- Email: [email protected]
The use of bis- (2-alkoxyethyl) ethers as antifreeze in naphthalene-1,4-dioxane scintillation mixtures
InternationalJournal of AppliedRadiationand Isotopes,1961, Vol. 12, pp.
E-9.
PergamonPreu Ltd. Printedin NorthernIreland
The Use of Bis-( 2-alkoxyethyl)Ethers
as
Antifreeze in Naphthalene-1,4=Dioxane Scintillation Mixtures F. A. LOEWUS Western
Regional Research Laboratory, Albany, California, U.S.A.
*
(Received 15 AptiZ 1961) Aqueous radioactive samples can be counted in naphthalene-1,4-dioxane scintillator mixtures at temperatures below 0°C without freezing by replacing a portion of the 1,4-dioxane with bis(2-methoxyethyl)ether (diglyme) or bis-(2-ethoxyethyl)ether (diethyl carbitol). As little as 2 ml of diglyme or diethyl carbitol will allow 15 ml samples containing 1 ml of water to be counted at -4°C with better than 90 per cent of the efficiency of the pure naphthalene-1,4dioxane system. L’EMPLOI DANS
DES ETHERS BIS/2-ALKOXYETHYLIQUES LES MELANGES A SCINTILLATION AVEC L’1,4-DIOXANE
DE
LA
COMME ANTIGEL NAPHTALINE
On peut compter les echantillons radio-actifs aqueux dans les melanges scintillants naphtaline-1,4-dioxane aux temperatures audessous de 0°C sans congelation, en remplaqant une portion de 1’1,4-dioxane par de l’ether his/2-mtthoxytthylique (diglyme) ou par de l’tther his/2-Cthoxytthylique (carbitol ditthylique). Une quantitt de seulement 2 ml. de diglyme ou de carbitol diethylique permettra le comptage des Cchantillons de 15 ml. contenant 1 ml. d’eau a 4°C a mieux que 90 pour cent de l’efficacitt du systtme pur de naphtaline-1,4-dioxane. HPMMEHEHBE BHC-(2-AJIHOICCH3THJI) B@,MPOB B HAHECTBE AHTHcDPH30B B CMECHX [email protected]~JIBOKCAH AJIFI HHIflHOCTHbIX CHBHTBJIJIHTOPOB PaJQ4OaKTHBHOCTb o6paauos BOAHOti CMeCH [email protected]~IJOKCaH AjIR HEIlJ&KOCTHbIX ~~HKTE~JIJIFIT~~~B MOWHO HaMepHTb II npx TeMnepaTypax Kuwe O"C, ~CJIIIaaMeHHTb qacTb l.&~~OKcaHa 6kiC-(2-MeTOKCH3THJI)B@ApOM (AEIFJIHMOM) HJIH 6HC-(2-3TOKCWTEiJI)B@%pOM (API3THJlKap6UTOJIOM). fio6aBneKHe AIllYIIlMaHJIU AI13THJI Kap6HTOna B KOJIU~eCTBaX HaCTOJlbKO MC-LJIHX K~K~M~~O~BO~R~TI~~M~~FIT~~~~HO~KTI~BHOCT~~~-MMJIJIHJIEIT~OB~IX~~~~~~~B, coAepHtaqkix no 1 in Bo~br, npa TeMnepaType -4”C, npwieM a@$eKTnBHocTb KaMepeHdi HeCKOJIbKO BbIUIe 900/O B@@KTMBHOCTH %ICTOfi CHCTeMbI [email protected].
