822
ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978
LITERATURE CITED (1) A. A. Nemodruk and Z . K. Karalova, "Analytical Chemistry of Boron", translated by R. Kondor, Ann Arbor-Humphrey Science Publishers, Ann Arbor, Mich., 1969. (2) R. J. Lishka, J . Am. Water Works Assoc., 53, 1517 (1961). (3) G. S. Spicer and J. D. H. Strickland, Anal. Chim. Acta, 18, 231 (1958). (4) G. S. Spicer and J. D. H. Strickland. J . Chem. Soc.. 1952, 4650. (5) H. S. Roth and B. Miller, Arch. Pharm., 297, 660 (1964). (6) D. W. Dyrssen, Y. P. Novika, and L. R. Uppstrom, Anal. Chim. Acta, 60, 139 (1972). (7) M. J. Taras, J . Am. Water Works Assoc., 50, 827 (1958). (8) "Standard Methods for the Examination of Water and Wastewater", 13th ed., America Public Health Association, Washington, D.C. 1971, p 69. (9) J. J. Bloomfield, J . Org. Chem., 27, 2742 (1962). (10) J. F. W. McOmie, M. L. Watts, and D. E. West, Tetrahedron, 24, 2289 (1968). (1 1) L. J. Bellamy, "The Infra-red Spectra of Complex Molecules", 2nd ed., John Wiley and Sons, New York, N.Y., 1958, p 142.
(12) D E Williams and J Vlamis, Anal Chem , 33, 1098 (1961)
' Present address, the Dow Chemical Co , Freeport, Texas Jack L. L a m b e r t * J o s e p h V. P a u k s t e l i s R o d e r i c k A. B r u c k d o r f e r ' Department of Chemistry Kansas S t a t e University Manhattan, Kansas 66506
RECEIVED for review August 15,1977. Accepted January 23, 1978. This research was supported by t h e National Science Foundation, Grant No. CHE-7403024.
AIDS FOR ANALYTICAL CHEMISTS Problems in Obtaining Adequate Seals with Screw Cap Containers and Their Daily Variation in Weights Larry
E. DeVries," Elmer Gubner, and Linda D. Jackson
Naval Surface Weapons Center, Electrochemistry Branch, Materials Division, White Oak Laboratory, Silver Spring, Maryland 209 10
When experimenting with lithium-boron alloys ( I , 2), it was necessary to transfer the alloys to experiments outside of glove boxes and to weigh samples outside of glove boxes. T h e alloys react more rapidly with air t h a n pure lithium does. Screw cap tubes or bottles which had low helium leakage rates seemed the best solution to the problem of handling the alloys in air. Helium was used for the atmosphere in the glove boxes. Experiments revealed three problems: many screw cap containers leak excessively, many cap liners contain reactive materials, and nonleaking containers change weight from day to day.
RESULTS A N D D I S C U S S I O N Tests revealed t h a t some types of glass containers were unacceptable because their screw caps leaked helium at a high rate (>1.5 X cm3/s). I n some cases, the cap liners themselves appeared to react with the alloys. In other cases, t h e liners were porous and contained air, moisture, or organic solvents. Before bottles and caps were put into a glove box, they were treated in the entry port of the box. T h e entry port was evacuated three times and filled with helium each time after evacuation. This did not remove air or volatile materials sufficiently from t h e caps. In a few days t h e alloys reacted with these materials. Bottled samples would not necessarily be used for a few days so those caps could not be used. For caps that leaked helium a t a high rate, various films (Teflon, polyethylene, and Parafilm) were used to see if t h e leakage rate could be reduced. One to five layers were p u t over t h e top of the bottle and the cap screwed tightly against the bottle top. Films generally did not reduce t h e leakage rate much below 1.5 X 10" cm3/s for bottles leaking at or above that rate initially. Glass tubes which did give adequate protection if treated properly were culture tubes manufactured by Corning Glass Works (Corning, N.Y. 14830). T h e screw caps had a Teflon liner with a rubber backing. Large tubes 25 m m X 150 m m with a helium leakage rate a t / o r below 1 X cm?/s were used. T h e y had a n average cap weight of about 6.4 g and an TI% paper not subject to U S Copyrighi
Table I. Variation in Weight of Selected Culture Tubesa Days after initial weight
3 5 7 9
11
Av wt change, mgb A=
Stand dev
- 1.0 -1.2 - 1.2 - 1.1
0.2 0.2 0.2 0.2 0.2
-0.5
Avwt change, mgb
Stand dev
B C
+0.2 +0.1 t 1.5
0.2 0.4d 0.2 0.3
+2.7
0.4d
+0.6
The valThe 11 glass tubes were 1 3 m m X 1 0 0 m m . ues are the average difference between the initial weight and the weight o n the day given. Group A contained six tubes and group B five. Tube 19 showed a - 0.5-mg variation from the average weight change on the fifth day and tube 23 showed a 0.5-mg variation o n the eleventh day. a
