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Ind ian Journal or Pure & Appli ed Physics Vol. 37. September 1999. pp. fiR9-fi9H

A new approach in identifying very prominent polyaromatic hydrocarbons (PAHs) in petroleum fractions using second derivative

synchronous excitation fluorescence spectroscopy (SDSEFS) I

V Swal11 inadhal11 , C Santhal11l11a*. C V Rama Sa~try, G Viswanaclh & Y L N Murthy

Andh ra University. Visakhapatnalll

and

Pradeep KUI1~ar

Indian Institute of Petroleum. Dehra Dun

Received 13 August 1998: revised 22 June 1999; accepted

A new method called second derivative synchronous excita tion Iluorescence spectroscopy (SDSEFS) is applied to identiry

promi nent PA Hs in three petro leum rractions in the ranges 350- 370°C. 375-400°C and 400- 53()°C. In the ri rst rraction (350-

:170°C) anthracene. 1.2- hellz'lI1 thracene. tluoranthene. phenanthrene and pyrene: in the second rracti on (J75-4(XlOC) anthracene.

1.2- henzanthracene. chrysenc. Iluoranthene and pyrene and in the third fraction (400- 53()OC) anthracenc. 1.2-benzanthraccnc.

chryscnc. fluoranthene and pyrene could he iderHil 'icd .

I Introduction The method o f sy nc hronous excitati on flu orescence

spectrosco py (SEFS) is appli ed for the first time by

Ll oyd 1· -1 to study the forensic research. Its applicab ility

in simul taneous ana lysis of mUlti-component mixture

has been successfull y take n up in a seri es of in vesti ga­

tions by T uan Vo- Dinlr"X, Sy nchronous flu orescence

spec troscopy is c lass ifi ed in to three types')

( i) Sy nchrono us exci tati o n flu orescence spec tros­

copy in whi ch a constant wavele ngth inte rva l 6A is kept

constant between ""'Ill and ""'X with the same scan rate o f the monochromators. Thi s is considered to be s imple,

e legant, sensiti ve , se lec ti ve and is the most commonl y

used tec hnique; (ii ) Constant energy sy nchronous fluo­

rescence spectroscopy mainta ining a constant frequency

d iffe rence varying s imultaneously the exc itation and

emi ss ion wave length s. ( iii ) Va riabl e separati on sy n­

chronous excitati on fluorimetry dea ling with the vari ­

a t io n o r exc itati o n an d em iss io n w a ve leng th

simultaneous ly, but at d iffe rent scan rates .

T he first method is app l ied qual itati ve l y and q uanti ­

tati ve ly as we ll as in detec ting simultaneously the com­

ponents o f a sy ntheti c mt xture in automobile engine o il.

c rude o il s1o, soots, pet ro ls. ex haust depos its, tars, petro­

':' Principal Investigator. CS IR Project. Departmelll or Ph ys ics

leum residues, o il spots, rubber, o il po lluti on, rubber

pollution , wate r pollutio n and as a matter of fact mi x­

tures containing severa l polynuc lear aro matic hydrocar­

bon s, s u c h as a nthrace n e, b e n zo-a-py re ne ,

be nzo-e-pyrene, 2,3-be nzoflu ore ne, c hrysene, 1,2,5 -

di be nzanthracene, d i be nzo thi ophe ne, f1u oranth enc,

flu orene. phenanthre ne, pe ry le ne, pyrene. etc . Sy nchro­

nous luminescence spectroscopy is a lso used in severa l

applicati ons of bio logical and environmenta l interest.

ll1is method is a lso app li ed in the de tecti on of clrugs and

metabolites simultaneously. The theory of the sy nchronous spectroscopy is we ll

de veloped by Tu an Vo-Dinh . For the applica tion o f thi s

method one has to necessaril y have a Data Bank of the

synchronous spectrum where in a particul ar sing le line

is considered as the monitoring frequency of that COI11 -

pound to be identi fied . Based on SLich finger print va lues.