DIE
VERWENDUNG MITTEL IN
VON DI-(2_ALKOXYATHYL)-ATHER ALS NAPHTALIN-I,4-DIOXAN-SZINTILLATORGEMISCHEN
ANTIGEFRIER-
Radioaktive Proben in wasseriger Lbsung kdnnen in Naphtalin- 1,4-Dioxan Mischungen bei Temperaturen unter 0°C gezahlt werden, ohne dass Gefrierung eintritt, wenn ein Teil des 1,4Dioxans durch Di-(2-Methoxyathyl)-Ather (Diglym) oder Di-(2-Ethoxyathyl)-Ather (Diathylcarbitol) ersetzt wird. Die Verbindung von 2 ml Diglym oder Dilthylcarbitol gestattet die Messung von 15 ml Proben, welche 1 ml Wasser enthalten, bei 4”C, wobei die Empfindlichkeit verglichen mit reinem Naphtalin-1,4-Dioxan mehr als 90% betrlgt. + A laboratory of the Western Utilization and Research Department of Agriculture. 6
Division, Agricultural
Research
Service, United States
The use of his-(2-alkoxyethyl)ethws as antificcze in naphthalene-I,4dioxarte THE naphthalene-1,4-dioxane liquid scintillator mixture, which was first described by FURST et u2.o) and later modified by LANGHAM et al.@) and WERBIN et u1.@), has proved to be an extremely useful and versatile solvent mixture for counting tritiated water and aqueous solutions of tritiated compounds. However, the relatively high melting point of 1,4-dioxane ( + 11%) has limited this system to use above O”C, usually in the range +2 to +5”C depending upon the purityofthe dioxane and the amount of water and In contrast to this naphthalene added. system, toluene-soluble compounds and inhomogeneous systems in which toluene is the scintillator solvent are normally counted between -4 and -8°C. It would be highly desirable if the naphthalene-1,4-dioxane system could be modified to permit aqueous samples to be counted at this lower temperature range for at least two practical reasons. First, the temperature adjustment required in changing from one solvent system to the other could be avoided. This adjustment is, at best, sluggish, due to the bulk of the counter and the insulated (high vacuum) nature of the photomultiplier elements. Second, it would permit continuous counting
scintillation mixtures
7
of samples, regardless of their solvent composition, in counters equipped with automatic sample-changing devices. This communication describes a modification of the naphthalene-1,4-dioxane mixture which allows aqueous samples to be counted at sub-zero temperatures with relatively small loss in counting efficiency. The antifreeze used is a bis-(2-alkoxyethyl) ether, either bis-(2_methoxyethyl)ether, commonly referred to as diglyme(4), or bis-(2-ethoxyethyl)ether, commonly referred to as diethyl carbitol. The latter has been tested singly as a scintillator solvent by DAVIDSON and FEIGELSON(~) and found to have 32 per cent of the efficiency of toluene. The naphthalene-1,4-dioxane-diglyme and naphthalene-1,4-dioxane-diethyl carbitol mixtures described in the present paper are clear colorless solutions which are miscible with water over a wide range. About 10 per cent of bis-(2-methoxyethyl)ether in the naphthalene-1,4-dioxane mixture will prevent freezing at -4” in samples containing 6 per cent water. The counting efficiency under this set of conditions will be about 1213 per cent of the total number of Hs disintegrations.
EXPERIMENTAL A Packard Tri-carb series 314A liquid scintillation spectrometer equipped with an automatic sample changer was used. Samples were counted at a discriminator window setting of 1O-50 using 1150 V and a counting chamber temperature of -4°C. Under these conditions, a background count of 25-30 counts/min was obtained with a 20 dram glass vial containing 15 ml of naphthalene-I ,4-dioxane scintillator mixture in the countingposition. Solventsandchemicalswere obtained from the indicated commercial sources and were used without further purification. 1,4-Dioxane. Bis-( 2-Methoxyethyl) ether.
Eastman No. 2144 Eastman No. P6843 and Aldrich Chemical Com-
P""Y
Bis-(2-ethoxyethyl) ether. Naphthalene (recrystallized from alcohol). 2,5-Diphenyloxazole (PPO). 1,4-Bis-2- (5-phenyloxazolyl) benzene (POPOP).
Eastman
No. 4738
Matheson, Coleman, Bell No. 2616 Packard Instrument co. Packard Instrument co.
