Pipettes checking

Mowery C Calibration system reduces pipette checking time. Clin Lab Prod 2000 29, May... 

As demonstrated in Fig. 7, which shows the results for a pipette checked using the gravimetric method, the coefficient of variation (CV, defined as the ratio of the standard deviation to the mean) for a run consisting of ten measurements of a given volume increases considerably when the dispensed liquid volumes are less than 5 pi. Evaporation, buoyancy, vibration, and the effects of static electricity are the primary causes of these results. A possible alternative method to determine microscale droplet volumes is one based on measurement of the concentration of a liquid solution. Two practices, also recommended by the ISO standard [5], are commoifly used, namely, the photometric and titrimetric methods. 

Procedure. To determine the purity of a sample of boric acid, weigh accurately about 0.8 g of the acid, transfer quantitatively to a 250 mL graduated flask and make up to the mark. Pipette 25 mL of the solution into a 250 mL conical flask, add an equal volume of distilled water, 2.5-3 g of mannitol or sorbitol, and titrate with standard 0.1 M sodium hydroxide solution using phenolphthalein as indicator. It is advisable to check whether any blank correction must be made dissolve a similar weight of mannitol (sorbitol) in 50 mL of distilled water, add phenolphthalein, and ascertain how much sodium hydroxide solution must be added to produce the characteristic end point colour. 

Pipette 25 mL barium ion solution (ca 0.01 M) into a 250 mL conical flask and dilute to about 100 mL with de-ionised water. Adjust the pH of the solution to 12 by the addition of 3-6 mL of 1M sodium hydroxide solution the pH must be checked with a pH meter as it must lie between 11.5 and 12.7. Add 50 mg of methyl thymol blue/potassium nitrate mixture [see Section 10.50(C)] and titrate with standard (0.01 M) EDTA solution until the colour changes from blue to grey. 

To determine the calcium in the calcium-magnesium mixture, pipette 25 mL of the solution into a 250 mL conical flask, add 25 mL of the buffer solution and check that the resulting solution has a pH of 9.5-10.0. Add 2mL of the Zn-EGTA solution and 2-3 drops of the indicator solution. Titrate slowly with the standard EGTA solution until the blue colour changes to orange-red. 

Pipette 25 mL of the solution to be analysed into a 250 mL conical flask and dilute to 100 mL with de-ionised water the original solution should be about 0.02M with respect to calcium and may contain barium to a concentration of up to 0.2M. Add 10 mL sodium hydroxide solution (1M) and check that the pH of the solution lies between 11 and 12 then add three drops of the indicator solution. Titrate with the standard CDTA solution until the pink colour changes to blue. 

The concentration of the potassium bromate can be checked by the following method pipette 25 mL of the solution into a 250 mL conical flask, add 2.5 g of potassium iodide and 5 mL of 3M sulphuric acid. Titrate the liberated iodine with standard 0.1M sodium thiosulphate (Section 10.114) until the solution is faintly yellow- Add 5 mL of starch indicator solution and continue the titration until the blue colour disappears. 

The radii of both orifices can be either on a micrometer or a submicrometer scale. If the device is micrometer-sized, it can be characterized by optical microscopy. The purposes of electrochemical characterization of a dual pipette are to determine the effective radii and to check that each of two barrels can be independently polarized. The radius of each orifice can be evaluated from an IT voltammogram obtained at one pipette while the second one is disconnected. After the outer surface of glass is silanized, the diffusion-limiting current to each water-filled barrel follows Eq. (1). The effective radius values calculated from that equation for both halves of the d-pipette must be close to the values found from optical microscopy. 

The reaction is monitored by 1H NMR with sample preparation as follows A 0.3-mL aliquot of the reaction mixture is removed and concentrated under reduced pressure for 10 min. The resulting residue is dissolved in 0.5 mL of methyl sulfoxide-d (DMSO-d6> (Cambridge Isotope Labs) and filtered through a pipette with a glass wool plug directly into an NMR tube. The sample is checked on a Bruker ARX-500 MHz instrument. The checker used a Bruker 300 MHz instrument, which sufficed. 

Fill the glass pipette with mineral oil (dyed with 4-amino-3-nitrotoluene MP Biomedicals, Irvine, CA, Cat. 154757) to check that the tip is patent. 

The unit is equipped with devices such as remote switches to alleviate problems such as missing the pickup of a test tube or pipette tip. In a sequence of events, the robot would pick up a test tube and move to a location that has a remote switch. It would then press down the switch which would send a response to the controller. The Zymate program and the response from the switch location would indicate whether the robot had picked up the test tube. If the response was positive it would continue with the assay. If negative, it would take other actions that might be programmed into the system. These actions might include another attempt at picking up the test tube or a system shutdown. These actions thus allow safety checks on system operation or status. 