fo r eac h PAH, as deri ved under spec if ic condit ions of

in vesti gati ons, a search, fo r the presence o f such peaks,

in the mi xtures of di ffe re nt concentrati ons, in the syn­

c hronous spectra recorded at d iffe rent 6A va lues (con­

stant diffe re nt wave length pa ramete r) in solut ions or

suitable solvents, revea ls the presence or otherwise of

the compound in a mi xture . Whil e extend ing thi s method to mi xtures one may

come across a number of peaks which need to be iden-

690 INDIAN J PURE APPL PHYS, VOL 37, SEPTEMBER 1 999

tified again with the help of the data bank of the deriva­tive spectra and also with the help of spectral records of the excitation and emission of basic compounds . So far, in the appl ication of SDSEFS, the investigations have been confined to the s ingle peak synchronous value whereas the authors have extended the confirmation of presence or otherwise of a compound in a mixture not only by the single peak, which may correspond to pure electronic transition but also to the peaks concerned with vibrational transition as wel l . The latter can be clearly obtained by varying either the concentration of the so­

lution or the t1"A value which is the synchronous parame­ter. As far as the authors are awart; of, such an approach of identification through vibrational components has not been so far attempted, by any investigator. Whi le such a vibrational component is always avoided by others, in the present investigations it i s interesting to note that such appearances in the spectral features of the synchro­nous spectrum were also cons idered as equal ly as a guiding factor for the confirmation of the compounds in a mixture.

In the present paper, the authors attempted to identify sign ificant PAHs that are present in three different cut

fractions in the ranges 3S0-:nO°c, 37S-400°C and 400-530°C, obtained from the Indian Institute of Petroleum, Dehra Dun . The detai l s of the experimental method, the spectra recorded, analysis presented, the results ob­tained and the conclusions arrived at, are a l l described below.

2 Experimental Details The spectra have been recorded on Perkin-Elmer

LS-SB Luminescence Spectrometer. A 8.3W xenon arc lamp is used is used as an excitation source. The detec­tion devise is a standard photomu ltipl ier. The wave­length accuracy and repeatabi l ity are +1- 2 nm and +1- I nm or 1 0 nm s l its, respectively . Thi s instrument has been interfaced to a computer through RS232C port. Al l the spectra have been recorded on DeskJet printer. The scan speed is set at 480 nm/min and s l i t widths of the excita­tion and emiss ion monochromators are 2 .5 nm each.

2.1 Reagents

All the basic compounds investigated in the present study are of very h igh purity (suppl ied by Aldrich Com­pany) and are used as they are . The basic compounds studies are anthracene, I , 2- benzanthracene, chrysene, fluoranthene, phenanthrene and pyrene. The sol vent used is cyclohexane of HPLC grade. For basic com­pounds the concentrations of 1 0- 1 M, l a-

2M, 1 0-3 M,

1 0-4 M, 1 0-5 M and 1 0-6 M, in cyclohexane are prepared and for additional conformation other concentrations are also made u se of, if necessitated . In case of cuts, the

solutions are prepared '\) ( in ml) I V ( in ml) , where '\) i s cu t volume and V i s the solvent volume. The concentra­tion used are I m ll4 ml , 3 mll2S ml , 2 m l/2S ml , I ml/2S ml, 0.1 mll2S ml, 0.OIm/2S ml and 0.002 mll2S ml , any intermediate concentration or further d i l ution of the concentration is also considered as and when it is found necessary. The experimental work consi sts of two parts:

( I ) The preparation of Data Bank of anthracene, fluoranthene, phenanthrene, pyrene, chrysene and 1 ,2-benzanthracene in different molar concentrations in cy­clohexane and recording of ( i ) their excitation and emission spectra ( i i ) gross SEFS at different constant

values of /),"A fol lowed by their smoothened second de­rivat ive spectra. (2) the second palt of the experiment is on the three different cuts . The gross SEFS for each cut in different concentrations are recorded which are s imi­larly fol lowed by their smoothened and second deriva­t ive spectra. The experimental deta i l s on the basic compounds and the cuts, the resu lts obtained, the discus­sions carried out for the final analysis of the spectra to detect the various PAHs in each cut are presented .

3 Discussion It is presented in two parts . Part A deal s with the Data

Bank of bas ic compounds and Part B deals with the identification of basic compounds in the cuts .

Part A - The Data Bank survey of the basic com­pounds anthracene, 1 ,2- benzanthracene, chrysene, fluoranthene, phenanthrene, and pyrene, which are l i kely to be present i n the cuts consists of the fol lowing steps: (a) The excitation and emission spectra of all the basic compounds at different concentrations are re­corded, to have an idea of the range, overlaps and structure; ( b) The gross synchronous excitation spectra are recorded for each concentration varying the synchro­

nous parameter /),"A which is bei ng maintained as con­s tan t w h i l e s can n i n g s i m u l taneou s l y both the monochromators. From th i s one can infer a single peak, or the variations in the spectral appearance. With in­

crease in the value of /),"A the spectra are found to be shifted to violet s ide; (c) The second derivat ive of gross SEFS is recorded to study its fi ner detai l s . The immed i­ate smoothing of the second derivative spectrum is carried out to record the specific values of the spectra peaks, which are final ly considered . By way of an i l lus­tration the gross SEFS spectra and the corresponding

SWAMIN DIIAM eud:POLYAROMATIC HYDROCARBONS

GROSS SYNCHRONOUS SPECTRA IT 'S SECOND DERIVATIVE SPECTRA

r 1.-----

375

~ bA ~03nm

t:--! !

