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~i~w mu~rA~Vf~LIDAIREAD-iNSTRUCTIONSAEPORT 0u.uinA~, -0 -, EFORE-_COMPLETINGFORM
1. REPORT," R 12. GOVT ACCESSIONNO.'. -RECIRIENT'S _CAT ALOG'NUMBER
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RkPO0RT ON -COMBINED MREETkING OF tHE XX COLLOQUIUM T~ncitpr
-SPECTROSCOPICUM ,LNTERNATIONALE AND, 1TH INTER- ;G.' PERFORMING ORG. REPORT'NUMBER
NATIONAL- CONFRENCE ON, ATOMIC SPECTRoSCOP~y - -
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international conferenceatomic spectroscopy
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C2 Lj Highlights of a recent international conference are presented. The confer-ence, which combined the XX Colloquium Spectroscopicum Internationale and thl
7th International Conference on Atomic Spectroscopy, was held in Czechoslo-
~ vakia from August 30 to Sept. 8, 1977. Although the meeting covered a number_____of facets of analytical chemistry and spectroscopy, this report emphasizes
those parts dealing with atomic spectroscopy. In the report, trends in thisfield are identified and important now findings related.
OFF~ICE OF -NAVL ARESEACH1
Task- No., NR '05l-622'
J'PORT ON iOMBINED XEETING OF TkHE
1P SLLOQUIU.PECTROSCOPICUH NTR TIONALE *$(W9
INTERNATIONAL CONFERENCE ON'ATOMIC SPECTRObSCOPY '4 )
ftitGAr N. ieftje
Ddpartmeht of Cheistry
Indiana University -
Bloomington, Indiana 47401
Reproduction in whole or in part is permitted for
any purpose of the United States Government
Approved for public release; distribution unlimited
V ~FomAug46t 8'. thriougli, September 7, 1917, a ho mb:Lned meeting I bean, tho
VX coilo~tiiuin>,Spectrdijcopiciin 'Iitetnai-ioiale and the 7th ihtetnatkinal Colw-
feence on- St'ifiic Spedtroscdopy was held in, CLechsos k1.oak The confereiicQ
was -unusual in. -±ts- formbat in that it -consi§ted. of two- ,ptirts. The IWUs paft,,
,Atefided-by .all cbnfdrees,-was iel In- Pkague, Czechoslovakia froi& August 30
'to September,197 In -this, pr fial. pdft 6f -the ijitekfnatidjnal, niceting ,
a tie numbek of topic. were coVered, inldg I thi I pc~cp. ~a
fluotes§cencej, mass spectromeotry, icroprobe analysis, vibrational spectros-
-copy~j Wk spe ctr6scoPY1,, radio -analytical methlods, Mbstqbauer 'spec tros copy,
Auger spedtioscopyi-elect-ton spectr6scopy,,_and the observation of phonon01S in
s6lids. Because of the large -number of individuals attending this conferenice
(over- 1200), as maniy As 13 sessionis were held simultaneously, making 'if difz-
ficult to obtain an overall feeling for the breadth of topics, being discussed.
In this repot, I will deal-only with important aspects of atomic spectroscopy
which were covered during this series of sessions, since those bear most dir-
ectly on our efforts being supported by ONR.
Following this principal congress, six special-topic "mini-symposia"
were held at various locations throughout Czecboslovakia. Of greatest interest
to individuals involved in atomic spectroscopy were symposium 1 on "opt Imiza-
tion of spectrochemical methods", symposium 2 on "spectrochemical analysis of
metals", and symposium 3 on "electrothermal atomization processes in atomic
absorption spectroscopy". In a later part of this report, highlights of sympo-
sium 3 will be related.
