ago. This is an indication for the longterm signal stability of these detectors. 

Combi cassette. The ColorLock Gold assay kit is based on malachite green-molybdate colorimetric assay, and the yellow reagent turns green in the presence of phosphate. The stabilizer stabilizes acid-labile substrates and the molybdate complex to maintain signal stability. 

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