Injector port

A recent method, still in development, for determining total 4-nitrophenol in the urine of persons exposed to methyl parathion is based on solid phase microextraction (SPME) and GC/MS previously, the method has been used in the analysis of food and environmental samples (Guidotti et al. 1999). The method uses a solid phase microextraction fiber, is inserted into the urine sample that has been hydrolyzed with HCl at 50° C prior to mixing with distilled water and NaCl and then stirred (1,000 rpm). The fiber is left in the liquid for 30 minutes until a partitioning equilibrium is achieved, and then placed into the GC injector port to desorb. The method shows promise for use in determining exposures at low doses, as it is very sensitive. There is a need for additional development of this method, as the measurement of acetylcholinesterase, the enzyme inhibited by exposure to organophosphates such as methyl parathion, is not an effective indicator of low-dose exposures. 

Saturn 2000). The initial oven temperature was set at 90°C, then increased to 120°C with 10°C/tnin. The injector ports and the detector were held at 250°C. 

Two basic methods are used for SPME direct immersion of the fibre into the sample and headspace sampling. Experimental parameters comprise the polarity of the sample matrix and coating material, solvent and salting-out. Other parameters for optimisation of SPME conditions include desorption time, injector port temperature and initial oven temperature. 

The volatile substances were extracted from portions of 0. lg hair using solid-phase micro extraction (SPME). The method uses a fibre coated with an adsorbent that can extract organic compounds from the headspace above the sample. Extracted compounds are desorbed upon exposure of the SPME fibre in the heated injector port of a gas chromatograph (GC). 

Hall et al. (1985) reported that no 1,2-diphenylhydrazine (less than pg/L) was detected in the Nanticoke River near the Chesapeake Bay. The analytical method involved liquid-liquid extraction, concentration, and. analysis by GC/MS. The Contract Laboratory Program statistical database (queried April 13, 1987) reported that 1 2-diphenylhydrazine has been detected n water at i of 357 hazardous waste sites at a concentration of (96 ppb (CLPSDB 1987), and has been reported at 7 of 117, sites. n the national Priority List database (ATSDR 1990) The U.S. EPA Contract laboratory Program uses GC methods to analyze the contaminants of interest. Since 1,2-diphenylhydrazine oxidize, to azobenzene in the GC injector port and both 1,2-diphenylhydrazine and azobenzene, have the same GC retention time and mass spectra, reports of 1,2-diphenylhydrazine from the Contract Laboratory Program may actually represent detections of 1,2-diphenylhydrazine, azobenzene, or both (see Chapter 6 for more details). 

Elemental composition C 18.19%, F 57.57%, O 24.24%. Carbonyl fluoride may be analyzed by FTIR, GC or GC/MS. For the GC analysis, it may be transported with the carrier gas helium from the reaction vessel into a cryo-genically cooled injector port, then thermally desorbed and analysed by FID. The system should be free of moisture. The characteristic ions for mass spectroscopic identification are 66, 26, and 40. 

Elemental composition Ni 34.38%, C 28.13%, O 37.48%. The compound may be identified and measured quantitatively by GC/MS. An appropriately diluted solution in benzene, acetone, or a suitable organic solvent may be analyzed. Alternatively, nickel tetracarbonyl may be decomposed thermally at 200°C, the liberated carbon monoxide purged with an inert gas, and transported onto the cryogenically cooled injector port of a GC followed by analysis with GC-TCD on a temperature-programmed column. Nickel may be analyzed by various instrumental techniques following digestion of the compound with nitric acid and diluting appropriately (See Nickel). 

Elemental composition Se 40.92%, F59.08%. The gas may be dissolved in nitric acid and dilute hydrofluoric acid and the solution appropriately diluted and analyzed for selenium (see Selenium). The hexafluoride may be decomposed with ammonia at 200°C and product selenium analyzed by AA, and gaseous products nitrogen and hydrogen fluoride diluted with helium and analyzed by GC-TCD or GC/MS. Alternatively, selenium hexafluoride diluted with helium is introduced onto the GC injector port and analyzed by GC/MS. Molecular ions have masses 194, 192, 196, and 190. 

FIGURE 3.5 (A) A laboratory-built J,HPLC system with dual syringe pumps, an electronic injector port,... 

