approaches could have been used, the “constant time” method was used since it should provide highest reliability results for the pseudo-first-order reactions used in this work (13). The simulated response data were analagous to zero-order data, suggesting the use of the “variable time” method (13). These two groups of data, demonstrate that, when appropriate, the MOLD computer can be used for either the “variable time” or the “constant time” methods. CONCLUSIONS
The data reported above demonstrate some of the capabilities and limitations of the miniature on-line computer. The study of transient species was chosen to indicate the versatility in data acquisition and handling. There are possible applications for this system in static measurements. Atomic emission and absorption instrumentation could easily be interfaced, and programmed with as few as two instructions or, with averaging and scaling, as many as fourteen or fifteen instructions to provide direct concentration readout. With minor modifications, GC integration with direct mass readout could be achieved. It is probable that overlapping peaks could be resolved to the same extent that they can be determined graphically from a recorder chart. It should be obvious, however, that this instrument is not applicable to every situation. A tentative assignment for the MOLD system must be evaluated in terms of the sacrifices that might be encountered in simplifying the data handling procedure. Not only are there a limited number of mathematical operations available, but because of the small instruction memory, they can be applied only a few times. Still, the benefits gained with fast, easily obtained results could outweigh the possible loss of a small percentage of accuracy and/ or selectivity. There are at least two general situations in which such systems could be very attractive. One situation is that in which the number of routine computations is too (13) J. D. Ingleand S. R. Crouch, ANAL.C H E M . ,697(1971). ~~,
large to be handled manually, but is too small to justify a small general purpose-computer with required peripherals. The other situation is one in which a general-purpose computer is available, but the demands on its time for other purposes such as preparing requisitions, fling data, preparing reports, etc. are such that all of the routine computations required in the laboratory cannot be conveniently accommodated. The minature system would supply single valued data, in concentration format, either for manual recording or for computer recording and would minimize or eliminate the processing of raw data by the central system. An additional advantage of “back-up” data processing capability would be realized in the second situation during any down-time of the central system. Thus, in one situation the miniature system can serve as an alternative to the analog- and/or generalpurpose digital computers in current usage, while in the other it serves to complement the latter. In either situation, the system would be totally dedicated to a single task at one time. The cost of the system is such that multiple units could be afforded by most laboratories and the versatility is such that a single unit could perform many different duties at different times during a work-day. It is hoped that this report will help to stimulate interest among other chemists in the applicability of the digital components which are so readily available so that this field will enjoy a growth rate and general utility comparable to that observed for operational amplifiers during recent years. The estimated hardware costs for the system as constructed originally amounted to $650. At the time of this writing, it is estimated that a similar system could be constructed at a cost of about $300 for hardware and three weeks of construction time. RECEIVED for review December 13, 1971. Accepted March 30, 1972. This investigation was supported in part by PHS Research Grant No. G M 13326 from the National Institutes of Health and in part by a fellowship (RAP) from Phillips Petroleum.
Determination of T,race Quantities of Volatile Fluoride in Uranium Hexafluoride Using an Infrared Spectrophotometer Raymond Aubeau, Gerard Blandenet, and Guy Brogniart Commissariat
L’energie Atomique, Centre de Pierrelatte, Boite Postale no 16, 26 Pierrelatte France
This study describes a determination of volatile fluoride in uranium hexafluoride by infrared spectrophotometry in the range 0.1 to 1weight parts per million (wppm). The instrument used is a spectrophotometer equipped with a 50-cm-long dual path cell. According to the test accomplished and the sensitivity required, three versions are available: direct analysis; differential analysis; and analysis after absorption on sodium fluoride. These different technologies allow the contents of weight parts per million to be determined with a precision of 5 to 10%. DETERMINATION OF GASEOUS impurities occurring in the form of traces in UFs is generally made using chemical methods based on long and delicate processes (1). (1) “19 Methods for Uranium Hexafluoride Determination,” Head
Laboratory,C.E.A., Pierrelatte (1971). 1628
For industrial control, quicker and generally more reliable physical methods of analysis must be used. In our case, we have considered the three techniques most used in the range of gas analysis : gas-liquid chromatography, mass spectrometry, and infrared spectrophotometry. Gas-liquid chromatography of corrosive fluorinated compounds does not allow the results obtained with organic compounds, especially when determining traces. Polymer supports give very low efficiency columns. It seems, however, likely to develop considerably in the near future (2). Mass spectrometry is a costly technique rather badly suited for the analysis of such compounds. Indeed these compounds (2) G. Blandenet and R. Aubeau, 111 European Symposium on Fluorine Chemistry, Aix en Provence, 14/17 September, 1970.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 9, AUGUST 1972
on diagram
Figure 2.
