Electrodeless Discharge Lamps - Instrumental Analytical Chemistry - Lecture Slides, Slides of Analytical Chemistry

Download Electrodeless Discharge Lamps - Instrumental Analytical Chemistry - Lecture Slides and more Slides Analytical Chemistry in PDF only on Docsity! Electrodeless Discharge Lamps Docsity.com What are they made of? • Sealed quartz tube • Filled with an inert gas (Ar) • Small amount of metal or its salt Docsity.com What it provides • Provides radiant intensities in greater supply than a Hollow-Cathode Lamp (HCL) • Not as reliable as the (HCL) • But better for elements such as – Se, As, Cd, Sb Docsity.com Source modulation • Emitted radiation is removed via the monochromator • It is necessary to adjust the output the source so intensity will fluctuate at a constant frequency Docsity.com • Detector receives 2 signal – An alternating from the source – Continuous from the flame. These signals are then converted into electrical responses A high pass RC filter (section 2B-5) can be used to remove unadjusted signals Docsity.com Single-Beam • Several hollow- cathode sources • Chopper or pulsed power supply • Atomizer • Simple grating spectrometer with a photomultiplier transducer • 100% transmittance is set with a blank • The blank is replaced with samples to determine absorbance and transmittance Docsity.com Double Beam • Beam from hollow-cathode source is split by a mirrored chopper • One half passes through the flame and the other half goes around it • 2 beams recombine by a half silvered mirror and passed into a Czerny-Turner grating monochromator • Photomultiplier = transducer • Output = input to a lock-in amplifier • Ratio between reference and sample is amplified and fed to the readout • Since reference beam is not passed through the flame it cannot correct for loss of radiant power due to absorption or scattering by the flame Docsity.com