The Reagent Laboratory Barbee William Durham Ohio State University
Storing standard chloride solutions in
Columbus, 43210
plastic containers The Reagent Laboratory at Ohio State University pre- , pares a large proportion of the reagents used in the various scientific departments, the research and teaching labs, and the routine labs such as those in the University Hospitals. The products include chemical solutions, volumetric solutions, stains and indicators, photographic solutions, embedding compounds, and various kinds of high purity distilled water. Regular douhle distilled water is produced from recirculated steam by two 30-gal/hr stills and is stored in two 150-gal block tin lined tanks. Our demineralized double distilled water, about as pure as triple distilled water, is produced from recirculated steam by a 75-gal/hr still, with a monobed deionize1 in the line, and is stored in a third block tin lined tank. Water from this tank can be piped to a 10-l/hr Corning all glass still where it is again distilled to produce demineralized double distilled water, again distilled thru glass. We also use this all glass still to nroduce sinele. - . double. and tride. . . elass-distilled water. Recent analysis of our water by atomic absorption methods shows that our reeular double distilled water contains 0.03 ppm copper and our demineralized double distilled water, less than 0.01 ppm of copper. The Reagent Laboratory and the Glass Blowing Shop occupy a two story building which is located between OSU's two main chemistry buildings. It is staffed by six full time persons, about evenly divided between technical s and non-technical, and two part-time students. I t is one of a number of units in a centralized Lab Stores system at OSU, and is one of the very few such laboratories in American colleges or universities. Among the major advantages of this laboratory are: its quickly available service. the areat savings in cost of reagents, the involvement of hghly skilled-personnel in pergrming the service, and the considerable flexibility available. Variations in formulas. accordine to the desires of research workers. can be prepired quickry. Most of our products are available within 12-48 hr after receipt of the internal order. In July of 1951, the author of this article published, in this Journul, an article entitled, "Keeping Properties of
Certain Volumetric Solutions" which dealt with the stability of various volumetric solutions for periods of time from five months to nearly four years. The occasion for tbis publication was, as stated in the article, frequent inquiries from research workers concerning the stability of various solutions. The Possible Absorption of C02 Through Plastic
The oresent article concerns itself with the auestion which 6as arisen concerning the possible absorption of CO. throueh the walls of ~ l a s t i ccontainers, and an unexplained experience with-potassium, sodium, and zinc chloride solutions. The Biochemistry Laboratory of University Hospital first raised this qiestion in connection with electrolyte standards we prepare and furnish in plastic bottles. Most recently, the Analytical Division of the Chemistry Department raised this same question in connection with their order for some very accurately standardized 0.1 N NaOH. L. S. Tbeoboldl states that such absorption is a definite possibility, especially in the case of weak NaOH solutions such as 0.01 N. The fact that accurate records have been kept for more than 35 years affords tbis laboratory an opportunity to make observations which are not usually possible in most laboratories, and, our constant involvement in the preparation of reagents for a broad based demand, affords our staff the opportunity to gain skills and expertise not normally available to the usual laboratory technician. This skill and background has been used from time to time to save research workers valuable time, beyond that saved by their not having to make their own reagents. Table 1 indicates the manner in which we have approached the question at hand and the results. From this data, one might be tempted to conclude that standard NaOH does not absorb C 0 2 through the walls of plastic containers. However, the only justifiable conclu'Theobold, L. S.,Annlyst, 54,570,293-4, (1959).
Table 1 Tha Keeping Properties of Several NaOH Solutions in Plastic Containers Lot l
Date of Preparation
Normality When Prepared
7M614VS
June 14,1968
0.13052
8M291VS SMSBOVS
Mar. 27, 1969 ~ p r21, . 1970
0.2400 o.aiz8
8M737VS
Fsh. 18, 1971
0.3142
8M896VS
Jan. 4, 1972
0.5007
8M899VS SM968VS SMSVS
Jan.
10, 1972 M a y 30, 1972 Aug. 9, 1972
0.09985
0.02272 0.04964
Normality
Kind of Containar 1gal polyethylsna
Date of Restandardization
When Fastandardized
Change in Normality
ElaW Time
November 14, 1972
0.12998
-0.00059
6 yr, 5 mo
bottla (Nalgens) White plastic I/, ~ d , the k h d ndfor rommeroisl bleaohss ' / a gal thin plastic which had con, tained glycerine 1gal polvethyiene (Nalgene)
0.2898
-0.0002
0.3132
+o.ooos
3 yr. 8 mo 2 yr, 7 mo
0.3144
+O.0002
lyr,Omo
0.5W7
0.0000
10 mo
3 gal Pyrex carboy
5 881 polyethylene
--.--,
* .h n "
In each case, the aolvtion was NaOH. Lot t8MgG8VS was stored in Pyrex end wss cheeked s t this time as a oontml. Th- solutions were standardized against 0.1000 N o r 0.02500 N Potassium Acid Phthalate. Log ffSMS99VSwas also cheeked aaainst weighed portiona of PAP as a cross cheek on N/10 PAP.
