Sample Preparation 1 Baseline

Additionally, the inj ected matrix must also be miscible with the solvents used in the separations. For normal phase mode separations, all water must be removed from the injected matrix. Since many of the complex matrixes, such as plasma, urine, and other biological fluids contain a large amount of water, this requires more time consuming sample preparation. However, water can be injected into a polar organic or reverse phase mode separation. Even within the same mode, mobile phases that are very different can cause large disturbances in the baseline. Oda et al., (1991) solved this problem by inserting a dilution tube followed by a trap column in order to dilute the mobile phase used on the achiral column. Following the dilution tube, a trap column was used to reconcentrate the analyte of interest before the enantiomeric separation. 

As a consequence of the development of extraction methods for STA based on mixed-mode SPE columns, as well as of the recent introduction of instruments for the automated sample preparation allowing efficient evaporation and derivatization of the extracts, full automation of STA methods based on GC-MS analysis is also available. It needs GC-MS instalments equipped with an HP PrepStation System. The samples directly injected by the PrepStation are analyzed by full scan GC-MS. Using macrocommands, peak identification and reporting of the results are also automated. Each ion of interest is automatically selected, retention time is calculated, and the peak area is determined. All data are checked for interference, peak selection, and baseline determination. 

The second method is when TLC is used to compare an unknown substance with the pure substance. For example, an aspirin sample prepared in the laboratory could be compared with a pure sample of aspirin. Three spots are made on the baseline of the TLC plate one of the laboratory-prepared aspirin, a second of a sample of pure acetyl salicylic acid, and a third of a sample of both the laboratory and the pure samples (a co-spot). Once the plate has been developed, analysis is carried out by comparison. If the co-spot shows only one spot, it can be concluded that the laboratory-synthesised sample is exactly the same compound as the pure substance. 

Sampling mode effects The goal was to be able to measure at-line, with no sample preparation at all, using a fiber-optic probe or a remote sampling head. However, the area sampled by the hber-optic probe is much smaller than for the sample transport module. It was found that the remote (probe) spectra were very similar to the static (sample transport) spectra, but the baselines were shifted significantly higher and the absorbance peaks consequently reduced in intensity as before, the characteristic peak positions were not affected. Calibration models developed using spectra obtained with the hber-optic probe performed equivalently to those developed with the sample transport module. 

What constitutes a significant difference between two spectra When the differences are small, the answer depends on sample preparation and sample stability as well as accuracy of concentration determination, identification of and compensation for drift in the spectrometer, correct baseline correction, absence of bubbles in the sample, reproducible cleanliness of the cuvette, and the level of general handling procedures. Ultimately, an assessment of significance depends on the experience, competence, and confidence of the operator. 

Sample matrices with high levels of citric or other organic acids (e.g., cranberry juice) can result in poor resolution. This method of sample preparation isolates sugars (i.e., neutral compounds) from acids using anion-exchange mini-columns. Development of this protocol is based on research conducted by Hong and Wrolstad (1986). Although the procedure does require additional time (i.e., twelve samples per hour), it does result in improved resolution and a more stable baseline. 

Kaiser [3U used on-line sample preparation to determine trace anions in solvents, including isopropanol, acetone and Af-methylpyrrolidone. A large solvent injection can interfere with both the ion exchange separation and the conductivity detection by causing large disturbances in the baseline. In this application the anions were concentrated on a AG9-HC guard column and then the solvent was sent to waste before it could enter the analytical column. After the solvent was cleared from the AG9-HC concentrator column, the AG9-HC concentrator was switched in line with the AS9-HC analytical column for the separation. The method detection limits for chloride, sulfate, phosphate and nitrate are reported in the sub pg/1 range. 

Key words (GeoRef Thesaurus, AGI) geochemical surveys, baseline studies, stream water, stream sediments, floodplains, overbank sediments, soils, humus, sampling, sample preparation, FOREGS, manuals, Europe... 

The laboratory should verify and document the proper functioning of the software immediately after any new data acquisition or management systems have been installed. The baseline verification consists of manual calculations to confirm the correctness of all computer calculations. Ongoing verification takes place during laboratory data review process whenever a reviewer replicates one of the results generated by the computer or a manual calculation from a bench sheet. All information used in the calculations (raw data, calibration data, laboratory QC checks, and blank results) is kept on file for the reconstruction of the final result at a later date, should it become necessary. Bench sheets that document sample preparation are also kept on file for the same purpose. 

Equilibrate the column at 50° by pumping eluent at 0.9 mL/ min, until a stable baseline is obtained. Using the autosampler, inject duplicate 30-p.L measures of Sample Preparation and Standard Preparation. 

Serious consideration and time must be given to whether the component of interest is in exceptionally high concentration which, in such cases, may have to be diluted to fit calibration standards or, if low, may require pre-concentration. In some cases it may be necessary to carry out a trial-and-error to ascertain the approximate concentration of metals in samples. The low value must at least be at quantitative limits (i.e. ten times the standard deviation of baseline noise, to be confident of results see Section 3.8.1.7). If it is lower than ten times standard deviation of the baseline the sample may have to be preconcentrated prior to analysis to a level that can be comfortably detected and is suitable for reproducible measurements. The following is a list of common methods of sample preparation techniques. Choosing the correct method is of primary importance and poses a challenge to most analysts, particularly for unknown samples ... 

Table 1. All liquid sample preparation and chromatographic analyses were performed at Baseline/DGSI Inc., The Woodlands, TX. Electron microprobe analysis was performed by Ben Powell, Jim Hickey and Gary Lovell at the Phillips Petroleum Company facility, Bartlesville, Oklahoma.

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