Effects of pH and competing anions on the speciation of arsenic in fixed ionic strength solutions by solid phase extraction cartridges

摘要

Anion exchange resins (AERs) separate As(Ⅴ) and As(Ⅲ) in solution by retaining As(Ⅴ) and allowing As(Ⅲ) to pass through. Anion exchange resins offer several advantages including cost, portability, and ease of use. The use of AERs for the instantaneous speciation of As minimizes the effects of preservatives on As species analysis. The aims of this study were to: (1) Examine the effects of pH and competing anions on the efficacy of solid phase extraction cartridges (SPECs) for speciation of As in a 0.01 mol L~(-1) NaNO_3 background electrolyte. (2) Identify optimal conditions (e.g. flow rates) for As speciation. (3) Calculate method detection limits (MDLs) from spiked background electrolyte and percent recoveries of As species from spiked extracts of mine wastes. The most effective SPEC retained As(Ⅴ) through a range of environmentally relevant pH values (4-8). The mass loading capacity for As(Ⅴ) was reduced in the background electrolyte (0.006mg) compared with As(Ⅴ) in deionized H_2O (0.75mg). Some retention (10-20%) of As(Ⅲ) occurred on pre-wetted cartridges. Approximately 98% of spiked As(Ⅲ) passed through dry cartridges. The recommended flow rate (0.5mLmin~(-1)) was increased to 5mLmin~(-1) without significant effect on As(Ⅴ) retention. The presence of anions decreased the retention of As(Ⅴ) with sulfate and phosphate having the greatest impact. MDLs were 0.004mg L~(-1) for both inorganic species. Spike recoveries in 0.01 M NaNO_3 mine waste extracts averaged 94% for As(Ⅲ) and 107% for As(Ⅴ).