All samples were counted in clear low potassium glass vials supplied with metallined screw caps. Comparison of the observed counts with those obtained from an aliquot of standardized tritiated water (Packard Instrument Co. dated 2 June 1960 at 1.7 x lo6 d.p.m.) provided the basis for the efficiencies reported herein. To each solvent ( 1,4-dioxane, diglyme and
8
F. A. liewus
diethyl carbitol) was added 100 g/l. naphthalene, 7 g/l. PPO and 0.3 g/l. POPOP(6). All solids were dissolved before the final volume adjustment was made, since a slight volume increase was noted. Mixtures of 1,4-dioxane and diglyme or diethyl carbitol were prepared from the stock solutions. The volume ratios were such that the final volume was 14 ml in each sample. Tritiated water containing approximately lo5 d.p.m.
per ml was added to each sample. After thoroughly mixing the contents of each vial, the samples were placed in the sample changer at -4°C and held for at least 4 hr before recording the first count. Each sample was counted every 10 min and each set of samples recounted 4 times. All counts from a single sample fell within &5 per cent of the average count for that sample and, in most instances, the spread was even less.
RESULTS
14
12
0
2
6 4 l,4-Oioxone IO 4 6 6 ml. of Oiglyme or Diethyl Corbitol IO
ml.of
6
2
0
I2
I4
the mixture. When only a few microliters of water are to be added, additional diglyme or diethyl carbitol may be required to prevent crystallization of the dioxane-naphthalene mixture. Diglyme mixtures showed less quenching than diethyl carbitol over the Little if any entire range of mixtures. difference was observed between so-called “practical” and “refined” grades of diglyme in these mixtures. The size of the water sample to be added to the liquid scintillator mixture has some effect on the efficiency of counting, as seen in Fig. 2. The naphthalene1,4-dioxane liquid scintillator mixture, used to obtain the data in Fig. 2, contained 13 per cent diglyme. Counting was done at -4°C on samples that showed less than 1 per cent
Fm. 1. A plot of the efficiency (%) of naphthalene1,4-dioxane scintillator mixtures in which 1,4dioxane is replaced by increasing amounts of diglyme (“practical” grade 0 and A, “refined” grade n) or diethyl carbitol (0). Samples containing 1.0 ml of tritiated water are indicated as round symbols (0, 0) while those containing 0.25 ml are indicated as angular symbols (A, n).
Figure 1 shows the effect of replacing 1,4-dioxane with diglyme or diethyl carbitol on the efficiency of counting. Some scattering of experimental points occurred due to as the tritiated water sampling errors aliquots were added to the samples. This is most evident in the data obtained with 0.25 The arrows above the ml water aliquots. abscissa indicate the composition of the mixture required to protect a sample from solidifying at the indicated temperature when at least 0.23 ml of water is present in
I r&of
Water Added to Counting Mixture
FIG. 2. A plot of the efficiency of 14 ml samples of a liquid scintillator mixture to which was added 20 ~1 of tritiated water (3.2 x lo4 d.p.m.) and varying amounts of unlabeled water. The liquid scintillator contained 100 g naphthalene, 7 g PPO, 0.3 g POPOP and 130 ml diglyme in 1,4-dioxane to a total volume of 1 1.
The use of bis- (Z-aZkoxyethyl)ethers as antifreeze in naphthalene-1,4-dioxane
variation in counts between replicates at each experimental point determined. These results do not represent the best efficiencies obtainable with naphthalene1,4-dioxane. Chemicals and conditions were selected as representative of a practical approach toward counting aqueous samples below 072, the region normally used to count tohrene mixtures. Higher efficiencies can be achieved by using a broader window
scintillation mixtures
9
in the discriminator setting of the counter, by limiting the size of the aqueous sample and by further purification of the solvents. In most instances, however, the procedure outlined in this paper will suffice. Note: Reference to a company and/or product name by the Department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.
REFERENCES 1. FURST M.,
KALLMANN H.
and
BROWN F.
H.
Nucleonics 13, (4), 58 (1955). ‘2. LANGHAM W. H., EVER~OLE W. J., HAYES F. N. and TRUJILLO T. T. J. Lab. c&n. Med. 47, 819 (1956). 3. WERB~N H., CHAIKOFP I. L. and IMADA M. R. Proc. Sot. exp. biol. N. Y. 102, 8 (1959).
4. BROWN H. C., MEAD E. J. and SUBBA RAO B. C. J. Amer. them. Sot. 77, 6209 (1955). 5. DAVIDSONJ. D. and FE~GELSONP. Int. J. appl. Rad. Isotojes2, 1 (1957). 6. HAYES F. N. Packard Technical Bulletin. Packard Instruments, Illinois (1960).
