Question

GC Analysis

a) is best done on solids dissolved in a volatile solvent

b) on neat high melting solids

c) on neat volatile liquids or solids

d) none of the above

I just want to see if my reasoning is correct and if not, why: it would be a) because the GC will recognize the solid in solution as a disruption in the gas more easily than b or c.

Answer 1

Yes, you a re right. And I'll add the concept of gas cromatography here:

Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined). In some situations, GC may help in identifying a compound. In preparative chromatography, GC can be used to prepare pure compounds from a mixture.^[1][2]

In gas chromatography, the mobile phase is a carrier gas, usually an inert gas such as helium or anunreactive gas such as nitrogen. The stationary phase is a microscopic layer of liquid or polymer on an inert solidsupport, inside a piece of glass or metal tubing called a column (an homage to the fractionating column used in distillation).

In a GC analysis, a known volume of gaseous or liquid analyte is injected into the "entrance" (head) of the column, usually using a microsyringe (or, solid phase microextraction fibers, or a gas source switching system). As the carrier gas sweeps the analyte molecules through the column, this motion is inhibited by theadsorption of the analyte molecules either onto the column walls or onto packing materials in the column. The rate at which the molecules progress along the column depends on the strength of adsorption, which in turn depends on the type of molecule and on the stationary phase materials. Since each type of molecule has a different rate of progression, the various components of the analyte mixture are separated as they progress along the column and reach the end of the column at different times (retention time). A detector is used to monitor the outlet stream from the column; thus, the time at which each component reaches the outlet and the amount of that component can be determined. Generally, substances are identified (qualitatively) by the order in which they emerge (elute) from the column and by the retention time of the analyte in the column.

The precision of analytical results reflect how tightly the repeated measurements of a given sample agree with each other. One can have very precise results but still be totally wrong (inaccurate).

Precision can be subdivided into to major subcategories: reproducibility and repeatability. These terms are often used incorrectly. The repeatability of a measurement is the precision of the results for a sample when using the same measurement procedure, process, operator, instrument, operating conditions and location, over a short period of time. In capillary GC, for example, a repeatability of 1% relative standard deviation (RSD) in peak area is considered good.

Reproducibility is the precision of results for analyses that were repeated with some change in location, operator, measuring systems and/or measurement conditions. It should be obvious that reproducibility will always be worse than repeatability because there are more opportunities for various errors and biases to impact results.

This is why option a) is best choice.