1158
Anal. Chem. 1980, 52, 1158-1161
The sample was eluted with a 0.010 M solution of tetra-n-butylammonium perchlorate (TBAClOJ in water/methanol (70/30 v/v) a t a flow rate of 1.8 mL/min at room temperature. A calibration curve of peak areas vs. ethyl sulfate concentration was constructed using 1O-pL samples of aqueous solutions containing from 0.1 to 1.0% sodium ethyl sulfate. A straight line was obtained.
I
RESULTS AND DISCUSSION
I 0
2
4
E
8
IO
12
Time (min) Figure 1. Chromatogram for a BQAES sample containing 1.02% ethyl sulfate, 11 % sulfate, and 2 7 % phosphate
EXPERIMENTAL Apparatus. A Waters liquid chromatograph equipped with a Model M-6000A pump, a F-Bondapak CIS column (4 mm i.d. X 30 cm), a differential refractometer, and a Rheodyne Model 7120 injector was used. Chromatographic peak areas were integrated using a Hewlett-Packard Model 3354C Lab Data System. Reagents. Methanol, distilled-in-glass grade, was obtained from Burdick and Jackson Laboratories, Inc. Deionized water further purified by the Barnstead Nanopure System was used. Tetra-n-butylammonium perchlorate was supplied by the G. F. Smith Company. Sodium ethyl sulfate, from Pfaltz and Bauer Company, was recrystallized from water-ethanol and dried over concentrated sulfuric acid ( 5 ) . The product was assayed by ignition to sodium sulfate (6). Samples of bis(dibutylethy1ammonium)hexane-l,6-bis(ethylsulfate) (BQAES), containing from 0.1 to 25% ethyl sulfate in the presence of about 30% of phosphoric acid and various amounts of sulfate, were used. BQAES is a long-chain quaternary ammonium salt of the ethyl sulfate anion. Procedure. An accurately weighed sample of BQAES, from 0.1 to 0.5 g, was diluted to 5 mL with water in a volumetric flask. Ten microliters of the diluted sample was injected into the column.
Ethyl sulfate was successfully separated from t h e sulfate and phosphate present in the BQAES samples. The retention times for phosphate, ethyl sulfate, and sulfate were 2.8, 3.8, and 4.8 min, respectively. A typical chromatogram is shown in Figure 1. Over 50 samples were analyzed. T h e relative standard deviation of t h e method was within 1 2 % for ethyl sulfate of concentration greater t h a n 1'70. For samples containing less t h a n 1%ethyl sulfate, the precision was within &5% relative. T h e detection limit was around 0.1% ethyl sulfate in the presence of u p t o 20% sulfate. This amounts t o 10 pg of ethyl sulfate. The accuracy of this method was checked against an indirect spectrophotometric method ( 3 )using BQAES samples. T h e agreement was within 2% relative. T h e optimum concentration of t h e TBAC104 solution for t h e chromatographic elution was found t o be 0.010 10.002 M. Outside this concentration range, the ethyl sulfate and sulfate peaks were not completely resolved in t h e presence of high concentrations of sulfate. The effect of various diluents for the samples on the separation was studied. No difference in the chromatograms, other t h a n the change in sign of t h e solvent peak, was found when water, water/methanol (70/30 ./vi, or t h e eluent itself was used t o dilute t h e samples. This method should find applications in the determination of ethyl sulfate in a wide variety of samples, regardless of the size of the cations present. As was shown in this study, the concentration of the counterion used in the mobile phase was sufficient to swamp even the relatively large cation in BQAES t o effect the elution of ethyl sulfate.
ACKNOWLEDGMENT I thank J. N. Maloney, Jr., D. R. Senn, and N. H. Watkins for helpful discussions.
LITERATURE CITED (1) Calhoun. G. M.; Burwell, R . L., Jr. J . Am. Chem. Sac. 1955, 77, 6441-6447. (2) Kurz, J. L. J . Phys. Chem. 1962, 66, 2239-2245. (3) Sheffield, W. M. Unpublished work, Monsanto Chemical Intermediates Company, Pensacola, Fla., 1974. (4) Abe, K.; Tanirnori, S.;Hashirnoto, S. Bunseki Kagaku, 1966, 15, 1364- 1368. (5) Nguyen-Quang-Trinh, Compf Rend 1946, 222, 897-898 (6) Burwell, R L , Jr J . Am Chem Soc 1949, 7 1 , 1769-1771
RECEIVED for review December 20. 1979. Accepted February 13, 1980.