Overall, the principal con~gress and symposium 3 were well-organized, lo-1e Wks
cated in setthigs conducive to scientific exchange and well-attended by idiv- 130
'duals from throughout the world, In contrastL to 11oSt previous coirrelco, ''~
the locationA of th is mleetilig behind th10 Iron Curtain made it poss~ ble for many .. ..5ILITT CODES
AIna/i SPECIEL
2
'~tenEurpa and -Russian scien~tists, to attidl, thereby af fording :iii opipor
fuit for lnitethange which- ieldon arisds. Unfortunqteiy-, few seitlsts from
2the Uiited St~tes -wete able -t6 attend dndy it is, hoped that this report will1
Ofb~ide A udful oVerview- of, the pkoceedinigsi
gds616fns- were otganized- in, groipps -of -eight -talks,, -with An invited lec-tte
of '30'-finutes foilow~d -by seven submittied ,P~pefs. Ihvited- iectu~es liaive -been
-copiled in two volumes entittled " Proceedings of the XX ColoquiuchSpectroscopm.
icui Intefxiationale and- 7th Interniationali Conference on Atomic Spectroscopy" 4
4nd- is available ftom. the Czechbslovak Spectroscopic Society of -thle Czech~slo;-
V~k Acadeniy of Sciences, Pkagtue, Czechoslovakia. UnlikO in~ mos6t meetings-, al-i
P-1dftdty lectures Awere held on the same day, and were led'by a talk by Alan
Wlsh-of CSIRO-, Australia, on "Non-Dispersive Systems in Atomic Speetfoscopy.
Next, A.Ri Aliev, of the -U.S. S. R., spoke on "High-I esolutionh Vibration-- Rota;-
tion Spectra of Molecules". J. R~obin of Vfance then stimulated a lively di's- 1cussion with some comments on "What is the Fate of Internadtional Spddtroscopic
Contferehces". V4, Cer~iak of Czechoslovakia then delivered a lecture on "Elece-
tron Spectroscopy" and 0.11. Morrison of Cornell University considered "Elemental
Trace and Micru Aialysis of Biological Materials". Finally, 0. BfUmmar of the
Getman Democratic Republic spoke on "Developments and Trends in Local (Micro)
Analysis". Of these, the lectures by WAlsh and Moriisbnl are most getmane to
Atomic spectros copy and dese'rve further mention.
Walsh elaborated on a system first described in the Fifth International
Conference on Atomic Spectroscopy in Melbourne Australia, in 1975. The system
is extremely flexible and enables one to employ sputtering discharges (such as
a Grimm discharge or hollow cathode lamp) or flames in a variety of ways, in-
cluding their use as a primary sot;-ce of radiation, as an atom cell for gener-
-- ating atomic vapor f romi sample material, or as a resonance monochromator, For
3F
example, a nitrogen-separated air/acetylene flame could be used alternatively
as an atom- cell for atomic fluorescence spectrometry -or as a resonance mono
chromator in atomic emission; absorption, or fluirescence. When used as a
• resonance monhchtomator, th seParated flame serves to isola e a desired spec-
tral line from all. other background radiation falling upon it A detectbr(genera~iy a solar-bind photomuiplier), placed at an angle of 90 from
radiation -being directed onto :the zflame, detects, only radiation capable of
being absorbed and re-fluoresced by tile flame. therefore, the flame serves
as a monoc hromator which is specific for the resonance spectral lines of what-
ever atomisreside- wilthn the flame. In turn, because tile atoms residing in -the
flame can be varied merely by changing the identity of an aspirated aid n~ebu- -
lized iolution, the flame resohance monochromator is both versatile And selective.
