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Determination of trace amounts of siloxanes in water, sediments and fish tissues by inductively coupled plasma emission spectrometry
The Science of the Total Environment, 34 (1984) 169--176 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
169
D E T E R M I N A T I O N OF T R A C E A M O U N T S OF S I L O X A N E S IN WATER, SEDIMENTS AND FISH TISSUES BY INDUCTIVELY COUPLED PLASMA EMISSION SPECTROMETRY
N. WATANABE, Y. YASUDA, K. KATO and T. NAKAMURA Gifu Prefectural Research Institute for Environmental Pollution, Yabuta 8--58--2, Gifu-shi, 500 (Japan) R. FUNASAKA and K. SHIMOKAWA Gifu-ken Public Health Examination Center, Akebono-cho 6--4, Gifu-shi, 500 (Japan) E. SATO Yokaiti Hygienic Works Association, Shibaharaminami-cho, 1590, Yokaiti-shi, 527 (Japan) Y. OSE Gifu College of Pharmacy, Mitahorahigashi 5--6--1, Gifu-shi, 502 (Japan) (Received June 25th, 1983; accepted July 26th, 1983)
ABSTRACT A simple and rapid method is described for the separation and determination of organosilicones in water, sediment and samples of fish tissues, using inductively coupled plasma emission spectrometry. Organosilicone extract with petroleum ether is evaporated to dryness. The damp residue is dissolved in methyl isobutyl ketone, aspirated into the plasma. Optimisation of gas (plasma support, coolant and carrier) flow-rates and plasma height are discussed. Detection limit (28) is 0.01pgml -l for organosilicone and is adequate for environmental samples. Precision of the proposed method is 4.7% for river water, 10.8% for river sediment, 1.2% for sewage sludge and 13.3% for fish tissue. INTRODUCTION D i m e t h y l p o l y s i l o x a n e s (DMPS) are s y n t h e t i c p o l y m e r s w h i c h possess m a n y desirable p r o p e r t i e s such as l o w surface tension, w a t e r r e p e l l e n c y , t h e r m a l and c h e m i c a l stability, resistance to ultraviolet r a d i a t i o n and a pres u m e d biological inertness ( H o b b s et al., 1 9 7 5 ; Baker and B o d d y , 1 9 7 7 ; Mann et al., 1 9 7 7 ) . These p r o p e r t i e s have led to their extensive use in a variety o f industrial and d o m e s t i c applications, and t h e w i d e s p r e a d use o f siloxanes suggests t h a t t h e y m a y be released i n t o the e n v i r o n m e n t . 0048-9697/84/$03.00
© 1984 Elsevier Science Publishers B.V.
170 TABLE 1 OPERATING CONDITIONS SPECTROMETER
FOR
Oscillator frequency Incident power Reflection power Plasma height above induction coil Coolant gas flow-rate Plasma support gas flow-rate Carrier gas flow-rate Sample introduction rate Preburn time Integration time Wavelength
THE
SHIMADZU
ICPQ-100
EMISSION
27.12 MHz 1.8 kW (5W 9.7 mm Ar, 201 min- 1 Ar, 1.21.rain-1 Ar, 0.81 rain- 1 2.5 ml min-l 45 sec 20 sec 2881.5 nm
Some references to the environmental contamination resulting from these uses are available. Many authors have reported levels of siloxanes in environmental samples, including water and sediments (Pellenbarg, 1979; Environment Agency of Japan, 1981), sewage sludge (Tsuchitani et al., 1978; Pellenbarg, 1979) and biological tissues (Environment Agency of Japan, 1981). In these studies, siloxanes were determined by atomic absorption spectrometry (AAS), but the sensitivity of the m e t h o d is not always good enough to determine trace amounts of siloxanes in environmental samples. Recently, the argon supported inductively coupled plasma emission spectrometer (ICP) is rapidly coming to be an accepted analytical tool for environmental samples (Thompson et al., 1978; McQuaker et al., 1979; Rica and Kirkbright, 1982; Subramanian and Meranger, 1982). The application of ICP is still in its infancy for the determination of heavy metals in organic solvents. In this paper, we describe the analytical m e t h o d for levels of siloxanes in water, sediments and fish tissues with ICP.
