All of our detergents are crystallised to be greater than 99.5% pure as measured by TLC, HPLC, double melting point and by the following analytical procedures.
Measurement of purity (HPLC, TLC)
Each lot is first analyzed by TLC and HPLC. All detergents are greater than 99.5% pure. TLC was performed on silica gel (Merck 60 F (254), dichloromethane/methanol 7:1) and detection was effected by spraying the TLC plate with a solution of ethanol-sulfuric acid (9:1) followed by heating. HPLC was performed on a standard C18 column with an eluant of methanol/water. The ratio of methanol to water may vary from 65/35 to 85/15 depending on the hydrophobicity of the detergent. A 50% solution of detergent in MeOH is injected into the HPLC system as previusly described1.
Alcohol andα-isomer contamination
β-n-Alkylglycoside detergents are prepared by glycosylation of the hydrophobic alcohol with activated glucose or maltose acetates. Nearly all products are purified chromatographically and by crystallisation. Alcohols and α-isomers are completely removed during the manufacturing process. Trace amounts of this alcohol in the detergent lot can cause cloudiness in the detergent solution. The β-anomeric purity of the detergent is advantageous for the crystallization of membrane proteins.
Measurement of purity (Double melting point)The double melting properties of β-n-alkylglycosides have long been known2. Alkylglycosides have liquid crystal properties and they can form mesophases in the melt (a state of order between crystals and liquids). In the smectic A mesophase the amphiphilic rod-like molecules form layered structures - a microscopic separation by a sequence of hydrophilic and lipophilic layers. In the isotropic phase, the molecules are packed as a liquid in a random way. An optical polarised microscope equipped with a hotstage and a central processor is used to identify transition temperatures from the smectic A to the isotropic phase. Measurement of transition temperatures (double melting temperatures) gives a very sensitive test for the contamination of the crystalline detergent with hydrophobic alcohols, α-glycosides, solvents and others organic/ inorganic impurities.
Alkyl-glucosides and -maltosides have low absorbance throughout the UV region. MEGA detergents, containing amido group, have high absorbance at 230 nm. The absorbance of the 1% w/v detergent solution in water is measured in the UV region.
A very low level of aromatic impurity can still result in a large fluorescence background. The fluorescence of the detergent solution is compared to a standard 0.1% BSA solution. The excitation wavelength is 280 nm and the emission is measured at 345 nm.
Measurement of conductance gives a very sensitive test for the presence of ionic impurities. A solution of non-ionic detergent should have conductance nearly the same as de-ionised water.
Measurement of pH
The pH of the detergent solution at appropriate concentration is measured. The pH value of the solution should be neutral.
Solubility in water
Some of the impurities (e.g. hydrophobic alcohol) in detergent preparations are not soluble in water. Therefore cloudiness of a detergent solution at a concentration where it is known to be soluble indicates the presence of an insoluble impurity.
1. P. Fromme, H. T. Witt, Improved isolation and crystallisation of Photosystem I for structural analysis; BBA,1365 (1998) 175-184.
2. E. Fischer, B. Helferich; Liebigs Ann. Chem. 383, 68 (1911).
Critical Instructions for Optimal Storage of Detergents
n-Dodecyl-β-maltoside (DDM) CoA
DDM Certificate of Analysis
n-Decyl-β-maltoside (DM) CoA
DM Certificate of Analysis