Chromatograph sample injection

The stability of reference standard gas response factor can be maintained at high level of repeatability since the operating parameter of the gas chromatograph, sample injection technique, and room condition are held constant. Table 7 shows the response factor stabiUty of reference standard gas used in natural gas sample analysis for aperiod of month. 

Caffeine is extracted from beverages by a solid-phase microextraction using an uncoated fused silica fiber. The fiber is suspended in the sample for 5 min and the sample stirred to assist the mass transfer of analyte to the fiber. Immediately after removing the fiber from the sample it is transferred to the gas chromatograph s injection port where the analyte is thermally desorbed. Quantitation is accomplished by using a C3 caffeine solution as an internal standard. 

Another dynamic measurement is the LCEC technique which can be thought of, simpHsticaHy, as EIA using a chromatographic column positioned between the sample injection port and the detector. Bioanalytical systems (BAS) of West Lafayette, Indiana, specializes in instmmentation for LCEC. Their catalogs come with extensive bibhographies covering a variety of appHcations. 

SEC measurements were made using a Waters Alliance 2690 separation module with a 410 differential refractometer. Typical chromatographic conditions were 30°C, a 0.5-ml/min flow rate, and a detector sensitivity at 4 with a sample injection volume of 80 fil, respectively, for a sample concentration of 0.075%. All or a combination of PEO standards at 0.05% concentration each were used to generate a linear first-order polynomial fit for each run throughout this work. Polymer Laboratories Caliber GPC/SEC software version 6.0 was used for all SEC collection, analysis, and molecular weight distribution overlays. 

Introduce a 0.30 pL portion of the solvent extract into the gas chromatograph. It is found that solutions of concentrations greater than 0.3 M are unsuitable as they deposit solid and thus cause a blockage of the 1 jj.L microsyringe used for the injection of the sample. The syringe is flushed several times with the sample solution, filled with the sample to the required volume, excess liquid wiped from the tip of the needle and the sample injected into the chromatograph. 

The technique of column switching can increase the versatility of the liquid chromatograph significantly. Examples of the use of column switching will be given in the chapter on applications but, as the technique employs valves similar to those used for sample injection the... 

High-performance liquid chromatographic determination Inject an aliquot (Vi) of the soil and crop samples into the HPLC system. 

Gas chromatograph Sample injector Injection port Injection mode Column... 

The modem HPLC system is a very powerful analytical tool that can provide very accurate and precise analytical results. The sample injection volume tends to be a minor source of variation, although fixed-loop detectors must be flushed with many times their volume in sample to attain high precision. Assuming adequate peak resolution, fluorimetric, electrochemical, and UV detectors make it possible to detect impurities to parts per billion and to quantitate impurities to parts per thousand or, in favorable cases, to parts per million. The major sources of error in quantitation are sample collection and preparation. Detector response and details of the choice of chromatographic method may also be sources of error. 

Once into the 21st century, hyphenated instrumentation (i.e., those that couple two instruments together) became prevalent in laboratories. This is the combination of two or more, often different, instruments. In simple terms, the purpose is to first separate the analyte of interest and then to identify it. This takes place using a sample injected into the combined instruments. The most common of the hyphenated instruments is the gas chromatograph, the output of which is fed into a mass spectrometer to produce a gas chromatography-mass spectrometry (GC-MS) [35],... 

Table 9.11 shows the effect of this concentration on the responses of the other pesticides. In every instance the peak height was increased while the peak area remained constant. All of the columns used for this study were aged by repeated sample injections, but had not deteriorated to the point where they would normally be replaced. No values are included in Table 9.11 where the chromatographic system was not suitable for the pesticide concerned. 

S.No. Name of Substance Chromatographic Conditions Sample Injection only Solns for GLC Pharmacopoeal Requirement... 

S.No. Name Substance Chromatographic Conditions Sample Injection Qty. Solutions for GLC Calculations/ Observations... 

Solid phase microextraction (SPME) has been shown to be useful for the determination of chloroform in air (Chai and Pawliszyn 1995). This technique is based upon the absorption of chloroform into a polymer coated on a silica liber. Following equilibration of the liber with the atmosphere, chloroform is released via thermal desorption in the injection port of a gas chromatograph. Sample preparation is... 

Many manufacturers now offer other sample injection systems compatible with the vacuum lock used for the solids probe. These include small (e.g., 75-ml) heatable batch inlet systems, usually accessible via syringe (gas syringe or GC microliter syringe for liquids), which can be particularly useful as inlets for mass reference compounds. Other probes are designed as flexible, easily removed connections to a gas chromatograph via some form of interface. 

Static mode the sample (liquid or solid matrix) is placed in a glass phial capped with a septum such that the sample occupies only part of the phial s volume. After thermodynamic equilibrium between the phases has been reached (1/2 to 1 h), a sample of the vapour at equilibrium is taken (Fig. 20.4). Under these conditions, the quantity of each volatile compound present in the headspace above the sample is proportional to its concentration in the matrix. The relationship between the amount of sample injected into the gas chromatograph and its concentration in the matrix can be obtained by calibration (using internal or external standards). 

Reproducibility of peak height is also quite dependent on the reproducibility of the sample injection. This is especially important on early and thus normally quite sharp, narrow peaks. On such early peaks the width of the peak is controlled more by the injection time rather than the chromatographic process. A fraction of a second increase in injection time can double the width of these peaks and reduce peak height 50%. The peaks most subject to error in peak height measurement from injection problems are those with retention volumes between one and two times the hold-up volume of the column. Peaks beyond five to ten times the hold-up volume are negligibly affected by injection technique. 

Known concentrations of vapors can be prepared in the same way by injecting a known volume of a volatile liquid into the container using a microliter syringe normally used for liquid sample injection into a gas chromatograph. The density and molecular weight of the component are needed for the calculation. 

For hydrocarbons, using a 5-cnu gas sample injected into the chromatograph, McAuliffe indicates... 

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