Injection generally occurs through a resealable rubber septum. The injector port is held at 150-250° depending on the volatility of the sample and direct injection of 0.1-10 /A of sample is made onto the head of the column. The amount of sample injected onto a packed column is ca 1-2 pg per component. Injection into packed... 

A decongestant syrup was basified with ammonia and extracted into ethyl acetate, thus ensuring that the components extracted were in their free base forms rather than their salts, which is important for obtaining good chromatographic peak shape. Salts of bases will thermally dissociate in the GC injector port but this process can cause a loss of peak shape and decomposition. 

Urine (5 ml) urine spiked with 0.2% (v/v) isopropylamine is placed in a screw-capped 15-ml vial [28]. Pelleted potassium hydroxide (3 g) is added before sealing the vial with an airtight polytetrafluoroethylene-lined septum cap. Potassium hydroxide raises the pH of the sample to ensure that the amines are present as volatile bases. The vial is heated in an aluminium block at 90 C for 20 min. While still in this block, 2 ml head-space gas is withdrawn through the septum with a disposable syringe and injected immediately on the gas chromatography column. The operating temperatures of the column, injector port and detector unit are 70 C isothermal, 150 C and 200 C, respectively, with nitrogen carrier gas at 60 ml/min. This allows quantification of TMA and other amines. TMA N-oxide is measured after quantitative reduction into TMA. For this, titanous chloride (30%, w/v 0.2 ml) is added to 2 ml urine in a screw-capped vial and incubated for 30 min at room temperature. The sample is then diluted ten-fold with distilled water and analysed as described above. The result represents the sum of TMA and TMA N-oxide present in the sample. 

On-column injection is preferred, because it occurs at room temperature. Hot injector ports can lead to decomposition of the sample, and to racemization of chiral components. If a single oven system is used, then split injection offers some advantages because it is important not to expose the chiral column to large amounts of solvents. With an MDGC system, the heart-cutting technique removes the solvent from the chiral column, so on-column injection is preferred. 

When a sample is injected, the injector port is at a temperature sufficient to vaporize the sample components. Based on the solubility and volatility of these components with respect to the stationary phase, the components separate and are swept through the column by the carrier gas to a detector, which responds to the concentration of each component. The detector might not respond to all components. The electronic signal produced as the component passes through the detector is amplified by the electrometer, and the resulting signal is sent to a recorder, computer, or electronic data-collecting device for quantitation. 

To make the injection, we turn the handle of the injector to the load position (see Fig. 9.9). Push the syringe needle into the needle port and slowly push the barrel forward so the sample goes in as a plug. Leave the needle in the injector port to prevent siphoning of the sample out the waste port. The handle is thrown quickly to the inject position. This last step is done quickly to prevent pressure build up while the ports are blocked in shifting from one position to the other. Remember. Load slowly, inject quickly. 

Reference A. Discloses and enables a gas chromatograph, which shows a sample injector port, a column of 8 feet in length contained within an oven, a detector, and a graphical chart readout. 

Sample introduction is a major hardware problem for SFC. The sample solvent composition and the injection pressure and temperature can all affect sample introduction. The high solute diffusion and lower viscosity which favor supercritical fluids over liquid mobile phases can cause problems in injection. Back-diffusion can occur, causing broad solvent peaks and poor solute peak shape. There can also be a complex phase behavior as well as a solubility phenomenon taking place due to the fact that one may have combinations of supercritical fluid (neat or mixed with sample solvent), a subcritical liquified gas, sample solvents, and solute present simultaneously in the injector and column head [2]. All of these can contribute individually to reproducibility problems in SFC. Both dynamic and timed split modes are used for sample introduction in capillary SFC. Dynamic split injectors have a microvalve and splitter assembly. The amount of injection is based on the size of a fused silica restrictor. In the timed split mode, the SFC column is directly connected to the injection valve. Highspeed pneumatics and electronics are used along with a standard injection valve and actuator. Rapid actuation of the valve from the load to the inject position and back occurs in milliseconds. In this mode, one can program the time of injection on a computer and thus control the amount of injection. In packed-column SFC, an injector similar to HPLC is used and whole loop is injected on the column. The valve is switched either manually or automatically through a remote injector port. The injection is done under pressure. 