Minimizing Relative Error in the Preparation of Standard Solutions by Judicious Choice of Volumetric Glassware R. 6. Lam and T. L. Isenhour" Department of Chemistry, Universify of North Carolina, Chapel Hill, North Carolina
Numerous textbooks on analytical chemistry discuss t h e practical details concerning determinate a n d indeterminate errors which may arise during the manipulation of volumetric glassware ( I , 2 ) . Other textbooks ( 3 , 4 )present tables familiar 0003-2700/80/0352-1158$01 .OO/O
to nearly all analytical chemists, regarding the relative error in different volume pipets and flasks. These tables are usually condensed from the volumetric tolerances published by the National Bureau of Standards ( 5 ) . ?? 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 5 2 , NO. 7, JIJNE 1980
Table IA. List of t h e Standard Deviations (Capacity Tolerances) and Associated Relative Errors for Various Sizes of Volumetric Pipets (Class A) capacity pipet capacity, mL tolerance, m L i 0.007
1 2 3 4 5 10 15 20 25 a
0.01 0.01 0.01
0.015 0.02 0.u3T a 0.03 0.03
relative error, % 2
0.70 0.50 0.33 0.25 0.30 0.20 0.20 0.15 0.12
The value marked with a t was obtained from Ref. 5.
Table IB. List of t h e Standard Deviations (Capacity Tolerances) and Associated Relative Errors for Various Sizes of Volumetric Flasks (Class A) flask capacity, mL
capacity tolerance, mL
relative error, 7%
10.02 0.03 0.05 0.08 0.12 u.20 0.30
k0.20 0.12 0.10 0.08 0.048 0.40 0.03
10 25 50
100 250 500 1000
For t h e volumetric pipets and flasks found in a typical laboratory. there are hundreds of thousands of combinations of glassware t h a t may be used to dilute a stock solution in 1, 2, or n steps. And for preparing a specific concentration, there may be hundreds of combinations yielding the desired result. T h e tables for relative error in volumetric glassware can be utilized for selecting t h e optimum sizes of pipets and flasks t o use in performing a given dilution. This paper presents tabular d a t a on t h e optimum choice of volumetric glassware and t h e number of steps to use t o minimize the final relative error in the dilution process. There is no closed-form solution t o the problem and the number of combinations t h a t must be considered is often very large. Hence, the results of this study are presented as a table rather t h a n a n algorithm. DISCUSSION OF METHOD Equation 1 relates t h e concentration of the solution to be prepared, C,,,, with t h e concentration of the available stock solution, Cold, and t h e volumes of pipets (PI)and flasks (F,) employed in an rz-step dilution.
A concentration ratio C may be defined as Cnew./Cold such that Equation 2 holds. T h e propagation of error treatment (6) allows calculation of t h e relative error
in C (oc/C) as a function of the relative errors in P, and F, ( r s p , / p , , and nF,/Fi, respectively) as shown by Equation 3. 1=1
Tables IA and I B contain the standard deviations (capacity tolerances) and relative errors for several commonly available Class A volumetric pipets and flasks. These values have been condensed from more recent Federal specifications for volumetric glassware ( 7 , 8 ) than those given in ( 5 ) . Knowing these
1159
Table 11. Comparison of t h e Percent Relative Error Minima Found Using 1-,2-, and 3-Step Dilutions to Obtain a Given Concentration Ratio concn. ratio 0.800 0.600 0.500 0.400 0.300 0.250 0.200 0.160 0.150 0.120 0.100 0.080 0.060 0.050 0.040 0.030 0.025 0.020 0.016 0.015 0.012 0.010 0.008 0.006 0.005 0.004 0.003 0.002 0.001
1 step 0.19' a 0.23'
dilution steps 2 steps
3 steps -. _.
