Sample Stability in Solvents

Conversely, IPA has low absoibance up to 240 nm but is extremely viscous. Slow flow rates are typically used when IPA is the conversion solvent. IPA is also nonreactive under normal operating conditions. 

In conclusion, solvent instability or unique solvent properties may result in situations where the sample, solvent, column, or system integrity may be jeopardized. An understanding of the solvent and its potential chemical reactivities will save the chromatographer hours of lost time and avoid inaccurate or incorrect results. 

A completely separate yet extremely important aspect of sample/solvent compatibility is that of sample stability in the solvent. Hiere are three distinct scenarios here. 

consider the overall stability of the sample in the preparation solvent Note that this solvent may or may not be identical to the mobile phase (although it is generally recommended that the preparation solvent and mobile phase be the same so as to avoid system peak generation, etc.) Sanqjles (this includes standards) spend a large amount of time interacting with the preparation solvent. The time from completion of the preparation to the actual analysis is often hours. In some instances this has been shown to be crucial in cases of protein denatuiation in solvents [31] and on columns [32] decomposition of derivatized analytes [33] time, temperature, and light effects in the case of ascorbic acid [34] and pesticide residue decomposition on support media such as graphitized carbon and C,g silica [35]. 

Second, when a sample is not made up in the mobile phase itself, there may be equilibrium issues when the sample is injected into the mobile phase. For example, if the sample is prepared in a solvent that is stronger than the mobile phase, then solubility may be exceeded when the injection plug is diluted by the mobile phase. This type of non-equilibrium sample overload can result in peak fronting (see Fig. 1.16). 

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Sample stability in solvents is a key consideration for any analysis but is particularly important in PAH analyses [160]. The PAHs acenaphthene (458), fluoranthene (94), benz[a] anthracene (4.3), benzo[A ]fluoranthene (76), benzo[a]pyr-ene (9), and dibenz[a,/ ]anthracene (36), all EPA priority pollutants, photodegrade in methanol (time in minutes for 50% decomposition is given in parentheses). The presence of various solvent/solute photodegradation adducts was confirmed by GC/MS. Therefore, the proper choice of solvent in tandem with careful sample manipulation is essential for reproducible and accurate results. 

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