373 6nm

373

:l

U [ (1]

20nm

W >-f-

(f)

Z W f-

3&0

Z I

I 3 52

r ~' 50nm

328 75nm

327

250 300 350 400 450 250 300 350 400 450 500

WAVELENGTH (nm)

f'i 1! . I - Anth racene synchronous and its second derivative spe(, tra at dirfcrent boA valucs at conc I O- 'iM in cyclohcx '1I1C

smoot he ned second derivative spec tra for 10-5 M, an­

thrace ne, are g ive n in Fi g. I .

A ll the above detail s wi ll constitute the complete

Data Bank fo r the g ive n molecu le and a re final ly con­

sidered fo r a compari son w ith the derivat ive sy nchro­

nous spectra obtained in the c ut s for a sea rch of each

molec ule. The second deri vali ve spectral detai Is of all

the s ix compounds at d ifferent conce ntrations are pre­

sented in Figs 2 and 3 . From the spect ral characteristics

of the basic compounds as obtained from the Data Bank ,

the following points are of significance. Synchronous

spect ra show characterist ics details of the following

nature:

(a) As the concentration decreases the synchronous

s ingl e peak is shifted towards viol e t. A similar feat ure

is observed a lso when t:.."A is increased at any concentra­

ti on of the so lution . It is inte rest ing to note that the

appearance of the exc itati on bands coul d be prominently

obse rved in the sy nc hron ous spectrulll recorded at

hi ghe r va lues of t:.."A. This feature is found to be common

at all conce ntration s; (b) 1n gene ral , a si ngle pea k i ~

observed at lower values of t:.."A which is considered to

be the finger print for the molec ule unde r cons ideration .

INDIAN J PURE APPL PHYS , VOL 37, SEPTEMBER 1999

ANTHRACENE

rowe. 1 M 6~ ;10 nm

CONe . 0.5101 3nm

CO IJC.10-' M 10nm

- 3 10 M '3 nm

-4 CON C. 10 M 3 n m

- 5 CO NC. 10 M 3nm

350 400 450 500 WAVELE NGT H (nm)

l,2-BENZAN THRACENE _2

cowe. 10 M 6 ~ ; 3' nm

- 3 CONe.10 M 30nm

-4 IllNC. 10 M 30nm

- 5 CO Nt 10 M 30nm

~ 300 500 700

CONC. 10- 51'1 90 nm

- 6 - CON C. 10 iii 90 nm

250 350 450 WAVELENCTH ( nm)

CHR YSENE

W"F om -3

CONC . 10 M 50nm

- 4 CONC .10 M 5Gnm

CO~C . 10-6

M 1.0 nm

250 350 l,50 WAVE LENGTH ( nm)

rig . 2 - Data bank or <lnthr.lCcnc. 1.2-bclll<lnlhraccll c :1Il cl chryscnc

SW AMINADHAM I!( al:POL Y AROMATIC HYDROCARBONS

FLUORANTHENE PHENANTHRENE PYRENE _2

CO~C. 10 nmA1=3nm _ 1

ctlNC.10 M H = 20 nm

- 3 COWL 10 M 10nm

~ -3

FFm: 3:m

- 2 F,m I , " , ,

r

- 3 CONC 10M 50 n m -

CONC.10- t. M 50 nm -4

CONC .10 M 50nm

-,

! ! ! I

350 450 - 5

CONC. 10 M 50 nm -6

CONe. 10 nm SOnm - 5

CONC.lO M 50nm

250 350 450 300 400 500 - 6

CONC .10 M 75nm WAVELENGT tl (nm) M 30nm

~ 3 DO 400 WAVELENGTH (nm)

-6 CONt 10 ttl 50 nm

ZSD 35 0 450 WAVELENGTH (o m)

Fig. J - Data bank of Iluorantilcnc, phcn:lnthrenc illld py rcnc

<194 INDIAN J PURE APPL PHYS, VOL 37, SEPTEMBER 1 999

In certain molecules a single peak in the synchronous

spectrum is observed only at higher values for D..'A which is, i n general , found to be the characteristic of the excitation spectrum. This peak is however observed in the synchronously scanned spectrum as a prominent one and can be considered as finger print .