__
0.16'
--
__
0.18' 0.22' 0.14' 0.17 0.28 0.22' 0.35 0.13' 0.16' 0.21' 0.13"
0.25 0.28 0.22 0.24 0.26' 0.27 0.29' 0.23 0.23 0.27 0.20 0.22 0.26 0.19 0.21 0.23' 0.25 0.27 0.18' 0.20' 0.24' 0.18 0.20 0.24' 0.20' 0.20'
-_
+
0.16' 0.20' 0.12' 0.15' 0.25 0.20' 0.33 0.20 0.25 0.33 0.30 0.25 0.33 0.50 0.70
+
+ +
__ __
0.29 0.31 0.32 0.33 0.29 0.30 0.33 0.28 0.28 0.31 0.26 0.27 0.29 0.30 0.31 0.26 0.27 0.30 0.24 0.26 0.29 0.25 0.25
a t denotes the optimum value found for a given concentration ratio.
values, t h e relative error contributed by particular sizes of glassware can be calculated using Equation 3. 'The q / C values resulting from using different sizes of volumetric glassware and varying numbers of steps to achieve the s x n e C value can then be compared and an optimum procedure determined. In practice, the number of steps used to perform a given dilution would rarely be more than two or three. It is desirable t o limit the number of steps because of the I ime, glassware, and reagents required and the error introduced by the analyst reading and adjusting a meniscus during each step in t h e preparation of a solution. Also, as may be seen later, the relative error advantage may not be great enough to warrant t h e extra effort of carrying out additional steps. Because of these considerations, a maximum of 3 was chosen for n. This allowed, using the sizes of glassware listed in Tables IA and IB, over 250000 possible ways to dilute a stock solution in 1, 2 , or 3 steps. However, only 29 of the 63 possible 1-step dilutions give unique C values. By only using the optimum glassware volumes for these 29 concentration ratios as individual steps in the multistep cases, the total number of 1-,2-, and 3-step dilutions to be considered was reduced one order of magnitude. Using the computing facilities a t the UNCCC (University of North Carolina Computation Center), these possible dilution sequences were sorted into groups, each group containing the dilution sequences resulting in the same value of C. The relative error for each possiblch n-step dilution was calculated according to Equation 3, and the optimum from each group (for each unique C value) was determined. If more than one possible dilution sequence gave the same minimum relative error within a group, the one requiring t h e smallest aliquot of initial solution was chosen. RESULTS For the 29 unique concentration ratios obtainable by 1-step dilutions, the optimum dilution sequences for the 1-, 2 - , and
1160
ANALYTICAL CHEMISTRY, VOL. 52, NO. 7, JUNE 1980
Table 111. List of Pipet ( P ) and Flask ( F ) Sizes (in m L ) t o Use in Achieving a Given Concentration Ratio Using an n-Step Dilution concn. ratio 0.800 0.640 0.600 0.500 0.480 0.400 0.360 0.320 0.300 0.250 0.240 0.200 0.180 0.160 0.150 0.128 0.125 0.120 0.100 0.960 E-1 0.900 E-1 0.800 E-1 0.750 E-1 0.720 E-1 0.640 E-1 0.625 E-1 0.600 E-1 0.500 E-1 0.480 E-1 0.450 E-1 0.400 E-1 0.375 E-1 0.360 E - 1 0.320 E-1 0.300 E-1 0.256 E - 1 0.250 E-1 0.240 E-1 0.225 E-1 0.200 E-1 0.192 E-1 0.180 E-1 0.160 E-1 0.150 E-1 0.144 E - 1 0.128 E-1 0.125 E-1 0.120 E-1 0.100 E-1 0.060 E-2 0.900 E-2 0 , 8 0 0 E-2 0.750 E-2 0.720 E-2 0.640 E-2 0.625 E-2 0.600 E-2 0.500 E-2 0.480 E-2 0.450 E-2 0.400 E-2 0.375 E-2 0.360 E-2 0.320 E-2 0.300 E-2 0.256 E-2 0.250 E-2 0.240 E-2 0.225 E-2
step 2
step 1 steps P
