Application of Karl Fischer`s Method to materials that only release

Application of Karl Fischer`s Method to materials that only release

— 300 —
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M . Gorizález-Morín, M . Barrera-Niebla and M . Pérez-Sanchez, Journal
Electroanalitycal
[6]
Chemistry,
of
411 (1996) 1.
K . B . Oidham and J. Spanier, The Fractional
Calculus,
Academic Press,
New
A p p l i c a t i o n o f K a r l F i s c h e r ' s M e t h o d to materials that
o n l y release water at high temperatures
Y o r k (1974).
[7]
J. Spanier and K . B . Oldham, An Atlas
of Functions,
Hemisphere,
Washington,
D C , and Springer, Berlin (1987).
[8]
A . M . Bond and K . B . Oldham, J. Electroanal.
[9]
K. B .
Oldham
Science,
and
J. C.
Myland,
Chem. ,158 (1983) 193.
Fundamentals
of
Electrochemical
Academic Press, San Diego (1994).
[10]
M . González-Morin, Tesina de Licenciatura,
[11]
M.
[12]
AJ.Bard
Barrera-Niebla,
M . González-Morin
Sons, 1980.
1 I i
TII' oVi lltfilulo ' I • 1 • I • i.. c Minciro
H i l d a Amwin. 44b) S. M i n n i e InfesLi todev Portugal
11
Universidad de L a Laguna, 1993.
and
M . Pérez-Sánchez,
An.
Quirn.,
89(1993) 493.
and
Marta E . Themudo , Aquiles A Barms and Margarida Bastos
1
1
fiHjrli Ihjnmlnmiaiipt I
2 Ccntro dc irivcTiliajtcAo cm Oulmica II.P.
L.R.Faulkner,
Electrochemical
Methods,
John
Wiley
and
Ria rja I'amno Alcgre. 687. 416WW7 Porto, Portugal
OiltinrlwrJ fc.up.pl)
•. i H l i . K l i i - it
fil I
Abstract
The present work describes the development o f a new experimental set-up to allow
determination o f water in solid materials that can not be analysed by the traditional Karl
Fischer's coulometric titration, as they are not soluble in Karl Fischer's solution and
they only release water at high temperatures.
For this purpose, a new tubular oven was designed and tested, where the temperature
can be raised up to 1000 °C,
Different geological
which can be coupled to a Karl Fischer Coulometer.
samples were tested, and the results were crossed with other
traditionally used methods for this type o f determinations.
Introduction
The determination o f the water content o f some materials is very important, both from
the point o f view o f their production and commercialisation and for the study and
characterization o f their chemical and physical properties.
The present work focus water determination in different geological materials. T h e
traditional method for the determination o f the total water content in rocks is the
Penfield's Method [1]. Nevertheless, it is considered a method o f low precision and low
accuracy, as it is biased by other volatile components o f the sample, that will be treated
as water by the method.
Portugaliae Etecfochlmlca Acta, is (200!) 30?-3i i
— 302
-
-
303
-
T h e a d a p t a t i o n o f the t r a d i t i o n a l K a r l F i s c h e r ' s c o u l o m e t r i c m e t h o d [2] here d e s c r i b e d
was d e s i g n e d
f o r this w o r k c a n b e seen i n
figure
1, a n d t h e s c h e m e o f the t o l a l
arose f r o m the n e e d to d e v e l o p a m e t h o d to a s c e r t a i n the v a l i d i t y a n d l i m i t a t i o n s o f the
e x p e r i m e n t a l s e t - u p i n figure 2 .
Pen field method.
In a l l cases a M c t l l e r a n a l y t i c a l b a l a n c e ( + 0 . 0 0 0 3 g ) w a s u s e d .
T h e c h e m i c a l e q u a t i o n that d e s c r i b e s the r e a c t i o n i n the c o u l o m e t r i c c e l l is [3]:
A s d r y i n g agents, m a g n e s i u m p e r c h l o r a t e ( M e r c k , p.a.), s u l f u r i c a c i d ( M e r k , p.A.) a n d
m o l e c u l a r s i e v e s ( M e r c k , 0.4 a n d 1.0 n m ) w e r e u s e d .
h + S0
2
+ 3 R N + C H 3 O H + H 0 -*
2
2 R N H I + RNSO4CH3
(1)
w h e r e R is a n a l q u i l , c i c l o a l q u i l , a r i l o r a c i l f u n c t i o n o f the s o l v e n t .
