Programmed total sample transfer

The transfer can only be partial for concentrated extracts (split mode), or a total transfer of the sample into the column for trace analysis is performed (splitless mode). Both injection methods require a different parameter setting, choice of inlet liners and oven program start temperature to achieve the optimum performance. Also the possible injection volumes need to be considered. The operating procedures of split injection and total sample transfer (splitless) differ according to whether there is partial or complete transfer of the solvent/sample on to the column. 

The splitless technique therefore requires working with temperature programs. Because of the almost complete transfer of the sample on to the column, total sample transfer is the method of choice for residue analysis (Grob, 1994, 1995). 

The gaseous sample is passed slowly through the injector and the organic substances retained on the adsorbent. Before injection the PTV can be heated to a low temperature with the split still open to dry the Tenax material, if required. For transfer of the sample to the GC column, the split valve is closed and the PTV is heated to effect the total sample transfer of the concentrated components. After about 30-120 s, the temperature program of the oven is started and the split valve is opened (Figure 2.78). The PTV remains at the same temperature until the end of the analysis. This last step is particularly important in cryo-enrichment because the cooled adsorbent could become enriched with residual impurities from the carrier gas, which would lead to ghost peaks in the subsequent analysis. 

The purpose of this injection technique is to introduce the entire injected sample into the column and use it for trace determination. Different techniques can be used, but the most common is the solvent effect technique, which uses the same instrumentation as used for spht injection (Figure 2.4). In splitless injection, the sample is introduced into the heated liner as in split injection and brought into the gas phase. Contrary to the spht injection, the splitter outlet valve is now dosed. Hence, the total sample volume (1-2 ml of gas) is transferred to the column. When splitiess injection is carried out, the column inlet temperature is kept at a temperature that is 20-50 °C lower than the solvent Bp. Hence, when the sample arrives at the column inlet, the solvent condenses as a thick film on the column wall. This film will act as a plug of stationary phase into which the sample components will be dissolved. Following the sample transfer to the column, which will take 2 min when 2 pi is injected and the carrier gas flow rate is 1 ml min , the column oven temperature is increased. The solvent evaporates first from the column entrance and thereafter the analytes, which will subsequently be separated in the column. The sphtter valve is opened when the whole sample has been transferred to the column in order to wipe out remains of the sample before the next injection. This injection technique is used for trace determinations and can only be carried out in combination with temperature programming. 

The additive standards for the MS library were dissolved in a suitable solvent and a sample was injected into the GC/MS system, or a sample was transferred into an injection port liner as is done for real world samples. Additive standards were mn at temperature program rates of 10 °C or 15 °C due to the lack of the necessity for multi-component separation. The actual temperature program used is listed on each Total Ion Chromatogram (TIC). 

Gray (39) developed a program which accepts the DSC sample and baseline data, matches the isothermal, performs cumulative and total area integrations in units of cal/g, corrects the temperature for thermal lag, and tabulates and plots ordinate values in specific-heat units as well as cumulative area in enthalpy units. The analog data from the DSC instrument are digitized and transferred to paper tape with the use of the Perkin-Eimer ADS VI Analytical Data System for Thermal Analysis. The data are digitized every two seconds or every 0.133°. A computer plotter then plots the DSC curve and also the cumulative peak area in specific enthalpy units, cal/g. 

The NIR spectra can be used for reconstruction of water chemistry, or other environmental parameters, from lake sediments. This approach requires establishment of transfer functions by calibration of MR spectra from surface sediment samples against measured parameters of the water, such as pH, total phosphorus (TP) or total organic carbon (TOC). These transfer functions can then be applied down-core for inference of past water quality. A similar application is in contemporary lake monitoring programs. Surface sediment samples could be taken, for example, each 5th year for MR measurements and subsequent inference of sevCTal wate chemistry parametCTS, or other environmental parameters, for which transfer functions are available. In this approach effects of diagenetic processes on MRS, which may be a problem in down-core studies, are circumvented. 

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