As a first step by considering second derivative spec­tra of anthracene at various concentrations and for vari­

ous D..'A values. a search is carried out to pitch upon a single prominent peak probably observable at l owest

possible D..'A values. If in any case the peak is observed along with additional structure then a cont inuous search is made through the various D..'A values unti l a prominent single peak is observed . This feature can be treated as replacement for the former observation . The same pro­cedure is adopted for other molecu les as wel l .

Some of the basic compounds could not be prepared at higher concentrations. Even though higher concentra­tions are prepared for some compounds, a gross synchro­nous spectrum cou ld not be recorded . I n certain molecules the spectrum could not be recorded ti l l a particular D..'A value i s reached . In al l such cases also. the result ing single peak value can be taken as a prominent identifying feature. In addit ion to these, i t is felt that the synchronous spectra of each molecule at different values

of D..'A also characteristical ly show significant derivative spectra. A l l such peaks are also to be taken as additional Data Bank against each concentration, which are equal ly important in confirming the molecule. These are shown in Figs 2 and 3. The Data Bank* thus prepared is made use in identifying the PAHs in the various cuts.

PW1 B - Analysis and Identification of PAHs in various cuts :

The fol lowing procedure is adopted to establ ish cor­respondence between the concentration of the basic compounds and that of the cut through the ident ification of the finger print of the compound as gi ven in the Data Bank : ( I ) The search. for s imi larity and consistency of the spectra recorded for both the higher through lower concentrations of the bas ic compound with the spectra of the corresponding concentrations of the cut, is made

for the same D..'A value . This procedure is adopted for the

spcctra at a l l correspond ing values of f..'A; (2 ) Use of addi tional Data Bank i s a lso carried out with a view to observe certa in prominent features which are a l so read­i ly recognizable i n the cuts . This add itional Data Bank genera l ly consists of peaks belonging to ei ther exeita-

':' Data Bank is ava i lahle wi th the author

tion or emission bands (vibrational) of the basic com­pounds; (3) As the first step the single peak value of the

spectrum at the lowest D..'A (electronic) is concentrated. If it is found necessary the i dentification of compound, is carried out with the help of the excitation and emission

bands which are observed at higher D..'A values. I f at the

lowest value of D..'A the synchronous spectrum is showing structure then it necessitates one to look into the spec­

trum at h igher D..'A values for a single peak. An example of anthracene is detailed below:

In the SDSEFS of anthracene solutions at highest

concentration (1M) investigated, the peak is 399 nm (D..'A = 3 nm). A search for this peak at D..'A = 3 in the cut- I cou ld be noticed at 3 ml/2S ml and 2 mll2S ml as 398

nm and 399 nm respective ly . I t is not observed at higher concentration of the cut- I i .e . I mll4 m l . Proceeding to the next concentration ofO.SM, the peak observed at 396

nm can be compared with the peak derived at 1 .5 mll2S ml of the cut. It is noticed that the peak at the lower concentration of the anthracene could not be very promi­nently observed even at lower concentrations of the cut- I . It is also noticed that the basic anthracene peak value is not changed in lower concentration ( i .e . ) 1 0-4 M downwards. These matching detai l s are needed for the final analys is . The presence of the finger print peak can

also be seen i n the spectra recorded at various higher tJ.'A values. with a shift to violet . These resul ts throw l ight on the fol lowing:

( i) The presence of the anthracene in cut- I ; ( i i ) an approximate concentration of anthracene in a specific concentration of the cut: ( i i i ) an attempt to study of higher concentration more than I M for anthracene may not be of much use as the variation of the excitation peak is not very much different in 1 M, O.SM and 10- 1 M solutions; (iv) beyond 1 M concentration it may not be possible to detect the presence of anthracene as such if the cut contains more than this concentrat ion, one has to d i lute the cut suitabl y to detect the anthracene; (v) if at a particu lar concentration any compound is not detect­able then it does not mean that it is not present in the cut but it necessitates one to experiment on different con­centrations of the cut as wel l . S imilar procedure is adopted for detection of f1uoranthene. phenanthrene. pyrene and I ,2-benanthracenc as wel l . Thei r presence is a lso estab l i shed by usi ng the addi tional Data Bank as wel l in cut- I (Fig . 4) . It i s felt necessary that the absence of chrysene in cut- I needs to be estab l ished.

