Marian STOŃ, Henryk SZMACIŃSKI, Jan TROJANOWSKI

M arian STOŃ, Henryk SZMACIŃSKI, Jan TROJANOWSKI
U n iv ersity of E ducation in S łu p sk
ASSAYING THE MERCURY LEVEL IN WATER BY THE
LUMINESCENCE METHOD
C o n t e n t s : 1. Introduction, 2. Experim ental, 3. R esults and discussion; Stresz­
czenie; R eferences
1. INTRODUCTION
T he m echanism of photolum inescence, i.e. th e shining of substances
a fte r rem o v al of th e source of excitatio n rad iatio n , is ex p lain ed on th e
basis of a d iag ram of e n e rg y levels of a m olecule, suggested b y J a b -
Fiig. 1. Schem atic diagram of energy levels of a m olecule
Rys. 1. Schem at poziom ów energetycznych m olekuły
łoński [4] (Fig. 1). B y absorbing lig h t of e n erg y hv, th e m olecule passes
from th e g round sta te S 0 to an excited sta te S 1 or to h ig h e r states. T he
life tim e of th e excited sta te is re la tiv e ly sh o rt (of th e ord er of 1 0 ~8 s)
and, a fte r th e rm a l re la x a tio n to th e zero oscillation level, its deactiv a­
tion is observed. F ro m th e sta te Si th e m olecule m ay r e tu r n to th e
ground sta te by a v a rie ty of w ays, e.g.:
(i) b y rad ia tio n tra n sitio n w ith em ission of flu o re sc e n t light of
e n erg y h \ i;
(ii) b y 'ra d ia tio n le ss tra n sitio n to th e S 0 state;
(iii) by rad iatio n less tra n sitio n s to th e u n sta b le trip le t sta te T lt
w hich m ay su b seq u e n tly pro d u ce re ta rd e d flu o rescen ce [1] or fluorés"
cence w ith em ission of a q u a n tu m w ith energy*hv2.
E n erg y losses of a m olecule d u rin g th e rm a l rela x atio n in th e
ex cited sta te sh ift th e fluorescence sp ectru m to w a rd s longer w aves
in resp e c t of th e absorption sp e ctru m (S tokes’ rule). R ad iatio n tra n lS s u o iiis —►S 0 are em ployed in th e lum inescence analysis. Q u a n tita tiv e
analysis of th e c o n te n t of a flu o re sc e n t substance in a sam ple can be
p e rfo rm e d a fte r tak in g into account all processes accom panying irra d ia ­
tion of th e sam ple w ith lig h t of in te n sity I 0. T he am o u n t of en erg y
absorbed b y th e solution depends on th e p ro p ertie s of th e m olecules, such
as th e m olar ab so rp tiv ity , e, th e ir co ncentration, c, and p a th len g th , d,
over w hich lig h t is absorbed. T aking into account th e L a m b ert-B e e r
law leads to th e follow ing eq u ation for in te n sity of th e absorbed r a ­
diation, la:
(1)
I a = I o (1 -
e - £C" )
The com ponent of th e in te n sity used for th e analysis is given by:
(2)
h = ff h
w h e re f f is th e absolute q u a n tu m yield of th e fluorescence. F o r
co n cen tratio n eq. (2) assum es th e form
low
(3)
7/"= 10 vf t d c — Ac
Eq. (3), providing th e basis of q u a n tita tiv e lum inescence analysis, holds
fo r solutions obeying th e L a m b e rt-B e e r law . This fe a tu re ru le s out
specific in te rac tio n s of th e m olecules w ith th e so lvent and in te rm o lec u la r interactio n s. T hese conditions provide lim itatio n of th e a p p lic a b r
lity of eq. (3) fo r th e d e te rm in a tio n of c o n cen tratio n of a lu m in escen t
substance based on th e m ea su rem e n t of its lum inescence in ten sity . In
th e flu o rim e tric analysis, selection of th e w a v e len g th exciting th e so"
lu tio n is also im p o rta n t. F ro m eq. (3) it follow s th a t th e h ighest se­
n sitiv ity of d e te rm in a tio n is w hen
( 4)
dir
,
cd
IoVf id — max
T his show s th a t th e excitatio n should be accom plished w ith a w ave
of a len g th fo r w hich th e ex tin ctio n coefficient has a m ax im u m v a lu e
(assum ing th a t th e ab sorption sp ectru m superim poses th e ex citatio n
spectrum ).