T h e c e l l c o m p o n e n t s w e r e d r i e d in a n o v e n at 7 0 ° C , a n d the m o r e d e l i c a t e parts w i t h a
m a n u a l a i r d r i e r . A f t e r t h i s , the c e l l w a s c h a r g e d w i t h 100 m l o f H y d r a n a l - C o u l o m a t A
T h e q u a n t i t a t i v e d e t e r m i n a t i o n o f the w a t e r c o n t e n t is t h u s b a s e d o n the r e a c t i o n o f H 0
(Riedel-de Haen) and immediately closed. T h e cathodic compartment was
w i t h a n e q u i v a l e n t a m o u n t o f 1 [4]. In this c o u l o m e t r i c t e c h n i q u e , the i o d i n e n e c e s s a r y
about 5 m l o f H y d r a n a l - C o u l o m a t C ( R i e d e l - d e H a e n ) . After this the system w a s
for the r e a c t i o n is p r o d u c e d b y the a n o d i c o x i d a t i o n o f i o d i d e , as:
turned o n , a n d a l l o w e d t o d r y a n d s t a b i l i z e .
2
2
filled
with
T h e a d d i t i o n o f the s o l i d s a m p l e c a n b e m a d e d i r e c t l y ( i n d i r e c t titration) - i n t h i s case it
21 - > I i + 2e"
was w e i g h e d o n a w e i g h i n g s p o o n , c o v e r e d w i t h p a r a f i l m , a n d a d d e d q u i c k l y to the c e l l
t h r o u g h o n e o f the o p e n i n g s . I n the cases w h e r e this w a s not p o s s i b l e , a d r i e d s a m p l e
S i n c e i o d i n e i s c o n s u m e d as l o n g as there i s w a t e r present, a n e x c e s s o f i o d i n e w i l l
h o l d e r i n c e r a m i c s w a s w e i g h e d w i t h the s a m p l e a n d w a s q u i c k l y i n t r o d u c e d i n the o v e n
i n d i c a t e t h e e n d - p o i n t o f the t i t r a t i o n , d e t e c t e d
at the d e s i r e d t e m p e r a t u r e . T h e c a r r i e r gas, n i t r o g e n ( A i r L t q u i d e , N 4 5 a n d N 6 0 ) w a s
as a s u d d e n d r o p i n t h e p o t e n t i a l
difference.
t u r n e d o n , a n d c o n n e c t e d to the m e a s u r i n g c e l l as d e p i c t e d i n figure 2 . In t h i s c a s e , a
Water contents u p to a m a x i m u m o f 5-10 m g water can b e determined i n a short time
b l a n k e x p e r i m e n t w a s p e r f o r m e d before e a c h e x p e r i m e n t , i n the s a m e c o n d i t i o n s as the
( c i r c a 10 m i n u t e s ) . T h i s m e t h o d i s p a r t i c u l a r l y u s e f u l f o r s a m p l e s o f l o w w a t e r c o n t e n t
m e a s u r i n g e x p e r i m e n t . T h e a m o u n t o f s a m p l e to b e a d d e d h a d to b e a d j u s t e d t o t h e
( 1 0 p g - 10 m g ) , i.e. t o w o r k i n the p p m range. A s t h e c o u l o m e t r i c t i t r a t i o n i s a n
water c o n t e n t o f the s a m p l e .
a b s o l u t e m e t h o d , it d o e s n o t r e q u i r e c a l i b r a t i o n [5]. A l l t h i s m a k e s it a s i m p l e , fast a n d
T h e r e s u l t s are p r e s e n t e d i n w a t e r p e r c e n t a g e , d e f i n e d as
accurate technique.
