I prefer n-hexane, as opposed to hexane fraction, for most NP work, and also n-hexane over n-heptane - because the non-volatile matter is usually lower, and UV transparency may be slightly better - which both are helpful when scaling to preparative. Non-volatile matter is often the critical parameter for preparative work.
Product quality and batches can vary quite a bit, and most suppliers specifications will give an indication, but their CoAs often also just show the product has passed specification, rather than actual numbers.
Product, grade and supplier comes down to what works for you, but the chromatography will not change much, however some detectors can be affected by the different properties, especially if using RI - hexane can be quite noisy on some.
Normal phase hydrocarbon solvents pick up non-volatile matter really easily, so I try to minimise transfers. Note that popular higher-grade solvents can be cheaper than less popular lower grades, consider Chromasolv Hexane Fraction example below, so always ask your suppliers about popular stock grades, container sizes, and prices.
Example specifications - ( Non-volatile matter %, UV@wavelength, cost/L ), and please note that some < will also be <=). As you see, general rules don't cover all products/suppliers, and there are plenty of exceptions.
Ex Aldrich - Chromasolv Grades.
Hexane
Plus n-C6 ( <0.0001, 0.20@210, 0.05@220, A$103 )
>95% n-C6 ( <0.0005, 0.30@210, 0.10@220, A$80.50 )
Plus >98.5% C6 Fraction ( <0.0001, 0.05@225, A$72 )
>98.5% C6 Fraction ( <0.0005, 0.30@210, 0.10@220, A$73 )
Heptane
Plus 99% nC7 ( <0.0001, <0.10@225, A$86.50 )
>96%, nC7 ( <0.0003, 0.40@210, 0.10@220, A61.50)
Ex Merck - Lichrosolv grade,
Note the residue is % mass/volume, and so will be reported as about 50% lower than equivalent % mass/mass, UV is % transmission.
Hexane
98.0% nC6 ( <0.0001, 50%T@210, 80%T@220 )
99.0% C6 Fraction ( <0.0002, 60%T@210, 80%T@220 )
Heptane
99.3% nC7 ( <0.0002, 50%T@210, 80%T@220 )
There are disadvantages with using n-hexane, especially with regard to much greater toxicity and volatility ( samples in vials evaporate faster, some RI detectors are noiser ), and also in ambient pressure silica columns, where the exotherm can cause bed disruption on larger columns.
Please keep having fun,
Bruce Hamilton