Special injectors

Nitro Nobel A process for making nitrate esters such as nitroglycerol. A special injector is used to mix the liquid polyol with the nitrating acid. 

Many other special devices and procedures have been reported. For example, a special injector is commercially available to permit direct on-column injection for OT columns. One final variation is an injection port that allows the sample to be injected simultaneously on two columns. One recent example of its use is in the analysis of PCBs.4... 

One other procedure involves introducing the sample with a special injector. In order to facilitate insertion through the sampling hole in the graphite tube, solid sample injectors operated similarly to conventional autosamplers have been used that work like a microsyringe and introduce amounts of sample ranging from 0.5-5 mg with reproducibility comparable to that of manual solid sample insertion [34]. 

A great deal of Improvement Is being made In general equipment to minimize band broadening. It Is Important to eliminate or minimize dead volumes. Special Injectors with minimum dead volvime are being experimented with to optimize separations. Similarly, detectors with small cell volumes are being developed... 

For capillary columns able to handle only a small capacity of sample, even the smallest volume that it is possible to inject with a micro-syringe (0.1 p.L), can saturate the column. Special injectors are used which can operate in two modes, with or without flow splitting (also called split or splitless). 

The gas chromatograph can be used for meaningful analysis only after the appropriate column and detector have been selected. However, there is still an important aspect of gas chromatographic analysis that needs to be mentioned. This involves the introduction of the sample into the column. Sample introduction is achieved by using special injectors. There are five techniques to introduce sample into the column. 

Various ways of introducing a sample into a pyrolyser of the tubular reactor (furnace) type have been described. The sample can be introduced into the pyrolysis zone with the aid of a magnet [73], directly by means of a special injector for solid samples [74] and by gravity (free fall) [75]. The latter type of furnace pyrolysers includes a simple vertical device developed by Japanese investigators [75]. It meets the general requirements imposed on pyrolysers of this type, namely (1) it is made of an inert material (quartz) ... 

Hydrocarbon-continuous dispersions are potentially promising and they deserve investigation. Special injectors should be considered to produce dispersions with high interfacial areas. Such injectors are currently used to produce dispersions in aromatic nitration processes (30). 

Challinor [611,620] has reported the use of pyrolysis derivatisation techniques, simultaneous pyrolysis methylation (SPM), cq. THM. In Py-THM-GC the sample (about 5 /xg) is typically placed in the hollow of a flattened Curie-point pyrolysis wire with approximately 0.5 /u-L tetramethyl ammonium hydroxide (TMAH) (25 wt.% aqueous solution) or tetramethylsulfonium hydroxide (TMSH). The prepared wire is then immediately located in the py-rolyser without allowing aqueous TMAH to evaporate and pyrolysis is carried out at the predetermined temperature. Special injectors for chemolysis (e.g. PTV injector) allow THM also for furnace PyGC experiments. Moldoveanu [499] has listed other common derivatisations utilised in GC analysis. 

Flow measurements using tracers are performed in all piping systems carrying oil, gas or water including separators, compressors, injector systems, and flares. Calibration of elsewhere difficult accessible flow meters is regularly performed by the tracer methods, which are based on international standards. Tracer flow measurements are also well suited for special purposes... 

The injector is a special type of jet pump, operated by steam and used for boiler feed and similar services, in which the fluid being pumped is discharged into a space under the same pressure as that of the steam being used to operate the injector. 

The efficiency of an ejecdor or jet pump is low, being only a few percent. The head developed by the ejector is also low except in special types. The device has the disadvantage of diluting the fluid pumped by mixing it with the pumping fluid. In steam injectors for boiler feed and similar seiwices in which the heat of the steam is recovered, efficiency is close to 100 percent. 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

Container composition and tamper evidence is discussed in the EPARs. There is also discussion of containers in cases where special systems such as two-compartment cartridges are used. Any particular points relating to multiple withdrawals of doses from the container will also be included. Special issues relating to pen injectors will be included. 

As mentioned previously, introducing the sample to the flowing mobile phase at the head of the column is a special problem in HPLC due to the high pressure of the system and the fact that the liquid mobile phase may chemically attack a rubber septum. For these reasons, the use of the so-called loop injector is the most common method for sample introduction. 

However, those who have worked with smaller diameter columns have often experienced lower performance and other difficulties. This is primarily due to extra-column effects the bandspreading in the injector, detector and tubing, or the gradient delay volume of the instrument. Troubleshooting guidelines for sorting out the causes of these difficulties are available in Reference f. With proper care, 2-mm columns can be run on a standard modern HPLC instrument with few difficulties. Smaller i.d. columns require special instrumentation. 

For the water analysis, automation is clearly best achieved with an auto-injector for the mechanical handhng of the samples coupled with on-hne data capture, using the computer to analyse the peak data. Serious consideration was given to employing the very considerable in house automation experience to construct a purpose-built auto-injector. However, in the interests of a speedy implementation of the automatic system, it was decided to purchase a commercially available auto-injector and to concentrate the laboratory s efforts on the area of on-hne data capture. Interfacing the complete system assembly via a data communications network required the development of a special control device (commhox), which allowed the LGC hardware to run unattended hut provided an audible warning in event of a fault condition. 

Ejectors and injectors are the two types of jet pumps of interest to chemical engineers. The ejector, also called the siphon, exhauster, or eductor, is designed for use in operations in which the head pumped against is low and is less than the head of the fluid used for pumping. The injector is a special type of jet pump, operated by steam and used for boiler feed and similar services, in which the fluid being pumped is discharged into a space under the same pressure as that of the steam being used to operate the injector. 

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