T h e K a r l F i s h e r m e t h o d has b e e n w i d e l y u s e d for the d e t e r m i n a t i o n o f w a t e r i n different
% H2O =
M a s s o f titrated w a t e r
* JQQ
M a s s o f sample
m a t e r i a l s that react d i r e c t l y , o r d i s s o l v e , i n the K a r l F i s c h e r s o l u t i o n [6], F o r t h e s e , the
m e t h o d i s fast a n d s i m p l e . In cases l i k e t h e o n e w e d i d s t u d y [7,8,9], there is the n e e d to
i n t r o d u c e a n o v e n , s o that the w a t e r c a n b e l i b e r a t e d f r o m the s a m p l e , before b e i n g
Results and Discussion
titrated i n the c e l l . T h i s i m p l i e s a d a p t a t i o n s to the o r i g i n a l c o u l o m e t r i c i n s t r u m e n t , a n d a
n u m b e r o f n e w v a r i a b l e h a d t o b e s t u d i e d a n d o p t i m i s e d . A n o v e n w a s d e s i g n e d for the
D i f f e r e n t types o f e x p e r i m e n t s w e r e p e r f o r m e d w h i c h w i l l n o w b e d e s c r i b e d separately.
present p u r p o s e , w h i c h w a s tested a n d m o d i f i e d t h r o u g h o u t the w o r k .
• Determination o f the water content o f the atmospheric environment
E x p e r i m e n t a l Procedure
A K a r l F i s c h e r C o u l o m e t e r 6 5 2 K F , M e t h r o m , w a s u s e d for the w a t e r d e t e r m i n a t i o n s .
T h e flux c o n t r o l f o r the c a r r y i n g gas w a s from K e y I n s t r u m e n t s . T h e t u b u l a r o v e n that
T h i s e x p e r i m e n t w a s p e r f o r m e d i n o r d e r to q u a n t i t a t e the e n v i r o n m e n t h u m i d i t y a n d to
test the i n s t r u m e n t s e n s i t i v i t y f o r a m o u n t s o f w a t e r o f this o r d e r o f m a g n i t u d e . A
s y r i n g e w a s filled w i t h a i r , a n d i n j e c t e d i n t o the m e a s u r i n g c e l l . T h e a d d i t i o n o f 1 m l o f
air w a s f o u n d t o h a v e w a t e r a m o u n t s b e t w e e n
0 a n d 13.8 u.g, d e p e n d i n g o n the
—
304
— 305 —
-
a t m o s p h e r i c h u m i d i t y c o n d i t i o n s . T h i s result s h o w s that e x t r e m e care m u s t be u s e d o n
was the a d o p t e d d r y i n g s y s t e m , p r o d u c i n g b a n k e x p e r i m e n t s w i t h v a l u e s o f 3 0 - 4 0
sample management,
ug/'min.
as v a r i a t i o n i n the d e g r e e o f h u m i d i t y o f the l a b o r a t o r y c a n
introduce a significant error in the determinations.
For the a c t u a l e x p e r i m e n t s the N
2
pressure w a s m a i n t a i n e d at 1.5 k P a / c m . F o r l o w e r
2
pressures the e x p e r i m e n t s take too l o n g t i m e , a n d for h i g h e r p r e s s u r e s the b u b b l i n g is
t u m u l t u o u s , g i v i n g rise to p r o j e c t i o n s o f t h e c a t h o l y t e .
• A c c u r a c y test
T o c h e c k the i n s t r u m e n t p e r f o r m a n c e i n t e r m s o f a c c u r a c y , w e i g h e d s a m p l e s o f d i s t i l l e d
water, i n the r a n g e 4 m g - 3 0 m g , w e r e i n j e c t e d i n t o the m e a s u r i n g c e l l . T h e r e s u l t s
p r e s e n t a m a x i m u m r e l a t i v e e r r o r o f 1.6%, i n d i c a t i n g a g o o d a c c u r a c y .