In the talk by George Morrison, the importance -of trace elements in
biological materials was underlined and- methods currently available for the
analysis of such trace metals were compared. These methods included atomic
absorption spectrometry (AAS), electrothermal AAS, emission spectroscopy (e.g !
dc arc or spark spectroscopy), inductively coupled plasma tomic emission
(ICP), instrumenta. neutron activation analysis (NAA), spark source mass spec-
trometry (SSMS), and x-ray fluorescence (XRF). Morrison pointed out that
most trace elements now known to be essential were not realized to be important
as recently as seven years ago. Moreover, many of these same elements are toxic
when given in larger doses; consequently, the importance of accurate, rapid,
inexpensive trace element analysis is becoming increasingly important. Un-
fortunat 'ly, no single technique provided sufficiently high sensitivity for
all elements now known to be important. Overall, electrothermal atomization
AAS provided the best compromise of high sensitivity, acceptable accuracy and Iprecision, and low instrumental cost. Unfortunately, this technique is it*-
~4
-herently slow and could determine only one element at a tim ai'lkfing it some-
what uiattractive. in add.ition, the high cost and limited appiiication :tO
6thei biological materials than- blood serum makes the, inductively coupled
plasma- technique somewhat unappealifig. 'Nonetheless, Morrison. felt that these
.tWo techfiiques -.with, further development, would likely be the methods of
-choice for the determination of elements in. biological -matrices., Other efiher-
.ging techniques, such as microwave-induced , plasma (MlU) spectrometry could
alter the picture in the .future, however.
In the balance of the principal piart of the -congress, several trends4
'seemed evident. One approach, which seemed' t0 gain,'momentdm is the coupling
of atomic absorption-spectrometry and plasma spectrometry with separations
techniques such as liquid and gas chromatography. Such a combination enables
one ,to determine not only which elements ate present in a samnple but also to
determine the state of such elements or in what compounds they are bound.
:Speciation of this kind is becoming increasingly important in clinical studies,
anvironmental endeavots, and ia other areas; we are likely to see increasing
effort along these lines in the future.-
Another technique which appeared to be gaining momentum is Zoeman-modula-
tion atomic absorption spectrometry. In this method, a magnetic field is used
to split the atomic spectral lines in either a source lamp or in the atoms
generated from a sample into components which are polarized perpendicular~ly to
each other. By employing a rotating polarizer, it then becomes possible to
resolve the fine structure induced by the magnetic field. If such splitting
is inddced in the sample atoms, and if one of the resulting spectral ca3ipone:'ts
lies in the original location of the spectral line while the other, perpendic-
ularly polarized component is shifted, it becomes possible to perform back-
ground correction much mtore en:actly than with any other technique. Background
co ofi isci i-ci~d nmayaity s, eas f-h -(ninn etr)
Nefli, the techn';que Appears to -be simple to imnplem~ent and relativelay ifi"
6eheni;Ve to, install In conVenitipnel atomic ab§6fPt16n e juiprenti
Two, other trends, which ate evident and which wti Ibp underscored, by
d6mminents to be -made in the f ollow'iii paragraphs, ate thle entrefichint -of
relectrto the fmal aLomi~aLion techllL' uvu; 1t6 atomic abopif speet roscopy ad
tile continued' increase in etiusiasin Over plasma soueces. Althlough atoili
spectroscopists ate becoinig cognizant of the pitfalls of electrdthermal Aitom-
izatioii, the sebsitivity-, con~venience, and smfAll gampld i6eiuirements of theV
tehiqeoverride these objectii In thle artea of iductively coupled pla ;-
mas, one of the primary endeavors is tow~t'd under~tanting the plas~ma And td.
ducing its cost. In efforts to reduce the P Asmd' s cost, Attemplts are being
made to use lower powers, to employ more efficient plasma torches, and to
reduce the plasmats cooling gas (argoni) requirements. Mictowave-induced Olas -
inns w~ere ailso in evidence and their practicality was emphasized by thle intro-
duction of a ommercial MIP system by a firm called ED'L Research, loca~od in
the United Kiiigdom. In the following paragraphs, several papers highligh.4 ng
these trends will be discussed briefly. Because of space and time require-
ments, a comprehensive converage of the conference proceedings will not be
attempted; rather, specific lectures will be mentioned which Appeared to
of fer novel in.-3ights, unusual depth of understanding, or which opened up new
areas of interest to atomic spectroscopists.
