1 |
DETERMINATION AND SPECIATION OF TELLURIUM IN ENVIRONMENTAL SAMPLES USING HYDRIDE GENERATION ATOMIC FLUORESCENCE SPECTROSCOPY (HG-AFS)Alzahrani, Ali 27 January 2014 (has links)
This thesis focuses on developing a new method to measure trace tellurium (Te) in
different environmental samples such as lake waters, mine tailings and sediments. The developed
technique is based on Hydride Generation Atomic Fluorescence Spectroscopy (HG-AFS), a
technique that can measure low concentration of Te and also allows for Te speciation at low cost
and high efficiency in various environmental samples.
To validate the method that could be used to determine Te speciation in various types of
environmental samples, a series of tests has been designed for finding the best conditions to
measure Te(IV) using HG-AFS and obtain accurate and reliable results. Those tests include the
stability of the signal, the acidity of the solution, the volatility of Te after digestion of solids, the
reduction from Te(VI) to Te(IV), the detection limit of the technique, and the validity of two
digestion methods under the optimum (HG-AFS) instrumental settings.
An interference study including the most common elements in the Earth’s crust such as
(Ni, Fe, Pb, Cr, Cu, Co, Zn, Mn and Mo) was also performed. The results of this study showed
that Cu(II) can severely interfere with Te quantification decreasing the Te signal to almost zero.
Therefore, different masking agents such as 8-hydroxyquinoline, 1,10-phenanthroline, urea and
thiourea were tested to reduce and eliminate this interference.
|
2 |
Estratégias analíticas para determinação de arsênio e selênio em amostras de alimentos utilizando a espectrometria de fluorescência atômica com geração de hidretos – HG AFSCavalcante, Dannuza Dias 02 1900 (has links)
Submitted by Ana Hilda Fonseca (anahilda@ufba.br) on 2014-10-21T14:15:47Z
No. of bitstreams: 1
Tese - Dannuza Cavalcante.pdf: 1879788 bytes, checksum: 0fd9cc5ca387348e35095d0c92a17183 (MD5) / Approved for entry into archive by Ana Hilda Fonseca (anahilda@ufba.br) on 2014-10-29T17:23:53Z (GMT) No. of bitstreams: 1
Tese - Dannuza Cavalcante.pdf: 1879788 bytes, checksum: 0fd9cc5ca387348e35095d0c92a17183 (MD5) / Made available in DSpace on 2014-10-29T17:23:53Z (GMT). No. of bitstreams: 1
Tese - Dannuza Cavalcante.pdf: 1879788 bytes, checksum: 0fd9cc5ca387348e35095d0c92a17183 (MD5) / CNPq / Neste trabalho que está no âmbito do PRONEX, foram desenvolvidas estratégias
analíticas para a determinação de arsênio e selênio em amostras de alimentos por HG
AFS. Foram realizados três trabalhos distintos. O primeiro consistiu no emprego da
amostragem e
m suspenção para determinação de arsênio em amostras de arroz.
Procedimentos de amostragem de suspensão foram avaliados para determinação de
As por geração de hidreto acoplado a AFS, usando HNO
3
e sonicação por 30 min. As
amostras foram preparadas com KI e
m ácido ascórbico e com HCl 6 mol L
-
1
, para
determinação As total. A exatidão foi confirmada por análise do material de referência
certificado NIES SRM 10b de farinha de arroz, a precisão foi confirma com valores de
RSD abaixo de 5,9 % e limites de detecçã
o e quantificação de 0,91 e 3,04 ng L
-
1
,
respectivamente. Este método foi utilizado para determinar o teor de arsênio em 24
amostras de arroz que foram adquiridas em supermercados da cidade de Salvador,
Bahia, Brasil. O conteúdo de arsênio nos três tipos
de arroz (branco, parbolizado e
integral) variou de 0,12 a 0,47 μg g
-
1
. O segundo trabalho foi o desenvolvimento de
método analítico para determinação de selênio em ovos. Três tipos de ovos foram
adquiridos (codorna, galinha e pata) em feiras e supermercad
os de Salvador. A
digestão foi realizada mediante adição de HNO
3,
H
2
O
2
30% v v
-
1
e HCl 6 mol L
-
1
,
utilizando o bloco digestor com dedo frio. As condições para a pré
-
redução e geração
do hidreto de selênio foram otimizadas
empregando o planejamento fatorial e a matriz
de Doehlert. As condições ótimas foram: concentração de HCL 5,3 mol L
-
1
,
concentração do borohidreto de sódio 2,6 % (m/v), volume de KBr 10% 1,0 mL e
tempo de pré