Volurne51. Number 11. November 1974
/ 737
Table 2. The Keeping Properties of Sodium and Potassium Chloride Solutions in Polyethylene and Glass Containers %lutinn
Container
5M 667 VS
M/5 NaCl
PolyeU.rlane
6M
785 VS
M/2 NaCl
Polyethylene
8M 400 VS
M/1 NsCL
Soft Glass
8M 860 VS
M/1 NsCl
Polyethylene
M/10 KC1
Polyethylene
M/10 KC1
Pyrex
~ . "~~~~b~ t
Normality Date when Restandaudilad P r e o a d Normalitv DH 3-18-58
881 CL
61M
63M 376 C'
65M
100 C'
7M
772 VS
M/10 KC1 M/10 KC1
Soft Glass
Pyrex
7M 345 VS
M/2
KC1
Soft Glass
8M 457 VS
M/1 KC1
Soft Glass
0.2WO
1-17-63 0.5000 9-8-69 1.0065
10-21-71 0.2046 4.8 10-21-71 0.5495 10-21-71 1.0074 10-21-71 0.9962 10-21-71
9-19-69 0.100 0.0993 6-3-10 10-21-71 0100 0.1005 5-26-11 10-21-71 0.100 0.1013 2-13-67 0.1017 5-25-66 0.49% 11-15-70 1.0099
Date Reatandardiaed Normality rH
11-7-73
7-27-72
0.2081 7-27-72 0.5604 7-27-72 1.0121 7-27-72 1.0124 7-27-72 0.1011 7-27-72 0.1014 7-27-72 0.1012 7-27-72 0.1025 7-27-72 0.5087 7-27-72 1.0160
Date Reatandardimd Normality pH
5.9
9.6
0.2102 11-6-73 0.5818 11-7-73 1.0298
11-6-73
0.1018
11-6-73
0.10128 11-6-73
0.5175
8.6
a ~hese were not originally prepared as volvmetrie solutions. Blanks indicate that determinations wethere was no more of that solution on hand. Time elapse denoted by years-months elapsed.
Table 3. The Keeping Properties of Zinc Chloride Solution in Polyethylene and Glass Containers EDTA 0.1 M zinc Lot Number
container Used
Fahr
Obtained
Soft GISoft Glass Polyethelene P0lyethde"e Polyethelene Pyrex Glass Pyrex Glass Pyrex Glass F'yrex Glass
sion that can be made is that these seven NaOH solutions showed no appreciable change when stored in these plastic containers for long periods of time. Sodium and Potassium Chlorides in Polyethylene In July of 1971, the Biochemistry Laboratory of University Hospital brought to our attention the fact that their chloride results on the electrolyte solutions, which we were furnishing, were not what they should have been. We ran some chloride determinations on the stock solutions we had been using and did so again nine months later. When we noticed a trend of increased titre in the NaCl solutions, we ran chloride determinations on some other solutions which had been previously standardized and found this trend again with NaCl but not KC1 (Tahle 2).
738
/
Journal
of Chemical Education
4.75 4.65 10.0
5.45
9.4 9.50 8.55
Total Change Normality pH
Time
Elapse" 15-8
+0.0102
-0.05
0.0818
-1.25
+0.0233 +0.0162 +0.0018 +O.W13
+0.4
10-10
0.OOw +O.W08 +0.0191 +O.W61
4-2 0-9 2-9
3-5 2-6 6-5 6.2
-0.05
not done on those dataa: in a m e instan-
1-8 bsea-
Zinc Chloride in Polyethylene In October of 1973 the auestion of standard solution storage was again raised when we noticed a discrepancy between the stated purity of EDTA and the results obtained by titration against standard zinc solution. Upon investigation (see Table 3), it was found that 0.1 M zinc, prepared hy dissolving the metal in weak HCI, tends to increase in titre when stored in polyethylene containers. Table 3 shows the results of titrating 0.05 M EDTA with several 0.1 M zinc standards. The results show that the older the zinc standard the weaker the EDTA appeared to be. In reality, as shown by the results obtained by titrations against fresh zinc standards, the titre on the zinc standards had increased with age, especially when stored in polyethylene. Two possible explanations of this titre increase have been advanced: (1) Some kind of a molecular exchange between the solution and the ~ l a s t i ccontainer. with the difference in size of the sodium; potassium, a n d zinc molecules being a factor; or 2) traces of metal, perhaps used in the manLfacture of the plastic, are leached out o n long standing and react along with the zinc. Another indication of this possible change is that the p H of several of these solutions, which had been stored in plastic, had varied considerably more from near neutral than had those which were stored in glass. Of particular interest is the observation that solutions stored in polyethylene became more and more acid as time passed. While far from being conclusive, this data indicates that the storage of standard NaCl and ZnClz solutions in polyethylene is contra-indicated.