• O v e n conditions
T h e o v e n (figure 1) c o n s i s t s o f a q u a r t z t u b e , d i a m e t e r 2 0 m m a n d l e n g t h ( i n the h o t
z o n e ) 12 c m . T h e q u a r t z tube is c l o s e d o n b o t h e n d s w i t h c i r c u l a r m e t a l l i c l e a d s ,
c l a m p e d w i t h a n o - r i n g . T h e e n d c l o s e r to the o p e r a t o r has 2 h o l e s , o n e for i n l e t a n d the
• P r e c i s i o n test
F o r the p r e c i s i o n test ( r e p e a t a b i l i t y ) t w o c h e m i c a l s w e r e u s e d : a c e t o n e ( M e r c k , p.a.) a n d
other for the o u t l e t o f the c a r r i e r gas. T h e final a r r a n g e m e n t o f 1 a n d 2 f o r i n a n d o u t gas
N , N - D i m e t h y l f o r m a m i d e ( M e r c k , p.a.). S a m p l e s w e r e t a k e n w i t h a c a r e f u l l y d r i e d 5 0 0
was c r u c i a l for a g o o d a c c u r a c y o f t h e s a m p l e m e a s u r e m e n t s , as the o t h e r a r r a n g e m e n t
p i H a m i l t o n s y r i n g e (gas tight), a n d s m a l l a m o u n t s w e r e i n j e c t e d i n t o the m e a s u r i n g
p r o d u c e d b i g losses b y w a t e r c o n d e n s a t i o n o n the c o l d z o n e , before e n t e r i n g the
c e l l . In e a c h m e a s u r e m e n t the s y r i n g e w a s w e i g h e d before a n d after i n j e c t i o n i n t o the
measuring vessel.
v e s s e l , to d e t e r m i n e the m a s s o f a d d e d s a m p l e . F o r N , N - D i m e t h y l f o r m a m i d e a w a t e r
content o f 0 . 0 2 6 %
was obtained w i t h a relative standard deviation o f
14%
(10
replicates). F o r acetone a water content o f 1.08% was obtained w i t h a relative standard
d e v i a t i o n o f 4 % (9 r e p l i c a t e s ) . T h e s e r e s u l t s c o n f i r m the g o o d p r e c i s i o n o f the m e t h o d ,
t a k i n g i n t o c o n s i d e r a t i o n t h e l o w w a t e r c o n t e n t o f the s a m p l e s .
• C a r r y i n g gas
F i r s t , t h e w a t e r c o n t e n t o f n i t r o g e n as d e l i v e r e d w a s d e t e r m i n e d , c o n n e c t i n g the gas
d i r e c t l y to the m e a s u r i n g c e l l , at a p r e s s u r e o f circa
1.0 k P a / c m , b u b b l i n g u n d e r the
2
l i q u i d surface o f the c a t h o l y t e . I n i t i a l l y n i t r o g e n N 4 5 w a s u s e d , w h i c h h a d w a t e r
F i g u r e 1. T u b u l a r o v e n . 1 - o u t l e t f o r N ; 2 - i n l e t for N ; 3 - T h e r m i s t o r ; 4 - O - r i n g ;
2
2
5 - O v e n w a l l ; 6 - R e f r a c t i v e w a l l ; 7 - s a m p l e h o l d e r ; 8 - h e a t i n g part of the o v e n
contents o f 400-500 ug/min.
A n attempt w a s m a d e to r e d u c e the w a t e r c o n t e n t o f N 4 5 b y p a s s i n g the gas t h r o u g h a
w a s h i n g flask w i t h c o n c e n t r a t e d s u l p h u r i c a c i d , b e f o r e e n t e r i n g the m e a s u r i n g u n i t . T h i s
r e d u c e d the w a t e r c o n t e n t to a l e v e l o f circa
3 0 0 p g / m i n , a v a l u e that is s t i l l t o o h i g h .
• D i r e c t K a r l F i s c h e r ' s titration of water in geologic samples
Samples o f m a s s - 1 0 - 6 0 m g were w e i g h e d i n a w e i g h i n g s p o o n , c o v e r e d w i t h parafilm,
a n d a d d e d d i r e c t l y to the m e a s u r i n g v e s s e l t h r o u g h o n e o f its o p e n i n g s . T h e o b t a i n e d
A n o t h e r q u a l i t y o f n i t r o g e n , N 6 0 , w a s t h e n u s e d , w i t h a w a t e r c o n t e n t as d e l i v e r e d o f
mean water percentage
o n l y circa
hygroscopic water ( H 0 )
100 u g / m i n .
