ANALYTICAL EVALUATION OF Α-Acids IN HOP EXTRACTS AND IN HOPS*

. Even traces of accessible iron will affect the quantition of these bitter acids markedly ( Table 2). Removal of iron and other metal traces to such a degree that interference is avoided in the a-acids chromatography is not easy and the silica gel has to be boiled at least four times with 1 N hydrochloric acid.Extensive and careful washing is also essential. The remaining iron then seems to be encapsulated in the silica gel matrix and thus unavailable for reaction with adsorbed solutes. A typical chromatographic silica gel has a surface area of about 400 m*/g.With a specific density of 2.5, a silica sheet of 20x 20 m or 400 m2 area is only 1 nm thick. Occluded iron atoms must therefore be very close to the surface of the silica gel webbing. It should be easy to remove them with acid. Since this is not the case, residual metal traces must be concentrated in the thicker parts, where alveoles of the porous material meet each other. Table 1 shows that the 5 silicagels we investigated, all contain appreciable amounts of metal traces; even the spherical one. It is therefore probable that other or all silicagels contain similar amounts of trace elements. Possible sources of these trace elements are the starting water glass solution, metal abrasion in the hammer mill andlor in the particle classifier, impurities in water and acid solutions.The interfering metal traces can also be removed by acid treatment after derivatization. Boiling octadecyl reversed-phase silica gel with 1 N or 12 N hydrochloric acid in methanol-water for 3 hours does indeed lead to an improvement of the a-acids analysis (see Table 2). The amount of bonded phase after this acid treatment, as ascertained by TGA, was the same as before. The retention times too had not changed. This was rather surprising considering the statements in the literature about the pH stability range (-pH 1-8) of reversed-phase or other silica gel. The particle size of the silica gel has no influence with regard to the above comments.

show abstract

“…The internal standard is trans-chalkone. [3]. Rows 2,3,4 and 5with selfmade octadecyl derivatized silicagel.…”

Section: A-acids Analysismentioning

confidence: 99%

Trace elements in HPLC silica gel

Verzele¹,

Potter²,

Ghysels³

1979

J. High Resol. Chromatogr.

Self Cite

View full text Add to dashboard Cite

show abstract

European Brewery Convention Analysis Committee Sub-Committee on Analysis of Hops and Extracts: Methods of Analysis of Hop-Extracts

1973

Journal of the Institute of Brewing

View full text Add to dashboard Cite

show abstract

Quantitative Analysis of Hops and Hop Extracts by High Pressure Ion Exchange Chromatography

Vanheertum

Verzele

1973

Journal of the Institute of Brewing

Self Cite

View full text Add to dashboard Cite

E.B.C. ANALYSIS COMMITTEE: COLLABORATIVE TESTSA new analysis for hop acids in hops and hop extracts is described. It is based on recent developments in high pressure liquid chromatography using pellicular anion exchange column filling material.Quantitative evaluation of a-acids, /?-acids and oxidation products in hops and hop extracts is carried out by standard addition of pure humulone. The a-acids are completely separated from other hop substances before quantitation. The results of a-acids determinations must therefore be more accurate than was formerly possible and they are compared with conductometric titration results which are systematically higher. This is to be expected as it becomes more and more obvious that paper strip and conductometric analysis are not selective enough and determine fractions as "a-acids" which are in fact oxidation products of the hop acids.

show abstract

ANALYTICAL EVALUATION OF Α-Acids IN HOP EXTRACTS AND IN HOPS*

Cited by 12 publications

References 6 publications

Trace elements in HPLC silica gel

Trace elements in HPLC silica gel

European Brewery Convention Analysis Committee Sub-Committee on Analysis of Hops and Extracts: Methods of Analysis of Hop-Extracts

Quantitative Analysis of Hops and Hop Extracts by High Pressure Ion Exchange Chromatography

Contact Info

Product

Resources

About