Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Ice Maker Uses - Instant making ice - Three different ice sizes - 12 pieces of ice in 10 minutes Operation - fill water in reservoir. Make sure the water is not over the ice collecting tray. - connect to power - select the desired ice cube size - Press start and the ice maker begins to work - if indicator’ DEFICIENT’ with noise sound ‘DI’ take out basket and add water - if indicator’ ICE FULL’ red with noise ‘DIDI’TAKE OUT ICE WITH A SCOOP Press STOP Remove drain plug to drain remaining water, screw the drain plug back in place after water has been drained Caring - clean the inner liner, ice collecting tray, water box, ice shovel and evaporator frequently. When collecting, unplug the unit and remove the ice cubes. Use diluted water and vinegar to clean the inside and outside surface. Do not spray the ice maker with chemicals or diluted agents such as acids, gasoline or oil -keep ventilation openings in the appliance enclosure or in the built in structure, clear of obstruction. -if the machine is reused for a long time and the water pump cannot pump sufficiently due to air inside, deficient water indicator turns on. Press the start button again it starts to work properly -if the compressor just stops, wait for 3mins then restart - Always change with fresh water before starting ice production at initial instillation or after long shut off periods Automatic Autoclave Sterilizer Uses - For the sterilization of equipment For the sterilization of microbial media Operation - Open door and take out heater cover Turn the water valve to ’FILLING’ to fill water in the chamber. Then turn it to ‘CLOSE’ to stop filling Put heater cover back to chamber. Then arrange sterilization items into the chamber. Select ’STERILIZATION TEMP’ Press the ’POWER’ switch Select ‘STERILIZATION TIME’ Close the door. Press the START BUTTON Start HEATING by heater. The heat indicator should be lightened. Cold air will be exhausting by the steam trap. Pressure rises to a preset value Complete sterilization Buzzer sound for 40seconds. Turn water valve to DRAINING Take out your items only when the pressure gauge reads zero. Turn the valve to close then open the door Maintenance Daily Wipe inside chamber. Door and gasket with a damp lint cloth Check the water level and top up with distilled water only. Drain off the water inside the chamber every time after running a cycle Weekly Drain off the remaining water of water reservoir and refill with distilled water Remove the cap of water reservoir and find the safety valve. Put the ringlet of the safety valve to check its working status. Monthly Clean the chamber and piping system with ’CHAM-MATE’ Use clean water to scrub the water reservoir thoroughly Annually Contact distributor for maintenance Check the silicon door gasket, steam trap safety valve and heater Check function of printed circuit board Check temperature during sterilisation Spectrophotometer It measures transmittance that is the amount of light that passes through a solution at a given wave length The transmittance is usually converted to absorbance. According to Beer –Lambert law Absorbance =-log transmittance Absorbance is directly depended to the concentration of the solution and A=abc Where A=absorbance a=molar absorptivity b=path length of a sample holder c=concentration of the solution Calibration Done to verify working status of the spectrophotometer This is usually done by careful inspection of the standard curve of a chemical species that is known to obey the Beer Lambert law. Linearity of the standard curve is a good indication of instrument linearity and low stray light level A solution of potassium dichromate i usually used prepared in 0,01N sulphuric acid Maintenance Turn the machine off and disconnect power cord before performing any maintenance procedure Several of the maintenance procedures involve components located in the Maintenance Lamp compartment Allow the bulbs to cool before replacing them. They can be either tungsten-halogen lamps or deuterium lamps Printer maintenance; the built in printer requires thermal paper. Before installing a new roll of paper clean the printer head Centrifuge It is used for separating mixtures with differences in particle size. Those with a bigger particle will settle at the bottom of the mixture. Operation Connect correctly to power. It is very important to balance the centrifuge when putting samples into the bucket. First close and lock the centrifuge lid Select time by first pressing the set button and then +or- button the press set Select speed then +or- then press set To open the centrifuge make sure it has stopped. This is noted by reflection of 0.0 on the speed screen. One can then unlock the centrifuge rid, open and remove buckets and tubes. If the centrifuge is still in motion the lid will not unlock. Maintenance Clean all buckets thoroughly at regular intervals. Very care full remove all glass splinters which may be in the buckets before returning them in position. The motor bearings are grease, packed before leaving the factory and require no maintenance. The centrifuge body needs to be cleaned periodically with silicon or wax polish. Incubator Uses; for the growth of microbial cultures using various microbial media. Operations Connect cord to a200to250AC mains Turn the electrical button mains Turn the of-off one Temperature is controlled using the far right knob Turn the knob to the required temperature of which the temperature will reflect after 5 to 10mins For a temperature of 100degrees the reflection takes longer A thermometer can be put in one of the shelves to control the temperature Maintenance Switch power off Clean the inside regularly Remove shelves and swab using absolute alcohol to kill most bacteria and yeast Wash outside regularly. ALL THE PETRI DISHES SHOULD BE BURNT after every microbiology practical session for they are an environmental hazard. Magnetic