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DETERMINATION OF THE GERMANIUM CONTENT OFLIGNITE BY ATOMIC ABSORPTION SPECTROMETRY USINGA SOLID SAMPLE AND A GRAPHITE FURNACE ATOMISERBora Ergenoglu a & Aral Olcay ba Chemistry Department , Cumhuriyet University , Sivas, Turkeyb Chem.Eng.Dept. , Ankara Univ., Science Faculty. , Ankara, TurkeyPublished online: 15 Mar 2007.

To cite this article: Bora Ergenoglu & Aral Olcay (1990) DETERMINATION OF THE GERMANIUM CONTENT OF LIGNITE BY ATOMICABSORPTION SPECTROMETRY USING A SOLID SAMPLE AND A GRAPHITE FURNACE ATOMISER, Fuel Science and TechnologyInternational, 8:7, 743-752, DOI: 10.1080/08843759008915953

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FUEL SCIENCE AND TECHNOLOGY INT'L., a(?), 743-752 (1990)

DETERMINATION OF THE GERMANIUM CONTENT OF LIGNITE BY ATOMIC ABSORPTION SPECTROMETRY USING A SOLID SAMPLE AND A GRAPHITE FURNACE ATOMISER

. . Bora Ergenoglu , Aral Okay

,.Cumhuriyet University, Chemistry Department,Sivas Turkey Ankara Univ.,Science Faculty,Chem.Eng.Dept..Ankara Turkey

ABSTRACT

The germanium content of lignite is directly determined using a solid lignite sample. A standard solution of Ge was added to pow- dered coal samples which were then dried. A simple metallic bar with a cavity in it was used to introduce the sample into the fur- nace. Optimum temperature programming was determined to obtain Ge signals as free as possible from matrix interferences. Under opti- mum conditions 1 ng of Ge could be determined in a solid sample. The sensitivity of Ge as (Absorbance/g Ge) was ahout 500 times gre- ater,in solid sample analysis then in liquid sample analysis.

INTRODUCTION

Although Atomic Ahsorption Spectrometry (AAS) is a well-estab-

lished technique for trace element determination, it hes heen litt-

le used for the analysis of germanium. Some investigators (Amos and

Willis 1366; Popham and Schrenk 1968; Kirkbright et. a1 1969) used

flame atomisation and determined the atomic absorption characteris-

tics of Ge. Attempts were also made to improve sensitivity by sol-

vent extraction and nebulisation (Yanagisowa et. el 1969; ~ollock

1971; Shimomura et. a1 1978). Other workers used a carbon furnace

for atomisation and hydride generation was exploited to determine

Ge in aqueous media (Braman end Tompkins 1979; Andreae and Froelich

1981; Gordon and Froelich 1984).

CopyrightO 1990 by Marcel Dekker, Ins.

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7 4 4 ERGENOGLU AND OLCAY

The aim of t h e p r e s e n t work was t h e de te rmina t ion of germanium

i n l i g n i t e samples by AAS us ing a g r a p h i t e fu rnace a tomiser . To

i n v e s t i g a t e atomic a b s o r p t i o n c h a r a c t e r i s t i c s of Ge pre l iminary work

was c a r r i e d o u t wi th s t a n d a r d Ge s o l u t i o n s . S ince a c i d mix tures were

used t o decompose t h e l i g n i t e samples, t h e e f f e c t s of a c i d mix tures

were a l s o s t u d i e d . Cons iderab le suppress ion of t h e s i g n a l s was ob-

se rved when Ge was in t roduced i n t o t h e fu rnace i n 2M HpS04 and s i g -

n a l s completely d i sappeared i n ZM H,P04. Some enhancement of s i g n a l s

i n HNO, was observed b u t H C l had no e f f e c t s .

To e l i m i n a t e i n t e r f e r e n c e by a c i d s ano ther method of sample pre -

p a r a t i o n was sought . Burning t h e sample and d i g e s t i n g t h e ash i n aqua

r e g i a seemed s u i t a b l e , bu t no atomic s b s o r p t i o n s i g n a l s cou ld be ob-

se rved even i f d e t e c t a b l e amounts of Ge had been added t o t h e sample

b e f o r e ashing. Disappearence of t h e s i g n a l s was i n t e r p r e t e d ' a s remo-

v a l of Ge From t h e medium i n t h e form of i ts v o l a t i l e compounds du-

r i n g t h e course o f t h e combustion process . I t may be assumed t h a t , if

t h e ash ing p r o c e s s was c a r r i e d o u t i n a carbon furnace a tomiser then

d e t e c t i o n o f Ge would be p o s s i b l e whi le i t was l e a v i n g t h e mat r ix .