EXPERIMENTAL
Apparatus A Shimadzu ICPQ-100 inductivity coupled plasma emission spectrometer, interfaced to a programmable calculator and dot-impact printer, was used for the determination of siloxanes. The operating conditions for the spectrometer used in this work are given in Table 1. An ultrasonic bath (Kokusai Denki Co.) was used for the extraction of siloxanes in sediment and samples of fish tissue. All glassware used was cleaned with chloroform and petroleum ether to ensure freedom from contamination with siloxanes.
Reagents Stock solution of organosilicone ( 5 0 0 m g l - 1 ) , dissolved in methyl isobutyl ketone (MIBK), was prepared from Toray silicone fluid SH-200 (100 cp) and octaphenylcyclotetrasiloxane. A fresh working solution was
171
2.0
2.0
_~ 1.9
c
tll L_
1.9
1.8
*:_ 1.8 JO
/
ell
1.?
1.7 E
E
1.6
1.6
I
I
l
r
J
r
I
1.2
1.3
1.4
1.5
1,6
16
18
Plasma
support
gas,
t rain -L
Cool.ant gas f l o w - r a t e
20 , !. rain ")
Fig. 1. E f f e c t o f p l a s m a s u p p o r t gas flow-rate o n o r g a n o s i l i c o n e response. C o o l a n t gas flow-rate, 201 rain- 1 ; carrier gas flow-rate, 0.81 m i n - 1. Fig. 2. E f f e c t o f c o o l a n t gas flow-rate o n o r g a n o s i l i c o n e response. P l a s m a s u p p o r t gas flow-rate, 1.21 rain -1 ; carrier gas flow-rate, 0.81 m i n -1.
prepared daily from the stock solution b y dilution with MIBK; the stock and working solutions were stored in teflon flasks. High-purity water, obtained by passing tap water through an ion-exchange column and subsequent distillation, was used for cleaning and sample preparation. Argon and other reagents used in this work were of analytical grade.
Analytical procedure (i) Liquid sample; 500--4000 ml was placed in a separating funnel and extracted twice with two aliquots (2 x 1 0 0 m l ) of petroleum ether by shaking vigorously for 10 min. Combined petroleum ether extracts were dehydrated with anhydrous sodium sulfate, then rotary evaporated to dryness. The residue was dissolved in 5 ml MIBK. The organosilicone concentration (/zg m1-1 ) was obtained by reference to a linear working curve prepared from octaphenylcyclotetrasiloxane. (ii) Sediment or samples of fish tissues; solid samples (5--50 g) were placed into 200 ml erlenmeyer flasks with a ground glass stopper, then allowed to stand overnight after addition of 100 ml petroleum ether. The samples were extracted with ultrasonics for 15 min, dehydrated with anhydrous sodium sulfate and then rotary evaporated to dryness; the residue was taken up to 5 ml with MIBK. The organic silicone concentration (#g g- 1 ) was determined by the m e t h o d of procedure (i).
172
2.2~ "'~ 8L 1.z~
o
W
1.0
0.6
I
1
I
I
I
I
0.5
0.6
0.7
0.8
0.9
1.0
Carrier
gas
flow
rate
t t
r a i n -)
Fig. 3. Effect of carrier gas flow-rate on organosilicone response. Plasma support gas flowrate, 1.21 min- 1; coolant gas flow-rate, 201 rain- 1.