E-9.
PergamonPreu Ltd. Printedin NorthernIreland
The Use of Bis-( 2-alkoxyethyl)Ethers
as
Antifreeze in Naphthalene-1,4=Dioxane Scintillation Mixtures F. A. LOEWUS Western
Regional Research Laboratory, Albany, California, U.S.A.
*
(Received 15 AptiZ 1961) Aqueous radioactive samples can be counted in naphthalene-1,4-dioxane scintillator mixtures at temperatures below 0°C without freezing by replacing a portion of the 1,4-dioxane with bis(2-methoxyethyl)ether (diglyme) or bis-(2-ethoxyethyl)ether (diethyl carbitol). As little as 2 ml of diglyme or diethyl carbitol will allow 15 ml samples containing 1 ml of water to be counted at -4°C with better than 90 per cent of the efficiency of the pure naphthalene-1,4dioxane system. L’EMPLOI DANS
DES ETHERS BIS/2-ALKOXYETHYLIQUES LES MELANGES A SCINTILLATION AVEC L’1,4-DIOXANE
DE
LA
COMME ANTIGEL NAPHTALINE
On peut compter les echantillons radio-actifs aqueux dans les melanges scintillants naphtaline-1,4-dioxane aux temperatures audessous de 0°C sans congelation, en remplaqant une portion de 1’1,4-dioxane par de l’ether his/2-mtthoxytthylique (diglyme) ou par de l’tther his/2-Cthoxytthylique (carbitol ditthylique). Une quantitt de seulement 2 ml. de diglyme ou de carbitol diethylique permettra le comptage des Cchantillons de 15 ml. contenant 1 ml. d’eau a 4°C a mieux que 90 pour cent de l’efficacitt du systtme pur de naphtaline-1,4-dioxane. HPMMEHEHBE BHC-(2-AJIHOICCH3THJI) B@,MPOB B HAHECTBE AHTHcDPH30B B CMECHX [email protected]~JIBOKCAH AJIFI HHIflHOCTHbIX CHBHTBJIJIHTOPOB PaJQ4OaKTHBHOCTb o6paauos BOAHOti CMeCH [email protected]~IJOKCaH AjIR HEIlJ&KOCTHbIX ~~HKTE~JIJIFIT~~~B MOWHO HaMepHTb II npx TeMnepaTypax Kuwe O"C, ~CJIIIaaMeHHTb qacTb l.&~~OKcaHa 6kiC-(2-MeTOKCH3THJI)B@ApOM (AEIFJIHMOM) HJIH 6HC-(2-3TOKCWTEiJI)B@%pOM (API3THJlKap6UTOJIOM). fio6aBneKHe AIllYIIlMaHJIU AI13THJI Kap6HTOna B KOJIU~eCTBaX HaCTOJlbKO MC-LJIHX K~K~M~~O~BO~R~TI~~M~~FIT~~~~HO~KTI~BHOCT~~~-MMJIJIHJIEIT~OB~IX~~~~~~~B, coAepHtaqkix no 1 in Bo~br, npa TeMnepaType -4”C, npwieM a@$eKTnBHocTb KaMepeHdi HeCKOJIbKO BbIUIe 900/O B@@KTMBHOCTH %ICTOfi CHCTeMbI [email protected].
