A comparison of log Kow (n-octanol–water partition coefficient) values for non-ionic, anionic, cationic and amphoteric surfactants determined using predictions and experimental methods

Environmental Sciences Europe

Table 2 Experimental log K_ow/D values for 12 surfactant test compounds and 2 reference compounds

Details of the test and reference compounds and their test conditions				Experimental log K_ow/D values determined using HPLC, slow-stirring and solubility ratio methods						Mean^g	Standard deviation
Class	#	Abbreviation	pH	HPLC [3]	HPLC [7]	Slow-stirring [2]^a	Solubility ratio method (using different CMC methods)
Class	#	Abbreviation	pH	HPLC [3]	HPLC [7]	Slow-stirring [2]^a	Surface tension [11]^a	SPME [6]^a	Literature mean CMC values [6]^a
Non-ionic	1	C8EO4	7	4.20	3.50	2.64	ND^c	ND^c	ND^c	3.42	1.10
	2	C12EO4	7	6.40	ND	4.33	ND^c	ND^c	ND^c	5.37	1.46
	3	C12EO8	7	6.50	5.31	3.96	3.19	3.29	3.28	4.55	1.73
Anionic	4	C12AS	7	NA	NA	1.92	− 0.11	− 0.61	− 0.42	0.91	1.44
	5	C12E4S	7	NA	NA	1.47	2.29	2.45	2.04	1.88	0.580
	6	C12 carboxylate	7	NA	NA	3.15 (5.20)	1.60 (3.65)	2.51 (4.56)	1.13 (3.18)	2.38	1.10
	6	C12 carboxylate	2	NA	NA	4.47 (4.47)	ND	ND	ND	4.47	NR
	6	C12 carboxylate	9	NA	NA	1.47 (5.52)	ND	ND	ND	1.47	NR
Cationic	7	C12TMAC^d	7	NA	NA	0.68	2.25	2.21	2.24	1.47	1.11
	8	C16TMAC^d	7	NA	NA	1.83	3.65	3.46	3.06	2.74	1.29
	9	C18BAC^d	7	NA	NA	1.32	3.03	4.99	3.07	2.18	1.21
Amphoteric	10	C12–16ADB^d	7	NA	NA	3.69	1.88	ND	1.61	2.79	1.28
	11	C12AAPB^d	7	NA	NA	2.59	1.75	ND	1.94	2.17	0.594
	12	C12DAO^d	7	NA	NA	0.71	ND^c	ND^c	ND^c	0.71	NR
Reference (neutral)	13	ATR	7	2.60	ND	2.67^e	ND	3.07	3.12	2.64	0.049
Reference (ionised)	14	PCP	7	NA	ND	2.90^f (5.55)	ND	1.05^b (3.70)	0.81^b (3.48)	2.90	NR

NA not applicable, as the HPLC method is only applicable to non-ionic compounds, ND not determined, NR not relevant
^aLog K_ow values in brackets are calculated values of the neutral form of the compound, corrected for ionisation using Eq. 2
^bLog K_ow values of pentachlorophenol have been calculated using the literature water solubility value of pentachlorophenol
^cNot possible to determine solubility in n-octanol quantitatively, so no log K_ow data presented
^dThese cationic surfactants are permanently ionised under the test conditions
^eLiterature log K_ow value for atrazine is 2.61
^fLiterature log K_ow values for pentachlorophenol are 5.05 (at pH 5.1) and 5.87 for ionised and corrected neutral forms respectively [38]. A further similar literature value of 5.12 has also been reported [39]
^gCalculated using only values fully generated in this study (HPLC, Slow-stirring and Solubility ratio (based on CMC values determined by the surface tension method only)