RESULTS AND DISCUSSION
Optimisation of gas flow-rates and plasma height In determining trace amounts of organosilicone in MIBK, the effect of variations of one of the three gas flow-rates (coolant, plasma support, carrier) with the other two held constant and with the plasma height being fixed at 9.7 mm above the induction coil, is shown in Figs. 1--4. Figure 1 shows the effect of plasma support gas flow-rate on the organosilicone response. The change in response was small for the variation of plasma support gas flow-rate with the coolant gas flow-rate (201 min -1 ) and carrier gas flow-rate (0.81 min -1 ) held constant. Below a flow-rate of 1.21 min -~ , measurement became impossible because of extinction of the plasma torch. Figure 2 shows the effect of coolant gas flow-rate on the organosilicone response. Sensitivity increased as the coolant gas flow-rate increased from 161 min-1 to a m a x i m u m level with the plasma support gas flow-rate (1.21 min-1) and carrier gas flow-rate (0.81 min -1 ) held constant. Figure 3 shows the effect of carrier gas flow-rate on the organosilicone response. Maximum emission occurred for a flow-rate of between 0.7 and 0.81 min-1, with the plasma support gas flow-rate (1.21 min -1) and coolant gas flow-rate (201 min- 1) held constant. Figure 4 shows the effect of plasma height on organosilicone response at the selected flow-rates. Emission intensity varied markedly with small changes in plasma height; the best compromise position was between 7 and 10 mm.
173
2.0
1.at., >, 1.6-
1.4-
"~ 1.2--
1.0 I 2.0
I 4.0
I 6.0
I 8.0
Height
above
work coit
I 10
I 12
,mm
o f p l a s m a h e i g h t o n organosilicone response. Carrier gas flow-rate, 0 . 8 ] rain -1 ; plasma support gas flow-rate, 1.21 m i n -1 ; coolant gas flow-rate, 2 0 ] r a i n -1 . Fig. 4. E f f e c t
0.5
B
3.0
--
/
0.4
~
o.3
~
0.2
2.0
1.0 LU
0.1
0
[
I
I
1
2
3
1 0
Organosilicone ( ~ J g / m t )
Fig. 5. C a l i b r a t i o n
curve of organosilicone
5
10
15
20
in MIBK
at t h e s e l e c t e d
operating
conditions.
Calibration curve and detectability Eight reference solutions containing 5, 10, 20, 30, 50, 100, 150 and 2 0 0 p g of organosilicone on 1 0 m l MIBK were prepared by diluting the stock solution of octaphenylcylotetrasiloxane. Each solution was analyzed by ICP under identical operating conditions listed in Table 1; two readings were made in each case and the results were averaged. Figure 5 shows the
174 110 Toluene 100
.~"
[3,
90 ~z o o (3.
Heavy oi[
70
tK
60
5o 1
I
I
I
10
10 2
103
104
] n t e r f e r e n t / DMPS
Fig. 6. E f f e c t o f t o l u e n e , vegetable oil a n d h e a v y oil o n t h e r e c o v e r y o f o r g a n o s i l i c o n e .
calibration curve which gave a straight line; a wide working range of 5-200 pg of organosilicone per 10 ml of MIBK phase was obtained. The detection limit can be expected to be 0.01pg m l - l , provided it is defined as the concentration of organosilicone in pg ml-1 that produces an emission intensity twice the background variability. The detection limit of ICP is though to be more than two orders of magnitude lower than that of AAS (Paralusz, 1968; Neal, 1969; Kunde, 1977).
Interferences Other workers have indicated t h a t toluene, vegetable oil and heavy oil in MIBK phase affect the determination of trace organosilicone, although the presence of inorganic silicone compounds did not interfere (Neal, 1969; Tsuchitani et al., 1978; Pellenbarg, 1979). Various amounts of toluene, vegetable oil and heavy oil were added to a fixed a m o u n t of DMPS (200 #g) in 10 ml MIBK and their effect on measurements was examined. Figure 6 shows the effect of toluene, vegetable oil and heavy oil at the concentration ratio (interferent/DMPS) between 5 and 104. Results in Fig. 6 are given as the percentage of interference-free response. The response for toluene was n o t affected at levels up to 104 , but the response for vegetable and heavy oils was affected by more than a factor of 50. For environmental samples such as river waters, industrial effluents and river sediments, the presence of vegetable and heavy oils at normal levels can be tolerated.