DIE
VERWENDUNG MITTEL IN
VON DI-(2_ALKOXYATHYL)-ATHER ALS NAPHTALIN-I,4-DIOXAN-SZINTILLATORGEMISCHEN
ANTIGEFRIER-
Radioaktive Proben in wasseriger Lbsung kdnnen in Naphtalin- 1,4-Dioxan Mischungen bei Temperaturen unter 0°C gezahlt werden, ohne dass Gefrierung eintritt, wenn ein Teil des 1,4Dioxans durch Di-(2-Methoxyathyl)-Ather (Diglym) oder Di-(2-Ethoxyathyl)-Ather (Diathylcarbitol) ersetzt wird. Die Verbindung von 2 ml Diglym oder Dilthylcarbitol gestattet die Messung von 15 ml Proben, welche 1 ml Wasser enthalten, bei 4”C, wobei die Empfindlichkeit verglichen mit reinem Naphtalin-1,4-Dioxan mehr als 90% betrlgt. + A laboratory of the Western Utilization and Research Department of Agriculture. 6
Division, Agricultural
Research
Service, United States
The use of his-(2-alkoxyethyl)ethws as antificcze in naphthalene-I,4dioxarte THE naphthalene-1,4-dioxane liquid scintillator mixture, which was first described by FURST et u2.o) and later modified by LANGHAM et al.@) and WERBIN et u1.@), has proved to be an extremely useful and versatile solvent mixture for counting tritiated water and aqueous solutions of tritiated compounds. However, the relatively high melting point of 1,4-dioxane ( + 11%) has limited this system to use above O”C, usually in the range +2 to +5”C depending upon the purityofthe dioxane and the amount of water and In contrast to this naphthalene added. system, toluene-soluble compounds and inhomogeneous systems in which toluene is the scintillator solvent are normally counted between -4 and -8°C. It would be highly desirable if the naphthalene-1,4-dioxane system could be modified to permit aqueous samples to be counted at this lower temperature range for at least two practical reasons. First, the temperature adjustment required in changing from one solvent system to the other could be avoided. This adjustment is, at best, sluggish, due to the bulk of the counter and the insulated (high vacuum) nature of the photomultiplier elements. Second, it would permit continuous counting
scintillation mixtures
7
of samples, regardless of their solvent composition, in counters equipped with automatic sample-changing devices. This communication describes a modification of the naphthalene-1,4-dioxane mixture which allows aqueous samples to be counted at sub-zero temperatures with relatively small loss in counting efficiency. The antifreeze used is a bis-(2-alkoxyethyl) ether, either bis-(2_methoxyethyl)ether, commonly referred to as diglyme(4), or bis-(2-ethoxyethyl)ether, commonly referred to as diethyl carbitol. The latter has been tested singly as a scintillator solvent by DAVIDSON and FEIGELSON(~) and found to have 32 per cent of the efficiency of toluene. The naphthalene-1,4-dioxane-diglyme and naphthalene-1,4-dioxane-diethyl carbitol mixtures described in the present paper are clear colorless solutions which are miscible with water over a wide range. About 10 per cent of bis-(2-methoxyethyl)ether in the naphthalene-1,4-dioxane mixture will prevent freezing at -4” in samples containing 6 per cent water. The counting efficiency under this set of conditions will be about 1213 per cent of the total number of Hs disintegrations.
EXPERIMENTAL A Packard Tri-carb series 314A liquid scintillation spectrometer equipped with an automatic sample changer was used. Samples were counted at a discriminator window setting of 1O-50 using 1150 V and a counting chamber temperature of -4°C. Under these conditions, a background count of 25-30 counts/min was obtained with a 20 dram glass vial containing 15 ml of naphthalene-I ,4-dioxane scintillator mixture in the countingposition. Solventsandchemicalswere obtained from the indicated commercial sources and were used without further purification. 1,4-Dioxane. Bis-( 2-Methoxyethyl) ether.
Eastman No. 2144 Eastman No. P6843 and Aldrich Chemical Com-
P""Y
Bis-(2-ethoxyethyl) ether. Naphthalene (recrystallized from alcohol). 2,5-Diphenyloxazole (PPO). 1,4-Bis-2- (5-phenyloxazolyl) benzene (POPOP).
Eastman
No. 4738
Matheson, Coleman, Bell No. 2616 Packard Instrument co. Packard Instrument co.