View of cells and thermostats
are highly aggressive because of source corrosion and filament corrosion in particular. Infrared spectrophotometry is used most frequently for the analysis of liquids and solids and much less to analyse gaseous compounds. This paper outlines the performances reached with this lastmentioned technique in the case of the analysis of traces of fluorides in UFs in volatile form. The method used consists
of measuring infrared absorption of gaseous fluorides present in UFs by a dual beam spectrophotometer. Three versions of this method have been developed: Version 1: Direct analysis: The analysis cell is filled with uranium hexafluoride sample, while the reference cell is kept under vacuum. Version 2: Differential analysis: The analysis cell is filled with sample uranium hexafluoride and the reference cell contains uranium hexafluoride under the same
ANALYTICAL CHEMISTRY, VOL. 44, NO. 9. AUGUST 1972
1629
0 , phase
Figure 3. Sampling container
to3
/ 10
5
15
Pressure
Figure 4.
'n Fhsml
Calibration curves
pressure. UFP, used in the reference cell is of nuclear quality (under specifications of the U.S. Federal Register 29.1 1.67 p 16829). Version 3 : Direct analysis after absorption. Uranium hexafluoride and most of the fluorides are fixed on sodium fluoride. EXPERIMENTAL
Apparatus. The apparatus, Figure 1, includes in addition to the spectrophotometer and the two cells: a trap containing sodium fluoride (used in version 3), a n assembly allowing the preparation and introduction of gaseous compounds, pressure gauges and sensors, vacuum pumping devices (primary vacuum lo-' Pascal), a temperature maintenance device for 1630
the cells and gas sampling between 20 and 70 "C. Because of hazards, such as corrosion, involved in the use of ClF,, the materials used in the installation are Teflon (Du Pont), Monel, and stainless steel. SPECTROPHOTOMETER. The instrument used is a Leitz 111G spectrophotometer with the following main characteristics: source, Nernst filament; detector, thermocouple with potassium bromide window; grating, depending on the range explored: 2.5 to 19 pm (4000 to 526 cm-'); best resolving power: 2 cm- in the range of 5000 cm-I. CELLS (Figure 2). Cells, made of Monel alloy, are 483 mm long (optic paih 966 mm), with an inner diameter of 86 mm. They are fitted with two valves t o allow pressure build-up and drainage operations. Windows are made of silver chloride, a material which allows both a correct transparency to infrared radiation over the infrared range explored and correct corrosion resistance to fluorides. Procedure. PRELIMINARY TREATMENT OF THE INSTALLATION, Preliminary treatment of the installation (passivation) is required on one hand to eliminate the interactions of the various components of gaseous compounds on the surface, and on the other hand to maintain satisfactory transmittance in the infrared range explored. We have experimented with three types of treatment. Pre-treatment with CIF3. This type of treatment is generally used in laboratories working with fluorine compounds and consists of vacuum build-up and pumping for 12 hours at 60 "C; 5 admissions of 1300 Pascal ClF, at 60 "C; and passivation with lo4 Pascal C1F3 during 24 hours at 60 "C. This procedure leads to progressive transmittance loss, especially in the range 2.5-6 pm and 16-19 pm. As this degradation is generally attributed t o the presence of chlorinated decomposition substances (C102F-C103F), we have experimented with a fluorine pre-treatment. Pre-treatment with fluorine. This included vacuum buildup and pumping for 12 hours at 60 "C; 5 admissions of 1300 Pascal fluorine at 60 'C; and