Injection, technique

In actual practice the soluble component usually is injected into the substrate solution after the insoluble monolayer has been spread. The reason is that if one starts with the solution, the surface tension may be low enough that the monolayer will not spread easily. McGregor and Barnes have described a useful injection technique [265]. 

An injection technique in capillary electrophoresis in which pressure is used to inject sample into the capillary column. 

To date (ca 1997), steam methods have been appHed almost exclusively in relatively thick reservoirs containing viscous cmde oils. In the case of heavy oil fields and tar sand deposits, the cycHc steam injection technique has been employed with some success. The technique involves the injection of steam at greater than fracturing pressure, usually in the 10.3—11.0 MPa (1500—1600 psi) range, foUowed by a soak period, after which production is commenced (15). 

Cool on-column injection is used for trace analysis. Ah. of the sample is introduced without vaporization by inserting the needle of the syringe at a place where the column has been previously stripped of hquid phase. The injection temperature must be at or below the boiling point of the solvent carrying the sample. Injection must be rapid and no more than a very few, usuahy no more than two, microliters may be injected. Cool on-column injection is the most accurate and reproducible injection technique for capihary chromatography, but it is the most difficult to automate. 

Worldwide demand for blast furnace coke has decreased over the past decade. Although, as shown in Figure 1, blast furnace hot metal production (pig iron) increased by about 4% from 1980 to 1990, coke production decreased by about 2% over the same time period (3). This discrepancy of increased hot metal and decreased coke production is accounted for by steady improvement in the amounts of coke required to produce pig iron. Increased technical capabihties, although not universally implemented, have allowed for about a 10% decrease in coke rate, ie, coke consumed per pig iron produced, because of better specification of coke quaUty and improvements in blast furnace instmmentation, understanding, and operation methods (4). As more blast furnaces implement injection of coal into blast furnaces, additional reduction in coke rate is expected. In some countries that have aggressively adopted coal injection techniques, coke rates have been lowered by 25% (4). 

Flow injection techniques can be used to inject sample volumes as small as 10 jiL into a flowing stream of water with little degradation of detection limits. Frit nebulizers have efficiencies as high as 94% and can be operated with as litde as 2 jiL of sample solution. 

Generation of test atmospheres of organic vapours by the syringe injection technique Generation of test atmospheres of organic vapours by the permeation tube method On-site validation of sampling methods... 

Sorbent tube standards preparation by the syringe injection technique... 

The main aims in environmental analysis are sensitivity (due to the low concentration of microcontaminants to be determined), selectivity (due to the complexity of the sample) and automation of analysis (to increase the throughput in control analysis). These three aims are achieved by multidimensional chromatography sensitivity is enhanced by large-volume injection techniques combined with peak compression, selectivity is obviously enhanced if one uses two separations with different selectivi-ties instead of one, while on-line techniques reduce the number of manual operations in the analytical procedure. 

Contrary to popular opinion, slow injection of a large sample (3-5 pt ) by split injection is best. The mass spectrometer total ion current will return to the baseline more quickly using a slow injection technique. 

Solvent Injection The solvent injection technique involves the injection of solutions of lipid in solvents with high vapor pressure (ether, fluorocarbons, ethanol) into excess aqueous phase under reduced pressure. In general, the aqueous phase is maintained above the phase transition of the lipids (Te) and a reduced pressure... 

Wahl and Deck were able to obtain an estimate of an assumed second-order rate coefficient ( 10 l.mole" .sec at 4°C) using a separation procedure based on the extraction of Fe(CN)e by a chloroform solution of Ph AsCl, in the presence of the ions Co(CN)g and Ru(CN)6, to reduce the exchange between the iron species in the two liquid phases. A similar estimate was obtained using a precipitation method in the presence of the carrier Ru(CN)6. A direct injection technique was used as short reaction times were necessary. Wahl has reviewed the large induced exchanges occurring in the chemical separation methods. The extraction procedure when the carriers Co(CN)6 and Ru(CN) are present provides the most satisfactory method of separation. ... 

Eichler and Wahl have attempted an isotopic study ( Os and Os) of the exchange reaction between Os(dipy)3 and Os(dipy)3 using a direct injection technique so that reaction times 7 x 10 sec were possible. With total osmium 10" M in aqueous sulphate media at 0 °C complete exchange was observed. The separation methods used were, (a) perchlorate precipitation (in presence of iron(II) carrier) and (6) extraction with p-toluenesulphonic acid in nitromethane, of the osmium(II) complex. A lower limit of 1 x 10 l.mole. sec was placed on the rate coefficient (0 °C, 3.0 M H2SO4). Dietrich and Wahl using the line broadening effect produced by Os(dipy)3 on the nmr spectrum of Os(dipy)3 have been able to propose a value of > 5x 10" l.mole . sec at 6 °C in D2O (0.14 M [Cr] and 5x10 M [D- ]). 

Numerous types of GC injectors have been manufactured over the past four decades. The most commonly used injection techniques have been reviewed and described by Grob, who correctly states that analysts must fully understand the techniques before they can make the most appropriate choice for their particular application(s). For most GC capillary column applications, the split/splitless, programmed-temperature vaporization (PTV) and on-column injectors remain the most popular. However, over the last few years, technology has progressed rapidly to provide injectors that allow more of the sample extract on to the GC column without overloading it. 

Adsorption or catalytic decomposition of labile substances by the syringe needle can be a problem for some compounds using hot vaporizing injectors [25]. For open tubular columns deactivated fused silica syringe needles and cold on-column Injection techniques are used to minimize this problem. Alternatively, syringes fitted with a needle shroud for cold-needle injection can be used [26]. 

Certainly, the precision and accuracy of the PTV techniques are generally superior to those of the classical hot split and splitless techniques and approach those obtained by cold on-column Injection [ 34,36,37, -54-57,62,64]. However, less is known concerning optimization of PTV injection and probably more parameters have to be considered than for cold on-column injection. The latter is, consequently, the preferred injection technique for most samples, except those contaminated by larg< amounts of involatile Impurities and for headspace vapors. 

Figure 3.3 Discriaination of n-alkanes depending on injection technique. A, filled needle B, hot needle C, cold on-coluan. A and B were obtained using a 1 40 split. Saaple n-alkanes 1 10,000 in hexane. (Reproduced with peraission froa ref. 24. Copyright Dr. Alfred Huethig Publishers). ...

Solid samples are usually dissolved in a suitable solvent and injected as described for liquids. Alternatively, the se ples can be encapsulated in glass capillaries which are then pushed or dropped into the heated injection block and crushed by a mechanical device [32,33]. This form of injection is particularly useful for the analysis of trace volatiles which would be hidden in the solvent front with conventional injection techniques. 

The attractive features of spllti ess injection techniques are that they allow the analysis of dilute samples without preconcentration (trace analysis) and the analysis of dirty samples, since the injector is easily dismantled for cleaning. Success with individual samples, however, depends on the selection of experimental variables of which the most Important sample... 

---