All samples were counted in clear low potassium glass vials supplied with metallined screw caps. Comparison of the observed counts with those obtained from an aliquot of standardized tritiated water (Packard Instrument Co. dated 2 June 1960 at 1.7 x lo6 d.p.m.) provided the basis for the efficiencies reported herein. To each solvent ( 1,4-dioxane, diglyme and
8
F. A. liewus
diethyl carbitol) was added 100 g/l. naphthalene, 7 g/l. PPO and 0.3 g/l. POPOP(6). All solids were dissolved before the final volume adjustment was made, since a slight volume increase was noted. Mixtures of 1,4-dioxane and diglyme or diethyl carbitol were prepared from the stock solutions. The volume ratios were such that the final volume was 14 ml in each sample. Tritiated water containing approximately lo5 d.p.m.
per ml was added to each sample. After thoroughly mixing the contents of each vial, the samples were placed in the sample changer at -4°C and held for at least 4 hr before recording the first count. Each sample was counted every 10 min and each set of samples recounted 4 times. All counts from a single sample fell within &5 per cent of the average count for that sample and, in most instances, the spread was even less.
RESULTS
14
12
0
2
6 4 l,4-Oioxone IO 4 6 6 ml. of Oiglyme or Diethyl Corbitol IO
ml.of
6
2
0
I2
I4
the mixture. When only a few microliters of water are to be added, additional diglyme or diethyl carbitol may be required to prevent crystallization of the dioxane-naphthalene mixture. Diglyme mixtures showed less quenching than diethyl carbitol over the Little if any entire range of mixtures. difference was observed between so-called “practical” and “refined” grades of diglyme in these mixtures. The size of the water sample to be added to the liquid scintillator mixture has some effect on the efficiency of counting, as seen in Fig. 2. The naphthalene1,4-dioxane liquid scintillator mixture, used to obtain the data in Fig. 2, contained 13 per cent diglyme. Counting was done at -4°C on samples that showed less than 1 per cent
Fm. 1. A plot of the efficiency (%) of naphthalene1,4-dioxane scintillator mixtures in which 1,4dioxane is replaced by increasing amounts of diglyme (“practical” grade 0 and A, “refined” grade n) or diethyl carbitol (0). Samples containing 1.0 ml of tritiated water are indicated as round symbols (0, 0) while those containing 0.25 ml are indicated as angular symbols (A, n).
Figure 1 shows the effect of replacing 1,4-dioxane with diglyme or diethyl carbitol on the efficiency of counting. Some scattering of experimental points occurred due to as the tritiated water sampling errors aliquots were added to the samples. This is most evident in the data obtained with 0.25 The arrows above the ml water aliquots. abscissa indicate the composition of the mixture required to protect a sample from solidifying at the indicated temperature when at least 0.23 ml of water is present in
I r&of
Water Added to Counting Mixture
FIG. 2. A plot of the efficiency of 14 ml samples of a liquid scintillator mixture to which was added 20 ~1 of tritiated water (3.2 x lo4 d.p.m.) and varying amounts of unlabeled water. The liquid scintillator contained 100 g naphthalene, 7 g PPO, 0.3 g POPOP and 130 ml diglyme in 1,4-dioxane to a total volume of 1 1.
The use of bis- (Z-aZkoxyethyl)ethers as antifreeze in naphthalene-1,4-dioxane
variation in counts between replicates at each experimental point determined. These results do not represent the best efficiencies obtainable with naphthalene1,4-dioxane. Chemicals and conditions were selected as representative of a practical approach toward counting aqueous samples below 072, the region normally used to count tohrene mixtures. Higher efficiencies can be achieved by using a broader window
scintillation mixtures
9
in the discriminator setting of the counter, by limiting the size of the aqueous sample and by further purification of the solvents. In most instances, however, the procedure outlined in this paper will suffice. Note: Reference to a company and/or product name by the Department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.
REFERENCES 1. FURST M.,
KALLMANN H.
and
BROWN F.
H.
Nucleonics 13, (4), 58 (1955). ‘2. LANGHAM W. H., EVER~OLE W. J., HAYES F. N. and TRUJILLO T. T. J. Lab. c&n. Med. 47, 819 (1956). 3. WERB~N H., CHAIKOFP I. L. and IMADA M. R. Proc. Sot. exp. biol. N. Y. 102, 8 (1959).
4. BROWN H. C., MEAD E. J. and SUBBA RAO B. C. J. Amer. them. Sot. 77, 6209 (1955). 5. DAVIDSONJ. D. and FE~GELSONP. Int. J. appl. Rad. Isotojes2, 1 (1957). 6. HAYES F. N. Packard Technical Bulletin. Packard Instruments, Illinois (1960).