Ammonium dihydrogen phosphate

Chemicals Risedronate and 1-octyltriethylammonium phosphate as an ion-pairing (IP) reagent were obtained from LKT Laboratories (St. Paul, MN, U.S.A.). Ammonium dihydrogen phosphate, calcium chloride, 1 M hydrochloric acid, and 1 M sodium chloride were obtained from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). Ethylenediamine-N,N,N′,N′-tetraacetic acid, disodium salt (EDTA/2 Na), as a chelating agent, and tetrabutylammonium bromide were obtained from Sigma-Aldrich (St. Louis, MO, U.S.A.). Methanol was obtained from Kanto Chemical Industries (Tokyo, Japan). 2-Pyridylacetic acid hydrochloride, as an internal standard (IS), etidronate (ca. 60% in water, ca. 4.2 mol/L), and ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), used as a calcium scavenger, were obtained from Tokyo Chemical Industry (Tokyo, Japan). OASIS ® HLB cartridges (Waters Corporation, Milford, MA, U.S.A.) were used for solid-phase extraction. Ultrapure water was generated using a Millipore Milli-Q Plus system (Merck Millipore, Billerica, MA, U.S.A.).

Standard solutions (1000 mg/L) of Cd 2+ , Ni 2+ , and Pb 2+ were purchased from Wako Pure Chemical, Japan. A tetramethylammonium hydroxide (TMAH) solution was diluted with a 25% TMAH solution (TAMAPURE AA grade, Tama Chemicals, Japan) to 12.5% with water. A 2-(5-bromo-2-pyridylazo)-5-(Npropyl-N-sulfopropylamino)phenol disodium salt (5-Br-PAPS) (0.4%) solution was dissolved 0.4 g of 5-Br-PAPS (Dojindo, Japan) in 100 mL of water. A phenolsulfonate (PS -, 0.5 mol/L) solution was dissolved 11.6 g of sodium p-hydroxybenzesulfonate dihydrate (Kanto Chemical, Japan) in 100 mL of water, which was then purified by the addition of a 0.1% PAN {1-(2-pyridylazo)-2-naphthol} ethanol solution, followed by solid-phase extraction with Inertsep-C18 cartridges (GL Sciences, Japan). To prepare a benzethonium (Ben + , 0.1 mol/L) solution, 4.5 g of N-benzyl-N,N-dimethyl-2-{2- [4-(2,4,4-trimethylpentan-2-yl)phenoxy]ethoxy}ethanammonium chloride (Kanto Chemical, Japan) was dissolved in 100 mL of water. An ammonium dihydrogen phosphate (0.5%) solution dissolved 0.5 g of ammonium dihydrogen phosphate (Wako, Japan) in 100 mL of nitric acid (2 mol/L). A mixed cellulose ester membrane filter (0.45 μm pore) (Advantec, Japan) was used to filter the environmental water. All reagents were of analytical grade and water was obtained by using a Direct-Q 3UV (Millipore).