Detectors reach

A simple gas chromatographic method determines total arsenic in urine as arsine with a PN detector. The detection limit is 50 ng. The gas sample is separated on a 1.2 m glass column filled with Chromosorb 103 80-100 mesh at a furnace temperature of 30 C [153]. MMAA and DMAA are separated as thioglycolic acid methyl esters on a glass column (1.8 m, 2 mm ID) packed with Chromosorb G AW-DMCS coated widi 2.5% XE-60 for flame ionization detection. The detection limit is 10 ng [154]. Triphenylarsine formation is a more time-consuming method. But the combination of a gas chromatograph with a microwave emission spectrometric detector reaches a detection limit of SO ng/Iiter. The method is also applied for the determination of alkylarsenic acids [132,155], Atomic absorption spectrometers [134] and mass spectrometers [135] were also used as detectors of gas chromatographs. 

A thermal detector has a heat capacity H = 10 J/K and a thermal conductivity to a heat sink of G 10 W/K. What is the temperature increase AT for 10 W incident cw radiation if the efficiency P = 0.8 If the radiation is switched on at a time r = 0, how long does it take before the detector reaches a temperature increase AT(t) = 0.9 A Too What is the time constant of the detector and at which modulation frequency co of the incident radiation has the response decreased to 0.5 of its dc value ... 

With the development of photoelectric devices, the manual detection of null positions in polarimetry became superseded by instrumental measurements of the endpoint. As would be anticipated, measurements can be made far more easily and accurately using photoelectric detection of the null position. Early versions of automated polarimeters used the halfshade method, but the two light intensities were measured using photomultiplier tubes. The position of the analyzer was rotated until the difference in signals detected by the two detectors reached a minimum. Other methods have made use of modulated light beams, and variations on the method of symmetric angles. A wide variety of detection... 

The time response of a photoconductive detector is limited by the carrier lifetimes. PbS detectors for instance have time constants between 0.1 - 1 ms while InSb detectors reach a few us. For measurements of fast transient signals photodiodes are more suitable (see Sect.4.5.8). 

The most common GC selective detectors are listed in Table II together with their analytically important features. These selective detectors have been finding an increasing utilization in the analysis of environmental and biological mixtures. As seen from Table II, sensitivities at the low nanogram level are very common, while some detectors reach levels even below picogram amounts. Parallel uses of a nonselective and a selective detector are quite popular in chemical identification efforts. 

Any radiation reaching the detector that does not follow the optical path from the source to the detector. 

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