2
v a l u e s are p r e s e n t e d i n table 1, t o g e t h e r w i t h the r e s u l t s o f
a n d total w a t e r ( H 2 0 ,
OIa
i ) o b t a i n e d by the t r a d i t i o n a l m e t h o d s
D i f f e r e n t d r y i n g agents w e r e tested thereafter - s i l i c a g e l , m a g n e s i u m p e r c h l o r a t e a n d
used i n Instituto G e o l ó g i c o M i n e i r o ( I G M )
m o l e c u l a r s i e v e s - e i t h e r a l o n e o r i n different c o m b i n a t i o n s . T h e m o s t efficient d r y i n g
m e t h o d for H 0 " a n d the P e n n f i e l d m e t h o d f o r H 0 , i a i ) .
w a s o b t a i n e d w i t h the use o f m o l e c u l a r s i e v e s , p a r t i c u l a r l y w i t h p o r e s i z e 1.0 n m . T h i s
2
f o r the s a m e s a m p l e s (the
2
0
gravimetric
-
306
- 307 —
-
A n a l y s i s o f these v a l u e s s h o w s that, for m o s t o f t h e s a m p l e s , the d i r e c t t i t r a t i o n b y K a r l
F i s c h e r is not able to d e t e r m i n e e v e n the total a m o u n t o f h y g r o s c o p i c w a t e r , H 0 ~ , i.e.,
2
the o b t a i n e d v a l u e s are m u c h l o w e r t h a n the o n e s o b t a i n e d b y g r a v i m e t r i c a n a l y s i s a n d
the P e n f i e l d m e t h o d . N e v e r t h e l e s s , for the s a m p l e s i d e n t i f i e d as S D 5 , M S D b ' a n d
S D 3 B , w h i c h h a v e l o w w a t e r c o n t e n t s (less t h a n 0 . 5 % ) , the K a r l F i s h e r ' s d i r e c t t i t r a t i o n
method
s e e m to d e t e r m i n e
a c c u r a t e l y the h y g r o s c o p i c
water content. A
possible
e x p l a n a t i o n o f these r e s u l t s is that, as the s a m p l e s d o n o t d i s s o l v e i n K a r l F i s c h e r ' s
reagent, w h e n the w a t e r c o n t e n t is h i g h p r o b a b l y the s o l i d - l i q u i d i n t e r f a c i a l c o n t a c t is
not e n o u g h to a l l o w d e t e c t i o n o f the total a m o u n t o f surface water.
F i g u r e 2 . S c h e m e o f the e x p e r i m e n t a l s e t - u p . V - v a l v e for c o n t r o l l i n g N
flux; F - flux
2
m e a s u r i n g u n i t ; D - d r y i n g u n i t s ; S - s a m p l e h o l d e r ; O - o v e n ; Q - h e a t i n g part o f the
Table 1 -
Results o f
H 0" e H 0
2
2
( D t a
i
in geologic samples o b t a i n e d b y the t r a d i t i o n a l
o v e n ; C - c o u l o m e t r i c t i t r a t i o n c e l l ; M - m a g n e t i c stirrer.
m e t h o d a n d r e s u l t s o f w a t e r % o b t a i n e d by K a r l F i s c h e r ' s m e t h o d b y d i r e c t t i t r a t i o n .
Table 2- Results o f % water content o f g e o l o g i c samples analysed by K a r l
Sample
% HjO
(a)
% H O,
2
0 W
(b)
% H 0(K.F.)
F i s c h e r ' s t i t r a t i o n w i t h c o u p l e d o v e n at 110°C a n d 9 5 0 °C.
2
1.43
SD1
2.07
SD2
2.07
3.38
0.95
SD4
2.26
4.01
1.10
SD5
0.0B
0.35
0.06
SD6
0.5!
1.00
SD9A
1.30
CHa4
Temperature of the oven / " C
a
0.25
240
9
2.35
0.20
3
1.92
0.83
241
2
1.23
0.01
2
6.92
0.15
0.47
4.51
0.82
242
4
0.45
0.00
4
4,40
0.34
MSDb'
0.33
14.86
0.44
243
2
0.66
0.03
2
7.02
0.27
SD3B
0.43
3.12
0.51
244
2
0.72
0.03
2
6.53
0,25
2
6.12
0,16
w a s tested
at t w o different
oven
t e m p e r a t u r e s : 1 1 0 °C e 9 5 0 °C. T h e s e t e m p e r a t u r e s w e r e c h o s e n i n a n a l o g y w i t h the
t r a d i t i o n a l m e t h o d s for the d e t e r m i n a t i o n o f t h e t w o types o f w a t e r -
1 1 0 °C f o r t h e
h y g r o s c o p i c w a t e r a n d 9 5 0 °C f o r the total water.