inpper, #§7"', Pzofeggot (XAI.J. Alkcmhdde-dsued oe6fiscii
wok-,on, -Tser and flames. In paliticular-, recent ihVOAOrI-gat-0* 011-tif I
§AtUtdttoi Of A~tomiic -transitions was butlined and, tho Iiiflilie of, 11ht Lclm-;
Ojdfal- characteristics of the, saturation -pkdtd~g -wAtl emphas.*idd. 141wva
rel 1at i Vely long (Midcto$eq6fids); exciting laser jpulse is cimployed, fluorescene
-gdnerdtdd -uttde cddtiods -of nieatr-deegy-level s IatufAtioh exkhibited',a -a
-cay which was -attributed to ioniiati6fi of the forscing dtd § Additi6ni
of oxygen to the flame, increased the effect and' it was, 06§tulated that 6 the f
species hliiing 'high dlectcon Affinities would peo-dude the same 'behavior-.
Whei -this behavior exists, a ,plot of, fluo~rescence intensity V. iit
source power does not level 6ff as predifted -by-ordiniary satUr~tion -theory,
but continues to increase. Ai~thdk-intteresting observationi 1s that -the
AppAtent excitation spedtrum of atom§ obtained under 9Aturation conditions
i§, §ignificantly -broadened, the -reason for §udh broadening being thiat satura"
tion At the peak of the spectral line occurs first and reaches a limiting
Value while fluorescence at the wings of the line continues to-increase,
leading to an apparently broadened profile. In another interesting study,
Alkemade's group examined level mixing Which occurs upon twow-ph6toh excita-
ti6n in sodium. A diumber of excitation transitions wete induced by a two-
* -photon process and fluiorescence was observed from almost every state which Vwas examined. This unexpectedly high degree of level mixing could explain
the surprisingly hiigh inc ident. source powv L wi i Ls r i-eqird to Sa LtraLIc
many atomic transitions.
In paper #13, Paul Boumans and coworker delloer addressed the question
of ionization in an inductively coupled plasma. Such plasmas exhibit both
high electron and ion concentrations but a relatively low susceptibility
to ionization interferences. Moreover, the ratio of ions to atoms in such
Li
a plasa-i ii 1,73 orders of magnitude higher than would-be predicted by a mbdel
-based- i n, lcal thermodynamic equilibfium4 According- to. Bouman. these obseet
vati0&L§ can be: explained by vie-ing argon metastable atoms both as ionizers
Aft ad ii~afitS. that' is, the h~igh energy (11.55- -1.-71' ev), of metastab-leargon is beiw the grouhd state energy (:15.75 eV5) of ai argon ion. 'herefore, A
the- rgon metastable energy ,is high enough to o Ize iniany atotls through col-
lisins (i.e. Penning iOnization), -but is also capable of being thermally
ionized itself. Because the predicted condentratin oif argon metastable ions
in an ICP is high (1014 per cubic centimeter), it could play a dominaht role
in determining the overall ion concentrations in the pIAsma and might account
for the unexpectedly high ion concenttations;
in two papers dealing with torch design and operation in an tCP,. R;M.
