Cationic surfactants

Due to the lack of volatility of quaternary ammonium salts, GC analysis requires derivatisation or degradation to convert them into volatile compounds [133]. Thus, alkylbenzyl dimethyl ammonium halides (ABDACs) have been derivatised as trichloroethyl carbamates and cyanamides for GC-ECD and GC-NPD [134] analysis and the method was applied to their determination in natural waters [135]. The chain length of the raw material fatty acids of quaternized triethanolamines (esterquats) was determined by GC by reacting with methanol/sulfuric acid to yield the fatty acid methyl esters [136]. Several authors have used the Hofmann degradation method, which converts a quaternary ammonium hydroxide into a tertiary amine and an olefin for the analysis of quaternary amines by GC. Thus, alkyltrimethyl- and dialkyldimethyl-ammonium halides refluxed with sodium methoxide in N,N-dimethylformamide gave the expected dimethyldialkylamines [137], but the method was further improved by diluting the sample in methanolic potassium hydroxide with the degradation occurring in the GC injection port [138]. The alkyl chain distributions of commercial benzalkonium chlorides have also been determined [139].

Determination of ABDAC in wet wipes by debenzylation after alkaline degradation with potassium tert-butoxide has been reported and the conditions of the degradation reaction have been studied [140]. Recently, ABDACs have been determined in river water and sewage effluents by SPE followed by GC-MS of alkyldimethyl amines formed from the SPE eluate by the Hofmann degradation with potassium tert-butoxide [141]. The method allows their quantitation at # 0.1 mg L"1 in 500 mL of water. Figure 2.1.9 shows as an example the extracted ion chromatogram of dialkylamines present in river water, (a) prior to debenzylation and (b) after Hofmann degradation, as well as their EI mass spectra whose base peak at m/z = 58 corresponds to [CH2=N(CH3)2]+. The simultaneous analysis of alkyltrimethyl-, dialkyldimethyl- and trialkylmethylammonium salts by applying pyrolysis GC and selective detection using a thermionic detector has been reported [142].

The determination of cationic surfactants in the environment by GC and GC -MS is very scarce, as described above, but this is not the case for several compounds related to cationic surfactants. Thus, long chain tertiary amines that are amenable to direct analysis by GC have been

Images Cationic Surfactants

Fig. 2.1.9. Mass chromatograms (m/z 58) of alkylbenzyldimethylammonium chlorides as their corresponding alkyldimethylamines and the internal standard (undecyldimethyl-amine) (a) prior to debenzylation and (b) after Hofmann degradation with potassium tert-butoxide; and EI mass spectra detected in river water. Reproduced with permission from Ref. [141]. © 2001 by American Chemical Society.

Fig. 2.1.9. Mass chromatograms (m/z 58) of alkylbenzyldimethylammonium chlorides as their corresponding alkyldimethylamines and the internal standard (undecyldimethyl-amine) (a) prior to debenzylation and (b) after Hofmann degradation with potassium tert-butoxide; and EI mass spectra detected in river water. Reproduced with permission from Ref. [141]. © 2001 by American Chemical Society.

identified in different environmental samples including sludges, coastal waters and sediments [107,109,143-145], seawater [146] and biota [147]. These trialkylamines come from trace impurities in quaternary ammonium salts used as fabric softeners in household laundry detergents and present a homologous distribution of odd-even carbon number alkyl derivatives having 14-18 carbons in the alkyl chain. Long chain alkylnitriles, which are intermediates in the production of cationic surfactants, have also been identified as impurities in formulations and were found in urban coastal environments [107,143,147].

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