passivation with lo4 Pascal fluorine during 24 hours at 60 "C. N o improvement over the first treatment was found. Pre-treatment with UFP,. This consisted of vacuum build-up and pumping for 12 hours at ambient temperature; subsequent admissions with dry nitrogen under increasing pressure up to lo6Pascal a t ambient temperature; passivation with 1500 Pascal of UFG during 45 minutes at ambient temperature. This process allowed an excellent transmittance to be obtained over the whole infrared range explored. It was therefore used for this study. Method. During the analysis period, the installation is kept a t a temperature of 70 "C. Before each determination, the analysis cell is put under primary vacuum (lo-' Pascal) for two hours. It is then filled t o a given pressure with U F G to be analyzed. For version 3, the analysis cell containing the sample is connected t o the U-shaped trap containing sodium fluoride, previously dried at 300 "C under vacuum for 12 hours. Before proceeding to the analysis, one has to wait for total absorption of the UFG,which may take several hours. Sampling. To obtain perfectly homogeneous samples, it is desirable to use a specific sampling container (Figure 3). These containers allow samples to be taken either in gaseous state or liquid state. Sampling in the gaseous state will only be made if the whole sample is in gaseous state at the experiment temperature. Larger samples which also include a liquid state must be sampled in the liquid state taking the composition of gaseous state into account, if necessary. Calibration. Calibration is the same for all three versions. The standard used (COMURHEX-FRANCE) has a minimum purity of 99.5 in volume. For each gas a t the analysis wavelength, a graph featuring the optical density values cs. pressure is drawn. For some compounds the calibration graph is not linear (Figure 4) because the Lambert-Beer law is
ANALYTICAL CHEMISTRY, VOL. 44, NO. 9, AUGUST 1972
..
100 10090-r w
I
1
I
I
1
I
80 70 60 50 40 30 20 10
1
1
rn
-
1
I
1
'
I
v)
.v)
I
n a
--
-
I
f
I
L
w
L,
NEW ANALVSiS OF THE F k T
1001 T 100 I 1 ' 1 1' I 90o- r 9
I
TI-LL.&
-
I
I
I
I
I
I
10
11
I2
I
M m iR E
8070 -
701301--60 50-
40-
30
20
-
TO
-
1 . -
?3 ~~~
Y
15
16
17
I
18 l9pn
~~
Figure 5. Mutual influence between impurities and IR cell Pressure 3 X
I
1
I
I
I
I
1
Pascal; cell SQO mm; temperature 60°C
I
I
I
I
I
I
I
I
I
I
Figure 6. Exaltation of infrared bands ANALYTICAL CHEMISTRY, VOL. 44, NO. 9, AUGUST 1972
1631
100% T
\
IXA FiG.7a
OKT
Figure 7. Recording of T Z conversion of a AT in optical density (100 Z transmittance = 15 cm) u. A is an impurity with its specific band disturbed by a band of another compound B (at a wavelength X A). To is the transmittance corresponding to B Band and AT, the transmittance of impurity A b. Conversion of a 3-mm height band (minimum sensibility limit) in optical density for several values of To
not applicable. We will also find that exaltation phenomena of absorption bands can occur for some impurities.
f
W
a
RESULTS AND DISCUSSION
of a mixture of UF6 4- impurities. The impurities concentra-
Table I. Direct Analysis-Sensibility Limits
BF3
Wave- Wavelength, number, cm-l w 1445 6.92
BrFj
15.5
645
350-90
CrOrF2
12.65
791
5600-70
MoF~
13.5
741
940-12
PF i
10.5
952
2400-30
240-3
9.75
1026
2000-25
200-2.5
SFfi
10.55
948
720-9
72-0.9
SiFa
9.7
1031
880-1 1
88-1.1
VOF,
9.45
1058
8000-1 00
80@10
14.08
710
440-25
CF3H
7.25
1379
14400-1 80
1440-1
CF:;Br
8.28
1207
1600-20
160-2
CFa
7.78
1285
CF&-CFsCl
9.5
1053
8800-1 10
880- 1
C F2Cl-CF a
10.15
985
5600-70
560-7
Cfs-CF3
8.95
1117
2800-35
260-4.5
C Fa-C F:-C Fs
9.9
1010
5600-70
560- 7
CF?-CFa-CFl-CF?