Barnes (paper #7) and Kornblum and deGalan (paper #8) found that ICP torches
could be operated at relatively low gas flows and input powers, Simply by
slightly modifying the torch. Through theoretical modelling, Barnes found
that an increased cooling gas swirl velocity should reduce pressure in the
dis diarge and thereby require less coolant gas flow. Accordingiyj the inlet
tube for coolant gas was constricted and placed at an angle to increase the
swirl velocity. With this modification, the linear coolant velocity was
between 8 and 10 meters per second at a flow of 5 liters per minute; at a jcentral (aerosol entry) flow velocity of 50-60 meters pet second, the
torch could be operated at 0.95 kilowatts, whereas a central velocity of J30 meters per second required only 0.5 kilowatts. Kornblum and de Galan Jdiscovered that an increase in the central tube channel length (where aerosol
is introduced) made the central gas flow more laminar and narrower in its
velocity profile, resulting in a better penetration of the plasma by aerosol
species. This modified central tube was placed 2 millimeters below the lip
of the adja.ceftt coicehtkic.,quart7- tube. With -this modifltcatidn, the gfeatcise
signal was four-' at, the lowest opetable deiitkal flow, Afid t lobw -(0O.5 kilo -
watts) input power.- However. the grdatdst line-to--backgrbufid ratio was tfdund
at higher powers. (1.5 -kilowatts) anid- at relatively hiigh central -fi6w, -(2
liters per minute),,.,
John~ C. Travis -and, h i! -cowotkets -at the 'NdtionI: Murdau -or- Standnrds p
described- some of their recent work in-6pto~galvanic spectroscopy.- ThLs -tech"~
-niqut,, whose name should .perhaps be dh~nged to something like photon- asgis ted
ionization, was- firstdesctibed in ,Physical Revie , Volume 26, page 195 (1925).
lloWdveif, the NBS group- was the first to Attempt to exploit 'the phenomenon, f 6f
.anAlytiddl use. In the new configuratilon, two rods ser.Ving as electrodes
were placed OUtSide a flame and one oentimeter above the burner top;, a vo-lvage
is- then applied between the rods (Which aee cathodic) kind the buftier Lopl)
(which is grounded). When atoms ate introduced into the flame in a manner
idenitical to that employed, in AAS, And a. laser tun ed to a spectral line of
those atoms beamed through the flamie, a change iii current between the elec -
trodes and the burner top is detected. Although Travis did not dwell on the.
mechanism of the phenomenon, it probably arises through thermally induced
and photon-assisted ionization. That is, although some atoms will be tlier.-]
mally ionized in the flame anyway, the number of ions which are pfoduced
is increased by raising a substantial number of the atoms to higher energies.
through laser absorption. At present, use of this technique for analysis
appears limited in scope because of high background ionization which exists
in most flames and because of the large influence on ionization to be ex-
pected by concomitant elements in a typical sample. However, Travis indica-
ted that a large number of transitions not commonly employed in atomic spec-
trometry can be used in opto-galvanic spectroscopy, making it poss5ible to
eOmploy, a natrower range of laser wavelengths thah would -othe~i§e be rez
qUired. This Advantage is. ignificant i.n laser spectroscopy, because -of
-the limited-' wavelength range- over which each dye can -be emoloyed in a-
~tyidal laser. Iin 'symposium 3. following, the main -cofigress, the dominanit Obeme wa', the
examination--Lof atomizaition mLechafijsms In electteo-tefitcrw aitomic abhoeptioi
spectrometry., Unfortuhately,, most -of the letures. 'whlch- were presented
conitained only- material which -had been discussed -bef 6o- or was available
in- the open litetatutdi. in Addition, miost of the mechanisms which -have
beeri proo-sed are-merely simple mdifications -of theoriesproposed earlier
by,-BV. -L'Vov, and& which -are expOldined, in detail aid- with clarity in his ]b66k-(tdi Absorption, Soectroscooy, translated from th'e 'Russii~ 6id dvail-
Able from the National Technical Information, Service, Springfield, Virginia "1
22151).
An, interesting variant on -the -atomization mechanism theme was the paper
~Presented by-Leo de Galan (papef4-542) who realized that the observed time
behavior of atom concentration above an electrdthermadl atomizer can be des- i
ctibed as a convolution of the atom supply rate (,Vaporization rate) - and the
atom removal rate. Accordingly, -the two functions were separated and ina6-
suked ifidependently arid the resulting convolution compared with observations.
