There are a wide variety of dispensing systems, each with advantages and disadvantages for specific applications. Reagent Dye Solutions for protein tests may be dispensed by UDY's Reagent Dye Dispensor, a Bottle Top Dispensor, or Micro-Pipets depending on the sample type and other requirements.
The Reagent Dye Dispensor, illustrated in Figure 6, is the preferred method for dispensing Reagent Dye Solution for most protein tests because of its high accuracy. Bottle Top Dispensors are used in protein testing only when maximum accuracy is not required, and the limited number of samples makes use of the regular Reagent Dye Dispensor less practical.
When a powdered sample is to be mixed with a liquid reagent, such as in the React-R-Tube, it is normally better to add the liquid reagent first. This minimizes the powder sticking to the bottom of the React-R-Tube.
Reagent Dye Dispensor
The Reagent Dye Dispensor includes a Tripod Support, a 4 Liter or 20-Liter Dispensing Carboy, and an Automatic Pipet Assembly. (See Figures 5 and 6).
Assemble the Tripod Support. Note that the legs angle about 7 degrees from vertical. Use care in screwing them in so that the legs don't get cross threaded. Threads will strip easily if not started properly. Place the empty dispensing carboy on top of the support.
Secure the clamp firmly on the pipet support rod near the bottom. Set the pipet barrel horizontally on its support, and secure with rubber O-rings. Position the four-way stopcock in the clamp with the handle to the right (right handed use). Connect the tygon tube leading from the dispensing carboy to the center inlet tube of the stopcock. Also, connect the tygon tubes from the stopcock to each of the two ends of the pipet barrel. The ends of the tygon tubes can be softened by dipping them in hot water to simplify stretching them over the tube ends. Close the stopcock by rotating the white stopcock plug clockwise with the orange handle until the handle is in a horizontal position. The plug should be adjusted with the orange nut so that turning the stopcock plug is not difficult, but tight enough to prevent leakage. To fill the carboy, temporarily place it on the counter, remove its cap and open the vent (lower the pipet clamp on the support rod if necessary). Add Reagent Dye Solution to the carboy using a funnel. Cap the carboy and reposition the pipet on the vertical support. Keep the vent closed when the dispensor is not in use.
Filling the Pipet Barrel
Place a clean dry beaker or other container below the stopcock dispensing tip. Now rotate the orange stopcock handle clockwise to a vertical position to fill the
pipet. ALWAYS ROTATE THE HANDLE CLOCKWISE TO OPEN AND CLOSE. The pipet will fill and empty by gravity flow.
Remove air bubbles from pipet barrel by tilting ends. This will alternate stretching the O-ring clamps while dispensing solution. The pipet is precalibrated to deliver 40.00 ml. NOTE: Dispensing is complete when the moving plunger in the pipet barrel abruptly stops. IMMEDIATELY turn the stopcock clockwise to the horizontal position. Make sure the delivery tip is free from air bubbles and doesn't have a drop hanging from it. Reagent Solution in the beaker may be returned to the dispensing carboy.
Open the vent cap. Rotate the stopcock clockwise (view from handle end) until the handle is vertical to dispense solution. Immediately after flow stops, rotate the stopcock handle clockwise until it is horizontal. Continue subsequent dispensing with clockwise rotation of the handle. Close the vent cap when no further dispensing is anticipated for several hours. Rotation of the stopcock counter-clockwise will cause the nut to slowly loosen and allow solution to leak from around the plug.
Before solution is dispensed for the first time of the day, shaking the Carboy (close cap and vent first) should be used to remix into the solution any water condensed in the carboy above the liquid level. After mixing, dispense four volumes of solution (160 ml) into a clean dry beaker to ensure that all solution is uniform. This will also expel air bubbles and flush out the dispensor tip where dye concentrates and crystallizes as water evaporates. The dispensed solution can be added back to the carboy.
Be sure the stopcock dispensing tip is completely filled before dispensing dye for samples. It should not have an extra drop hanging from it. An extra drop will form on the tip of the stopcock if not turned off immediately after the flow stops. The extra drop can be removed by touching the tip to the side of a beaker or other container.