Pipette plasma, urine (both 50 pi), or CSF (200 pi) into an Eppendorf tube. Add 50 pi internal standard. Add twice 250 pi acetonitrile while vortexing. Spin down the protein at 12,000 rpm (12,000 xg) in the refrigerated microcentrifuge for 10 min. Transfer the supernatant to an evaporation vial and blow nitrogen at 37°C until dry. The residue is taken up in 200 pi buffer and vortexed. Check the pH (11). Transfer to another Eppendorf vial, add 20 pi methyl chloroformate, react at ambient temperature for 5 min (check pH > 6). Stop the reaction with 20 pi 6 M HC1 (check pH=l). Centrifuge again at 12,000 rpm (12,000xg) and 4°C for 10 min (two layers will form). The upper layer is transferred to an autosampler vial. 

The method was checked by analysis according to Kjeldahl (reduction of the fixed nitrogen to ammonia) and by analysis of measured amounts of nitric oxide let into the cylinder from a pipette. 

Step 12. Pipette 2 mL of standardized yttrium carrier into the solution and stir, Add concentrated NH4OH drop-wise until white Y(OH)3 precipitates and then add 5 mL in excess. Centrifuge, decant into a centrifuge tube, and save the supernate until the results of the analysis for yttrium have been checked. Record the time. 

Step 6. Transfer with a pipette a predetermined quantity of sample to a counting container calibrated for counting efficiency. Close and label it. Swipe the outside of the container and count swipe to check for radioactive contamination. If no radioactive contamination is detected, proceed to Step 7. If contamination is found, thoroughly clean container with a detergent solution and ethanol until no contamination remains. To assure cleanliness, seal the counting container in a plastic bag. 

Since a thiosulfate solution is susceptible to attack by sulfur-metabolizing bacteria, it may be wise to check the standardization of the stock solution with a standard solution of KI03. Place 1.3 to 1.4 g of KIO3 in a weighing bottle, dry it for several hours at 110°C, cool in a desiccator, and weigh it exactly on an analytical balance. Transfer this salt to a clean 100-mL volumetric flask and make up to the mark with distilled water. Rinse a clean 5-mL pipette with several small portions of the iodate solution and then carefully deliver a 5-mL sample into a 250-mL Erlenmeyer flask. Add about 20 mL of distilled water, 5 mL of a 0.5 g/ml KI solution, and 10 mL of 1 MHCl. Titrate at once with the thiosulfate solution until the reddish color turns orange and then yellow and becomes pale. At this point add about 0.5 g of Thyodene indicator, mix well, and titrate until the blue color disappears. 

A calibration schedule details the calibration of balances, volumetric glassware, automatic pipettes, thermometers, pH and conductivity meters, wavelength and photometric scales etc. The schedule consists of periodic external checks, employing a suitably accredited calibration service, supported by more regular in-house performance checks. 

Type C laboratories can be fitted out in normal chemical laboratories. The floors, walls and benches should be free of grooves, and the ventilation should be good. It is recommended that all operations with radionuclides be carried out in tubs and that suitable containers be provided for solid and liquid waste. Because of the risk of incorporation, all mouth operations (e.g. pipetting with the mouth) are strongly forbidden. For wiping of pipettes and other equipment, paper tissue is used. Monitors must be available at the working place, to detect radioactive substances on the equipment and to check hands and working clothes for radioactivity. 

GIass pipettes - always check lHat jg pipette is a drain dowh type. There- mV -be.oltf-blowout gip ttei (urktog in-the%.. . bacjf of.drawers. -... 

Contamination. Some plasticizers may leach from vessels, especially with some organic solvents, such as DCM. Glass may adsorb ions and other molecules and then leach them into solutions, especially under acidic or alkaline conditions. Pyrex glass is stronger than ordinary soda glass (rarely found except in specific items such as Pasteur pipettes and melting point tubes, but check if you are not sure) and can withstand temperatures up to 500 °C. 

Add 10 mL of distilled water to the reaction flask, grasp this with a clamp, swirl the mixture over a free flame to dissolve all the product, and cool under the tap. Remove a drop of the solution on a stirring rod, add it to 0.5 mL of a 0.3% solution of ninhydrin in water, and heat to boiling. If any unacetylated DL-alanine is present a purple color will develop and should be noted. Pour the solution into a 20 x 150-mm test tube and rinse the flask with a little water. Add 1.5 mL of concentrated ammonia solution, stir to mix, check the pH with Hydrion paper, and, if necessary, adjust to pH 8 by addition of more ammonia with a Pasteur pipette. Add 10 mg of commercial acylase powder, or 2 mL of fresh acylase solution, mix with a stirring rod, rinse the rod with distilled water, and make up the volume until the tube is about half full. Then stopper the tube, mark it for identification (Fig. 3), and let the mixture stand at room temperature overnight, or at 37°C for 4 h. 

Preparation of the sample Pipette 0.5 ml of serum into the Kodak Ektachem HDL tube. Immediately cap and mix thoroughly for 30 seconds using a vortex mixer. The sample will become cloudy during mixing. Let the mixture stand for at least five minutes. Centrifuge the tube for ten minutes at 1500 g or alternatively for five minutes at 10000 g. Visually check the supernatant for clarity. After centrifugation the clear supernatant is directly transferred to a sample cup and the precipitate is ejected. 

The flow rate should be checked regularly and this can be achieved by fitting a graduated pipette on the reservoir side of the pump. Medium can be drawn into the pipette using a syringe, and the flow rate calculated from the time taken for a set volume of medium to be withdrawn. 

---