Recovery and precision The recovery of organosilicone by the proposed m e t h o d was evaluated by processing distilled water, river sediment and fish tissue spiked with known
175 TABLE 2 RECOVERY OF DMPSa IN WATER, SEDIMENTS AND FISH SAMPLES Sample
Amount of sample
DMPS added (pg)
DMPS found (//g)
Recovery (%)
Distilled water
1,000 ml 1,000 ml
20 200
13.5 141
67.5 70.5
69.0
10 g 10g 10g
0 20 200
12.6 24.5 124.4
59.5 55.9
57.7
10 g 10g 10g
0 20 200
1.3 10.3 107
45.0 52.8
48.9
River sediment
Fish tissue
aDMPS; Toray silicone fluid SH-200, 100 cp. TABLE 3 PRECISION ATTAINED BY THE PROPOSED METHOD FOR THE DETERMINATION OF ORGANOSILICONE Sample
No. of separate determinations
Concentration range (ppm)
Average value (ppm)
Coefficient of variation (%)
River water River sediment Sewage sludge Fish tissue
5 8 8 4
0.0125--0.0138 1.10--1.44 8.31--8.66 0.104--0.136
0.0132 1.30 8.50 0.121
4.7 10.8 1.2 13.3
q u a n t i t i e s (20 and 2 0 0 pg) o f DMPS. Table 2 s h o w s the r e c o v e r y o f DMPS in water, s e d i m e n t and fish tissue. A d d i t i o n s o f DMPS in water, s e d i m e n t and fish tissue samples were r e c o v e r e d with yields o f 69.0, 57.7 and 48.9%, respectively. T h e r e c o v e r y o f DMPS in solid samples b y the p r o p o s e d m e t h o d was i n t e r m e d i a t e b e t w e e n t h e r e c o v e r y b y S o x h l e t (Pellenbarg, 1 9 7 9 ) a n d b y D e a n Stark e x t r a c t i o n s ( T s u c h i t a n i et al., 1978), while no studies have been r e p o r t e d on the r e c o v e r y o f DMPS in w a t e r and samples o f fish tissue. In a test o f precision, f o u r d i f f e r e n t kinds o f e n v i r o n m e n t a l samples, river water, river s e d i m e n t , sewage sludge and fish tissue were e x a m i n e d . Table 3 s h o w s t h e precision a t t a i n e d by the p r o p o s e d m e t h o d . The c o e f f i c i e n t o f variation was 4.7% f o r river water, 10.8% f o r river s e d i m e n t , 1.2% f o r sewage sludge and 13.3% for fish tissue. The p r o p o s e d m e t h o d gives g o o d precision and is a c c e p t a b l e f o r the d e t e r m i n a t i o n o f trace o r g a n o s i l i c o n e in e n v i r o n m e n t a l samples.
176 ACKNOWLEDGEMENT
The authors wish to thank Mr. S. Nishiwaki, President of Gifu Prefectural Research Institute for Environmental Pollution, for his critical reading, al~d permission for publication.
REFERENCES Baker, C. D. and M. R. Boddy, 1977. Determination of silicone antifoam in beer. J. Inst. Brew., 83: 158--159. Environment Agency of Japan, 1981. Chemicals in the environment. No. 7, p. 70. Hobbs, E. J., M. L. Keplinger and J. C. Calandra, 1975. Toxicity of polydimethylsiloxanes in certain environment systems. Environ. Res., 10: 397--406. Kunde, M. K., 1977. Determination of silicones in vegetable oils by nonflame atomic absorption spectrophotometry. Fette Seifen Anstrichm., 79: 170--173. Mann, H., B. Ollenschlager and H.