Injection block

In a typical experimental arrangement, the injection block heater of the gas chromatograph is used to heat a short catalyst bed containing platinum, palladium, copper or nickel coated on a diatomaceous support. The catalyst bed can be the top portion of a packed column or a precolumn connected to a packed or open tubular column. Hydrogen carrier gas flows through the heated catalyst bed (220-350 0) and then into the column. The sam B is injected by... 

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. 

Condenser temperature(s), in a multiple coil condenser at each separately injected block of coils... 

Temperatures column, 175°C detector, 200°C injection block, 225°C. Carrier gas nitrogen at 40ml min-1. 

These workers used an ARC 34000 inductively coupled plasma emission spectrometer with flow-injection hydride generation. The 189.04nm line (3nd order) was used for arsenic measurement. The flow-injection block and Buckler peristaltic pump, as described by Liversage et al. [125] were also used for the determination of arsenic by hydride generation. 

Neither the thermal nor the cobalt-catalyzed decomposition of 3-butene-2-hydroperoxide in benzene at 100 °C. produced any acetaldehyde or propionaldehyde. In the presence of a trace of sulfuric acid, a small amount of acetaldehyde along with a large number of other products were produced on mixing. Furthermore, on heating at 100°C., polymerization is apparently the major reaction no volatile products were detected, and only a slight increase in acetaldehyde was observed. Pyrolysis of a benzene or carbon tetrachloride solution at 200°C. in the injection block of the gas chromatograph gave no acetaldehyde or propionaldehyde, and none was detected in any experiments conducted in methanol. 

The cleanest product composition may be effected by decomposition of the pure hydroperoxide or solutions in the injection block of the gas chromatograph. In carbon tetrachloride solution only methyl vinyl ketone and methyl vinyl carbinol were produced, the ratio of ketone to alcohol being 2.9. No definite traces of products from isomerized hydroperoxide were observed. 

Some of the present liner designs can be used for on-column injection by placing the head of the column about 1/8 inch from the septum. The syringe needle can thereby extend at least 2 inches into the column. The injection block temperature should be set at or below the temperature limit of the liquid phase in the column. Greater injector temperatures should be avoided because the liquid phase will be stripped off or decomposed at the front of the column and result in baseline drift or large, skewed peaks. 

Light hydrocarbons were extracted, isolated, and characterized chro-matographically following techniques of Dunton and Hunt (2). Sediment studies require no special modifications other than more stringent precautions to avoid contamination because of the lower concentrations in sediments than rocks. Figures 2 and 3 are both based on analyses from the same technique, but in Figure 3 the chromatograms were produced as part of a routine, automatic operation. Extracts are encapsulated in indium and then introduced into the heated injection block presentation is somewhat compressed, but results are comparable. 

A 100 pi aliquot of the extract that had been purified by thin-layer chromatography was evaporated, treated with Tri-Sil (50 pi) and allowed to stand for two hours to complete the reaction. The derivatised solution (1 - 5 pi) was analysed by GC under the following instrumental conditions initial temperature, 150 °C (maintained constant for 0.5 minutes) final temperature, 280 °C (maintained constant for ten minutes) temperature programme, increasing at 10 °C per minute injection-block temperature, 275 °C flame ionisation detector temperature, 300 °C and nitrogen flow-rate, 20 ml/min. 

Chromatographic System Use a suitable gas chromatograph equipped with a flame ionization detector (FID). Use a 1.5-m x 4-mm (id) column packed with 3% OV-1 on 100- to 120-mesh diatomite CQ or 100- to 120-mesh Gas Chrom Q, or equivalent. Program the oven temperature from 90° to 330° at 4° to 6°/min. The nitrogen carrier gas flow rate is 86 mL/min. Set the injection block temperature at 275° and the detector block temperature at 350°. 

