International Pipette Method

Robinson pipette stand, with rack and pinion arrangement for raising and lowering pipette and scale. 

Next day keep it on a hot plate at about 70°-80°C adding 5ml portions of hydrogen peroxide at 1 hour interval with occasional stirring. 

Continue till large bubbles cease to evolve, to ensure complete oxidation of organic matter. 

Boil gently for about an hour to decompose excess peroxide. 

Allow the contents to cool and add 25 ml of 2(N) HCl (if soil contains more than 2% carbonate more HCl may be added). 

---

Note Refer to the text to refresh your memory concerning the method of standard additions and the internal standard method. Use a good fume hood when preparing the standards. All flasks and pipettes should be water-free. 

It is probably more popular to perform microcalorimetry in the static mode. In the so-called internal hygrostat method, the compound under investigation is sealed into a vial with a sealed pipette tip containing the saturated salt solution chosen to give the required RH. 

Though human error is usually the cause, proper method development can make a difference in reducing this type of error or variations. First, a large volume of IS, such as 200 pL should be used when it is added by a repeater pipette because small volumes (such as 50 pL or less) are more prone to imprecision than large ones. In addition, it would be extremely difficult to visually spot missed or doubled addition for an internal standard when its volume is much smaller than that of samples and/ or other reagents (e.g., buffer). Second, it would be helpful to reduce errors by adding the usually colorless IS solution first and then incurred samples, which are usually colored, such as slight yellowish for plasma samples or dark red for whole blood samples. 

Another sedimentation method involves the ANDREASEN PIPETTE. This glass apparatus is inexpensive and consists of a bottle having an internal sampling tube and calibrated sampling volume (5 ml). One draws a sample... 

Precipitations are usually carried out in micro centrifuge tubes. After centrifuging, the precipitate collects in the bottom of the tube. The supernatant liquid may be removed either by a capillary dropper (Fig. 2.13) or by means of a transfer capillary pipette. The latter consists of a thin glass tube (internal diameter about 2 mm this can be prepared from wider tubing) 20 to 25 cm in length with one end drawn out in a micro flame to a tip with a fine opening. The correct method of transferring the liquid to the... 

An international collaborative study involving 24 laboratories using 21 laser diffraction instruments manufactured by sk different manufacturers was performed in 1994. Sedimentation and the electrical sensing zone (ESZ) methods were used as reference methods in comparing results. Two irregularly shaped polydisperse quartz materials (BCR 67 and BCR 69, certified using the Andreasen pipette sedimentation method, obtained from the Community Bureau of Reference (BCR) of the Commission of the European Community) were used in the study [64]. In this investigation the standard deviations reported by each... 

---