-H. Reichenbach-Klinke, 1977. Untersuchunger zur Wirkung von Siliconolen auf Regenbogenforellen. Fisch. Umwelt., 3: 19--22. McQuaker, N. R., P. D. Kluckner and G. N. Chang, 1979. Calibration of an inductively coupled plasma-atomic emission spectrometer for the analysis of environmental materials. Anal. Chem., 5 1 : 8 8 8 - 8 9 5 . Neal, P., 1969. Note on the atomic absorption analysis of dimethylpolysiloxanes in the presence of silicates. J. Assoc. Off. Anal. Chem., 52: 875--876. Paralusz, C. M., 1968. Trace organic silicon analysis using atomic absorption spectroscopy. Appl. Spectrosc., 22: 520--526. Pellenbarg, R., 1979. Environmental poly(organosiloxanes) (silicones). Environ. Sci. Technol., 13: 565--569. Rica, C. C. and G. F. Kirkbright, 1982. Determination of trace concentrations of lead and nickle in human milk by electrothermal atomisation atomic absorption spectrophotometry and inductively-coupled plasma emission spectroscopy. Sci. Total Environ., 22: 193--201. Subramanian, K. S. and J. C. Meranger, 1982. Simultaneous determinatin of 20 elements in some human kidney and liver autopsy samples by inductively-coupled plasma atomic emission spectrometry. Sci. Total Environ., 24: 147--157. Thompson, M., B. Pahlavanpour, S. J. Walton and G. F. Kirkbright, 1978. Simultaneous determination of trace concentrations of arsenic, antimony, bismuth, selenium and tellurium in aqueous solution by introduction of the gaseous hydrides into an inductively coupled plasma source for emission spectrometry. Analyst, 103: 568--579. Tsuchitani, Y., K. Harada, K. Saito, N. Muramatsu and K. Uematsu, 1978. Determination of organosilicone in sewage sludge by atomic absorption spectrometry. Bunseki Kagaku, 27: 343--347.
169
D E T E R M I N A T I O N OF T R A C E A M O U N T S OF S I L O X A N E S IN WATER, SEDIMENTS AND FISH TISSUES BY INDUCTIVELY COUPLED PLASMA EMISSION SPECTROMETRY
N. WATANABE, Y. YASUDA, K. KATO and T. NAKAMURA Gifu Prefectural Research Institute for Environmental Pollution, Yabuta 8--58--2, Gifu-shi, 500 (Japan) R. FUNASAKA and K. SHIMOKAWA Gifu-ken Public Health Examination Center, Akebono-cho 6--4, Gifu-shi, 500 (Japan) E. SATO Yokaiti Hygienic Works Association, Shibaharaminami-cho, 1590, Yokaiti-shi, 527 (Japan) Y. OSE Gifu College of Pharmacy, Mitahorahigashi 5--6--1, Gifu-shi, 502 (Japan) (Received June 25th, 1983; accepted July 26th, 1983)
ABSTRACT A simple and rapid method is described for the separation and determination of organosilicones in water, sediment and samples of fish tissues, using inductively coupled plasma emission spectrometry. Organosilicone extract with petroleum ether is evaporated to dryness. The damp residue is dissolved in methyl isobutyl ketone, aspirated into the plasma. Optimisation of gas (plasma support, coolant and carrier) flow-rates and plasma height are discussed. Detection limit (28) is 0.01pgml -l for organosilicone and is adequate for environmental samples. Precision of the proposed method is 4.7% for river water, 10.8% for river sediment, 1.2% for sewage sludge and 13.3% for fish tissue. INTRODUCTION D i m e t h y l p o l y s i l o x a n e s (DMPS) are s y n t h e t i c p o l y m e r s w h i c h possess m a n y desirable p r o p e r t i e s such as l o w surface tension, w a t e r r e p e l l e n c y , t h e r m a l and c h e m i c a l stability, resistance to ultraviolet r a d i a t i o n and a pres u m e d biological inertness ( H o b b s et al., 1 9 7 5 ; Baker and B o d d y , 1 9 7 7 ; Mann et al., 1 9 7 7 ) . These p r o p e r t i e s have led to their extensive use in a variety o f industrial and d o m e s t i c applications, and t h e w i d e s p r e a d use o f siloxanes suggests t h a t t h e y m a y be released i n t o the e n v i r o n m e n t . 0048-9697/84/$03.00
© 1984 Elsevier Science Publishers B.V.