To measure the supply function, atoms were remjoved rapidly from the region
above an electrothietmal. atomizer by rapidly flowinig gas through the atomnizer
observation region. The atom removal function was obtained by stopping the
gas flow and adding atoms to the observation region extremely rapidly (through-
flash volatilization of rapidly vaporizing elements such as mercury). For
the supply function, these workers found that simple first order release
kinetics don' t accurately describe observations. Also, the removal rate is
only a function of gas temperature, indicating that no wall process is involved
10
(tleast for mercury). Although the resulting mathemtical d6nivoutioin of
Atom release and remfo.val funictions appear -sifiilAk to ob~efed atoi-, concen-
tration-timde behadvior,, the -approach -is lim.tdi cp.Secfcly
4atoms -appear to hdvOe -dif fere - imoval functions, -perhaos. caused by changes
,in-adsoiption on the walls -of the dectrothermA1 atoizier. Fo6r e xalp Le, tho,
measu'red, leAd atom supply fuinct16n-, convoluted with a -morcury removal. -unc-
tionh does not- have the, saiie- aopnearance as the observed atom, concehtfation
vs.- t-iinelot. Work is procedding to ovefctome this liitation. In- an
interesting, final comment, de Galan noted that optimfal results ifi-the Use
of ele66ttothermial atomizers woul~d'be obtainid '-whein the time constant for
supply exactly dqualled-the time conistanft for release 6 result which could
be accomplished by heating an electro.thermal Atomizationt c-ll At a rate of4
Approximately, 10001K per second And to, use a, tube -(for 6, Varian CRA 63
system) whidli is 5 centimeters long and 4 iiii~etets inside diametek.
In perhaps the most innovative talk of the mihini -symp6§ium, RAY W6odriff
(paper #544) described some te cent work using a cons tant-tefinpefatufe graphite
furnace atomizer (Appropriately termed the "Woodriff furnAce" ). Wi th such
Aatomizer, the time required for atomizatibfi can be relht~d to th e total
length of time required for a constant number of atoms to enter and depart
the atom reservoir. To obtain the Appropriate measurement, the observed
time behavior of Absorbanice is measured and A line drawn across the resulting
plot at A lower, fixed absorbance level. -Btcause this absorbAnice represents
a fixed atom concentration in the cell, the length of the drawn line can be
unambiguously related to the atom cell's time constant. Moreover, because
a single time constant implied loss of atoms through a diffusion process
alone, a plot of the length of the straight line vs. sample weight should
be linear. If such linearity is not observed, a sample loss mechanism other
Z Z7111
than diffusiofi must be operative. 1 a related study,, Wiootrifi aud :NM'rilkovic
examined the, migration of atoms vaporized from -a cons anL~temperaUire
furnace. h :their measurements, such 4 furnace was operated in its normal
way., but -allowed to cool before atomizaftion was complete. The tube was
then cut into segments and the distribution of atoms Along -66 length of'
the tube de~trmihed by conventional atomic absorption sp ctrom ,try. Wood-
riff postulated that this distribution, which was different from elemenit
to element, -could be emjloyed as a kind of "atom chromatography" (mny term) I
and might enable one to overcome sample mattix interferenices. Of course,
the, technique would not be applica lie to elements such as silver and cad"
mium, which are lost primarily through diffusion rather than through ab-"
sorption, although other elements such as potassium and aluminum could be
separated readilyi
Although the foregoing account is highly selective and provides only
an overview of the proceedings and content of a prestigious international
conference, further information is available in the articles cited earlier
and from the individual authors. in addition, the author of the present
article would be happy to supply further information, if it is desired.,i
IiIi
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Dr. E. E. Wells China Lake, California 93555 1Naval Research LaboratoryCode 616oWashingon, D.C. 20375 1
Dr. D. L. VenezkyNaval Research LaboratoryCode 6130Washington, D.C. 20375 1
Dr. If. PreiserUniversity of Ari{onaDepartment of ChemistryTuson, Arizoa 805725
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