n
—
246
• K a r l F i s c h e r ' s titration of water in geologic samples with coupled oven
K a r l Fischer's titration w i t h coupled oven
H,0
%. mean
H O % , mean
Sample
(a) Gravimetric method; (b) Penfield method
The
950
110
t h e o v e n , w h i c h w a s a l r e a d y e q u i l i b r a t e d at the d e s i r e d t e m p e r a t u r e , w i t h a c o n s t a n t
f l o w ofN2 w h i c h c a r r i e d the l i b e r a t e d w a t e r to the m e a s u r i n g c e l l (see figure 2). A t least
7.47
0.21
252
3
0.60
0.07
3
6.09
0.22
253
2
0.64
0
2
6.74
0.23
ii - number of replicates
c = standard deviation (when n>3) or mean deviation (when n=2)
T h e s a m e s a m p l e s w e r e a n a l y s e d at I G M w i t h the t r a d i t i o n a l m e t h o d s -
gravimetric
m e t h o d for H 0 " a n d P e n f i e l d m e t h o d f o r H 0 i a i - a n d a l s o by t h e so c a l l e d " l o s s o n
2
E a c h s a m p l e w a s w e i g h e d i n a d r i e d c e r a m i c s s a m p l e h o l d e r , a n d transferred q u i c k l y to
Z
2
[ 0
i g n i t i o n " ( m e a s u r e s the a m o u n t o f v o l a t i l e c o m p o n e n t s ) . In table 3 w e c a n see a l l these
results for
comparison. The
r e s u l t s are p l o t t e d
i n figure
3, where
the
obtained
differences c a n b e m o r e c l e a r l y s e e n .
2 r e p l i c a t e s w e r e m e a s u r e d for e a c h s a m p l e . T h e o b t a i n e d r e s u l t s are p r e s e n t e d i n table
In b o t h cases (at 110°C e 9 5 0 ° C ) the K a r l F i s c h e r ' s m e t h o d w i t h c o u p l e d o v e n p r o v i d e d
2.
g o o d r e s u l t s . T h e r e s u l t s present g o o d r e p e a t a b i l i t y a n d a g o o d a g r e e m e n t w i t h the
-
308
-
-
309
-
v a l u e s o b t a i n e d b y the t r a d i t i o n a l m e t h o d s . T h i s w a s v e r y i m p o r t a n t as it s h o w e d that,
these v a l u e s are s m a l l e r t h a n the total water. In o r d e r to try to u n d e r s t a n d t h i s , e a c h
o n the c o n t r a r y to the p r i o r b e l i e f , the P e n f i e l d ' s m e t h o d c a n d e t e r m i n e w i t h a c c u r a c y
s a m p l e w a s a n a l y s e d for its m a j o r e l e m e n t s . T h e o b t a i n e d r e s u l t s are p r e s e n t e d i n table
the total w a t e r i n g e o l o g i c s a m p l e s . T h e present results, t h u s , s e r v e d to v a l i d a t e this
4, together w i t h the v a l u e s for H 0 " , HjOtotaj a n d " l o s s o n i g n i t i o n " . It c a n b e s e e n that
method.
the s a m p l e s that present l o w e r v a l u e s for " l o s s o n i g n i t i o n " t h a n f o r H z O n n i h a v e a h i g h
2
F e O c o n t e n t , n a m e l y , s a m p l e s 2 4 1 , 2 4 2 , 2 4 3 , 2 4 4 , 2 5 2 a n d 2 5 3 . M o r e , the h i g h e s t the
T a b l e 3 - R e s u l t s o b t a i n e d for H 0 " e H O t
2
2
0 [ d
by K a r l Fischer's method with coupled
o v e n a n d b y the t r a d i t i o n a l m e t h o d s ( g r a v i m e t r i c a n d P e n f i e l d ) a n d r e s u l t s for the
"loss
F e O c o n c e n t r a t i o n the largest is the difference.
on ignition" method.