2. EXPERIMENTAL
T he choice of an organic m olecule u se fu l for a p a rtic u la r flu o rim e tric
assay depends on its lu m in escen t p ro p e rtie s and th e chem ical m eth o d
n ecessary to p re p a re th e sam ples fo r m ea su rem e n t. In th is m ethod,
rho d am in e B (C 2 8 H 3 CIN 2 O 3 ) w as used as a lu m in escen t m olecule. T he
a u th o rs of th e a rticle s [2 — 6 ] found th a t in th e p rese n c e of m e rc u ry
com pounds rh o d am in e B form ed rh o d am in e — m ercu ric (RB-Hg) com ­
plexes e x h ib itin g photolum inescence over th e visible ran g e. T he a b ­
sorption sp e ctru m of th e R B -H g com plexes w as m easu red on a S P E CORD U V -V IS (C. Zeiss) sp ectro p h o to m eter. Em ission sp ectra w ere
m easu red using th e e q u ip m e n t show n in Fig. 2.
Fig. 2. Block diagram oi the m easuring appliances
Rys. 2. Schemait blokow y aparatury pom iarow ej
The excitatio n w av elen g th , Xex= 5 4 5 nm , w as obtained by m eans
of a xenon lam p L (X B O /lO l), w a te r filte r FW , m onochrom ator M l
(SPM 2 Zeiss) and lens
T he excitatio n rad ia tio n w as d ire c te d by
m eans of m irro r Z on c u v e tte K in w hich th e sam ple w as placed. T he
fluorescence lig h t of th e R B -H g com plexes w as passed by th e lens
sy stem S 3 and S 2 into th e slit of m onochrom ator M2 (SPM 2). P h o to ­
c u rre n t fro m th e p h o to m u ltip lie r P h (M12 FC51 W erk f u r F ein sch elelek tro n ik ) w as rea d out by m eans of an e le c tro m e te r (219A UNITRA)
or reco rd ed on re c o rd e r R (K-200 Zeiss). S am ples w ere p re p a re d as
d escribed in [7].
3. RESULTS AND DISCUSSION
A stu d y of th e tim e-resp o n se of th e absorption sp e ctra rev e a le d th a t
optical d e n sity of an e x tra c t containing th e rh o d a m in e -m e rc u ry com -
Fig. 3 Sipecfcra of absorption (
the rhodam ine-m ercury com plex
----- — ) and fluorescence ( -------------- ) of
Rys. 3. W.idima absorpcji ( --------rodiam inowo-rtęciowego
■) i flU'orescencji ( -------------- ) kom pleksu
p lex es stabilized itself w ith in 2 h o u rs a fte r its p re p a ra tio n (Fig. 3).
T his fe a tu re does n o t im pose tim e lim itatio n s for p erfo rm in g th e lu ­
m inescence analysis.
Fig. 4. Tim e response of the optical density of an extract containing the
RB-Hg com plexes
Rys. 4 Zależność gęstości optycznej ekstraktu zaw ierającego kom pleksy RB-Hg
od czasu
T he m ea su rem e n ts of th e in te n sity of flu o rescen ce of th e R B -H g
com plexes w ere accom plished a t 800 nm in th e ty p e B a rtific ia l sea
w a te r p re p a re d a fte r th e P o lish S ta n d a rd P N -66/C -06502 and in th e
artificia l B altic Sea w a te r p re p a re d by using a p ro ced u re developed by
T rzosiriska [8], N orm alized absorption and em ission sp ectra a re show n
in Fig. 4. T able lists m ean v alues of th e in te n s ity of flu o rescen ce of
th e com plex corresponding to d efin ite am ounts of m e rc u ry added to th e
solution, and m ean sta n d a rd deviations.