170 TABLE 1 OPERATING CONDITIONS SPECTROMETER
FOR
Oscillator frequency Incident power Reflection power Plasma height above induction coil Coolant gas flow-rate Plasma support gas flow-rate Carrier gas flow-rate Sample introduction rate Preburn time Integration time Wavelength
THE
SHIMADZU
ICPQ-100
EMISSION
27.12 MHz 1.8 kW (5W 9.7 mm Ar, 201 min- 1 Ar, 1.21.rain-1 Ar, 0.81 rain- 1 2.5 ml min-l 45 sec 20 sec 2881.5 nm
Some references to the environmental contamination resulting from these uses are available. Many authors have reported levels of siloxanes in environmental samples, including water and sediments (Pellenbarg, 1979; Environment Agency of Japan, 1981), sewage sludge (Tsuchitani et al., 1978; Pellenbarg, 1979) and biological tissues (Environment Agency of Japan, 1981). In these studies, siloxanes were determined by atomic absorption spectrometry (AAS), but the sensitivity of the m e t h o d is not always good enough to determine trace amounts of siloxanes in environmental samples. Recently, the argon supported inductively coupled plasma emission spectrometer (ICP) is rapidly coming to be an accepted analytical tool for environmental samples (Thompson et al., 1978; McQuaker et al., 1979; Rica and Kirkbright, 1982; Subramanian and Meranger, 1982). The application of ICP is still in its infancy for the determination of heavy metals in organic solvents. In this paper, we describe the analytical m e t h o d for levels of siloxanes in water, sediments and fish tissues with ICP.
EXPERIMENTAL
Apparatus A Shimadzu ICPQ-100 inductivity coupled plasma emission spectrometer, interfaced to a programmable calculator and dot-impact printer, was used for the determination of siloxanes. The operating conditions for the spectrometer used in this work are given in Table 1. An ultrasonic bath (Kokusai Denki Co.) was used for the extraction of siloxanes in sediment and samples of fish tissue. All glassware used was cleaned with chloroform and petroleum ether to ensure freedom from contamination with siloxanes.
Reagents Stock solution of organosilicone ( 5 0 0 m g l - 1 ) , dissolved in methyl isobutyl ketone (MIBK), was prepared from Toray silicone fluid SH-200 (100 cp) and octaphenylcyclotetrasiloxane. A fresh working solution was
171
2.0
2.0
_~ 1.9
c
tll L_
1.9
1.8
*:_ 1.8 JO
/
ell
1.?
1.7 E
E
1.6
1.6
I
I
l
r
J
r
I
1.2
1.3
1.4
1.5
1,6
16
18
Plasma
support
gas,
t rain -L
Cool.ant gas f l o w - r a t e
20 , !. rain ")
Fig. 1. E f f e c t o f p l a s m a s u p p o r t gas flow-rate o n o r g a n o s i l i c o n e response. C o o l a n t gas flow-rate, 201 rain- 1 ; carrier gas flow-rate, 0.81 m i n - 1. Fig. 2. E f f e c t o f c o o l a n t gas flow-rate o n o r g a n o s i l i c o n e response. P l a s m a s u p p o r t gas flow-rate, 1.21 rain -1 ; carrier gas flow-rate, 0.81 m i n -1.
prepared daily from the stock solution b y dilution with MIBK; the stock and working solutions were stored in teflon flasks. High-purity water, obtained by passing tap water through an ion-exchange column and subsequent distillation, was used for cleaning and sample preparation. Argon and other reagents used in this work were of analytical grade.
Analytical procedure (i) Liquid sample; 500--4000 ml was placed in a separating funnel and extracted twice with two aliquots (2 x 1 0 0 m l ) of petroleum ether by shaking vigorously for 10 min. Combined petroleum ether extracts were dehydrated with anhydrous sodium sulfate, then rotary evaporated to dryness. The residue was dissolved in 5 ml MIBK. The organosilicone concentration (/zg m1-1 ) was obtained by reference to a linear working curve prepared from octaphenylcyclotetrasiloxane. (ii) Sediment or samples of fish tissues; solid samples (5--50 g) were placed into 200 ml erlenmeyer flasks with a ground glass stopper, then allowed to stand overnight after addition of 100 ml petroleum ether. The samples were extracted with ultrasonics for 15 min, dehydrated with anhydrous sodium sulfate and then rotary evaporated to dryness; the residue was taken up to 5 ml with MIBK. The organic silicone concentration (#g g- 1 ) was determined by the m e t h o d of procedure (i).
