โ Scribed by R.R. Brooks; C.R. Boswell
No coin nor oath required. For personal study only.
IZeforc the intr~)du~tion of cathode-layer cxcitntion in the D.C. arcI, anode excitation was the usual tf2i:tinicpe in spcctrochernicnl analysis. Although the use of ancJdC! cscitation derlincd s<>mc\vhi~t following the discovery of the cathode-layer effect, it has been more widely usctf in recent years and both mctflotls would appear to b,e of equ;\l interest today. Little has been pubiist~ccl on :L comparison of the z mctbo 'I'nur.orc~ have, liowc\*cr, used the data of a number of indol~r?nclcnt workers to compare anode ant1 c\*~rti~otlc-layer cxcitntic-rn ant1 have conclucled that the advantnges of catt~rAAaycr excitation have been overstated in the l>iLSt. 'I'licy appear, on balance, to fnvour anode excitation but stress the difficulty Of making compnristrns on tlnta obtnincd uncicr cliff~r~nt ex~~erirnetlt~~l conditions. Ttle met-its,of either of the z methods h;lsc been ttiscusscd by scvcnrt other workers+". STRASHE~M AS t) C,\BI'I~RDR" have comparccl ;modc and cathoclc-lngcr excitation for the analysis of Cr, Co, Ni, 251, 'I?, V, Sn, Mo and 1% nncl conclude tliat the prccisions ohtninrrblc by the t\vo methods arc similar. l-Iowcvcr, their conclusions arc based solely on the slr~pes of working curves for tlic various line pairs and bear no rclatinn to coefficients of variation of rC?pliCilte arcings. SKoHXYAI<o'~O has cliscusricct the relative volatilisntion of some x5 elements in nnode nncl c:&hode-layer excitation.
The purpnsc of this paper is to examine the potcntialitics of cathode excitation (as distinct from cathode-layer excitation) irt spcctrachemic~~l analysis nncl to compare it directly with anode cscitation under the same experimental conditions. In order to obtain ZL rn~~l~il~~ful comparison nf the z techniques, the following properties were studied: absolute sensitivity, times required for complete consumption of the sample, rates of volatilisation, times for complete volatili.sation of each element, background intensities, self-absorption and finally, the r~l~r~~cIucibilit~ of intensity ratios of it number of line pairs in 3 different matrices. Although ttlc results will only hold for the experimentat conditions used in these studies, there is little reason to supl~osc that they will not apply to a much wider range of experimental conditions. A study of spectral longitudinal intensity distribution was not carried out since this is already well known" and morcovcr, the optical system of the spectrograph was arrangecl to provide uniform illumination at the slit. No study was made of arc temperatures as these have hcen invcstig:lted by many other worker+-16.
๐ SIMILAR VOLUMES
A system ensuring the initial stability of conditions for the emission spectra of plant ash is achieved by the use of a carbon cathode and a graphite anode in an oxygen atmosphere. The selected shape of the graphite anode located on a water-cooled base partially controls the volatilization rate of %