Chrysene - From the total survey of the second derivati ve spectra of the cut- l taken at various concen-

SW AMINADHAM el ai: POL Y AROMATIC HYDROCARBONS 695

CUT·1 3ml/25ml 6~=-10 nm

FA ( 10- Z M) ( 407)

350 450 550

-2 FA 10 M 10 nm

395 406

350 450 550 3~ 450 550

CUT-1 0.002ml/25mI03 nm CUT·1 0.002ml/z5 mL 50 nm

: _ 6 AN (10 M)

350 450 250

i . __ AN(352) \, --!"--o::::FA(10-s M)(35S )

',_ . .. - 1 . 2-~ (1O- 6M)(340) " Py 10- M (333)

___ _ PH(lO- s M) (297. )

350 450

_ 6 An 10- 6 M 50nm PY 10 M 03nm

305

377

352

1.2-8 10- 6 M 50nm

-6 PY 10 M 50 nm - 5

PH 10 M 50nm -6

FA 10 M 50nm

361 295 334

250 350 450 250 350 450 250 350 450 WAVELENGTH (nm)

Fig. 4 - Idcntification of PA Hs in cut-!

trat ions and at various 6A values it is not iced that at onl y

one concentration i.e. 0 .5 1111125 1111 a sl11all peak of 36()

nm could be noticed at 6A= 3hl11. II' one considers thi s

peak as due to chrysene, the characteri stic strong peak

or 332 nl11 at 6)\. = 30 nm or IO-J M of chrysene also

should be present in the cut - I . The absence of thi s

feature exc ludes the presence of chrysene up to 0. 1

mll2S 1111. For further diluti ons of the cut, if we have

taken the concentration of chrysene as 10-1 M in the

concentrati ons of the cut ranging 0.5 mll2s mlup to 0.1

1111125 ml one should have observed at 6A =50 nm and

6A=90 nm peaks of va lues 3 13 nm and 29 1 nm respec­

ti ve ly. The absence of these confirms the absence of

chrysene at 10-1 M. The same feature is observed in

f urther di lution of the cuts in which a search is made for

the presence of lower concentrat ion of chrysene. A

INDlAN J PURE APPL PHYS , VOL 37, SEPTEMBER 1999

CUT-2 0.1ml/ 25ml Ll;\=30nrn

CR 1()4rvx3S?) .> 1,2-Bl0-~(379·) ______ AN 10- zM ( 3B7)

_2 - AN 10 M 30nrn

_2 1 2 - B 10 M 30nm

_4

CR 10 M 30 nm

- 1 r PY 10 M 300m r= 300 400 300 400 500

CUT-2 0.002mi/25mt03nm CUT - 2 0.002 mlj 25ml 50nm

p~ . ,-- -- --- __ __ FA 1O: 5M(356) .: -- -- - -- - - - -- . An 10 - M (345) , . _ 4 ,.-- -- - --- ---12-810 M(337) , __ __ ___ PY 10- 6 M( 330)

--- - CR 10- 5 M(312) 1 t , !

-6 PY 10 M 3nm

- 4 1,2 -8 10 M 50nm AN 10- 4 M50nm

~~ FA 10- 5 M 50nrn 50nm

250 350 450 250 350 450 250 350 450 550

WAVE L ENGTH ( nm)

Fig . .5 - Idenl ifical ion 01' PAHs ill clll -2

sea rch in thi s manner definitely confirms the absence or

chrysene.

I rien l ijic{f/ iOI7 oj' PAHs ill 1'111 -2 - Sim il ar procedure

is ex tended to search 1'0 1' the basic compounds in cut-2

keepi ng in v iew he basic Data Bank , additional Data

Bank and al so LI compari son or the spectra details of the

basi c compounds identified or otherwi se in cut- I wi th

those identiried in cut-2 . 1n thi s manner, anthracene,

I ,2-benzanthracene, f1u oranthene, and py relle, could be

identifi ed. While the presence of chI' sene could he

prominently detec ted, the absence o r phenanthrene i<,

also signifi ca ntly noti ced, in thi s cut-2. (Fig. 5).

