Yunhua Gao

Development of column-pretreatment chelating resins for matrix elimination/multi-element determination by inductively coupled plasma-mass spectrometry

Chelating resins, two kinds of iminodiacetate derivatives (IDA) of cross-linked chitosan (CCS) were synthesized and investigated for adsorption capacity, matrix elimination and collection/concentration of analytes by a column pretreatment in a multi-element ICP-MS determination method. The adsorption behavior of 54 elements at the 10 ng ml(-1) level on chitosan derivatives in a packed mini-column was systematically examined. Almost 30 kinds of metal ions were recovered quantitatively at pH 5 with CCS-HP/IDA (cross-linked chitosan possessing N-2-hydroxypropyl iminodiacetic acid groups) column. Compared with available chitosan-iminodiacetate resin, CHITOPEARL CI-03, the recovery of the metal ions such as Cu, Pb and La is satisfactory with CCS-IDA (cross-linked chitosan possessing N,N-iminodiacetic acid groups) and CCS-HP/IDA using 2 M nitric acid as an eluent, which may be attributed to the difference of cross-linking and macroporous structure. Compared with Chelex-100, the adsorption efficiency is in the order: Chelex-100 > CCS-IDA > CCS-HP/IDA, especially in the chelating ability for alkaline earth metals. The resin with a longer spacer (CCS-HP/IDA) showed higher adsorption selectivity between heavy metal ions and alkaline earth metals at pH < 7. The separation efficiency of the major matrix cations in seawater (Na. K, Mg, Ca) has also been investigated, and matrix interference was negligible even in a seawater sample at pH 5 with CCS-HP/IDA. The recoveries of Mn at pH 5 with CCS-HP/IDA or Chelex-100 were almost 100%. However, those of Mg with each resin were 4 or 98%, respectively. The adsorption capacities of synthesized CCS-HP/IDA for Cu(II), Pb(II) and La(III) were 0.90, 0.65 and 0.34 mmol g(-1), respectively. Therefore, the chelating chitosan resins developed are applicable to the pretreatment of trace amounts of elements in various kinds of water samples.

Sequential-injection on-line preconcentration using chitosan resin functionalized with 2-amino-5-hydroxy benzoic acid for the determination of trace elements in environmental water samples by inductively coupled plasma-atomic emission spectrometry

A new chelating resin using chitosan as a base material was synthesized. Functional moiety of 2-amino-5-hydroxy benzoic acid (AHBA) was chemically bonded to the amino group of cross-linked chitosan (CCTS) through the arm of chloromethyloxirane (CCTS-AHBA resin). Several elements, such as Ag, Be, Cd, Co, Cu, Ni, Pb, U, V, and rare earth elements (REEs), could be adsorbed on the resin. To use the resin for on-line pretreatment, the resin was packed in a mini-column and installed into a sequential-injection/automated pretreatment system (Auto-Pret System) coupled with inductively coupled plasma-atomic emission spectrometry (ICP-AES). The sequential-injection/automated pretreatment system was a laboratory-assembled, and the program was written using Visual Basic software. This system can provide easy operation procedures, less reagent consumption, as well as less waste production. Experimental variables considered as effective factors in the improvement sensitivity, such as an eluent concentration, a sample and an eluent flow rate, pH of samples, and air-sandwiched eluent were carefully optimized. The proposed system provides excellent on-line collection efficiency, as well as high concentration factors of analytes in water samples, which results in highly sensitive detection of ultra-trace and trace analysis. Under the optimal conditions, the detection limits of 24 elements examined are in the range from ppt to sub-ppb levels. The proposed method was validated by using the standard reference material of a river water, SLRS-4, and the applicability was further demonstrated to the on-line collection/concentration of trace elements, such as Ag, Be, Cd, Co, Cu, Ni, Pb, U, V, and REEs in water samples.

Photometric titration of small amounts of cationic surfactants in an aqueous medium

A photometric titration method for cationic surfactants with tetrabromophenolphthalein ethyl ester (TBPE) as an indicator was developed. In the presence of a non-ionic surfactant (Triton X-100), TBPE was dissolved in an acidic aqueous medium, giving a yellow colour in the acidic form (TBPE·H). When a bulky cation (Q+) was added, TBPE·H reacted with Q+ to form an ion associate (Q+·TBPE–), and the colour changed from yellow to blue. This colour reaction was used for the detection of the end-point. Direct and indirect titration methods for the determination of cationic surfactants were examined. Dodecylbenzenesulfonate ion (DBS–) was used as a titrant for cationic surfactants in the direct titration. The colour changed from blue to yellow at pH 3.6, and absorbance changes were monitored with a fibre-optic sensor with a 630 nm interference filter. Benzyldimethyltetradecylammonium (zephiramine) ion was found to be the preferred titrant in the indirect titration. The titrant was added to a solution of cationic surfactant containing a known excess amount of anionic surfactant DBS– at pH 3.6. Cationic surfactants at concentrations from 5 × 10–6 to 1 × 10–3 mol dm–3 could be determined.

Novel indicator system for the photometric titration of ionic surfactants in an aqueous medium. Determination of anionic surfactants with distearyldimethylammonium chloride as titrant and tetrabromophenolphthalein ethyl ester as indicator

A photometric titration method for anionic surfactants with tetrabromophenolphthalein ethyl ester (TBPE) as indicator was examined. In the presence of a non-ionic surfactant (Triton X-100), TBPE was dissolved in an acidic aqueous medium giving a yellow colour in the acidic form (TBPE·H). When a bulky cation (Q+) was added, TBPE·H reacted with Q+ to form an ion associate (Q+·TBPE–), and the colour changed from yellow to blue. Distearyldimethylammonium ion was the preferred titrant. The titrant was added to a solution of anionic surfactant at pH 3.2, and absorbance changes were monitored with a fibre-optic sensor with a 640 nm interference filter. Anionic surfactants at concentrations from 5 × 10–6 to 2 × 10–4 mol dm–3 could be determined, and the standard deviations and the relative standard deviations for ten replicate titrations of 25 cm3 of 2 × 10–4 mol dm–3 of various anionic surfactants were 0.03–0.15 cm3 and 0.03–1.65%, respectively.