Speciation of arsenic in sulfidic waters

Table 2 Elution times and concentrations of arsenic and co-eluted sulfur in model solutions with ΣH₂S/ΣAs = 0.8 (Exp. 3) and ΣH₂S/ΣAs = 26 (Exp. 7) (Fig. 2; Table 1)

Exp.	Species	Elution time/s	Arsenic/μmol L^-1	Sulfur/μmol L^-1	Molar ratio (S/As)^a
3	Arsenite	217	12.3	n.d.	-
	Arsenate	827	0.20	n.d.	-
	S-As (1 : 1)	922	0.17	^b	-
	S-As (2 : 1)	1024	0.43	0.97	2.25
	S-As (3 : 1)	1129	0.32	1.06	3.31
	S-As (4 : 1)	-	n.d.	n.d.	-
7	Arsenite	231	0.14	n.d.	-
	Arsenate	815	0.04	n.d.	-
	S-As (1 : 1)	914	0.05	^b	-
	S-As (2 : 1)	1016	1.16	2.78	2.40
	S-As (3 : 1)	1119	10.6	30.5	2.88
	S-As (4 : 1)	1205	0.28	1.09	3.91

^aAmong all samples variability of molar S/As ratios for the 2 : 1, 3 : 1, and the 4 : 1 complexes was 2.1 ± 0.3, 3.1 ± 0.7, and 4.2 ± 0.3, respectively. ^bThe first S-As complex is likely to be a 1 : 1 complex -but in most cases the sulfur from this thioarsenite species co-eluted with sulfur from other sulfur species. This was evidenced by non-coincident retention times for As and S peaks. n.d., not detected.

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