T h i s reasoning l e d t o t h e i d e a of determining Ge d i r e c t l y i n t h e s o l i d

sample.

EXPERIMENTAL

Apparatus

A Warian Tectron AA-6 atomic spec t rometer wi th a Perkin-Elmer

HGR-72 atomiser and a deuter ium background c o r r e c t o r was used t o mea-

s u r e atomic a b s o r p t i o n . S i g n a l s were recorded with an Oxford 3000 re -

corder .

Reagents and Samples - A s t a n d a r d Ge s o l u t i o n 1000 ppm c o n c e n t r a t i o n was provided from

BOH (U.K.). I t was d i l u t e d t o t h e r e q u i r e d c o n c e n t r a t i o n s wi th doubly

d i s t i l l e d water .

Procedure

0.2 g of f i n e l y powdered l i g n i t e samples were a c c u r a t e l y weighed

on a watch g l a s s and t h e r e q u i r e d volume of s tandard Ge s o l u t i o n was

added ( i . e . 50 u 1 of 20 ppm s t a n d a r d s o l u t i o n was added o n t o 0.2 Q of

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GERMANIUM CONTENT OF LIGNITE 745

lignite sample in order to prepare a sample containing x+5 ppm Ge, x

being the unknown concentration of Ge in lignite). This procedure was

repeated with the addition of different amounts of standard solution

to the same amount of sample. Thus a series of standardised samples of

different Ge concentration were obtained.

A simple tool, a metallic bar with a cavity at one end, (Figure 1)

was used to introduce the sample into the furnace atomiser. Powdered

sample was loaded into the cavity with a slim spatula and the probe

was then charged into the Furnace. The average weight of one cavity

volume of sample was 2.54 mg with a standard deviation from the mean

of 1.0 %.

The following heat treatment was applied to the solid lignite

sample: Heating at 1000~~ for 20 s (interference removing step), then

at 2 1 0 0 ~ ~ for 10 s (atomisation step), and finally at 2 5 0 0 ~ ~ for 10 s

(furnace cleaning step).

Atomic absorption was measured at 265.2 nm wave length, the other

parameters for instrument setting were those indicated by the manufac-

turers.

RESULTS AND DISCUSSION

Sensitiuity and Precision of Sample Handlinq

The mean value of 25 weights of one cavity-full of lignite sample

was 2.54 mg and the standard deviation from the mean value was 1.0 %.

Rlthough the method of sample introduction appears somewhat inaccurate

the data obtained from the experiments showed that it was quite satis-

factory for AAS and comparable with the accuracy of micropipetting used

to introduce liquid samples into the furnace. Considering the fact that

any error in liquid volumes would be multiplied in the results by dilu-

tion factor, a better accuracy would be claimed as opposed to liquid

sampling. Reproduciblity and proportionality of the atomic absorption

signals (Figure 4 ) were other indications of the reliability of the

method. Care must be taken in controlling both the particle size of the

solid sample and the volume of the standard solution added to the sample

to obtain high sensitivity. If the volume of the standard solution is

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ERGENOGLU AND OLCAY

Figure 1. Cross section of the tool used to feed the sample into

the furnace.

too small an homogenous wetting would not be achieved. On the other hand,

it the volume is too large some of the standard solution would remain on

the watch glass. To avoid the problem, one must take into account both

the mas5 of the sample to be wetted and the concentration of thestandard

solution.

Temperature Programming

Work started with an arbitrary temperature programme. During the

heat treatment of the sample, the temperature of the furnace was inc-

reased from ambient to 2600°C in four steps. The temperatures of each

step were 650, 1700, 2400, 2600°c and the duration of each step was

20 s (sample starts to decompose at about 650 and leaves the furnace

completely around 2600~~). Comparison of the signals recorded with

and without using a background corrector (Figure 2) showed that most

of the interference absorptions occurred during the heat treatment of

the sample. To determine at which temperature step the Ge atomised

heat treatment o f the sample was repeated with gradually increasing

Ge concentration of the sample. The background corrector was used in

the course of this process. Ge atomic absorption signals became dis-

tinguishable at 25 ppm Ge added sample at the third temperature step

(Figure 3c).