Stirrer Uses It has the functions of heating, stable temperature and digital temperature display and timing. It is also an ideal instrument for all kinds of analytical instruments to stirring solutions. Measurement of pH - pH is a measure of the acidity or basicity of a solution - Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. - In a solution pH approximates but is not equal to p[H], the negative logarithm (base 10) of the molar concentration of dissolved hydronium ions (H3O+); a low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration. Universal indicator components Indicator Low pH color Transition pH range High pH color Thymol blue (first transition) red 1.2 – 2.8 yellow Methyl red red 4.4 – 6.2 yellow Bromothymol blue yellow 6.0 – 7.6 blue Thymol blue (second transition) yellow 8.0 – 9.6 blue Phenolphthalein colorless 8.3 – 10.0 fuchsia pH meter A pH meter is an electronic instrument used to measure the pH (acidity or alkalinity) of a liquid (though special probes are sometimes used to measure the pH of semi-solid substances). A typical pH meter consists of a special measuring probe (a glass electrode) connected to an electronic meter that measures and displays the pH reading. How a pH meter works When one metal is brought in contact with another, a voltage difference occurs due to their differences in electron mobility. When a metal is brought in contact with a solution of salts or acids, a similar electric potential is caused, which has led to the invention of batteries. Similarly, an electric potential develops when one liquid is brought in contact with another one, but a membrane is needed to keep such liquids apart. A pH meter measures essentially the electro-chemical potential between a known liquid inside the glass electrode (membrane) and an unknown liquid outside. Because the thin glass bulb allows mainly the agile and small hydrogen ions to interact with the glass, the glass electrode measures the electro-chemical potential of hydrogen ions or the potential of hydrogen. To complete the electrical circuit, also a reference electrode is needed. Note that the instrument does not measure a current but only an electrical voltage, yet a small leakage of ions from the reference electrode is needed, forming a conducting bridge to the glass electrode. A pH meter must thus not be used in moving liquids of low conductivity (thus measuring inside small containers is preferable). The pH meter measures the electrical potential (follow the drawing clock-wise from the meter) between the mercuric chloride of the reference electrode and its potassium chloride liquid, the unknown liquid, the solution inside the glass electrode, and the potential between that solution and the silver electrode. But only the potential between the unknown liquid and the solution inside the glass electrode change from sample to sample. So all other potentials can be calibrated out of the equation. The calomel reference electrode consists of a glass tube with a potassium chloride (KCl) electrolyte which is in intimate contact with a mercuric chloride element at the end of a KCL element. It is a fragile construction, joined by a liquid junction tip made of porous ceramic or similar material. This kind of electrode is not easily 'poisoned' by heavy metals and sodium. The glass electrode consists of a sturdy glass tube with a thin glass bulb welded to it. Inside is a known solution of potassium chloride (KCl) buffered at a pH of 7.0. A silver electrode with a silver chloride tip makes contact with the inside solution. To minimise electronic interference, the probe is shielded by a foil shield, often found inside the glass electrode. Most modern pH meters also have a thermistor temperature probe which allows for automatic temperature correction, since pH varies somewhat with temperature. Calibration and use For very precise work the pH meter should be calibrated before each measurement. For normal use calibration should be performed at the beginning of each day. The reason for this is that the glass electrode does not give a reproducible e.m.f. over longer periods of time. Calibration should be performed with at least two standard buffer solutions that span the range of pH values to be measured. For general purposes buffers at pH 4 and pH 10 are acceptable. The pH meter has one control (calibrate) to set the meter reading equal to the value of the first standard buffer and a second control (slope) which is used to adjust the meter reading to the value of the second buffer. A third control allows the temperature to be set. Standard buffer sachets, which can be obtained from a variety of suppliers, usually state how the buffer value changes with temperature. The calibration process correlates the voltage produced by the probe (approximately 0.06 volts per pH unit) with the pH scale. After each single measurement, the probe is rinsed with distilled water or deionized water to remove any traces of the solution being measured, blotted with a clean tissue to absorb any remaining water which could dilute the sample and thus alter the reading, and then quickly immersed in another solution. When not in use, the glass probe tip must be kept wet at all times to avoid the pH sensing membrane dehydration and the subsequent dysfunction of the electrode. A glass electrode alone (i.e., without combined reference electrode) is typically stored immersed in an acidic solution of around pH 3.0. In an emergency, acidified tap water can be used, but distilled or deionised water must never be used for longer-term probe storage as the relatively ionless water "sucks" ions out of the probe membrane through diffusion, which degrades it. Combined electrodes (glass membrane + reference electrode) are better stored immersed in the bridge electrolyte (often KCl 3 M) to avoid the diffusion of the electrolyte (KCl) out of the liquid junction. Occasionally (about once a month), the probe may be cleaned using