T a b l e 4 - V a l u e s for the m a j o r c o m p o n e n t s ( i n %)
% H 0-
% H;0"
(KF) Oen:I10°C
(G.M.)
240
2.35
1.89
7.47
241
1.23
1.24
6.92
242
0.45
0.36
4.40
243
0.66
0.43
244
0.72
Sample
2
246
% H Ot
2
o a l
%H;O
(KF) Oven: 950°C
l o r a l
L.I.,%
(P.M.)
7.50
8.28
for the a n a l y s e d g e o l o g i c s a m p l e s .
Sample
240
241
242
243
244
245
246
248
252
253
Si0
68.57
67.44
69.75
52.56
S2.67
4 .35
79.41
78.54
58.60
54.36
2
2
6.72
AI2O3
10.29
12.42
845
13.87
13.69
14.71
10.98
1236
1291
13.02
4.44
3.75
FeO
1.51
6.97
11.42
18.03
18.18
0.94
0.15
0.69
14.56
14.Î5
7.02
7.22
5.39
MnO
0.03
0.03
0.09
0.15
0.14
0.04
<0.02
0.05
0.12
0.13
0.44
6.53
6.84
5.18
CaO
<0.04
<0.04
<0.04
<0.04
<0.04
<0.04
<0.04
0.28
<004
<0.04
2.05
6.12
6.25
8.24
MgO
i.ni
1.87
2.37
4.12
3.16
0.35
0.05
0.11
3.64
3.70
0.96
1.17
Na 0
<0.20
O.20
O.20
<0.20
<0.20
O.20
<0.20
4.90
<o.a>
<0.20
K 0
0.11
0 12
<0O3
<0.03
<0.O3
<0.03
0.05
0 90
O.03
<0.03
Ti0
2
0.12
0.12
0.29
0.57
0.59
0.74
0.12
0.04
0.53
0.56
P 0
3
<0.03
<0.03
<0.03
0.04
O03
0.06
<0.03
<0.03
<0.03
0.05
6.84
10.42
6.25
M Si
6.44
7.04
6.80
248
0.14
0.12
252
0.60
0.52
6.09
6.44
5.10
253
0.64
0.64
6.74
7.04
5.68
2
2
Methods: K.F. - Karl Fischer; G . M - Gravimetric; P.M - Penfield; L I - Loss on Ignition
2
F i g u r e 3. C o m p a r i s o n o f the r e s u l t s o b t a i n e d for H 0 " a n d HiOtomi b y the K a r l F i s c h e r ' s
7.57
6.80
4.44
7.22
n <y
1.89
1.25
0.36
0.43
0.44
211
2.05
0 12
0.52
0.60
L.I.
8.28
6.72
3.75
5.39
5.18
1 111
1.24
1.17
5 10
5.68
L.I.—f^Ojrtal
+0.71
-11.(18
-0.69
-1.83
-1.66
+1.99
+029
-1J4
-136
H3O
2
m e t h o d w i t h c o u p l e d o v e n and the t r a d i t i o n a l m e t h o d s ( g r a v i m e t r i c a n d P e n f i e l d ) , as
w e l l as " l o s s o n i g n i t i o n " r e s u l t s .
Total
:
»H20-(K F I
XH20-1G M]
A
+0.69
I
OMZOtotal (P.M.)
A n h y p o t h e s i s to e x p l a i n t h i s s i t u a t i o n is to c o n s i d e r that d u r i n g the " l o s s o n i g n i t i o n "
a n a l y s i s a n o x i d a t i o n o f F e O c a n o c c u r , as it is d o n e
atmosphere. Fe w o u l d change
its o x i d a t i o n state
from
in a muffle,
+2
in a oxidant
to +3, a c c o r d i n g to t h e
reaction:
2 FeO + % 0
239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254
sample number
2
— Fe 0
2
3
T h e c o n s e q u e n c e o f t h i s o x y g e n u p t a k e i n s a m p l e s that c o n t a i n F e O w o u l d b e that t h e
final
v a l u e for the " l o s s o n i g n i t i o n " d e c r e a s e s
p r o p o r t i o n a l l y to t h e F e O
content,
I f w e c o m p a r e the v a l u e s o b t a i n e d w i t h the " l o s s o n i g n i t i o n " m e t h o d w i t h the v a l u e s
b e c o m i n g s m a l l e r t h a n the v a l u e for t o t a l w a t e r c o n t e n t . T o c o n f i r m this h y p o t h e s i s , a
for the total water, a n i n c o h e r e n t result a p p e a r s for s o m e s a m p l e s , n a m e l y , that s o m e o f
c h e m i c a l s t u d y w a s p e r f o r m e d i n o n e o f the s a m p l e s ( s a m p l e 2 5 2 - ref. M S D X X A ) .
