VOL.5, No. 3
SANITATION, SABETY, AND CONVENIENCE IN PIPETTING
343
SANITATION, SAFETY, AND CONVENIENCE IN PIPETTING*
Unsanitary practices connected with the use of pipets are common in many laboratories. Pipets often show in their upper ends a deposit of solid material from dried saliva. It is common for two or more people to put their mouths on the same pipet without rinsing it, and rinsing it fails often to get it clean. Many people put unclean fingers on the upper ends of pipets and then put their mouths where their fingers were. We show here some devices being tried in our laboratory to make the pipetting of solutions sanitary and a t the same time convenient and safe. Figure 1 shows a device for filling a pipet by means of a siphon. The rubber tip b is attached to the bottom of the pipet, and the pipet, in an upright position, is then lowered till the graduation mark is a little below the level of the top of the solution in the bottle. The flow is controlled by pressure between the thumb and forefinger on the siphon a, and no pinchcock is necessary. Incidentally, this siphon can be used in the same way to fill burets, and it can also be used without the rubber tip to fill burets from the top. There are no restrictions on its use for scientific purposes and anybody can make it. A simple and less breakable form for general laboratory use is that in which the tube within the bottle is rubber connected to a glass tube leading through the stopper, and where the glass elbow in the end of the siphon fits into the hole in the stopper directly instead of into a glass tube. A very convenient variation of this, where large classes are to use it, is to have a four-holed rubber stopper, three holes of which receive glass elbows a t the ends of three branches of the siphon, the branching being effected by means of glass or brass Y-tubes. Thoughtless students cannot raise the loop higher than the level of the liquid if the siphon is passed beneath a shelf or table supporting the bottle before i t is set in operation and hooked up. These siphons work well with water, and with many dilute aqueous solutions, but they cannot be used with anything that acts on the rubber. Figure 2 shows a device for filling a pipet by pressure. The air pressure is increased by means of the bulb b, best worked with the left hand while the pipet is held in place by means of the thumb and middle finger of the right hand. When the solution goes a little above the mark the index finger is placed on the top of the pipet, and the stopper a removed enough to bring the tip of the pipet into the neck of the bottle. The solution is then drawn down to the mark, and the drop touched off. It works satisfactorily where large experimental errors are allowable. When great ac*Read before the Division of Chemical Education of the American Chemical Society, Richmond, Virginia, April 13, 1927.
curacy is required some objections to i t are: that a large part of the outside of the pipet is wet by the liquid, thus causing too much to be delivered; that the pipet often fails to reach the last few hundred cc. of solution in the bottle; that objectionable fumes in excessive amounts may enter the bottle with so much pumping; and that the pumping may cause too much evaporation in the case of standard solutions. Figure 3 shows a device by means of which the first two objections to the apparatus shown in Figure 2 are overcome. By placing the left thumb
and left forefinger over the holes c, and exerting pressure on the rubber bulb with the left band all the solution in the bottle can be made to pass up tube a, and if a pipet or a buret be fastened in this tube by means of an air-tight stopper when the tube is large, or by means of a piece of very elastic tubing when the tube is small (Fig. 4) the solution will ascend the pipet or buret without wetting more than a centimeter of the outside of the tip. The pipet is held with the right hand, and the pressure is automatically released when the left band is removed. The solution in the pipet should be forced a few centimeters above the mark, and should not be drawn down until after the stopper is loosened. If it becomes neces-
sary to force more solution into a partly filled pipet after air is admitted to tube a it is well to first drain the pipet completely or to force the solution up tube a and bring it in contact with the bottom of the pipet before tightening the stopper. When the apparatus is not in use it can be made nearly air-tight by placing a stopper in tube a, or a rubber cap (Fig. 4) on the end of the pipet. Then, by removing the glass tube to which the bulb is attached and inserting a plug the apparatus can be made completely air-tight. All the mentioned objections to apparatus of the type shown in Figure 2
may be overcome by applying suction to the pipet (Fig. 3). But in doing this we are liable to fall into old unsanitary practices. Most of the unsanitary evil in pipetting can be gotten rid of, however, by having individual mouthpieces. These are easier than pipets to keep in sanitary condition, and they can be used exactly as if they were the upper ends of the pipets. Figure 5a shows a very simple device for using an individual mouthpiece. The upper end of the pipet is pushed about half way through a long, fairly heavy rubber stopper, and the individual mouthpiece, a short straight tube, is pushed nearly half way through from the other end. If a curved mouthpiece (Fig. 5b) be used, the pipet can be suspended. The solution is drawn up by suction applied to the mouth-