172
2.2~ "'~ 8L 1.z~
o
W
1.0
0.6
I
1
I
I
I
I
0.5
0.6
0.7
0.8
0.9
1.0
Carrier
gas
flow
rate
t t
r a i n -)
Fig. 3. Effect of carrier gas flow-rate on organosilicone response. Plasma support gas flowrate, 1.21 min- 1; coolant gas flow-rate, 201 rain- 1.
RESULTS AND DISCUSSION
Optimisation of gas flow-rates and plasma height In determining trace amounts of organosilicone in MIBK, the effect of variations of one of the three gas flow-rates (coolant, plasma support, carrier) with the other two held constant and with the plasma height being fixed at 9.7 mm above the induction coil, is shown in Figs. 1--4. Figure 1 shows the effect of plasma support gas flow-rate on the organosilicone response. The change in response was small for the variation of plasma support gas flow-rate with the coolant gas flow-rate (201 min -1 ) and carrier gas flow-rate (0.81 min -1 ) held constant. Below a flow-rate of 1.21 min -~ , measurement became impossible because of extinction of the plasma torch. Figure 2 shows the effect of coolant gas flow-rate on the organosilicone response. Sensitivity increased as the coolant gas flow-rate increased from 161 min-1 to a m a x i m u m level with the plasma support gas flow-rate (1.21 min-1) and carrier gas flow-rate (0.81 min -1 ) held constant. Figure 3 shows the effect of carrier gas flow-rate on the organosilicone response. Maximum emission occurred for a flow-rate of between 0.7 and 0.81 min-1, with the plasma support gas flow-rate (1.21 min -1) and coolant gas flow-rate (201 min- 1) held constant. Figure 4 shows the effect of plasma height on organosilicone response at the selected flow-rates. Emission intensity varied markedly with small changes in plasma height; the best compromise position was between 7 and 10 mm.
173
2.0
1.at., >, 1.6-
1.4-
"~ 1.2--
1.0 I 2.0
I 4.0
I 6.0
I 8.0
Height
above
work coit
I 10
I 12
,mm
o f p l a s m a h e i g h t o n organosilicone response. Carrier gas flow-rate, 0 . 8 ] rain -1 ; plasma support gas flow-rate, 1.21 m i n -1 ; coolant gas flow-rate, 2 0 ] r a i n -1 . Fig. 4. E f f e c t
0.5
B
3.0
--
/
0.4
~
o.3
~
0.2
2.0
1.0 LU
0.1
0
[
I
I
1
2
3
1 0
Organosilicone ( ~ J g / m t )
Fig. 5. C a l i b r a t i o n
curve of organosilicone
5
10
15
20
in MIBK
at t h e s e l e c t e d
operating
conditions.
Calibration curve and detectability Eight reference solutions containing 5, 10, 20, 30, 50, 100, 150 and 2 0 0 p g of organosilicone on 1 0 m l MIBK were prepared by diluting the stock solution of octaphenylcylotetrasiloxane. Each solution was analyzed by ICP under identical operating conditions listed in Table 1; two readings were made in each case and the results were averaged. Figure 5 shows the
174 110 Toluene 100
.~"
[3,
90 ~z o o (3.
Heavy oi[
70
tK
60
5o 1
I
I
I
10
10 2
103
104
] n t e r f e r e n t / DMPS
Fig. 6. E f f e c t o f t o l u e n e , vegetable oil a n d h e a v y oil o n t h e r e c o v e r y o f o r g a n o s i l i c o n e .
calibration curve which gave a straight line; a wide working range of 5-200 pg of organosilicone per 10 ml of MIBK phase was obtained. The detection limit can be expected to be 0.01pg m l - l , provided it is defined as the concentration of organosilicone in pg ml-1 that produces an emission intensity twice the background variability. The detection limit of ICP is though to be more than two orders of magnitude lower than that of AAS (Paralusz, 1968; Neal, 1969; Kunde, 1977).