-
redução de 30 min. O método apresentou limites
de detecção e
quantificação de 0,22 e 0,77 ng L
-
1
, respectivamente. O RSD ficou abaixo de 4,7 %
demonstrando boa repetibilidade. A exatidão foi comprovada através da análise do
CRM de tecido de ostra e também através de comparação com resultados obtidos e
m
análise no ICP
-
MS. O método foi aplicado em quatro diferentes grupos de amostras,
na clara e na gema separadas e na mistura dos dois, sendo que as concentrações
mínimas e máximas foram de 0,35 ± 0,01 a 0,88 ± 0,03 μg g
-
1
. O terceiro trabalho foi o
desenv
olvimento de método para determinação de arsênio em atum e sardinha
enlatados. As amostras foram submetidas a 3 procedimentos de preparo de amostra
(bloco digestor, forno de micro
-
ondas e forno mufla). As condições para a pré
-
redução
e geração do hidreto d
e arsênio foram otimizadas empregando o planejamento fatorial
e a matrix de Doehlert e as condições encontradas foram: tempo de pré
-
redução de 21
min, volume de pré
-
redutor KI 10 % (m v
-
1
) em ácido ascórbico 2% (m v
-
1
) de 1,0 mL,
concentração de HCl 4,7 mo
l L
-
1
e concentração de NaBH
4
de 2% (m v
-
1
). O método
mostrou
-
se preciso, com valores de RSD abaixo de 7,0 %. Um material de referência
certificado de tecido de ostra (NIST SRM 1566b) foi analisado para avaliar a exatidão
do método. O material foi submetid
o a três procedimentos de digestão. Através da
análise dos resultados pode
-
se observar que o valor obtido no forno de micro
-
ondas e
no bloco digestor foi cerca de metade do valor certificado, pois a arsenobetaina só é
convertida a arsênio inorgânico a temp
eraturas acima de 300 º C. O método foi
aplicado para 20 amostras de atum e sardinha enlatados e os valores de concentração
variaram de: 0,63 ± 0,10 a 3,28 ± 0,20 μg g
-
1 / In this work
is under PRONEX
,
strategies for analytical
determination
of arsenic
and
selenium
in food samples
by HG
AFS
were
developed.
Three
diferent
studies were
conducted.
The first
one
consisted
in the use of
sampling
in
suspension
for
determination of
arsenic in
rice
procedures were evaluated to As by hydride generation
coupled to AFS using HNO
3
and sonication for 30 min.
The samples were prepared
with
KI
in
ascorbic
acid and
6
mol
L
-
1
HCl
to determine
total As
.
The
accuracy
was
confirmed by
analysis of
certified reference material
NIES
SRM
10b
rice flour
,
precision
was confirmed
with
%
RSD
values
lower than
5.9%
and
limits of detection
and
quantification of
0.
91 and
3.04
ng
L
-
1
, respectively.
This method was used
t
o
determine the content
of arsenic in
24
rice samples
purchased at
supermarkets in the
city
of Salvador
,
Bahia
,
Brazil
.
The content
of arsenic
in the three
types of rice
(
white,
parboiled
and integral
)
ranged
from 0.12 to 0.47
μ
g
g
-
1
.
In the second study
we
developed a
method for determination
of selenium in
eggs. Three
types of eggs
were
purchased
(
quail,
chicken and
paw)
at fairs
and supermarkets
of Salvador
.
The
digestion
was performed
by adding
HNO
3
,
30%
H
2
O
2
(
v v
-
1
)
,
6 mol
L
-
1
HCI
and
, using
the
block
digester
cold
finger. The conditions for the
pre
-
reduction and
hydride
generation
of selenium
were optimized
using
factorial design
and
Doehlert
matrix,
the
optimal conditions
were
:
HCl
concentration of
5.3
mol L
-
1
,
the
2.6
% (
w
v
-
1
)
sodium
borohydride
concentration
,
1.0 mL
volume of
10%
(
w
v
-
1
)
KBr
and
pre
-
reduction
time
30
min. The
method has
limits of detection and
quantification
of 0.2
2
and 0.7
7
ng
L
-
1
,
respectively.
The
%
RSD
was below
4.7
showing good
repeatability
.
The accuracy
was
confirmed by
analysis of
CRM
oyster
tissue and also
by comparison
with
results
obtained
for
analysis
by ICP
-
MS.
The method was
applied to four
different groups of
samples
,
in
clear
and
separate
yolk
and
mix of the two
,
the minimum and maximum
concentrations
were
0.35
±
0.01 to 0.88
±
0.03
mg
g
-
1
.
The third
work was the
development
of a method for
determination
of arsenic
in canned
tuna
and sardines
.
The samples
were subjected to three
procedures for
sample preparation
(
digestion
block,
microwave
and oven
muffle
).