If dye crystallizes around the ends of the stopcock plug or delivery tip after prolonged non-use, it should be wiped off with a moist tissue. If the delivery volume is questioned, it may be checked by measuring the weight of Reagent Dye Solution dispensed. The correct amount is 40.37 g "0.08 g. NOTE: Moisture can evaporate out through the vent cap opening and the plastic walls of the carboy. This results in a gradual change in the dye concentration and requires periodic (monthly) checking and adjustment of the dye concentration if necessary. See Reagents Section following for instructions and concentration checks. The effect of this will be minimized if the carboy is kept as full as possible. When it is slightly less than one-half full, add more Prepared Reagent Dye.
Bottle Top Dispensors
Bottle Top Dispensors are available in various sizes. Consult UDY Corporation for proper size and type. The size used varies with the application, but it is generally the smallest size that will dispense desired volume of solution. Using the smallest size possible results in greater accuracy and precision. Dispensing of Reagent Dye Solution for Protein tests is the most common use and the most critical. It is covered by a separate section.
Reagent Dye Dispensing Using a Bottle Top Dispensor
The Bottle Top Dispensor is used to dispense Reagent Dye Solution when only a limited number of tests are being made and maximum accuracy is not needed. The ability to remove the dispensor from the bottle and then cap the dye solution in the glass bottle, enables the proper dye concentration to be maintained longer than is possible with the regular
Reagent Dye Dispensor. The following guidelines must be followed for successful use. See the section on Storage and Use of Reagent Dye Solutions.
1. When the dispensor is placed on the bottle, pump it with short strokes to flush it and remove air bubbles. This minimizes waste of solution and removes air bubbles more effectively.
2. Watch for air bubbles that will tend to form in the dispensor. Use several short strokes to expel air bubbles. If air bubbles reappear frequently, the filling tube may not be sealing adequately where it joins the dispensor body. Press it on tighter or cut off a small section, and reattach if necessary. When an air bubble is expelled into a sample, high test values will result. Therefore, the sample must be discarded and the test started over. Rinse the sample bottle with Reference Dye Solution or totally clean and dry it before reuse.
3. When raising the dispensor plunger at the beginning of a cycle, a drop of dye solution may be expelled from the tip of the dispensor if the top of the stroke is reached abruptly. This drop must not be included, and its formation should be avoided.
4. The delivery tip must be full of solution before dispensing dye for a sample test. If the tip is bumped, solution may drain out causing a mess. If this happens, be sure to dispense a small volume of solution to refill the delivery tip before dispensing dye for tests.
5. Water droplets form in the bottle above the liquid line after several hours. They must be mixed into the solution by gentle swirling of the bottle before dispensing dye. This will avoid changes in dye concentration.
6. The Dispensor has a small hole just about the threads to vent the bottle. Some moisture will evaporate through this hole. Keep it plugged or tape over it when the dispensor is not in use to avoid changes in dye concentration.
7. The Dispensor will require regular cleaning and flushing with water and cuvet cleanser solution. Clean dispensor and leave the dye solution bottle capped anytime testing is not anticipated for more than 3 days. Clean other times as needed and when changing to a new bottle of Reagent Dye Solution. If dye is allowed to crystallize in the dispensor, it may damage the dispensor. DO NOT FORCE THE PLUNGER. The entire unit can be rinsed with water.
8. Water remaining in the filling tube and body of the dispensor after flushing may affect the dye concentration. Remove water from the filling tube before installing the dispensor on a bottle of Reagent Dye Solution. If there is water in the tip or body of the dispensor, the Reagent Dye Solution dispensed while expelling air bubbles should be discarded.
9. The dispensor has been accurately calibrated to deliver the correct amount of Reagent Dye Solution (40.37 g "0.08 g). The adjustment is very sensitive. Do not loosen the setting knob. If the setting knob is loosened, the calibration must be rechecked by weighing the amount of solution dispensed. When retightening, do not use much force. The parts are easily broken.
10. Adapters are available which permit installation of the dispensor on top of 4 L Reagent Dye Solution Bottles. However, it is generally recommended that the smaller bottle provided be used and refilled as required to minimize potential problems in maintaining the proper dye concentration.