To increase the sensitivity of the atomic absorption signal, it

was essential that a temperature-renge in which the element Ge atomised

at a high ratio (and preferahly, on its own) without notable atomisation

of other constituents. This was achieved by dividing the temperature

range between 1700-2400~~ into slices and recording the AAS signal at

each slice with the other factors unchanged. In this way, Ge atomic

absorption signals wepe obtained as sharp and reproducible peaks

(Figure 4 ) .

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GERMANIUM CONTENT OF LIGNITE

Figure 2. Signals recorded from 5 ppm Ge added samples (a) without

using, (b) with using background corrector. Temperatures

of heating steps were 650, 1700, 2400 and 2 6 0 0 ~ ~ ; time

spent at each step was 20 s.

Figure 3. Signals recorded with background corrector from (a)

5 ppm, (b) 15 ppm, (c) 25 ppm Ge added lignite samples.

Temperature programming was the same as in Figure 2.

Optimum Location of The Sample in the Furnace

The location of the sample on the metal probe on which it was

charged into the furnace was a very significant factor in determi-

ning the sensitivity of the signals.. The reproducible signals shown

in Figure 4 could only be obtained after location of the optimum

point in the furnace where the sample had to be charged to get maxi-

mum sensitivity.

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ERGENOGLU AND OLCAY

Figure b . Atomic absorption signals after the optimization of the

conditions. (a) no Ge was added, (b) 4 ppm, (c) 8 ppm

Ge was added on samples. Atomisation was carried out at

2 1 0 0 ~ ~ in ID 3.

Determination of Germanium: Its Concentration in The Sample

Atomic absorption peak heights were plotted versus the additional

Ge concentration of the sample in Figure 5. Then the line was extrapo-

lated until it cut the concentration axis (Figure 5). From this graph,

Figure 5, the Ge concentration in the Orhaneli lignite was found to be

3.6 ppm.

The sensitivity of atomic kbsorption signals has also been found

to depend on the performance of the graphite furnace, the hollow cat-

hode lamp and also on the flow rate of purge gas.

Atomic Absorption Sensitivity of Ga and Its Relation to the Reaction

Mechanism

Under optimum conditions the AAS signal of Ge in lignite was found

to ha about 500 times more intense when the original sample was intro-

duced into the graphite furnace as a powder, compared to the conventi-

onal sampling technique where the sample is first ashed and then

dissolved in an acid to obtain the final solution to introduce into

the furnace. This observation indicates that the atomisation of Ge is

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GERMANIUM CONTENT OF LIGNITE

Figure 5. Absorbance-Concentration graph of Orhaneli lignite.

more efficient in the solid sample than in solution. The absorption

profiles given in Figure 6 is a clear indication of the superiority of

the solid sample technique. The difference in sensitivities could be

explained by considering atomisation mechanism.

The remarkable contribution to the reduction (atomisation) of metal

cations by the graphite furnace has already been reported in the lite-

rature (Aggett and Sprott 1974; Fuller 1974; Dean and Holcombe 1988).

It was suggested that upon heating, metal nitrates, sulfates, and

even halides tend to change into metal oxides and then the atomisation

process takes place either as a result of the thermal decomposition,

or by the reductive action of carbon on the oxides (Sturgeon and

Chakrabarti 1976).

Although no conclusive study of the atomisation mechanism of

Germanium is yet available, the enhancement of the intensity of the

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ERGENOGLU AND OLCAY

Figure 6. Rbsorption signals, (a) obtained by 8 ng Ge fed to the

atomiser on lignite. Rtomisation temp. 2 1 0 0 ~ ~ .

(b) obtained by 1000 ng Ge (50 "1, 20 ppm) fed to the

atomiser as standard solution. Atomisation temp.is

2 6 0 0 ~ ~ .

RRS signal of Ge reported in this study could reasonably be explained

by assuming that the above argument is also valid for the formation

of free Ge atoms; that is to say, when Ge was given to the furnace

in solution, atomisation was reached through the evaporation of Ge

and subsequent reduction by graphite of the furnace into elemental

form during the course of heat treatment of the sample. Since'the boi-

ling point of Ge is high (283O0C), its vapor pressure should be low

even at the highest furnace #temperature (2700~~). Consequently the

atomisation rate was slow and atomic absorption sensitivity of Ge was

low.

