Microlitre syringes

Microlitre syringe pipettes are available with capacities ranging from 10 to 250 ph and with the body of the pipette calibrated. When fitted with a needle tip they are particularly useful for introducing liquids into gas chromatographs (Chapter 9). 

The earliest injection method in hplc used a technique borrowed from gc in which a microlitre syringe was employed to inject the sample through a self-sealing rubber septum held in an injection unit at the top of the column. In another method, (stopped flow), the flow of mobile phase through the column was halted and when... 

I Dispense samples, standards and controls Precision dispensing or pipetting of samples, standards and controls Z510 Master Laboratory Station, or ZI90 Precision Microlitre syringe head... 

The combustion infrared technique has been used for the analysis of diluted sludges [34], Schaffer et al. [34] have used a blender to prepare suspensions of samples of this type. After the sample was homogenized, a microlitre syringe was used to remove a 20pL aliquot from the blender. However, the method described by Schaffer et al. [34] does not necessarily allow for the isolation of a representative portion of the sample in a 20pL aliquot [35]. This was found to be particularly true if the sample contained large particles which settled rapidly, and it must be assumed that the precision... 

Sampling Syringe A microlitre syringe of 10-p.L capacity capable of accurately delivering 1 to 10 p,L of sample into the pyrolysis tube. Three-inch x 24-gauge needles are recommended to reach the inlet zone of the pyroloysis furnace. 

Glassware and normal syringes can be dried in an oven then cooled in a desiccator over P2O5 or self-indicating silica gel, but it is not advisable to heat microlitre syringes and these should be dried under vacuum in a desiccator. 

Grant, D.W. Clarke, A. A study of the effects of instrument variables on accuracy and precision in gas chromatography. II. Errors associated with the injection of liquid samples by microlitre syringes. J. Chromatogr. 1974, 97, 115. 

A successful sampling valve is that due to Pratt and Purnell (Fig. 58) . A dead-space sample is first withdrawn, followed by a reacted sample. Cundall et claim a better valve is the push-pull type (Fig. 59), a variation of the valve used on some commercial glc instruments. For sample injections after fractionation, a constant volume and manometer is employed for gases, and precision microlitre syringes for liquids. 

Add 6 (xL ofthe Pt catalyst to the solution using the microlitre syringe. 

Capillary tubes are filled to a height 60-80 mm by the capillarity of the acrylamide-gel-forming solution. The surface of the gel solution is carefully overlayed with water-saturated n-butanol by means of a 25 xL Hamilton microlitre syringe. Polymerization is achieved at room temperature in less than 60 min. A 10 mm high stacking gel can be added. The gel surface is then rinsed with the running buffer. 

In order to achieve good separation, the sample must be injected into the column in one small dose, so that all components start their trip through the column at the same instance. One of the most popular injectors is the syringe injector (see Figure 6.2) whereby the sample, in a microlitre syringe, is injected through a neoprene/Teflon septum. 

Injection port facility for introducing the sample mixture into the mobile phase. In GC the injector is maintained at least 50°C above the maximum column temperature to be used and the sample is introduced via a rubber septum using a microlitre syringe for HPLC see multiport injection valves. 

After these straightforward procedures, methyl-ation procedures such as the use of DMF-dimethyl acetal reagents are very easy, requiring only a microlitre syringe (method 2.9.1), as is on-column pyrolysis of trimethyl-anilinium salts (method 2.8.2). 

If pivaloyl chloride is used, the amine or its hydrochloride (up to 5 mg) is suspended in chloroform (200 /il) and light magnesium carbonate (50 mg) is added. To the stirred suspension is added a 110% molar excess of pivaloyl chloride via a microlitre syringe, and the reaction is allowed to proceed at room temperature for 30 minutes. After centrifugation, the supernatant is evaporated to dryness in a stream of nitrogen or in vacuo, and the residue is dissolved in a suitable solvent for analysis by TLC or GC [138]. 

Blocked needles are a problem. The only effective way of unblocking them is with fine stainless steel wire, provided for the purpose by some manufacturers. This is fed in from the tip end widi a pair of forceps, and needs great patience and some skill. The moment one pushes too hard, the wire kinks and has to be discarded. One has to proceed a millimetre or two at a time. However, with the price of microlitre syringes, it is well... 

Although very small centrifugal filters are available commercially, iteration too is generally replaced by centrifugation and withdrawal of the supernatant, again with a microlitre syringe. 

The methanolic solution is exhaustively extracted with n-hexane after having been allowed to cool down, and the n-hexane extract is then concentrated to a volume of some 5 ml by evaporation on a water bath at 80 C. This residual volume is transferred into a 10 ml graduated flask and made up to the mark at 20 C with n-hexane. Aliquot parts are removed using a microlitre syringe and analyzed by gas chromatography. For a packed column the following programme can be recommended. 

Plates for thin layer chromatography UV fluorescence spectrophotometer Circulating air drying cabinet 60 C Microlitre syringe, 50 pi... 

A microlitre syringe is used to deposit a spot of the previously cleaned... 

Fig. 63. Transfer of a substance from a TLC-spot. a suction of the scraped-off substance with a special percolation tube 6 elution with a few drops of solvent c withdrawal of the extract with a micro-syringe d device for taking up the substance, together with adsorbent, in a definite amount of solvent. 1 glass plate 2 adsorbent layer S percolation tube with small plug of cotton wool 4 communication with reduced pressure 5 microlitre syringe...

Clean all glassware sequentially in soap solution, water, and acetone. Allow the acetone to evaporate and then dry the glassware in an electric oven (105 0 for at least 1 h. Caution Do not oven-dry microlitre syringes as they are easily damaged by overheating. 

Cool the reaction to 0°C using an ice-water bath and ensure that the solution is still stirring. Add styrene (114 p.L, 104 mg, 1 mmol) using a microlitre syringe and allow the heterogeneous slurry to stir vigorously at 0°C for... 

The titrand consists of 100 to 200 i,l of a solution of a sample dissolved in either carbon tetrachloride (for polyethers) or methylene chloride (for polyesters) delivered from a microlitre syringe. These organic solvents are dried over a molecular sieve (grade 5A). When the hydroxyl value is less than 100 mg/g of potassium hydroxide, the titrant is used at a 33.3% m/Vsolution for hydroxy valnes exceeding 100 mg/g it is made up to 20% m/V. 

---