-
310
-
T h e o b t a i n e d results s h o w e d that t h i s is c o r r e c t , i.e., the m a s s i n c r e a s e is a c t u a l l y d u e to
o x i d a t i o n o f F e O . F i g u r e 4 s h o w s that there is a v e r y h i g h c o r r e l a t i o n b e t w e e n the F e O
c o n t e n t a n d the difference b e t w e e n the p e r c e n t a g e v a l u e s o f the total w a t e r a n d " l o s s o n
i g n i t i o n " . F u r t h e r , as far as the p r e s e n t results c a n s h o w , it s e e m s that f o r F e O c o n t e n t s
Acknowledgements
M a r t a E . T h e m u d o t h a n k s Laboratório d o I n s t i t u t o G e o l ó g i c o M i n e i r o a n d A q u i l e s A .
Bamos
and Margarida
Bastos
thank
Fundação
p a r a a Ciência
e
a
Tecnologia
( C . I . Q . U . P . ) for financial s u p p o r t .
b e l l o w 6 . 5 % (intercept) there w i l l b e n o s i g n i f i c a n t d i f f e r e n c e , i.e., the o x i d a t i o n o f F e O
w i l l n o t be s i g n i f i c a n t a n d w i l l n o t false the a n a l y s i s result.
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o b s e r v e d d i f f e r e n c e b e t w e e n t h e v a l u e s o f total w a t e r a n d " l o s s o n i g n i t i o n " .
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potenciometria,
- is o n l y v a l i d i n cases w h e r e it c a n be g u a r a n t e e d that n o o x i d a t i o n r e a c t i o n takes
F a c u l d a d e de Ciências de L í s b o a , 1 9 7 9 , 1 6 , 1 5 1 - 1 6 0 .
utilizando
a solução
de
Karl
Fischer", B o i . Mus.Lab.Min.Geol.
p l a c e , o r at least n o t i n a s i g n i f i c a n t extent, a n d that e x t r e m e c a r e m u s t be t a k e n o n the
8 - K . Y a m a y a , " D e t e r m i n a t i o n o f the W a t e r c o n t e n t i n m u s c o v i t e s c o n t a i n i n g large
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amounts o f fluorine
by Karl
F i s c h e r t i t r a t i o n after
fusion with s i l i c o n
dioxide",
A n a l y t i c a C h i m i c a A c t a , 1 9 7 9 , 110, 2 3 3 - 2 4 3 .
Conclusion
The
present w o r k p r o v i d e s
geological
a n e w experimental set-up for water determination i n
s a m p l e s , w i t h a s p e c i a l l y d e s i g n e d o v e n to be c o u p l e d to a n o r m a l K a r l
F i s c h e r c o u l o m e t e r . It s h o w s that r e l i a b l e a n d r e p r o d u c i b l e results c a n be o b t a i n e d w i t h
t h i s m e t h o d . F u r t h e r , it a l l o w e d v a l i d a t i o n o f the P e n f i e l d m e t h o d , w h i c h is c o m m o n l y
u s e d i n g e o l o g i c a l a n a l y s i s , a n d p o i n t e d o u t the e x t r e m e care that m u s t be t a k e n w i t h
results from the " l o s s o n i g n i t i o n " a n a l y s i s .
9 -
C. Cipriani and G . Bernardini, "Research
in geochemical
methodology, VII:
Determination o f water b y titration with K a r l F i s c h e r reagent". A t t i . S o e . T o s c a n a s c i .
Nat. Pisa, M e m . P V . , Ser. A , 6 5 , pp.221-236.