28.12.2013 Views

preface to fifteenth edition

preface to fifteenth edition

preface to fifteenth edition

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

7.38 SECTION 7<br />

TABLE 7.19<br />

Sensitive Lines of the Elements (Continued)<br />

Wavelength, nm Element Sensitivity Wavelength, nm Element Sensitivity<br />

196.03 Se U2<br />

194.23 Hg II V1<br />

193.76 As U1<br />

193.09 C U1<br />

190.86 Tl II V1<br />

189.99 Sn II V1<br />

189.04 As U2<br />

183.00 I U2<br />

182.59 B II V2<br />

180.73 S U1<br />

178.38 I U1<br />

178.28 P U1<br />

154.07 Br II V4<br />

134.72 Cl II V1<br />

are steady-state techniques, are compared with the electrothermal or furnace technique which uses<br />

the entire sample and detects an absolute amount of the analyte element. To compare the several<br />

methods on the basis of concentration, the furnace detection limits assume a 20-L sample.<br />

Data for the several flame methods assume an acetylene–nitrous oxide flame residing on a 5- or<br />

10-cm slot burner. The sample is nebulized in<strong>to</strong> a spray chamber placed immediately ahead of the<br />

burner. Detection limits are quite dependent on instrument and operating variables, particularly the<br />

detec<strong>to</strong>r, the fuel and oxidant gases, the slit width, and the method used for background correction<br />

and data smoothing.<br />

7.4.1 Some Common Spectroscopic Relationships<br />

7.4.1.1 Electromagnetic Radiation. Electromagnetic radiation travels in straight lines in a uniform<br />

medium, has a velocity of 299 792 500 m · s 1 in a vacuum, and possesses properties of both<br />

a wave motion and a particle (pho<strong>to</strong>n). Wavelength is the distance from crest <strong>to</strong> crest; frequency<br />

v is the number of waves passing a fixed point in a unit length of time. Wavelength and frequency<br />

are related by the relation<br />

c v<br />

where c is the velocity of light (in a vacuum). In any material medium the speed of propagation is<br />

smaller than this and is given by the product nc, where n is the refractive index of the medium.<br />

Radiation is absorbed or emitted only in discrete packets called pho<strong>to</strong>ns and quanta:<br />

E hv<br />

where E is the energy of the quantum and h is Planck’s constant.<br />

The relation between energy and mass is given by the Einstein equation:<br />

E mc 2<br />

where E is the energy release and m is the loss of mass. Strictly, the mass of a particle depends<br />

on its velocity, but here the masses are equated <strong>to</strong> their rest masses (at zero velocity).<br />

The Wien displacement law states that the wavelength of maximum emission, m , of a blackbody<br />

varies inversely with absolute temperature; the product m T remains constant. When m is expressed<br />

in micrometers, the law becomes<br />

T 2898<br />

m

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!