Trace elements in HPLC silica gel

Abstract

. 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.

The effect of conditioning of fused‐silica capillaries on their electrophoretic performance

“…While many authors report the use of relatively dilute HCl solution (0.1 or 1 M), we used a rather concentrated (,6 M) hot solution for leaching. The rationale behind this treatment of the capillary with HCl is identical to that supporting the traditional "hot HCl-washing" used on older-generation chromatographic silicas, and lies on its ability to efficiently remove trace metals such as Na, Ca, and Fe, for instance, and in a lesser extent, Al and Ti, among others [15]. HCl-leaching is then aimed at removing trace metals from the silica surface while rehydroxylating it by forming additional silanols.…”

“…Trace metals such as iron, magnesium, and calcium can be reasonably well removed by HCl-leaching while others such as titanium and aluminum are much more strongly bound to the silica surface [14]. It should be recalled that before the introduction of modern high-purity (metal-free) silicas for LC packings, chromatographic grade silicas usually contained about 20 different metallic impurities at the ppm level and 15 more at the ppb level [6,15]. For this reason, it was a common practice to treat the silica gel with hot 1:1 v/v HCl prior to bonding in order to remove surface metals and hence achieve a better chromatographic support [15][16][17].…”

On the Analysis of Hop Bitter Acid

“…VAN DYCK AND H. CLAUS: HOP BITTER ACtDS II this particular problem will be published elsewhere. 13 Of the complexes tested, phosphoric acid turned out to be satisfac tory while still producing good chromatograms. Although it is possible to demineralize reversed phase silica gel so as to obtain correct results without adding complexcrs, this is extremely difficult.…”

“…Computation of percentages.-Against the chalkonc internal standard a series of increasing weight samples of pure humulone gave a straight calibration line over a concen tration range of 3 to 20 mg humulone per 100 ml HPLC solvent. 13 The equation for this line is y = 0-1753 . x + 0-0076 with a correlation coefficient of 0-99984 where y is the ratio of surface areas of humulonc over that of chalkone and x is the ratio of weights.…”

A rejuvenation method for poly(N,N‐dimethylacrylamide)‐coated glass microfluidic chips

“…However, they found that this "storage effect" could be minimized by filling the capillary with dry air of low relative humidity and sealing it afterwards. As discussed by Verzele et al, chromatographic grade silica may contain a variety of metals: Na, Ca, Fe, Mg, Al, and Ti [34] that are present at significant concentrations (e.g., several hundred ppm [35]) and influence the surface properties [36]. It is also well known that alkali ions such as sodium are leached out from the glass to an aqueous solution in contact with the glass (in a process of ion…”