LONG-CHAIN ALCOHOLS
Aliphatic alcohols occur naturally in free form but more usually in esterified or etherified form. Surfactants are frequently derived from fatty alcohols like fatty alcohol sulfates, ethoxylates, and alkyl polyglycosides. Sensitive techniques are often needed to evaluate their amounts in the environment or in biological samples. Thus, we give below a procedure based on a simple chemical derivatization which allows a high detection sensitivity (Meissner C et al., Chromatographia 1999, 49, 7).
Reagents and materials
Fatty alcohol standards (C12-C18), carbazole-9-carbonyl chloride (Fluka), 1-methylimidazole, RP-18 SPE cartridges (3 ml, 200 mg), RP-8 column for HPLC (125 x 4.6 mm I.D), acetonitrile, methanol, diethyl ether, HPLC pump and injector, fluorescence detector.
Procedure
Derivatization
: To 860 ml
dry acetonitrile 100 ml
fatty alcohol and 40 ml
methylimidazole catalyst were added. 1 ml carbazole-9-carbonyl chloride solution
(4 mg/ml) was added to the mixture. The reaction time was 30 min at 65°C.
The reaction mixture was purified from excess reagent by filtration through a RP
18 SPE cartridge conditioned with 2 ml methanol and 2 ml acetonitrile/water
(60/40, v/v). The cartridge was washed with 12 ml of acetonitrile/water
(60/40, v/v), air-dried for 10 min and eluted with 2 ml diethyl ether. After
removing ether under a nitrogen flow the residue is dissolved in 1 ml
acetonitrile. The derivatives were stable for more than 24 h in solution.
Fatty alcohol ethoxylates were derivatized according to the same procedure.
Separation
Acetonitrile
was pumped at a flow rate of 1.5 ml/min.
The excitation wavelength was 228 nm and emission was measured at 318 nm.
An example of trace analysis of fatty alcohols (injection of 200 ml of 10 nM
standards from 12 to 18 carbon atoms) is given below.