Our original method for A9-THC explored this problem to some extent. Rather than attempt the synthesis of deutero labeled A9-THC we decided to analyze A9-THC as its own methyl ether (Fig. 2). Our internal standard would be l-0-perdeuteriomethyl-A9-THC. It was proposed to convert A9-THC to its 1-0-methyl ether for the analysis. This was effected by the co-injection of trimethylanilinium hydroxide and A9-THC. At the elevated temperatures of the injector port the phenol is converted to its methyl derivative. This conversion is both reproducible and quantitative. It is therefore suitable for use in any analytical technique. ... 

The problem of lipophiles remained and here again we could make use of the acid functionality of the phenols. With less lipid soluble phenols such as the steroids, simple back extraction from organic solvent into strong base would have been sufficient. However, the high lipid solubility of A9-THC necessitated that extraction be carried out with Brodie s solvent (hexane and isoamyl alcohol) and that back extraction be done with Claisen s alkali, which is a mixture of KOH, methanol, and water. After acidification of the Claisen s alkali, A9-THC could be recovered by extraction. The external standard and the trimethylanilinium hydroxide were added and the extracted phenol (i.e. A9-THC) was converted to the 1-0-methyl derivative in the injector port and the determination carried out... 

Apparatus (See Chromatography, Appendix IIA.) Use a suitable gas chromatograph (HP 6890, or equivalent) equipped with a split injector port, a flame-ionization detector (FID), and a 30-m x 0.25-mm (od) GC capillary column (DB-5MS, or equivalent) having a film thickness of 0.25 p,m. 

For sample analyses, maintain the temperatures of the column oven, injector port, and detector at 180°, 250°, and 350°, respectively. Adjust the electrometer to provide about half of the full-scale deflection when 0.1 ng of PCP is injected. 

See Chromatography, Appendix BA.) Use a gas chromatograph equipped with a Thermal Energy Analyzer detector (Thermo Electron Corporation, or equivalent) and a 1.8-m x 3-mm (od) stainless steel column, or equivalent, packed with 20% Carbowax 20M, or equivalent, and 2% sodium hydroxide on 80- to 100-mesh, acid-washed Chromosorb P, or equivalent. Maintain the column at 170°. Set the injector port temperature to 220°. Use argon as the carrier gas, with a flow rate of 25 to 30 mL/min. Operate with a -110° to -130° slush bath. Adjust instrument parameters such as vacuum chamber pressure, oxygen flow, and calibration knob to obtain the proper sensitivity. 

Quantification of aroma compounds using GC and internal reference has long been a problematic issue.81 Detection response factor, peak shape, discrimination phenomenon at the injector port, and, of course, disproportion during sample preparation were more or less unavoidable. Stable isotopes used as internal standards combined with an MS detector have realized reproducible and far more accurate quantification. The major drawback of this method is the tedious process of preparing the isotope-labeled standards. 

After trimethylsilylation, GC analysis is conducted using a low-polarity capillary column and a flame ionization detector (Note 7). The recommended temperature program is 4 min at 100 °C, then 4°C/min to 240 °C, with the temperature of both injector port and detector at 260 °C. Programs of 2 min at 100 °C and subsequently 5 or 10°C/min to 240 °C are used for GC-MS analysis. Sample injection volumes are 0.2-2.0/d. 

Fig.l Gas chromatographic analysis of white wine sample by fused-silica column poly(ethylene glycol) type (15.00 m X 0.53 mm X 1.00 pm). Chromatographic conditions carrier gas hydrogen (3.6 mL/min) column temperature 40°C (4 min) —> 8°C/min 270°C injector port temperature 250°C detector temperature 300°C. Identity of the selected peaks (1) acetaldehyde, (2) acetone, (3) ethyl acetate, (4) ethanol, (5) ethanol,... 

Isothermal (flash pyrolysis). The temperature of the sample is suddenly increased (10-100 ms) to reach the thermal decomposition level (500 - 800°C). This process can be carried out by means of a platinum or platinum-rhodium filament heated by an electrical current directly coupled to the injector port of the GC. Some pyrolysis fragments are obtained in a very short time and can be directly sent to the column and detector. In spite of this short time for the pyrolysis, it is possible to indicate three different phases (a) heating (10 -10 s), (b) stabilization of the maximum temperature, and (c) cooling. However, the main drawback of this technique is the lack of equilibrium between temperatures with the pyrolyzer. 

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