average total tube weight of 38.7 g. Small tubes were also used. They were 13 mm X 100 mm with an average total tube weight of 14.6 g and a n average cap weight of 2.4 g. T h e tubes had a helium leakage rate of 1 X cm3/s. In t h e initial experiments, it was found t h a t t h e tubes continuously lost weight. A check revealed t h a t t h e porous rubber was filled with an organic solvent. Some solvent distilled away each time t h e tubes a n d caps were under vacuum prior to being filled with helium. T h e caps were baked a t 393 K for 109 h and then under vacuum a t 393 K for a n additional 1428 h. T h e large caps lost a n average of 0.23 g/cap for 12 caps. About 80% of t h e loss occurred during t h e first 109 h. Twelve small caps lost an average of 0.09 g/cap with most of the loss coming during t h e first 109 h. After this treatment, t h e caps leaked very badly. The rubber backing had shrunk causing the leaks. In a new experiment, new small caps were heated a t 308 K to 311 K for 384 h under vacuum. They reached a "constant" weight. T h e loss in cap weight for small caps averaged 0.05 g/cap. T h e helium leakage rate was 1 X PubllshPd 1978 9v the American Chemical Socletv
ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978
Table 111. Use of Blanks to Correct for Plastic Bottle Daily Weight Variationa
Table 11. Variation in the Weight of Selected Plastic Bottlesa Days after initial weight 3 4
5 6 8 9 10 11
12 15 16 18 19
Av wt change, mgb
Stand dev
2.2 2.2 2.6 2.6 1.6 2.2 2.5 - 0.7 - 0.1 - 0.4 +0.4 - 0.5 +1.3
0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.1 0.2 0.2 0.1 0.1 0.3
823
Dev from av in mg-bottle symbolC
Days after initial weighing 17
- 0.4-S
- 0.4-J,
0.4-N - 0.5-J, 0.4-N -0.6-J, 0.4-N
Blank' SampleC
20
23
29
Average weight change in mg ( A ) b and standard deviation ( B ) A B A B A B
A
B
2.2 2.3
4.0 4.0
0.4 0.4
0.5 0.4
4.7 5.4
0.6 0.6
4.1 4.1
0.5 0.5
Sample bottle weight change in mg ( A ) and blank sample bottle weight change in mg (B) A - 0.6-B,
0.4-L
a Eleven bottles of 6 0 m L were used. The values are the average difference between the initial weight and the weight on the day given. ' The values are for bottles that showed more than 0.3-mg deviation from the average.
cm3/s. Tests showed t h a t t h e 11 tubes with treated caps divided into two groups. Table I lists the results. T h e balance sensitivity was 0.1 mg. If a large enough number of tubes are originally used, enough tubes can be selected to furnish sample containers a n d blanks. Polypropylene bottles and polyethylene bottles with polypropylene caps were tested. Because they did not have cap liners, many bottles leaked helium a t greater rates t h a n 1.5 X cm3/s and were unacceptable. T h e manufacturers of t h e bottles are not known since they were not indicated on t h e bottles. Polyethylene bottles with polypropylene caps manufactured by Nalge were tested. Because of t h e cap and bottle t o p design, they did not need liners. On t h e average between 50-60% of a randomly selected group of bottles showed a leakage rate below 6 X lo4 cm3/s. T h e bottles tested were made of either linear or conventional polyethylene and were 60 m L in volume a n d 11.1g in average weight. In one experiment about 25 bottles were used. I t was noted that their empty weights (helium-filled) were quite constant for several days. T h e n they began to vary from day to day. I t was also noted t h a t they seemed to divide into three groups, each of which changed weight t h e same amount each day. T h e changes in weight might be either positive or negative. Experiments indicated t h a t while static charge might play a part, neither it nor moisture seemed t o be t h e total causes of the weight change. When weighed in a room with less than 5% relative humidity, t h e bottles continuously changed weight. Plastic bottles easily take a static charge. T h e light in a balance is grounded. T h e balance pan a n d area below t h e pan are not. Static charge from t h e bottle causes the pan t o be repelled from t h e bottom of t h e balance chamber. As the charge slowly bleeds off, the bottle appears to gain weight. T h e change can easily be 1 % of t h e containers weight. We were able to minimize this effect. We did not d o weighings in plastic containers in t h e dry room. It was decided to see if some bottles could be used as blanks. Their average change in weight on a given day could be applied t o t h e sample-filled bottles. Bottles filled with helium were placed in a vacuum desiccator. T h e desiccator's helium leakage rate was too low to be measured. T h e desiccator was removed from t h e glove box and placed near t h e balance for 16 h on the average before weighings were made. This allowed helium-filled bottles t o come t o balance-room temperature. I t avoided having moisture condense on bottles which were initially cooler t h a n t h e balance-room temperature. Two methods were used to fill bottles. No differences were noted between them. In one method, t h e bottles were opened and
B
- -- -A
B
A
B
A
B
0.3 4 . 6 - 0.6 2 . 3 - 0.1 5 . 3 -0.6 3.8 2.6 - 0.4 4.9 -0.2 4.4 - 0 . 3 3.7 - 0 . 3 0.1 4.5 0.2 4.2 -0.1 4.1 -0.1 2.1 2.6 - 0.4 6.2 - 1 . 5 4.8 -0.7 4.3 - 0 . 3 0.3 3.5 0.5 0.2 5.2 - 0 . 5 3.8 2.0 0.1 2.9 - 0.7 6.4 -1.7 4.4 - 0 . 3 3.9 0.4 4.1 - 0 . 1 2.2 0.0 5.2 - 0 . 5 3.7 1.4 3.5 0.5 0.5 5.3 -0.6 1 . 7 1.7 a Bottles of 60 m L were used. The values are the average difference between the initial weight and the weight on the day given. ' Five bottles were used for the blank determination and eight as sample bottles.