The co
nditions for the
pre
-
reduction and
hydride
generation
of arsenic
were optimized
using
factorial design
matrix
and
Doehlert
,
the
conditions
were:
pre
-
reduction time of 21 min,
volume of 1.0
mL of
10%
KI
(
w
v
-
1
)
(pre
-
reducing)
in
2%
a
scorbic
acid, HCl
concentration of
4.7
mol L
-
1
and
NaBH
4
-
in
2% (
v
m
-
1
).
The
method was
precise,
with
RSD
values
below 7.0
%.
A
certified reference
material
of
oyster
tissue (
NIST
SRM
1566b
)
was analyzed
to assess the
accuracy of
the method
.
The material
was subjected to
the three
digestion procedure.
From t
he
analysis of the
results
it can be seen
that the
value obtained in the
microwave
oven
and
the digester
block was
about half the
value of
the certificate
, as the
only
arsenobetaine
is
converted
to
inorganic arsenic
at
temperatures
above
300
°C. The
method was applied
to
20 samples of
canned
tuna
and sardines
and
concentration
values
ranged from
0.63 ±
0.1
0
to 3.28
±
0.2
0
mg
g
-
1
|
3 |
Metal mobility during metamorphism and formation of orogenic gold deposits: Insights from the Dalradian of ScotlandEngström, Adam January 2013 (has links)
Orogenic gold deposits occur within metamorphic belts throughout the world and have through time represented the source for over 25% of the world’s gold production. Although orogenic gold deposits are of great economic importance, controversies exist on the subject of fluid and metal sources and there have been few studies of gold´s distribution and mobility outside of large economic deposits. Research made by Pitcairn et al. (2006), on the Mesozoic Otago and Alpine schists of New Zealand, observed systematic depletion of Au and a suite of 6 associated elements with increasing metamorphic grade. This depletion was identical to the suite of elements enriched in the Otago gold deposits and provided strong evidence that orogenic gold deposits form due to metamorphic processes. The mobilization of metals was attributed to the recrystallization of sulfide minerals during prograde metamorphism causing dehydration and release of metal-rich metamorphic fluids. This thesis is part of a larger project aimed at testing the “Otago model” in a classic metamorphic terrain: The Dalradian metamorphic belt of Scotland. Rocks in the study are from the southern higlands group and the Appin and Argyll group which range in metamorphic grade from chlorite zone greenschist facies to sillimanite zone amphibolite facies. Three main aspects, which supplement earlier research, are addressed in this study: 1) Investigation of the sulfide paragenesis at Loch Lomond and Stonehaven was carried out to map the evolution of sulfides with metamorphic grade and the possible relations to the distribution of gold. Using SEM scanning to quantify the abundance of different sulfide minerals together with previous data on the Glen Esk region, a complex sulfide evolution pattern for the Dalradian Supergroup is identified. The sulfide evolution describes the same changes in texture and chemistry as observed in the Otago Schists but is made complex by the difference in geological evolution for the different regions. 2) Reinvestigation of the higher grade zones of Glen Esk (staurolite to sillimanite) was carried out as samples from the previous study were very weathered. Results from ultralow detection limit methods (HG-AFS and a gold detection method developed by Pitcairn et al. 2006) showed significant systematic depletion of Au and As with metamorphic grade. From chlorite to sillimanite zone average values of Au and As were showed to decrease by 65% and 88% respectively. Furthermore, a suite of 10 major and 12 trace elements were analyzed using ICP methods showing no trends of systematic depletion with increased metamorphic grade. 3) Investigation of Pb-Ag Veining and vein samples from each of the metamorphic index mineral zones in the Glen Esk area was carried out to identify fluid composition and ore mineralogy. Using microthermometry and Raman laser spectroscopy two distinct fluids were identified. The first type is a H2O-CO2-N2-salt fluid of low salinity (0-15 weight percent NaCl equivalent) and medium temperature (150 to 250 °C) locally containing minor amounts of CH4. It is found in the veins from the mineral index zones of Glen Esk and was formed in the ductile regime most likely related to late stage metamorphic devolatilization released during Caledonian uplift of the Dalradian. Pb-Ag veins from the locality of Hardhill host the second fluid type which was formed in the brittle regime accompanied by brecciation as a high salinity (15 to 20 weight percent NaCl equivalent) low temperature (70-140°C) H2O-salt fluid with calcic composition was precipitated. This fluid bears much resemblance to Carboniferous calcic brines responsible for economic base-metal precipitation with widespread occurrence in southwest Scotland and Northern Ireland. Results of this thesis show many similarities with the Otago study, with a connection between metal mobility and metamorphic grade, providing support for the dehydration model as a viable mechanism for the generation of orogenic gold deposits.
|
Page generated in 0.0145 seconds