Identificat ion o/PA Hs in cLIf-3 - In ~I si mi lar way <1.\

desc rib ed above, 1,2- benza nthrac ne, c hryse nc ,

f1u oranthene, and py rene cou Id be delected ~ in cut-3

(Fi g. 6) . ft is surpri sing to note that the molecule an thra-

SWAMINADHAM ('/ a/:POL YAROMA TIC HYDROCARBONS

CUT - 3 0.01m1/25ml [:;.A:::: 03nm

-3 ,."B'OC FA 10-

4 M 03 nm

300

CUT -3 0.002m1/50ml 03nm

AN 10- 6 M 03nm

CR 10- 3 M 03 nm

368

400 500

CUT-3 0.002ml/ 50ml 50 nm

_ 6 . . ___ An 10 _sM(372)

: ~----.FA 10 M(35B) ... . _ _ __ _ _ 1,2- BlO - S M ( 34 0)

.. - -- - -- - PY 10- 6M ( 333) :·.----- ---- - - CR10- sM ( 313)

I

- 5 12-810 M 50nm

[ CR 10 " M 50 om FA 10- 5 M 50 n m - 6 PY 10 M 50nm

I~- 36 1 L-~ __ ~ __ ~. __ ~

250 350 250 350 250 350 450 WAVELENGTH (nm)

Fig. 6 -- Idcntiri ca tion or PA Hs in CLit -]

4 Results and Conclusions

697

ce ll :::, could be detected in thi s cut of concentrati on,

(Ul02 mllS() ml as in the ran ge o r I(r~ M to 10-(' w hile

it could not be detected in higher concentrations of the

cut -3 .

Cut-l -- A nthracene and phenanthrene are promi­

nentl y observed at all !1A value~ in 0 . 1 ml /2S 1111 concen­

trati on o f the cut. In 3 mll25 ml o f the cut, fluoranthene

is prominentl y observed at all !1A values. Py rene and

69X INDIAN J PURE APPL PHYS, VOL 37, SEPTEMBER 1999

1,2-benzanthracene are prominentl y observed in the

concentrati on 0.002 mll2s ml and n.o I mll2s ml respec­

ti ve ly, at all £1"A values.

Cut-2 - A nthracene and fiuoranthene are promi­

nentl y observed at all £1"A va lues in I mll2s 1111 concen­tration of the cut. 1,2-benzanthracene and pyrene are

prom inentl y observed at all £1"A va lues in 0. 1 mll2S ml

concentrati on. Chrysene is c learl y observed in 0.0 1/25

ml concentrat ion at all £1"A va lues .

Cut-3 - 1,2-benzanthracene, fluoranthene and py­

rene are prominentl y observed at all £1"A values in con­centrati on 0. 1 mll2s ml of the cut. Anthracene is clearl y

observed onl y in concentration (l.002 mIlSO ml of the cut

at all £1"A va lues. Chrysene is prominentl y observed at all

£1A values in O.()I ml/2s ml concentration. From the

investigations carri ed out the foll ow ing sa lient features could be noticed.

(i) The Data Bank should be considered from as many

concentrations as poss ible for the basic compounds; (ii ) keeping in view the survey of the Data Bank, the sy n­

chronous exc itat ion derivati ve spectra of the cut s are al so to be in ves tigated in as many concentrations as

poss ibl e; ( iii ) a qualitati ve correspondence could be es tabl ished bet ween the concentration of the bas ic com­pound w ith that of t he cut: ( i v) a complete survey of the sy nchronous deri vat i ve spectra at va ri ous concentra­

ti ons of the cuts and at various £1"A va lues for the search

of the compounds through their Data Bank, recorded at

vari ous concentrat ion and vari ous £1A values of the basic

compounds is necessary. In addition , the exc itation and emi ss ion spectra also neeci to be considered as poin ts of

reference for the ex tension and structural detail s; (v) the

identi fication of the molecules through S DSEFS with ­

out resorting to any separati on technique:, is considered

to be worth pursuing if the data bank of the ex pected basic compound can be acqu ired as prerequi site.

Acknowledgement T he in vestigations are a part of the pro jec t on Petro­

chemica ls sponsored by the CSIR in CO llaborat ion w ith

TIP, Dehra Dun . T he authors are gratefu l to the CSIR for

the financial assistance. The authors are thankful to Dr Datta, Area Coordin ator TIP, Dehra Dun, f or hi s keen interest in the pursuit of work. The authors are than kful

to Shri R L Sharma, Scienti st IfP, Dehra Dun for pro­v iding the cuts. The authors are indebted to Dr T S R Prasada Rao, Director, lIP , Dehra Dun for hi s initi at ive, help and constant encouragement.

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