p u t into a glove box and resealed after each weighing. In t h e other method, t h e bottles once filled remained sealed throughout t h e experiment. However, they went through the same evacuation treatment as t h e opened bottles after each weighing. We found that if more than 50 bottles are checked, groups can be selected for which the daily variation in weight is nearly t h e same for t h e group. Table I1 gives t h e results for one group. One can see t h a t a selection can be made so t h a t the weight change of part of the 11 bottles can be used to calculate blanks. Any of t h e group could be selected t o calculate t h e blank. Of course occasionally a sample-filled bottle's weight will change much more or less t h a n t h e average. Generally, however, t h e results are better using blanks. T h e variation in weight is small; b u t when samples range in weight from 1 g down to 0.1 g, the error in not using a blank correction often ranges from a few tenths to a few percent. If there is a smaller group of bottles to select from (less than 50) a different approach for calculating a blank is necessary. This results from a larger spread of values around a n average daily weight change. T o calculate t h e blanks in T a b l e 111, weights from three bottles which were consistantly a t the high end of t h e daily weight changes were used along with t h e values for two bottles which were consistantly a t the low end of t h e weight changes. T h e other eight bottles were grouped nearer to the average and were used as sample containers. T h e d a t a in Table I11 are selected from 23 days of weighing over a period of 1 month. Of t h e 184 weighings of sample containers, only eight weights ( 4 % ) would be made worse by applying t h e blanks t h a n by not applying them. On 48% of the days, no corrected bottle weights were still in error by more than 1.0 mg. On 26% of t h e days, one of t h e eight corrected bottle weights was still in error between 1 a n d 2 mg. T h e remaining 26% of t h e days had 2 bottles with corrected weights still showing a 1-2 mg error. At no time did more t h a n two bottles have t h a t much error. At no time was t h e error 2 mg or more.
ACKNOWLEDGMENT T h e authors thank Raymond J. Zehnacker for making t h e helium leakage rate measurements.
824
ANALYTICAL CHEMISTRY, VOL 50, NO 6, M A Y 1978
LITERATURE CITED (1) S D James and L E DeVries, J
Electrochem soc , 123, 322 (1976)
(2) L E DeVries and E Gubner. this issue
RECEIVED November 18, 1977. Accepted January 20, 1978.
This work was supported by the Independent Research Program and the Molten Salt Battery and Lithium-Chlorine Ratter5 Programs of t h e Naval Surface Weapons Center, F'hite Oak, Md.
Effluent Detector for Chromatographic Columns Using Volatile Solvents Norman S. Radin" and Dan del Vecchio Mental Health Research Institute and Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48 109
Preparative liquid chromatography is ordinarily operated in conjunction with a fraction collector and t h e individual fractions are subsequently analyzed by some separate procedures. Recent developments in monitoring systems have in many applications made it possible t o follow the elution a n d assist t h e chemist in understanding the effected separation. All of the monitoring devices described or commercially available are of t h e continuous type, producing a record on a strip chart corresponding t o some physical property. Most monitoring devices are limited in their applicability, depending on a single physical property or chemical reaction, and interference by t h e elution solvent can be a serious obstacle. W e thought it would be useful t o have a device which would be independent of the solvent composition, provided the solvent was reasonably volatile, which could be used with a variety of detection techniques. T h e principle utilized was the evaporation of portions of the column effluent in t h e form of discrete spots on a long strip of paper, corresponding t o individual fractions in t h e fraction collector.
