Array detectors parameters

The dehydrogenation reaction was generally monitored by taking samples for reversed phase H PLC analysis. Diode array detectors for H PLC were relatively new at that time and proved valuable for quickly getting structural information on products of the reaction produced under different conditions. Key reaction parameters for adduct formation, overall concentration, BSTFA, TfOH, and DDQ charges, were optimized using a thermostated HPLC autosampler to sample reactions directly for analysis. Comparison of reaction profiles provided rate and reaction time information that was used to select a more limited number of reaction conditions that were scaled up to compare yields. 

The main components of an LC-MS are the HPLC apparatus, an optional UV or photodiode array detector, the interface, the mass spectrometer and a computer system for data management and evaluation. The interface is the key component of the LC-MS system. All other components must be adapted to the particular interface that is used. Most commercially available systems work with thermospray, electrospray, or particle beam interfaces. Each interface has a distinct mode of action and its own operational parameters. 

Infrared detector applications often require arrays of many detector elements. The use of arrays has several ramifications. It requires minimum electrical power dissipation in each detector element, so that the entire array can be cooled efficiently. It also requires reasonable uniformity of detector parameters among the elements of an array [4.6]. Another consequence of the increasing sophistication of array technology is the need for lower cost per detector element, so that the cost of a large array not become excessive thus cost per element can be a sort of economic detector parameter just as important as the technical detector performance parameters. There is also a trend toward... 

Separation parameters 3DCE system with diode array detector (Hewlett-Packard, Wald-bronn, Germany) uncoated fused-silica capillary 58 cm (50 cm to the detector) x50 jum i.d. 3D extended light path (bubble cell) from Hewlett-Packard running buffer 25 mM tetraborate, pH 8.6, containing 30 mAA SDS injections by positive pressure (50-200 mbar x sec corresponding to about 1-4 nl) voltage +20 kV temperature 30 C detection 320 nm. 

HPLC-MS analyses were carried out with a Waters Alliance 2690 HPLC (Milford, MA), with column heater, 996 Photodiode Array Detector, and a Micromass ZMD (Waters, Milford, MA) or Waters Integrity TMD mass spectrometer (Milford, MA). A Luna silica-2, 5 pm, 2.0 x 150 mm (Phenomenex, Torrance, CA) column was used at a temperature of 35°C. The ZMD MS was equipped widi an atmospheric pressme chemical ionization (APCI) source and parameters set as corona voltage, 3.5 kV cone voltage, 30 V source block temp, 125 C APCI heater, 400 C desolvation gas, 150 L/min cone gas flow, 100 L/min scan range, m/z 151-1000. Reversed phase LC-MS was performed using a Beckman HPLC with 126 pump, 168 PDA (Fullerton, CA), and a Thermoquest LCQ mass spectrometer (San Jose, CA). A Luna Cl8, 3 pm, 2.0 X 50 mm (Phenomenex, Torrance, CA) column was used at ambient temperature. The LCQ MS was equipped with an APCI source and parameters set as APCI vaporizer temp, 450 C source current, 5 pA sheath gas flow, 80 au aux gas flow, 20 au capillary temp, 150 C capillary voltage, 23 V scan range, m/z 250-1500. 

The analysis consisted of three stages, beginning with SPE of the dyes from pills, using a polyamide solid phase. Thin-layer chromatography was utiliz to screen the dyes via two solvent systems and solid supports (silica gel and cellulose), followed by confirmation by CE coupled to a diode array detector. The authors reported that the 14 dyes could be unambiguously identified with these parameters. 

In this way, it is possible to increase the concentration of the substance band at the head of the column, and the result is a better peak form. Finally, one should also consider various settings, such as sample rate (sampling time, sampling period), bunching factor, peak width, slit width in the case of a diode-array detector, etc. In this way, the peak form can also be improved measurably, without changing the real method parameters such as column or eluent. 

The performance of each array detector, not only for CS AAS, is described in particular by its dynamic range , which means the application area of the detector, where shot-noise limited absorbance measurements are possible. It depends on basic detector parameters and is calculated by the ratio between the saturation capacity and the square of the read-out noise. 

At this point, it may be asked if certain parameters can be changed to decrease the measurement time to allow maps to be acquired in reasonable times. Since the size of the remote aperture for most applications is smaller than 250 pm, it is valid to suggest that even smaller detectors should be installed in FT-IR microscopes so that the SNR is optimized for samples that are 50 pm or smaller in dimension. The answer is a very practical one it is simply very difficult to keep the beam aligned with the tighter tolerance required for the beam to be focused accurately on a detector that is smaller than 250 pm. As described later, the situation is different when array detectors with very small pixels are used for hyperspectral imaging. 

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