Manual syringe technique

FIGURE I Bovine aortic endothelial cells (A) and NIH fibroblast cells (B) cytoplasmically loaded with FDxLys (10 mg/ml) using the manual syringe loading technique (1-ml volume) detailed in the text. 

Since the early 1960s, there has been much discussion in the literature of syringe technique during the injection process. Most of this related to facilitating rapid and quantitative sample transfer into the inlet, despite slow, nonreproducible manual operation. These techniques, including cold needle, hot needle, solvent flush, and inclusion of air along with the sample, are not discussed in detail here, as for most hot injection methods (split and splitless), a fast autoinjector, readily available for all gas chromatographs and used as the standard in most industries, will provide excellent quantitative injections. For more information on manual injection techniques the reader is referred to Reference 3. 

Leggett et al (Refs 22 23) used a similar technique, except that their apparatus was static . TNT samples were placed in a 125ml vial equipped with silicone rubber septum cap. The vial was thermostatted and the sample and its vapor were allowed to equilibrate for 2—4 weeks. Vapor was withdrawn from the head-space with a stainless steel syringe and injected into a gas chromatograph. The concn of TNT in the headspace vapor was determined by manual triangulation of the peak, giving peak area/ volume, and dividing by the detector response factor (peak area/mass), as determined by injection of known quantities of TNT dissolved in benzene... 

Some techniques are known to provide higher variability than others. The choice of an appropriate method at the outset can improve precision. For example, a volume of less than 20 mL can be measured more accurately and precisely with a syringe than with a pipette. Large volumes are amenable to precise handling but result in dilution that lowers sensitivity. The goal should be to choose a combination of sample preparation and analytical instrumentation that reduces both the number of sample preparative steps and the RSD. Automated techniques with less manual handling tend to have higher precision. 

SPME is a patented sample preparation method for GC applications (32-36). The solvent-free technique was developed in 1989 by Janusz Pawliszyn (http. /Avww.science.uwaterloo.ca/ -janusz/spme.html) at the University of Waterloo in Ontario, Canada, and a manual device made by Supelco, Inc. has been available since 1993. In 1996, Varian Associates, Inc., constructed the first SPME autosampler. SPME involves exposing a fused silica fiber that has been coated with a non-volatile polymer to a sample or its headspace. The absorbed analytes are thermally desorbed in the injector of a gas chromatograph for separation and quantification. The fiber is mounted in a syringe-like holder which protects the fiber during storage and I netration of septa on the sample vial and in the GC injector. This device is operated like an ordinary GC syringe for sampling and injection. The extraction principle can be described as an equilibrium process in which the analyte partitions between the fiber and the aqueous phase. 

In contrast to the IS method, external standardization may be used in which several standard solutions of varying concentrations of the sample are prepared. Following constant volume injection of each standard solution, a plot of peak area (or height) versus concentration is made, and unknown sample concentrations are obtained from interpolation of the calibration curve. The success of this technique, however, is dependent upon the precision of injection volume, readily accomplished with automatic injection but less so when manual microliter syringes are used. 

Solid-phase extraction devices and applications are evolving rapidly, and novel techniques that stretch the classical definition of SPE are becoming routine. Pawliszyn introduced solid-phase micro extraction (SPME) in 1989,5,14 and a commercial apparatus is available from Supelco (Bellefonte, PA). The SPME apparatus is merely a modified syringe that houses a fused silica optical fiber coated with an immobilized polymer film. The fiber can be exposed for extraction and then retracted for insertion or removal from the sample vial or instrument. Both manual and autosampler devices are available and each can be adjusted for proper fiber depth. Several coatings are available with varying thickness including polydimethylsiloxane, polyacrylate, polydimethylsiloxane/divinylbenzene, and carbowax/divinylben-zene. In contrast to SPE, which is an exhaustive extraction approach, SPME will extract only a fraction of an available analyte, hence it is not suitable for the isolation of impurities and degradants in most applications.15... 

Demonstrate how the patient or family members are to administer medication. For example, show the proper injection techniques if the patient requires insulin injections or the correct use of bronchodilator inhalers for asthma. Don t assume that they can administer the medication after seeing you do it. Make sure to have the patient and family members show you how they plan to give the medication. This is especially critical when medication is given using a syringe, topical dmgs, and inhalers. The patient and the caregiver must have visual acuity, manual dexterity, and the mental capacity to prepare and administer medication. 

An alternative to liquid liquid extraction that is available to use takes advantage of the volatility exhibited by VOCs whereby the air remaining in a sealed vial above a liquid which is known as static headspace (HS) is sampled with a gas-tight syringe and directly injected into the GC FID for carbon-containing VOCs and into the GC ECD for chlorinated VOCs such as THMs. This technique is called manual HS-GC, as distinguished from automated HS-GC techniques. 

Analytes are introduced into GC colmtms with several techniques. An ahquot of a relatively concentrated vapor or air sample— for example, from a plastic bag or a canister—can be introduced into a short section of tubing of known volume, called a sample loop, and subsequently pinged with carrier gas into the GC colurmt Volatile analytes in ambient air samples in a canister or trapped on a solid phase adsorbent are usually concentrated and focused in a cryogenic trap or a secondary adsorbent trap, then thermally vaporized into the GC carrier gas stream. However, in some analytical methods, volatiles trapped on an absorbent are thermally desorbed directly into the GC colunm. Aliquots of organic solvent extracts from various aqueous and solid samples are usually injected with a syringe into the carrier gas stream in a heated injection port. Both manual and antomated syringe injection systems (autoinjectors) are used and the latter are generally very reliable, precise, and have the capacity to process many samples unattended. 

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