Concentration of m ercury in water, c, and the intensities o f photocurrent generated
by light of fluorizing com plex in artificial sea w ater (IM) and in artificial B altic
Sea w ater (IB)
Stężenie rtęci w badanej w odzie (c) oraz natężenie fotoprądu w yw ołanego przez
(u św iatło fluoryzującego kom pleksu w zastępczej w odzie m orskiej (IM) i bałtyckiej (I
■c [M]
IMX10-9 [A]
I BX10-s [A]
1.79+ 0.63
2.44+ 0.45
4.30± 0.92
7.17± 0.70
9.25+ 1.63
16.25± 1.42
23.10± 3.06
30.40± 2.30
49.74+ 3.59
70.95± 6.13
101.30+ 8.10
189.20+15.15
258.15+10.47
339.80+15.56
440.10+15.45
—
1.80+ 0.65
3.07+ 0.74
4.25+ 1.98
7.12+ 1.29
10.55+ 1.8-1
14.59+ 2.08
25.15+ 3.25
37.24+ 2.49
55.00+ 5.56
81.91+ 8.32
135.00+12.72
185.05+ 9.70
289.60+11.86
'
1X10-8
2X10-8
5X'10-S
I X 10-’
2X10-7
5X10-7
1X10-«
2X10-8
5XJ0-6
1XJ0-3
2X10-5
5X 10-5
1X10-4
2X 10-4
5X10-«
Fig. 5 p rovides graphic illu stra tio n of th e data in Table. T he in ­
te n s ity of flu o rescen ce of th e com plex for a given m e rc u ry concen­
tra tio n w as found to be low er in th e B altic Sea w a te r th a n in sea w a­
te r. T his w as due to d iffe re n t c o n cen tratio n s of N aC l in th e w a te r
exam ined according to th e re s u lts re p o rte d in [7],
T he lin e a r rela tio n sh ip of If — If [c] d e m o n strates convincingly the
possibility of em ploying th is m ethod for m e rc u ry assay in w a te r. In
spite *of its low d e te rm in a tio n lim it (2X10~6 g dm"3), th e m ethod has
m an y advantages. T he an alysis can be p e rfo rm e d in a re la tiv e ly sh o rt
tim e and sam ples can be p re p a re d at th e sam pling site, th u s elim in a­
tin g w h a t is d iffic u lt to d e te rm in e — th e processes of p e n e tra tio n of
m erc u ry into th e w alls of th e vessels. Fig. 5 suggests th a t th e m ethod
F is. 5. R elationships betw een fluorescence intensity of •complexes and co n ­
centration of m ercury in artifical sea w ater (M) and artificial B altic Sea w ater (fi)
Ry.s. 5. Zależność natężenia fluorescencji kom pleksów od koncentracji rtęci w
zastępczej w odzie m orskiej (M) i zastępczej w odzie bałtyckiej (B)
indicates good sensitivity. S m all variatio n s in th e m e rc u ry c o n c en tra ­
tion in solution pro d u ce larg e d ifferen ces in th e in te n sity of flu o re s­
cence of th e rh o d am in e-rn e rc u ry com plexes.
To be able to assay low er m e rc u ry co n centrations, th e in stru m e n ­
tatio n should be m odified. T he d e te rm in a tio n lim it of m e rc u ry could
be m a rk e d ly low ered b y c o n cen tratio n of th e rh o d a m in e -m e rc u ry
e x tra c t. A ccordingly, th e o bjectives of f u rth e r stu d ies w ill be to low er
th e d e te rm in a tio n lim it and ap p ly th e m eth o d for analysis of n a tu ra l
w aters.
M arian STOŃ, H e n ry k SZM A C IŃ SK I, J a n T R O JA N O W SK I
W yższa Szkoła Pedagogiczna w Słupsku
OZNACZANIE ZAWARTOŚCI RTĘCI W WODZIE METODĄ
LUM INESCENCYJNĄ
Streszczenie
Praca dotyczy m ożliw ości zastosow ania m etody lum inescencyjnej do określania
zaw artości rtęci w w odzie. Podstaw ą analizy ilościow ej jest tw orzenie się w roz­
tworach wodnych kom pleksów rodam inow o-rtęciow ych (RB-Hg), w ykazujących
fluorescencję w zakresie długości fal św iatła widzialnego. Zmierzono w idm a ab­
sorpcji i fluorescencji kom pleksów oraz w ykonano pomiary ich trw ałości w m ie­
szaninie ekstrahującej (benzen
eter etylow y w stosunku objętościow ych 2:1).
Stwierdzono liniow ą zależność natężenia fluorescencji kom pleksów w zakresie
10-8M — 5.10-4M rtęci w wodzie.
Pom iary w ykonano dla przypadku zastępczej w ody bałtyckiej i w ody m or­
skiej typu B, W skazano na m ożliw ość obniżenia granicy oznaczalności poprzez do­
konanie zatężenia ilości fluoryzujących kom pleksów w lum inezującej próbce.
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Y. S., Fiziko-khim icheskie m e lo d y analiza,
Khim a M oscov
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9 — Oceanologia