piece, and the index finger is placed on the end of it instead of on the end of the pipet. Control is more perfect than with the pipet alone in that the warmth of the thumb and middle finger does not expand the air in the pipet when they grasp the stopper instead of the glass. The mouthpiece must fit moderately tightly or the stopper may pull loose, and one must be careful not to push the pipet out of the stopper while inserting the mouthpiece. Where a stopper is to be permanently in place on the pipet a very tight fit can be obtained by heating the upper end of the pipet so it will burn the rubber a little as it is inserted. Figure 6 shows another device by means of which an individual mouth-
piece can be used. Here the pipet and the mouthpiece pass through a two-holed rubber stopper into a closed space made by slipping a buret cap or a small test tube or bottle on the stopper. These devices greatly reduce unsanitary practices, but they do not do away with the necessity of putting the mouth where the finger has been. This objection is overcome by the device shown in Figures 7, 8, and 9, where the individual mouthpiece is used, and the space about the top of the pipet can be opened or closed off by means of a stopper or a portion of the hand or finger. When the pipet is filled the index finger is slipped quickly in place. The device shown in Figure 9, which can be slightly improved by beveling the top of the pipet a little, is made wholly of glass except the rubber tube, a, for the insertion of the individual mouthpiece. I t was obtained for us
VOL.5, No. 3 SANITATION, SAFETY, AND CONVENIENCE IN PIPETTING
347
by Phipps and Bird, Inc., Richmond, Va. If patent rights can be obtained the Empire Laboratory Supply Co., Inc., of New York City will carry it in stock. By cutting the pipet a few centimeters below the cup one can get a sanitary attachment that can be used with any number of pipets, connection by means of a short piece of heavy rubber tubing only being necessary. The basic idea involved here was covered by Sharples' U. S. Patent number 553,004, granted 1896 and now expired, but this was an overflow type with the bulb of the pipet wholly surrounded by a jacket that Sharples called the overflow chamber, and he seems not t o have associated the idea with sanitation in connection with the use of
ordinary laboratory pipets. The smaller the hole in the lower end of the pipet, and the lower the graduation mark on the neck, the easier i t is t o get the finger in place in time t o control the flow, but when the hole is very small too much time is used in filling the pipet and also in allowing it to empty. It is not difficult to attain a happy medium. It is then possible sometimes with practice t o dispense with the jacket about the top of the pipet, and t o connect the mouthpiece with the pipet directly by means of a short or long piece of very flexible rubber tubing. With a little practice one can slip the rubber off and get the index finger in place in time to control the flow. Figure 10 shows the arrangement of apparatus for pipetting very large or very small amounts of dangerous solutions, such as Nessler's solution,
for example, from the bottoms of very large bottles. The extension tube b can be kept permanently in the bottle with a solid stopper in it. A pipet of any size with a rubber stopper on it is placed in the mouth of b, a U-shaped piece of glass tubing much constricted a t both ends is pushed into a very flexible piece of rubber tubing a, and the latter attached to the end of the pipet. This glass tube prevents kinking, and in case the liquid accidentally spurts up the pipet it slows its passage through the tube leading to the mouth. The mouthpiece of any shape goes in the other end of the flexible rubber tube. If it is constricted slightly it is the more easily inserted, and if it is curved like an S with its loops in planes a t right angles (Fig. 10e) i t can be hung on the neck of tube b when not in use. The rubber tube can be left attached to it, and the other end of the rubber can be hung in the other loop of the S. Figure 10c shows a plug for the air inlet through stopper d. When solution is to be pipetted, the plug is removed, and if made in the shape of a shepherd's crook it may be hung about the neck of tube b. When there is probability of the pipet being used again in a few days in the same bottle, the plug and pipet may be put in place and one end of the flexible tube a slipped on the pipet and the other on the end of the plug, making the bottle air-tight. A buret may be filled from the bottle in Figure 3 or Figure 10 by suction by passing the tip through a rubber stopper in the tube in the bottle and exhausting the air through a rubber stopper in the top of the buret. We have found apparatus shown in Figures 1, 3, 5a, and 9 most satisfactory in our class work. For making the apparatus shown in Figure 3, a nine-pound sulfuric acid bottle, a solid No. 5 rubber stopper, bored by ourselves, a No. 00 one-holed rubber stopper, and 14 mm. glass tubing of 12 mm. bore were used. The holes, c, were made with a paper punch. A nearly pure gum rubber tubing with a wall about 1 mm. thick was used for connecting pipets and mouthpieces. The troublesome coat of sulfur on rubber tubing and stoppers was removed by rubbing them with a wet file and rinsing with water.