Samples were routinely analyzed on a 5 x %" SS column packed with 5% SE-30 silicone gum on 60-80 mesh Chromosorb W. A second column 7 x 3/16" SS packed with 5% SE-30 silicone gum on 80-90 mesh Anakrom ABS, was used to verify the presence of isopropyl 2,4-D. Water-pumped nitrogen carrier gas was filtered through a 13X molecular sieve at a flow rate of 25 ml./min. The injection block temperature was 250°C., and column oven temperatures between 190° and 205°C. gave optimum peak separation for the columns used. The detector was removed and cleaned whenever the standing current dropped below 200 with a detector voltage of 60 volts. 

Due to their highly polar nature, barbiturates require derivatization prior to analysis by GC-MS. In such cases, the sample is dissolved in methanol, centrifnged, the supernatant recovered and placed in a derivatizing vial and is then blown down under nitrogen. The derivatization procednre, using 0.2 M trimethylanilin-ium hydroxide in methanol, is, in principle, the same as that used for other pre-column derivatizations. However, with this system the reaction does not occnr immediately because insufficient activation energy is available at ambient temperature for this to take place. Direct transfer of the reaction mixture onto the heated injection block of the gas chromatograph overcomes this problem and the derivatization reaction can then proceed. Snch a reaction, an example of flash alkylation is illustrated in Scheme 9.1. 

Never use a gas chromatographic syringe in an HPLC injection block. Gas chromatographic syringe needles have a tapered tip whereas HPLC needles have a square end on the tip. The tapered tip scratches the entiy port and causes the port to leak after a while. 

Figure 19-25. A syringe-loading injection block. (Courtesy - Alltech Associates Inc., Deerfield, IL)...

As a general rule, injection block heaters are set about 20 "C hotter than the column. This serves as a starting point further adjustments may be necessary if the peaks tail and there is no other cause for the tailing. 

The equipment consists of two electrode compartments (Fig. 2 a,i) which are directly connected with the current stabilized, power supply, an injection block (Fig. 2 d) and a narrow bore tube. To prevent a hydrodynamic flow between the two electrode compartments, a semi-permeable membrane (Pig. 2 h) is mounted. The separation compartment is a narrow bore tube of Teflon (PTPE) with an inside diameter of 0.2 mm and an outside di2uneter of... 

With this construction, the reactor could be fed in 5-fil pulses directly from the injection block into a stream of hydrogen or helium flowing at a rate of 282 standard cc per minute. A fraction of the product gases was conducted directly to the chromatograph column. 

Steam was supplied from a stationary boiler plant of the DKUR-10/39 type provided with Russian-made PSP equipment and with a "Takuma" Japanese-made steam injection equipment. The following numbered wells were used for steam injection block 1 wells 354, 356, 376 and 383 block U wells 256 and 257. In block I the steam treatment began in May 1970, and in block II, February 1970. 

This injection block is attached to micromanipulators. In operation, the capillary is first flushed with buffer to prepare it for separation. The bottom piece is then removed, and micromanipulators are used to center the capillary over a eell of interest. The cell is aspirated into the capillary, the vial holder is replaced, and high voltage is applied to drive the separation. 

FIGURE 21.17 Injection block. A capillary and electrode are threaded through the top two blocks. The third block forms a gas-tight seal and is used to pressurize a reservoir that pumps reagents through the capillary. The... 

Aspiration of a single cell typically requires a pulse of 11 kPa vacuum to the distal end of the capillary for 1 or 2 s. Control of such modest pressure is not trivial. Krylov developed an elegant method for generating an extremely reproducible vacuum. The distal end of the capillary is connected to a sheath-flow cuvette, and the waste stream of the cuvette is connected to a three-way valve. In normal operation, the valve directs the waste to a receiving reservoir. To inject a sample, the valve directs flow to a solenoid valve, which is connected to a water-filled piece of tubing that terminates in a beaker placed 1 m below the level of the injection block. A timer circuit is used to open the solenoid valve for a precisely timed period, during which time the injection end of the capillary is connected to a water column of 1 m high, which applies vacuum necessary to aspirate the cell within the capillary. 

---