EXPERIMENTAL Materials and Design. The physical arrangement of the device components is shown in Figure 1. The column effluent goes through a stream sampler, A, operated by compressed air. When the sampler is activated, an aliquot of the effluent (1.6 pL) is transferred t o the paper strip just below. The transfer is produced by a stream of air (0.2 mL/min) coming from a peristaltic pump. We use a Brinkmann Ismatec Mini-Micro 2/6 pump, fitted with a tube 0.015-in. i.d. The paper strip is held taut against the delivery tube of the valve by a weight attached to the front end of the strip, a "bulldog" paper clamp. After delivery of the desired number of 1.6-pL drops, the paper strip is advanced 11 mm by simultaneous activation of the air solenoid valve, B, and solenoids C and D. Solenoid D normally holds the paper strip against stopping block E and prevents slippage; when D is activated, it frees the strip. When solenoid E is activated, it pushes the notching block, F, down against the paper strip, producing two bosses (notch-like depressions), one on each edge of the strip. The bosses mark the location of each dried spot and act to minimize contact of the dried material with other surfaces that might contaminate or adsorb the material in the spot. Valve B causes the plunger in the pneumatic linear actuator, G, t,o move forward. Because time is required for the air to build up pressure in the cylinder, the plunger does not begin to move until solenoids C and D have completed their movements. Solenoid C is mounted in frame H so it moves-together with the paper strip-until the frame reaches stopping block E. The bottom plate in the frame has two small holes to accommodate the two projections at the bottom of notching block F. The latter is fastened firmly t o the solenoid plunger with two screws, which serve as set screws and attachment points for two return springs. A fraction of a second after frame H hits block E; power to the three solenoids is removed and springs in the solenoids and air cylinder return them to the rest positions (as drawn). The paper strip cannot move further because it is held by solenoid D. The distance between spot centers is determined by the distance 0003-2700/78/0350-0824$01 . O O / O
between the left edge of block E and the right edge of frame H. This gives ample separation between spots, which are about 5 mm in diameter. The timing control for the device also operates the fraction collector. It is set to control the collection time for each fraction and the number of drops to be dried on each position on the paper strip. One must estimate how much liquid to apply to each spot. This is done by estimating the weight of the material of interest that is expected, and the volume of liquid in which it is hoped elution will occur. For example, one might use a solvent pump delivering 2 mL/min and collect 5-min (10-mL) fractions. If 90 mg are expected to elute in 30 mL, the average concentration will be 3 pg/pL. If one wishes to deposit, on the average, 24 pg in each spot, one must set the timer to apply 8 p L , or five 1.6-pL drops during each 5-min collection interval. To make the five drops more representative of the collected fraction, we have set the timer to deliver the first drop after one half of the first subinterval; this is 0.5 min in the above example. The remaining drops in the run are deposited after full subintervals (1 min). This arrangement also ensures sufficient time to move the last drop from the sampling valve to the paper strip prior to movement of the strip. A stream of house air is used to dry each drop promptly after transfer to the paper. In the case of materials that are very soluble in the column solvent, there is migration to the edges of the drop, with formation of a ring of dried material. This helps to make the dried material more visible with the detecting reagent; if a more uniform spot is desired (for photometric determination), the air stream can be heated. To prevent loss of material and contamination ofthe fraction collector while the collector is moving, the column effluent is passed through a valve held just above the collection vessels (Figure 2). When the timer actuates the fraction collector and paper advance device, it also produces a brief latching pulse to close the valve. Effluent then accumulates in the reservoir above the valve. When the fraction collector movement is complete, a second latching pulse opens the valve. We use two different tips on the bottom of the valve: a narrow one (E) for small columns and a wider one (D) for higher flow rates. The latter is not suitable for slow columns because deposition of dry material can occur at the tip; the former is not suitable for fast columns because the reservoir will then overflow. Not shown in Figure 2 is a protecting glass cylinder held around the drip tip of D by means of an O-ring. This reduces evaporation of solvent and subsequent deposition of material on the tip. The timer used to control the spotter, fraction collector. and collection valve is a solid state device that was built in our shop. A suitable timer could be made with a variable speed cam-type microswitch controller: supplemented by a separate pair of short interval cam timers for the paper advance solenoids and the collection valve. We are presently adapting a microprocessor unit to fulfill the same functions while producing a solvent gradient. Procedure. For counting radioactive spots, we simply cut the strip with a scissors and deposit the sections in scintillation vials. This technique was used t o evaluate the uniformity of spot formation and look for trailing. A radioactive solution mas allowed to flow through the stream sampling valve and eight groups of spots were collected, consisting of 3, 6, and 1 2 drops/spot. c' 1978 American Cherrical Society