20 20 1 15 1 25 2 15 1 20 2 15 2 20 1 15 1 25 2 15 1 20 2 15 2 20 1 15 3 20 2 25 2 15 1 25 3 15 2 15 1 20 2 15 3 15 2 20 2 25 1 15 1 25 2 15 2 15 1 20 2 15 2 15 2 20 1 15 3 20 1 25 2 15 2 15 1 20 3 15 2 15 2 20 1 15 3 15 3 20 2 25 2 15 2 25 3 15 2 15 2 20 2 15 3 15 2 20 2 25 2 15 2 25 2 15 2 15 2 20 2 15 2 15 2 20 2 15 3 20 2 25 2 15 2 15 1
2
F 25 25 25 50 25 50 25 50 50 100 25 100 50
50 100 50 100 50 250 25 100
P
-
F
20
25
20
25
15 20
step 3
~-
P
F
25 25
20
50
15 20
25 50
20 25 20
50
50 50
20 15
50 25
25 20 20 25
50 50 25 100
20
20
25
50
250 100
25 250 100 250 500 250 100
20 15
25 50
25 15 20
100 2 50 50
20
50
20 15
100
15
50
500 100
25 250 500 25 1000 250 100
20
250
20
250
50
1000
25 250 250
20 15 20
50
50 100
1000
25 50 500 250 250 50 250 250 100
50 250 1000
250 500 250 500 250 1000 250 500 250 50 250 250 1000
20 20 25 20 25 20 15 25 25 20 20 25 25 25 20 15 25 25 15 20 25 20 25 20 15
50 50 100 100 2 50 50
15 20
250 250
20
250
15
250
100
250 500 50 250 100 250 250 250 100 500 100 250 250 500 250 1000 5 00
100
error, %
0.19 0.27 0.23 0.16 0.30 0.18 0.33 0.26 0.22 0.14 0.29 0.17 0.32 0.26 0.22 0.32 0.21 0.29 0.13 0.35 0.32 0.16 0.27 0.37 0.25 0.20 0.21 0.13 0.28 0.31 0.16 0.26 0.31 0.24 0.20 0.31 0.12 0.27 0.30 0.15 0.33 U.30 0.23 0.20 0.36 0.30 0.19 0.27 0.18 0.33 0.30 0.20 U.25 0.35 0.22 0.19 0.24 0.18
20
250
0.26 0.30 0.20 0.25 0.29 0.22 0.24 0.29 0.18 0.26 0.30
concn. ratio
0.200 E-2 0.192 E-2 0.180 E-2 0.160 E-2 0.150 E-2 0.144 E-2 0.128 E-2 0.125 E-2 0.120 E-2 0.100 E-2 0.960 E-3 0.900 E-3 0.800 E-3 0.750 E-3 0.720 E-3 0.640 E-3 0.625 E-3 0.660 E-3 0.500 E-3 0.480 E-3 0.450 E-3 0.400 E-3 0.375 E-3 0.360 E-3 0.320 E-3 0.300 E-3 0.256 E-3 0.250 E-3 0.240 E-3 0.225 E-3 0.200 E-3 0.192 E-3 0.180 E-3 0.160 E-3 0.150 E-3 0.144 E-3 0.128 E-3 0.125 E-3 0.120 E-3 0.100 E-3 0.960 E-4 0.900 E-4 0.800 E-4 0.750 E-4 0.720 E-4 0.640 E-4 0.600 E-4 0.500 E-4 0.480 E-4 0.450 E-4 0.400 E-4 0.360 E-4 0.320 E-4 0.300 E-4 0.250 E-4 0.240 E-4 0.200 E-4 0.180 E-4 0.160 E-4 0.150E-4 0.120 E-4 0.100 E-4 0.900 E-5 0.800 E-5 0.600 E-5 0.500 E-5 0.400 E-5 0.300 E-5 0.200 E-5 0.100E-5
step 2
step 1
x
steps P
F
P
F
500 250 500 500
500 50 250 500 250 250 250 500 500 500 250 500 500 1000 250 250
2 3 2 2 2 3
20 15 15 20 15 15
50
3
20 25 15 20 15 15 20 15 15 20 25 15 20 15 15 20 15 15 20 15 20 25 15 15 20 15 15 20 15 15 20 25 15 20 15 15 20 15 15 20 15 20 15 15 20 15 20 15 20 15 20 15
100 1000
25 20 15 20 25 20 20 25
500
20
1000
25 20 15 20 25 20 25 25 20 25 25 15 20 25
2 2 2 3 2 2 2 3 3 2 2 2 3 2 2 2 3
3 2 3 3 3 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
1000
50 500 1000 500 100
250 1000 500 1000 250 1000 1000
1000 250 250 1000
10 10
250 250 500 1000 250 250 250 250 250 250 250 250 250 500 250 250 250 250 250 250 500 500 250 250 500 250 250 250 1000 250 500 250 500 500 500 1000 500 1000 1000 1000 1000 1000
4 4
1000
20
15 15 20 15 20 15 10
1000
15
25 20 20 25 25 15 25 20
25 25 25 20 20 25 25 25 20 25 25 25 20 20 25 25 20 25 25 20 20 25 25 20 25 20
20 25 20
25 20 20 20 25 20 15 20 10
step 3
P
F
20
250
15 20
250 250
20
500
15 20
250 250
20
250
25 20
250 500
20 25 20
500 1000 250
25 20 15 20 25 15 20 25 20 25 20 15 20 25 15 20 20 25 20 15 20 15 20 20 25 20 20 15 20 20 20 20 15 20 20 20 20 20 25 25
1000 500 500 1000 1000 500 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000
1000
250 250 1000
250 250 250 1000
250 250 250 250 250 250 2.50 500 250 250 250 250 300
500 250 500
250 500 500 500 500 500 1000 1000 500 1000 1000 1000 l00U 1000 1000 1000 1000 1000 1000 1000
1000 1000 1000 1000
7c
