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[[Berkas:Pipettes.jpg|jempol|kanan|350px|Berbagai macam pipet]]
'''Pipet''', atau alat penetes [[kimia|cairan kimia]], adalah alat laboratorium yang digunakan untuk memindahkan volume cairan terukur.
Baris 39 ⟶ 38:
* Ketelitian dan ketepatan volume cairan
* Faktor-faktor lainnya
 
== Pipet berbantuan vakum ==
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[[File:Serological pippette.jpg|thumb|right|250px|Serological pipettes are used for large volumes and for sterile work, but require a pipette dispenser]]
 
Non-piston-driven vacuum assisted pipettes are hollow narrow cylinders which work like a straw and require the use of some kind of additional suction device.
Originally pipettes were made of soda-lime glass, but currently many are made of borosilicate glass which is tougher and more chemically resistant. Disposable and single use pipettes are often made of polystyrene. All of these are commonly used in chemistry, mainly with aqueous solutions. There are two types. One type, the volumetric(or bulb)pipette, has generally a large bulge with a long narrow portion above with a single graduation mark as it is calibrated for a single volume. Typical volumes are 10, 25, and 50 mL. The second type, the graduated pipette, is straight-walled and as the name implies has graduation marks along most of its length.
The pipette is filled by dipping the tip in the fluid, then drawing up the liquid by using a pipette filler to create a partial vacuum above the fluid. The surface of the fluid inside the pipette is generally concave and this is called the fluid meniscus. The fluid level is read at the bottom of the meniscus and by aligning it with the graduation marks while holding the pipette at eye level. Liquid is dispensed by releasing the vacuum created by the pipette filler ; slow release for gradual dispensing and complete removal for fast dispensing. With safe fluids the finger may be used on the open end of the pipette to control the vacuum. While moving the pipette to the receiving vessel, care must be taken not to shake the pipette because the column of fluid may "bounce". Complete emptying of the pipette is accomplished by either blowing the pipette out with air from the filler (blow-out pipettes), or touching the tip against the side of the receiving vessel, according to pipette type.
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=== Pipet volumetrik ===
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{{main|Volumetric pipettes}}
[[Volumetric pipettes]] allow the user to measure a volume of solution extremely accurately and then add it to something else. They are commonly used to make laboratory solutions from a base stock as well as prepare solutions for [[titration]]. They are typically marked to indicate one single volume in a particular size pipette (as are volumetric flasks). Many different sizes are available.
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=== Pipet graduat ===
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Graduated pipettes use a series of marked lines (as on a [[graduated cylinder]]) to indicate different calibrated volumes. These also come in a variety of sizes. These are used much like a burette, in that the volume is found by calculating the difference of the liquid level before and after liquid is dispensed. Historically, the accuracy of a graduated pipette was not as good as that of a volumetric pipette; however, with improved manufacturing methods, the accuracies listed by the manufacturer can equal volumetric pipets. {{Citation needed|date=October 2008}}
Two types of graduated pipettes exist:
* [[Mohr pipette]]s or drain-out pipettes have a 0ml mark before the start of the conical end, which is a dead volume.
* serological or blow-out pipettes have no 0ml mark as that corresponds to an empty pipette.
Graduated pipettes have +/- tolerances that range from 0.6% to 0.4% of the nominal volume when measured at 20C.Graduated pipettes are manufactured according to ISO specifications for accuracy and the arrangement of the graduations. A grade pipettes are more accurate than B grade pipettes and Volumetric pipettes are the most accurate of all.
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=== Dispenser pipet ===
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Various methods exist to handle the liquids inside a pipette. Before the advent of more sophisticated pipette dispensers, it was common practice to "mouth pipette" i.e. to aspirate fluid into the pipette by applying suction with one's mouth. Mouth pipetting is now considered unsafe due to the possibility of accidentally ingesting or inhaling toxic chemicals or [[pathogens]]. The main three types of pipette dispenser are the bulb filler, pipette pump and the electronic controller.
<gallery>
File:Bulb controller.jpg|Bulb fillers are the simplest cylindrical pipette controllers, employing pinch-valves.
File:Manual controller.jpg|Pipette pumps allow more accurate handling of the volume inside a cylindrical pipette.
File:Electronic controller.jpg|Electronic dispensers are expensive (200-300GB£), but allow easy, accurate handling.
</gallery>
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=== Aksesoris pipet ===
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*'''Pipette fillers''' are used to fill the pipette easily, avoiding the need for mouth pipetting.
*'''Pipette dispensers''' are battery-operated and are designed to be used with disposable pipette tubes. These pipettes cannot be calibrated and their accuracy is determined by that of the printed graduations on the disposable tubes.
*'''Light-guided pipetting systems''' are pipetting accessories which are computer based. They utilize flat screen LCD monitors or LED arrays to light up source and destination wells in microplates or vials for accurate well to well pipetting. Some of these systems use text to speech to alert the operator during plate or volume changes when pipetting lab protocols.
*'''Pipette tips'''. The pipettors and injection molded plastic disposable tips form together a reliable pipetting system. It is recommended to use original manufacturers tips to guarantee the precision and accuracy of the pipettes. The precision-made pipettor tips provide excellent reproducibility and accuracy. Pipettor tips are available in autoclavable boxes, refills and bulk packaging. Non-sterile, pre-sterilized and filtered tips are usually available in single trays as RNase, DNase and endotoxin certified free.
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== Pipet pasteur ==
Diperoleh dari "https://id.wikipedia.org/wiki/Pipet"