Micropipets calibration

Table 2-5 lists tolerances for micropipets from one manufacturer. As internal parts wear out, both precision and accuracy can decline by an order of magnitude. In a study17 of 54 micropipets in use at a biomedical lab, 12 were accurate and precise to <1%. Five of 54 had errors >10%. When 54 quality control technicians at four pharmaceutical companies used a properly functioning micropipet, 10 people were accurate and precise to <1%. Six were inaccurate by >10%. Micropipets require periodic calibration and maintenance (cleaning, seal replacement, and lubrication) and operators require certification.18... 

Calibrate your micropipet by measuring the mass of water it delivers [B. Kratochvil and N. Motkosky, Precision and Accuracy of Mechanical-Action Micropipets, Anal. Chem. 1987, 59, 1064]. A colorimetric calibration kit is available from Artel, Inc., Westbrook, ME 207-854-0860. 

Cadmium Calibration Standards Tare three clean, dry 4-oz polyethylene bottles (or equivalent). Add approximately 50 g of High-Purity Water to each. Slowly add 28 1 g of concentrated nitric acid, mix thoroughly, slowly add 12 1 g of concentrated hydrochloric acid, and mix thoroughly again. Using a precision micropipet, add 10, 50, and 500 pL, respectively, of Cadmium Stock Solution to one of each of the bottles. Dilute each solution to 100.0 0.1 g with High-Purity Water, and mix thoroughly to obtain calibration standards with 0.1, 0.5, and 5.0 mg/kg, respectively. 

The requirement for calibrated laboratory-ware for containing and dispensing solutions extends to all facets of the analytical procedure. It rests with the analyst to ascertain accuracy suitable to the application, of all devices used, including micropipets used in conjunction with electrothermal atomizers. The temptation to use other than appropriately calibrated containers, and chemical reagents of suitably high purity, and not to follow good analytical procedures as practised by those with only peripheral contact with analytical chemistry, should be avoided. 

The volume of water filtered through the plankton sampling net was carefully noted. For raw water, e.g. surface-water or reservoir water and influent slow sand filter, a sample of 15—20L was collected. For treated water, e.g. filtrate of rapid filters, 150 L samples were taken. The concentrate, collected into a small cylindrical container, was quantitatively carried over into a calibrated small polyethene bottle after that the small container was immediately rinsed with demi-water and the calibrated recipient was filled up to 50 mL. Netplankton samples were preserved with formalin. If necessary, further concentration was performed by a secondary nitration through a plankton net with size aperture of 30 nm. A suvolume of 50 juL of the concentrated sample, taken with a micropipet, was used for mounting and counting the preparation by means of a compound microscope. 

The quality of apparatus is crucial. The quality of the pipets directly affects the reliability of the analytical information. It is necessary to use measuring pipets of high quality for reliable measures of volume, e.g., clinical, serological pipets, micropipets, syringe pipets. Syringe pipets must be used for measurement of microliter volumes. In volumetric analysis more reliable burets are necessary. For small quantities of sample, micro- and ultramicro-micrometer burets are recommended. Only well-calibrated pipets and burets will assure the accuracy of volume determination. 

Cjrafting procedure The donor neural tube is transferred to the host embryo using a calibrated glass micropipet and placed in the groove produced by the excision, in the normal rostro-caudal and dorso-ventral orientation (see Note 15). 

Glass micropipets hand-drawn from Pasteur pipets are curved and calibrated according to use injection of liquids or transfer of pieces of tissues. Calibration of the micropipet according to the size of the rudiment to be transplanted (for instance, neural tube vs brain vesicle) is an important requirement. 

Three sets of spiked MCEF samples were prepared by injecting 15 pL of 5, 10 and 20 pg/mL dilute cadmium stock solutions on 37 mm diameter filters (part no. AAWP 037 00, Millipore Corp., Bedford, MA) with a calibrated micropipet. The dilute stock solutions were prepared by making appropriate serial dilutions of a commercially available certified 1,000 pg/mL cadmium standard stock solution (Fisher Chemical Co., Lot 913438-24) with the diluting solution (4% HNO3, 0.4% FICI). Each set contained six samples and a sample blank. The amount of cadmium in the prepared sets were equivalent to 0.5, 1 and 2 times the Action Level TWA target concentration of 2.5 pg/m for a 60 L air volume. 

A variety of manual spotters are available that are useful for applying 1-100 il of sample to a plate. The simplest of these devices are wooden applicator sticks, attenuated Pasteur pipets, and capillary tubes. For more precise delivery of sample, micropipets or microsyringes calibrated in microliters are recommended. 

About 0.03 ml. of this catalase solution is pipetted onto a watch glass ( a micropipet with calibrated delivery volume is useful). The substrate solution described above is swirled and the watch glass is dropped into it a stop watch is started simultaneously. The solution is swirled gently and a 2 ml. sample is withdrawn (u g a wide tipped pipet) and blown into a swirling solution of 2% H2SO4. The time of delivery is noted and the operation is rapidly repeated twice more. Blowout times of about 10, 20, and 30 seconds are easily achieved with some practice. Each of the three acid solutions is titrated with 0.01 iV KMn04, and the values together with... 

Place 30 to 60 mL of the cyclohexane sample to be analyzed into a 100-mL volumetric flask. Accurately add, using a micropipet or microsyringe, 25 pL of the internal stan rd to the flask and then All to the calibration mark with additional sample. Based on using 2,2-dimethylbutane as the internal standard with a density of 0.649 g/mL and cyclohexane with a density of 0.780 g/mL, the concentration of the internal standard will be 0.021 wt%. Similar calculations must be made for any alternative internal standard that may be used. Mix the above, blend thoroughly, and analyze using the chromatographic conditions stated in Table 2. 

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