pH-electrode cleaning solution; generally a 0.1 M solution of hydrochloric acid (HCl) is used, having a pH of about one. In case of strong degradation of the glass membrane performance due to membrane poisoning, diluted hydrofluoric acid (HF < 2 %) can be used to quickly etch (< 1 minute) a thin damaged film of glass. Alternatively a dilute solution of ammonium fluoride (NH4F) can be used. To avoid unexpected problems, the best practice is however to always refer to the electrode manufacturer recommendations or to a classical textbook of analytical chemistry. pH meters range from simple and inexpensive pen-like devices to complex and expensive laboratory instruments with computer interfaces and several inputs for indicator (ionsensitive, redox), reference electrodes, and temperature sensors such as thermoresistors or thermocouples. Cheaper models sometimes require that temperature measurements be entered to adjust for the slight variation in pH caused by temperature. Specialty meters and probes are available for use in special applications, harsh environments, etc. Pocket pH meters are readily available today for a few tens of dollars that automatically compensate for temperature (ATC, Automatic Temperature Compensation). Titration Titration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the titrant or titrator, of a known concentration (a standard solution) and volume is used to react with a solution of the analyte or titrand, whose concentration is not known. Using a calibrated burette or chemistry pipetting syringe to add the titrant, it is possible to determine the exact amount that has been consumed when the endpoint is reached. The endpoint is the point at which the titration is complete, as determined by an indicator. This is ideally the same volume as the equivalence point—the volume of added titrant at which the number of moles of titrant is equal to the number of moles of analyte, or some multiple thereof (as in polyprotic acids). In the classic strong acid-strong base titration, the endpoint of a titration is the point at which the pH of the reactant is just about equal to 7, and often when the solution takes on a persisting solid color as in the pink of phenolphthalein indicator. There are however many different types of titrations. Many methods can be used to indicate the endpoint of a reaction; titrations often use visual indicators (the reactant mixture changes color). In simple acid-base titrations a pH indicator may be used, such as phenolphthalein, which becomes pink when a certain pH (about 8.2) is reached or exceeded. Another example is methyl orange, which is red in acids and yellow in alkali solutions. Not every titration requires an indicator. In some cases, either the reactants or the products are strongly colored and can serve as the "indicator". For example, a redox titration using potassium permanganate (pink/purple) as the titrant does not require an indicator. When the titrant is reduced, it turns colorless. After the equivalence point, there is excess titrant present. The equivalence point is identified from the first faint persisting pink color (due to an excess of permanganate) in the solution being titrated. Preparing a sample for titration In a titration, both titrant and analyte are required to be in a liquid (solution) form. If the sample is not a liquid or solution, the samples must be dissolved. If the analyte is very concentrated in the sample, it might be useful to dilute the sample. A measured amount of the sample can be given in the flask and then be dissolved or diluted. The mathematical result of the titration can be calculated directly with the measured amount. Sometimes the sample is dissolved or diluted beforehand, and a measured amount of the solution is used for titration. In this case the dissolving or diluting must be done accurately with a known coefficient because the mathematical result of the titration must be multiplied with this factor. Many titrations require buffering to maintain a certain pH for the reaction. Therefore, buffer solutions are added to the reactant solution in the flask to maintain the pH of the solution. Some titrations require "masking" of a certain ion. This can be necessary when two reactants in the sample would react with the titrant and only one of them must be analysed, or when the reaction would be disturbed or inhibited by this ion. In this case another solution is added to the sample, which "masks" the unwanted ion (for instance by a weak binding with it or even forming a solid insoluble substance with it). Some redox reactions may require heating the solution with the sample and titration while the solution is still hot, in order to increase the reaction rate. For instance, the oxidation of certain oxalate solutions requires heating the solution to approximately 60 degrees in order to maintain a reasonable rate of reaction. Indicator Color on Acidic Side Range of Color Change Color on Basic Side Methyl Violet Yellow 0.0 - 1.6 Violet Bromophenol Blue Yellow 3.0 - 4.6 Blue Methyl Orange Red 3.1 - 4.4 Yellow Methyl Red Red 4.4 - 6.2 Yellow Litmus Red 5.0 - 8.0 Blue Bromothymol Blue Yellow 6.0 - 7.6 Blue Phenolphthalein Colorless 8.3 - 10.0 Pink Alizarin Yellow Yellow 10.1 - 12.0 Red Chromatography It is the collective term for a set of laboratory techniques for the separation of mixtures. It involves passing a mixture dissolved in a "mobile phase" through a stationary phase, which separates the analyte to be measured from other molecules in the mixture based on differential partitioning between the mobile and stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus changing the separation. Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for further use (and is thus a form of purification). Analytical chromatography is done normally with smaller amounts of material and is for measuring the relative proportions of analytes in a mixture. The two are not mutually exclusive.