0.20 0.32 0.29 0.22 0.24 0.34 0.28 0.18
1000
1000 1000 250 500 1000
error,
1000 1000 1000
1000 1000
0.26 0.20 0.31 0.29 0.22 0.24 0.34 0.26 0.17 0.26 0.20 0.29 0.29 0.22 0.24 0.32 0.26 0.25 0.27 0.22 0.29 0.29 0.24 0.30 0.32 0.25 0.27 0.33 0.27 0.22 0.29 0.24 0.30 0.32 0.25 0.27 0.33 0.27 0.29 0.24 0.30 0.32 0.25 0.33 0.27 0.28 0.23 0.30 0.25 0.33 0.27 0.28 0.30 0.25 0.33 0.27 0.30 0.28 0.30 0.32 0.32 0.35
1161
Anal. Chem. 1980, 52, 1161-1162
3-step cases were chosen. The minimum percent relative error corresponding to these optima are presented in Table 11. A blank in t h e table indicates t h a t no possible n-step dilution will yield that value of C. There are several interesting points t o be discussed. First, out of 29 possible C values given, 1 2 have smaller relative errors using a 2-step rather than a 1-step dilution process. This somewhat surprising result is resolved as follows. A majority of these 2-step cases occur near the bottom of t h e table, where the value of C is small. This is a region where in t h e 1-step case, the experimenter is forced t o use successively smaller sizes of pipets to obtain t h e low values of C. This leads t o an increase in the relative error to a point where it is advantageous t o utilize more steps employing larger sizes of pipets with relatively smaller errors. This argument also explains why seven of the 3-step dilutions show smaller errors t h a n the corresponding 1-step cases. T h e anomalies near the middle and t o p of Table I1 may occur because of the Federal specifications outlined in Table IA. I t may be seen t h a t t h e relative error is not a smooth function of pipet capacity between the pipet sizes of 3 a n d 5 mL, and is caused by the defined tolerances. T h e second major point is t h a t the relative error for the 2-step case is always less than for the 3-step case within the range of C spanned by the table. T h e 3-step case becomes Again, this agrees consistently better only when C I2 X with the intuitive argument outlined above, since the C values are not low enough to require small pipets to be used in the 2-step case. Finally, a substantial degree of increased precision may be realized by simply choosing the optimum set of glassware and number of steps t o use. For example, if a C value of 0.001 is desired, a factor of 3.5 increase in precision may be obtained by using a 2-step rather than a 1-step dilution. Although the increase is much less substantial in some other cases, there is a significant gain. It must be borne in mind, however, that this treatment accounts only for the random or indeterminate
error contribution to the dilution procedure. T h e systematic errors based on factors such as temperature, meniscus reading, and delivery errors on the part of the analyst may negate part or all of t h e gain presented by this method. Table I11 presents the optimally-sized glassware chosen t o minimize the indeterminate error for all of the unique 1- and 2-step dilutions. T h e table may not have widespread applications for instances where a certain volume of solution is required, or where there are limiting amounts of initial solution or solvent available. However, the table may be of instructive use and useful in areas as instrumental and electrochemical trace analyses. I t should be of particular concern in the construction of calibration curves for instrumental determinations in the nanogram to picogram range.