10.35
966
2800- 35
280-3.5
CFa-CF=CF-CF:,
8.35
1198
2800- 35
280-3.5
Gas
Wf
6
Pressure 104 Pascal vPPm5 28OC-35
Remarks The atmospheric water value disturbs the analysis of BF,. Not possible at lo5 Pascal: UFOcontribution.
560-7 75-1.9 PF: cannot be determined in presence of SiF4and SFs. SF6cannot be determined in presence of SiFa and PFj. SiFa cannot be determined in presence of PF; and S f 6. Not possible at lo5 Pascal: UF6 contribution.
Not possible: UFs overboarding.
Volume parts per million. *Weight parts per million.
1'
~~
1632
Pressure 105 Pascal vPPma 280-35
ANALYTICAL CHEMISTRY, VOL. 44, NO. 9, AUGUST 1972
THE SPECTROPHOTOMETER HAS NO ENERGY iN THiS RANGE
Figure 8. Determination of the impurities in UFc Pressure lo5 Pascal, temperature 60 T, concentration 7 vppm by impurity
the mixture. In our experimentation, no change was found in impurities concentration between the first and third introduction while UFs of the second introduction was not polluted. Thus, under the conditions of our experimental work, there is n o preferential adsorption to be observed over the cell surface for samples containing impurity rates close to those analyzed. Therefore it can be stated that with the precision of our measurements the cell has no influence on the composition of the mixture. (3) J. R. Nielsen, V. Thornton. and E. Brockdale, Rec. Mod. Pliys., 16, 307 (194.4). (4) D. F. Smith, Sprctroclzim. Acta, 12,224 (1958).
Infrared band exaltation of some impurities (Figure 6). Infrared band exaltation is a phenomenon which has been subjected to many studies (3-5). In our case the exaltation of infrared bands has been investigated with the following conditions. A mixture of impurities (without UF6) is introduced in the cell. After infrared analysis, a l o 4Pascal pressure of UF6 is added. Comparison of the spectra before and after introduction of UF6 reveals that the bands are submitted t o n o exaltation except for BF3 at 6.94 Fm. At this wavelength, UF6 contribution is negligible and cannot, consequently, be the cause of increased ( 5 ) J. Aubert, IlIrd European Symposium on Fluorine Chemistry,
Aix en Provence, 14/17 September, 1970. ANALYTICAL CHEMISTRY, VOL. 44, NO. 9, AUGUST 1972
1633
Table 11. Differential Analysis-Sensibility Limits Wave- Wavelength, number, cm-' Pm 6.92 1445
Gas BF3
Pressure l o 4 Pascal vPPm" 2800-35
Pressure 106 Pascal vPPm5 280-3.5
14.37
696
4800-60
BrFs
15.5
645
1600-20
CrOzFz
12.65
791
5600-70
MOF6
13.5
741
960-12
PF5
10.5
952
2400-30
240- 3
9.75
1026
2000-24
200-2.5
SF6
10.55
948
720-9
72-0.9
SiF4
9.7
1031
880-1 1
88-1.1
VOFs
9.45
1058
8000-100
WFa
14.08
710
800-10
CFsH
7.25
1379
14400-180
1440-18
CF3Br
8.28
1207
1600-20
160-2
CF4
7.78
1285
CFzC1-CFzCl
9.5
1053
8800-1 10
880-11
10.15
985
5600-70
560-7
CFs-CFs
8.95
1117
2800-35
280-3.5
CF3-CFrCFs
9.9
1010
5600-70
560-7
10.35
966
2800-35
280-3.5
8.35
1198
2800-35
280-3.5
CFzCl-CFs
CFz-CFz-CFz-CFz
b
Remarks The atmospheric water value disturbs the analysis of BF3. Not possible at los Pascal: UFe Contribution. Idem.
