|dc.description.abstract||Linear alkylbenzenes, LAB, formed by the Alel3 or HF catalyzed alkylation of
benzene are common raw materials for surfactant manufacture. Normally they are
sulphonated using S03 or oleum to give the corresponding linear alkylbenzene sulphonates
In >95 % yield.
As concern has grown about the environmental impact of surfactants,' questions have
been raised about the trace levels of unreacted raw materials, linear alkylbenzenes and minor
impurities present in them. With the advent of modem analytical instruments and techniques,
namely GCIMS, the opportunity has arisen to identify the exact nature of these impurities and
to determine the actual levels of them present in the commercial linear ,alkylbenzenes.
The object of the proposed study was to separate, identify and quantify major and
minor components (1-10%) in commercial linear alkylbenzenes. The focus of this study was
on the structure elucidation and determination of impurities and on the qualitative
determination of them in all analyzed linear alkylbenzene samples.
A gas chromatography/mass spectrometry, (GCIMS) study was performed o~ five
samples from the same manufacturer (different production dates) and then it was followed by
the analyses of ten commercial linear alkylbenzenes from four different suppliers. All the
major components, namely linear alkylbenzene isomers, followed the same elution pattern
with the 2-phenyl isomer eluting last. The individual isomers were identified by
interpretation of their electron impact and chemical ionization mass spectra. The percent
isomer distribution was found to be different from sample to sample. Average molecular
weights were calculated using two methods, GC and GCIMS, and compared with the results
reported on the Certificate of Analyses (C.O.A.) provided by the manufacturers of commercial linear alkylbenzenes. The GC results in most cases agreed with the reported values, whereas
GC/MS results were significantly lower, between 0.41 and 3.29 amu.
The minor components, impurities such as branched alkylbenzenes and dialkyltetralins
eluted according to their molecular weights. Their fragmentation patterns were studied using
electron impact ionization mode and their molecular weight ions confirmed by a 'soft
ionization technique', chemical ionization. The level of impurities present i~ the analyzed
commercial linear alkylbenzenes was expressed as the percent of the total sample weight, as
well as, in mg/g. The percent of impurities was observed to vary between 4.5 % and 16.8
% with the highest being in sample "I".
Quantitation (mg/g) of impurities such as branched alkylbenzenes and dialkyltetralins
was done using cis/trans-l,4,6,7-tetramethyltetralin as an internal standard. Samples were
analyzed using .GC/MS system operating under full scan and single ion monitoring data
acquisition modes. The latter data acquisition mode, which offers higher sensitivity, was used
to analyze all samples under investigation for presence of linear dialkyltetralins.
Dialkyltetralins were reported quantitatively, whereas branched alkylbenzenes were reported
The GC/MS method that was developed during the course of this study allowed
identification of some other trace impurities present in commercial LABs. Compounds such
as non-linear dialkyltetralins, dialkylindanes, diphenylalkanes and alkylnaphthalenes were
identified but their detailed structure elucidation and the quantitation was beyond the scope
of this study. However, further investigation of these compounds will be the subject of a