ACKNOWLEDGMENT The authors gratefully acknowledge the useful discussions of B. A. Hohne.
LITERATURE CITED (1) I. M. Koithoff and E. B. Sandeii, "Textbook of Quantitative Inorganic Analysis", 3rd ed., The Macmiilan Co.. New York. 1952. (2) D. A. Skoog and D. M. West, "Fundamentals of Analytical Chemistry", 2nd ed., Hoit. Rinehart and Winston, Inc., New York, 1969. (3) T. L. Isenhour and N. J. Rose, "Introduction to Quantitative Experimental Chemistry", Aiiyn and Bacon, Inc., Boston, 1971. (4) L. F. Hamikon and S.G. Simpson, "Quantitative Chemical Analysis", 1 l t h e d . , The Macmiilan Co., New York, 1958. (5) J. C. Hughes, "Testing of Glass Volumetric Apparatus", National Bureau of Standards Circular #602, U.S. Government Printing Office, Washington, D.C., 1959. (6) S. L. Meyer, Data Analysis for Scientists and Engineers", John Wiley and Sons, Inc., New York, 1975. (7) Federal Specification NNN-P-395D, "Pipet, Volumetric (Transfer)", U S . Government Printing Office, Washington, D.C., 1978. ( 8 ) Federal Specification NNN-F-289C, "Flask, Volumetric", U.S. Government Printing Office, Washington, D.C., 1974.
RECEIVED for review January 18, 1980. Accepted February 7, 1980. The support of the National Science Foundation, Grant No. Che-78-00632, is gratefully acknowledged.
Silicone Coated Oscillator for Density Meter Analysis of Caustic Samples Joseph 1.Rivera Applied Technology Group, Analytical Laboratories Department, Rockwell Hanford Operations, Richland, Washington 99352
Recent samples submitted to the Analytical Laboratory for density measurement have been generally high in hydroxide concentration, on t h e order of 8 M NaOH. A Mettler DMA 45 Calculating Density Meter has been used for t h e density determination of more than 1200 individual samples. However, t h e high concentration of hydroxide has resulted in frequent recalibration of the instrument. A siliconizing fluid with t h e trade name of Surfasil was described by the supplier as forming a film to glass which is unaffected by organic solvents and not easily hydrolyzed by either acids or bases. This liquid was tested as a possible aid in minimizing t h e frequency of recalibration. This coating has been shown t o be highly effective in preventing reaction of a hydroxide sample with t h e glass oscillator (sample tube).
EXPERIMENTAL Surfasil was obtained from Pierce Chemical Company (Rockford, Ill.). A 10% solution of Surfasil was prepared in xylene and left in the oscillator at 25 "C for 3o min. The cell was then alternately rinsed with water and acetone and dried by a continuous air stream passing through the cell. Calibration of the instrument was then performed as usual according to the manufacturer's instructions ( I ) . 0003-2700/80/0352-1161$01 OO/O
RESULTS AND DISCUSSION Prior to treatment of t h e DMA 45 oscillator with Surfasil, approximately 15 t o 20 samples were analyzed before a significant change was noted in the displayed density reading of water a t 25 "C. Since the density of water a t several temperatures is well known ( 1 , 2 )and since the density meter has a precision of *0.0001 g/cm3 according to the manufacturer's specificiations, a change of &0.0003 unit was felt to be significant. After the coating was applied to t h e oscillator, no recalibration was required even after analysis of more than 100 highly caustic samples. Specifically, after calibration the value for water a t 25 "C was 0.9971 g/cm3. Within 35 days a total of 174 samples were analyzed. T h e density of water was then measured as 0.9972 g/cm3 which was still within the suecified mecision limits of the instrument. Considering the effectiveness of the Surfasil coating on the DMA 45 meter, the silicone coating was also applied t o a 5-place Mettler DMA density meter in use by the Chemical Standards and Actinides Laboratory. Repetitive density analysis of standard solutions using this meter was giving unacceptable variations in the displayed values. The coating was therefore applied t o the meter not only as a protective caustic coating but also as a possible aid to stabilize t h e C 1980 American Chemical Society