560-7 94-1.2 PF; cannot be determined in presence of SiF4 and SF6. SF6 cannot be determined in presence of SiF4and PF5. SiF4cannot be determined in presence of PFj and SF.5.
800-10 Not possible at lo6 Pascal: UF6 contribution.
Not possible: UF6 overboarding.
Volume parts per million. Weight parts per million.
Table 111. Analysis after Absorption on NaFSensibility Limits Wave- Wavelength, number, cm-I wn 6.92 1445 15.5 645 12.65 791 13.5 741 10.5 952 10.55 948
Gas BF3 BrFs CrO2FZ MOF6 PFs SFs
Pressure io4 Pascal vPPm" WPPmb
... ... ... ...
...
720-9
... ... ... ... 100-1 '&U)
Pressure lo5 Pascal
...
... 72-0.9
... ...
10-0:
i '(sju)
9.7 9.45 14.08 8.7 8.28 7.78 9.5 10.15 8.95 9.9 10.35
1031 1058 710 1149 1207 1285 1053 985 1117 1010 966
... ...
...
... ...
... ...
2400-30 1600-20 160-2 8800-1 10 5600-70 2800-35 5600-70 2800-35
120-2 '(CjU) 80-1 (C/U) 6-0.1 (C/U) 880-11 (CjU) 570-7 (CjU) 2 8 W (CjU) 850-11 (CjU) 570-7 (CjU)
240-3 160-2 16-0.2 880-11 560- 7 280-3.5 560-7 280-3.5
12-0: 2 '(CIU) 8-0.1 (C/U) 0.6-0.01 (CjU) 88-1.1 (CjU) 57-0.7 (C/U) 28-0.4 (CjU) 85-1.1 (C/U) 57-0.7 (C/U)
CF&F=CF-CFs 8.35 a Volume parts per million. b Weight parts per million.
1198
2800-35
570-7 (CjU)
280-3.5
57-0.7 (CjU)
SiF4 VOFs WFe CF3H CF3Br CFd CFzCl-CRC1 CFzCl-CFs CFs-CFs CFa-CF&F:3 CFz-CFz-C FrCFz L
1634
A
...
...
ANALYTICAL CHEMISTRY, VOL. 44, NO. 9, AUGUST 1972
' The wavelength chosen for the analysis does not always correspond to the most sensitive band, but \to one which does not feature interaction with other fluorocarbon compounds.
Figure 9. Determination of impurities in UF6 (fluorocarbon compounds) Pressure UFc lo5 Pascal, temperature 6OCC,concentration of 22 vppm by impurity
absorption. The increase of optical density of MoFo and WF6 bands can be explained, however, by UF6contribution. In o u r operating conditions, only the BFI band (6.94 pm) undergoes an appreciable exaltation which should be taken into consideration. Range of Application. Tables I, 11, and I11 give the range of application of each version for introduction pressures of l o 4Pascal and lo5Pascal of UF6.
The upper and lower limit values are specified as follows: the upper limit value corresponds to an optical density of 0.8 (impurities UF6 contribution). The lower or minimum limit analysis is the quantity of impurities which corresponds on the diagram to a 3-mm band height. These limits have been established without using a scale expansion device. The sensibilities limits are given in volume part per million (vppm) and in weight part per million (wppm).