On the other hand, when Ge is given to the atomiser within lignite,

release of Ge during heat treatment as its volatile compounds Followed

by formation of free Ge atoms through thermal decomposition is quite

plausible. Volatile compounds of Ge might be Germanium nitrides or

Germanium sulfides, due to the presence of a substantial amount of sul-

fur and nitrogen in the lignites.

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GERMANIUH CONTENT OF L I G N I T E 751

This proposed mechanism is also supported by the fact that when

Ge was charged to the furnace in lignite, Ge atomic absorption signals

appeared at much lower temperature (around 1600~~) than the boiling

point of Germanium. Beside that, no atomic absorption signal could be

obtained when samples of Ge containing lignites were blended with

graphite. This observation was quite consistent with the proposed

theory. According to the proposed atomisation mechanism solid phase

reduction of Ge by graphite was to be expected. Dissappearence of the

signals upon mixing the lignite samples with graphite indicates that

the expected reduction of Ge in the solid phase took place. Once the

reduction of Ge in the solid phase occurred, no appreciable evapora-

tion of Ge would be expected at the temperature reached (2100~~).

ACKNOWLEDGMENT

The authors are greatful to the late Prof.R.Belcher, W.I.Stephen,

R.Townshend for their kind permission to use the laboratories of the

Analytical Chemistry Department of Birmingham University.

REFERENCES

Aggett J.,Sprott A.J., 19?ri, "Non-Flame Atomisation in Atomic Absorption

Spectrometry", Anal.Chim.Acta,~,421.

Andreae M.O.,Froelich P.N.,1981, "Determination of Germanium in Natural

Waters by Graphite Furnace Atomic Absorption Spectrometry with Hydride

Generation", Unal.Chem.z,287.

Amos M.D.,Willis J.B., 1986, "Use of High-temperature Premixed Flames

in Atomic Absorption Spectroscopy", Sprc t roch im.Ac ta ,~ ,1325.

Braman R.S.,Tompkins M.A., 1979, "Separation and Determination of

Hanogram Amounts of Inorganic tin and Methyltin Compounds in the

Environment", Anal.Chim.,l,lZ.

Dow

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752 ERGENOGLU AND OLCAY

Dean A.B.,Holcombe J.A.. 1988, "Mechanisms of Lead Vaporisation from

an Oxgenated Graphite Surface Using Mass Spectrometry and Atomic

Absorption", Anal.Chem.g,578.

Fuller C.W., 1974, "Kinetic Theory of Atomisation for Non-flame

Atomic Absorption Spectrometry with a Graphite Furnace The Kinetic

and Mechanism of Atomisation for Copper", Analyst,z,739.

Gardon A.,Froelich P.N., 1984, "Determination of Metilgermanium Species

in natural Waters by Graphite Furnace Atomic Absorption Spectrometry

with Hydride Generation", Anal.Chem.z,421.

Hirkbright G.F.,Sargent M.,West T.S., 1969, "Shielded Flame Emission

Burner Assembly for use with Atomic Absorption Spectrophotometers",

Talanta,s,1467.

Pollock E.N.,1971, "Gallium and Germanium in Limonite by Atomic

Absorption", Atomic Absorption Newsl.s,77.

Popham E.H.,Schrenk W.G.,1968, "Atomic flbsorption Characteristics of

Germenium", Spectrochim.Acta,~.543.

Shimomura S.,Sskurai H.,Hideyoshi M.,Yoshiki M., 1978, "Determination

of Germanium by Atomic Absorption Spectrometry After Solvent Extrac-

tion - Enhancement of Sensitivity by a Nebuliser Effect", Anal.Chim. Acta,E,69.

Sturgeon R.E.,Chakrabarti C.L.,1976, "Studies on Mechanism of Rtom

Formation in Graphite Furnace Atomic Absorption Spectrometry", Anal.

Chem.48,1972. -

Yanagisswa M.,Suzuki M.,Takeuchi T.,1969, "Trace Analysis by Flameless /

Atomic-absorption Spectrometry", Anal.Chim.Rcta.+,152.

Received: November 28, 1989

Accepted: December 8, 1989

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