Interferences Other workers have indicated t h a t toluene, vegetable oil and heavy oil in MIBK phase affect the determination of trace organosilicone, although the presence of inorganic silicone compounds did not interfere (Neal, 1969; Tsuchitani et al., 1978; Pellenbarg, 1979). Various amounts of toluene, vegetable oil and heavy oil were added to a fixed a m o u n t of DMPS (200 #g) in 10 ml MIBK and their effect on measurements was examined. Figure 6 shows the effect of toluene, vegetable oil and heavy oil at the concentration ratio (interferent/DMPS) between 5 and 104. Results in Fig. 6 are given as the percentage of interference-free response. The response for toluene was n o t affected at levels up to 104 , but the response for vegetable and heavy oils was affected by more than a factor of 50. For environmental samples such as river waters, industrial effluents and river sediments, the presence of vegetable and heavy oils at normal levels can be tolerated.
Recovery and precision The recovery of organosilicone by the proposed m e t h o d was evaluated by processing distilled water, river sediment and fish tissue spiked with known
175 TABLE 2 RECOVERY OF DMPSa IN WATER, SEDIMENTS AND FISH SAMPLES Sample
Amount of sample
DMPS added (pg)
DMPS found (//g)
Recovery (%)
Distilled water
1,000 ml 1,000 ml
20 200
13.5 141
67.5 70.5
69.0
10 g 10g 10g
0 20 200
12.6 24.5 124.4
59.5 55.9
57.7
10 g 10g 10g
0 20 200
1.3 10.3 107
45.0 52.8
48.9
River sediment
Fish tissue
aDMPS; Toray silicone fluid SH-200, 100 cp. TABLE 3 PRECISION ATTAINED BY THE PROPOSED METHOD FOR THE DETERMINATION OF ORGANOSILICONE Sample
No. of separate determinations
Concentration range (ppm)
Average value (ppm)
Coefficient of variation (%)
River water River sediment Sewage sludge Fish tissue
5 8 8 4
0.0125--0.0138 1.10--1.44 8.31--8.66 0.104--0.136
0.0132 1.30 8.50 0.121
4.7 10.8 1.2 13.3
q u a n t i t i e s (20 and 2 0 0 pg) o f DMPS. Table 2 s h o w s the r e c o v e r y o f DMPS in water, s e d i m e n t and fish tissue. A d d i t i o n s o f DMPS in water, s e d i m e n t and fish tissue samples were r e c o v e r e d with yields o f 69.0, 57.7 and 48.9%, respectively. T h e r e c o v e r y o f DMPS in solid samples b y the p r o p o s e d m e t h o d was i n t e r m e d i a t e b e t w e e n t h e r e c o v e r y b y S o x h l e t (Pellenbarg, 1 9 7 9 ) a n d b y D e a n Stark e x t r a c t i o n s ( T s u c h i t a n i et al., 1978), while no studies have been r e p o r t e d on the r e c o v e r y o f DMPS in w a t e r and samples o f fish tissue. In a test o f precision, f o u r d i f f e r e n t kinds o f e n v i r o n m e n t a l samples, river water, river s e d i m e n t , sewage sludge and fish tissue were e x a m i n e d . Table 3 s h o w s t h e precision a t t a i n e d by the p r o p o s e d m e t h o d . The c o e f f i c i e n t o f variation was 4.7% f o r river water, 10.8% f o r river s e d i m e n t , 1.2% f o r sewage sludge and 13.3% for fish tissue. The p r o p o s e d m e t h o d gives g o o d precision and is a c c e p t a b l e f o r the d e t e r m i n a t i o n o f trace o r g a n o s i l i c o n e in e n v i r o n m e n t a l samples.
176 ACKNOWLEDGEMENT
The authors wish to thank Mr. S. Nishiwaki, President of Gifu Prefectural Research Institute for Environmental Pollution, for his critical reading, al~d permission for publication.
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