+
ANALYTICAL CHEMISTRY, VOL. 44, NO. 9, AUGUST 1972
0
1635
Figure 10. Scale expansion Mixture of 0.7 Pascal pure gases, cell of 483 mm, temperature 60 “C
In the case of version 1, the lower limit values have been calculated in accordance with an infrared spectrum corresponding to lo4or lo5 Pascal of pure UF6, a graph (Figures 7a and 7b)
featuring the optical density of a 3-mm band height (impurities only) in the function of transmittance of the base line; and calibration graphs of the various impurities. The performances of the various versions illustrated in Figures 8 and 9 are specified hereafter. Version 1. Direct analysis (Table I). This version allows simple and quick analysis of most impurities. It’s necessary first to draw a spectrum of pure UF6. At a pressure of lo6 Pascal, it is impossible to analyze BrF, (15.5 pm), CF4 (7.78 pm), and WF6 (14.08 pm) because of the saturation of UF6 bands. Version 2. Differential analysis (Table 11). This version eliminates the influence of UF6 on the absorption spectrum. The lower limits of determination are below those of first version if the impurities bands (BrF,, CF4, WF6) are disturbed by UF6. As for version 1, the analysis is impossible when the bands of UF6 are saturated under direct analysis. Indeed in this case the spectrophotometer has no energy available under differential analysis. Version 3. Direct analysis after absorption (Table 111). Sodium fluoride absorbs UF6 and the greater part of the fluorides. As a result, this version allows only the analysis of SF6 and the main part of fluorocarbon compounds. Moreover, it offers the advantage of the determination of: CF3H with a higher precision than versions 1 and 2; CF4 not tested in versions 1 and 2; and SF6 in presence of SiF4 and PF6(absorbed on sodium fluoride). The analysis limits of these versions can also be considerably improved by use of scale expansion (Figure 10). Associated with a well-adjusted spectrophotometer, this accessory allows decreasing the analysis limits by a factor of 10 approximately with the same precision. RECEIVED for review August 4, 1971. Accepted January 12 1972.
Extraction of Anions into Chloroform by Surfactant Cations Relevance to Dye Extraction Method of Analysis of Long Chain Amines H. K. Biswas and B. M. Mandal Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadaupur, Calcutta-32, India Anion interference with the analysis of long chain amines by the dye extraction method has been investigated using the anionic dye, disulfine blue VN 150. For the anions examined, the degree of interference follows the order: C104- > I-> Br- > NO3-> CI-. This is also the order of extraction of the anions into chloroform by the ammonium ions. The interference is the result of a competition from the anions with the dye ion for extraction into the organic phase. Anions such as F-, Sod2-, and acetate do not interfere. Equilibrium constants for ion pair extraction of the interfering anions by cetyltrimethylammonium ion into chloroform have also been evaluated.
EXTRACTION OF ACIDS from aqueous solutions by long chain amines in organic diluents has been thoroughly studied (1-3). The ammonium salts produced in these extraction systems are (1) Y. Mercus, Chem. Rev., 63, 139 (1963). (2) G. H. ‘Morrison and H. Freiser, ANAL.CHEM.,36, 93R (1964). 1636
mostly water insoluble. One would also expect quaternary or nonquaternary ammonium surfactant ions to extract certain simple anions into organic diluents. These anions, therefore, are likely to interfere with the dye extraction method of analysis of long chain amines. The magnitude of interference should depend on the values of the equilibrium constant for the extraction of the interfering ions us. the dye anion (and should therefore vary from dye to dye). This aspect has not been given much attention in analytical work (4-6). For example, although Few and Ottewill ( 4 ) observed no interference from either 0.1 M NaCl or NaHC03 using orange I1 (3) R. M. Diamond, “Proceedings of the International Congress on Solvent Extraction Chemistry, Gothinberg, 1966, North-Holland Publishing Co., Amsterdam, 1967, p 349. (4) A. V. Few and R. H. Ottewill, Colloid Sci., 11,34 (1956). ( 5 ) G. V. Scott, ANAL.CHEM.,40,768 (1968). (6) A. Mukherjee and P. Mukerjee, J. Appl. Chem., 12, 127 (1962).
ANALYTICAL CHEMISTRY, VOL. 44, NO. 9, AUGUST 1972
