Anal. Chem. 2000, 72, 5466-5472
Analysis of Sulfonated Naphthalene-Formaldehyde Condensates by Ion-Pair Chromatography and Their Quantitative Determination from Aqueous Environmental Samples Carmen Wolf,*,† Thomas Storm,‡ Frank Thomas Lange,† Thorsten Reemtsma,‡ Heinz-Ju 1 rgen Brauch,† § ‡ Siegfried Helmut Eberle, and Martin Jekel
DVGW-Technologiezentrum Wasser (TZW), Karlsruher Strasse 84, D-76139 Karlsruhe, Germany, Department of Water Quality Control, Technical University of Berlin, Sekr. KF 4, Strasse des 17. Juni 135, D-10623 Berlin, Germany, and Heinrich-Sontheimer Laboratory for Water Technology, Wasserwerkstrasse 4, D-76137 Karlsruhe, Germany
An ion-pair solid-phase extraction (IPE), ion-pair chromatography (IPC) procedure with fluorescence detection for the quantitative analysis of sulfonated naphthaleneformaldehyde condensates (SNFC) was developed, which provides full resolution of SNFC up to a degree of condensation n ) 5 and partial resolution up to n ) 15. Liquid chromatography-electrospray ionization-mass spectrometry confirmed that SNFC elute in the order of condensation. Response factors in fluorescence detection proved to be mass-constant, thereby allowing us to determine total SNFC amounts. With this IPC method, the weight- and the number-average molecular weights of these high-volume production chemicals (kiloton per annum), used as synthetic tanning agents, concrete plasticizers, and dispersants, can be determined. Recoveries in IPE range from 73 to 85% in river Rhine water and from 79 to 93% in tap water for n ) 2 to n ) 7 with limits of detection of 3-8 ng/L for individual homologues from 500 mL of water. The IPE-IPC procedure was applied to samples of secondary industrial effluents, river Rhine water, a river bank filtrate, and a groundwater sample. SNFC up to n ) 6 were detected in the treated effluents. Total concentrations ranged from 208 µg/L in a secondary treated SNFC production effluent to 75 min) in the SPE extract of a technical SNFC mixture compared to the directly injected product. These highly condensated SNFC are, however, irrelevant in aqueous samples (see below). Analysis of Technical Products. Figure 5 displays the SNFC profiles of a concrete plasticizer and a synthetic tanning agent (syntane), both representing important applications of these compounds. The plasticizer mixture (Figure 5a) exhibits a wider mass range with a maximum at the pentamers (n ) 5) and a higher contribution of SNFC with higher molecular mass (RT g 80 min). In the syntane mixture (Figure 5b), the trimers are most prominent and the upper limit of condensation may be estimated to correspond to the docosamer (20:19-condensate), with a molecular mass of ∼4400. This upper molecular mass limit in the syntane appears reasonable insofaras tanning properties are ascribed to compounds up to a molecular mass of ∼2500. As outlined above, the order of elution of SNFC under the conditions selected for IPC follows their molecular mass. This behavior is inverse to that found in gel permeation chromatography. Nevertheless, a similar mathematical approach can be used (29) Loos, R.; Niessner, R. J. Chromatogr. 1998, 822, 291-303.
5470 Analytical Chemistry, Vol. 72, No. 21, November 1, 2000
Figure 5. Chromatograms of (a, top) 100 µg/L concrete plasticizer and (b, bottom) 100 µg/L tanning agent (for peak assignment, refer to Figure 2).
Figure 6. Molecular mass (log M in g/L) of the chromatographically separated SNFC oligomers (n e 15) against their retention time (tR) (dots). The line represents the calculation with A -6.8724, B 0.3927, C 0.0058, and D 3.147 × 10-5 (correlation between the measured and calculated data (r2) was 0.999).
to describe the relation between molecular mass and retention time (Figure 6). By extrapolating this equation toward higher degrees of condensation we are able to assign molecular masses also to those SNFC oligomers that are not chromatographically resolved (n > 15; tR > 80 min). With these two measures in hand, (a) a detection method that is mass related (fluorescence) and (b) a mathematical equation allowing calculation of molecular masses from chromatographic retention times, we are able to describe technical SNFC mixtures
Table 4. Concentrations (µg/L) of Naphthalenesulfonates and of SNFC in Biologically Treated Industrial Effluents, in the River, in the Bank Filtrate, and in the Groundwatera monomers
n)2
n)3
n)4
n)5
n)6
n)7
total SNFC
108 2.2 2.6 0.47 0.10
77 1.7 0.86 0.58 0.15
87 2.1 0.56 0.34
