Thermo-responsive polymer coated fiber-in-tube capillary microextraction and its application to on-line determination of Co, Ni and Cd by inductively coupled plasma mass spectrometry (ICP-MS)

The poly(N-isopropylacrylamide) (PNIPA) gel is a widely studied thermo-responsive material that exhibits discontinuous change in volume when the external temperature is increased. In this paper, PNIPA gel was prepared and applied as a novel polymer coating for fiber-in-tube capillary microextraction of trace Co, Ni and Cd followed by on-line ICP-MS detection. The PNIPA coating was synthesized by using ethylene triethoxysilane (ETEOS) as the cross-linking agent under acidic conditions. This siloxane incorporated PNIPA gel achieves a dramatically rapid response rate when the external temperature is changed. The micro-structure of PNIPA coating was examined by scanning electron micrograph (SEM). Various experimental parameters including pH, temperature, sample flow rate and volume, elution solution and interfering ions affecting the extraction of the target analytes have been carefully investigated and optimized. Under the optimized conditions, the limits of detection were 0.45, 4.6 and 6.9 ng L⁻¹ for Co, Ni and Cd, respectively. With a sampling frequency of 13 h⁻¹, the relative standard deviations (RSDs) for Co, Ni and Cd were 4.8, 5.1 and 6.4% (C = 1 μg L⁻¹, n = 7), respectively. The proposed method had been successfully applied to the determination of Co, Ni and Cd in human urine. To validate the proposed method, certified reference materials of NIES No. 10-b rice flour and GBW07601 (GSH-1) human hair were analyzed and the determined values were in a good agreement with the certified values. The PNIPA coated fiber-in-tube capillary can be reused for more than 150 times without decreasing the extraction efficiency.     

Polymer monolithic capillary microextraction combined on‐line with inductively coupled plasma MS for the determination of trace rare earth elements in biological samples

A rapid and sensitive method based on polymer monolithic capillary microextraction combined on‐line with microconcentric nebulization inductively coupled plasma MS has been developed for the determination of trace/ultratrace rare earth elements in biological samples. For this purpose, the iminodiacetic acid modified poly(glycidyl methacrylate‐trimethylolpropane trimethacrylate) monolithic capillary was prepared and characterized by SEM and FTIR spectroscopy. Factors affecting the extraction efficiency, such as sample pH, sample flow rate, sample/eluent volume, and coexisting ions were investigated in detail. Under the optimal conditions, the LODs for rare earth elements were in the range of 0.08 (Er) to 0.97 ng/L (Nd) with a sampling frequency of 8.5 h^?1, and the RSDs were between 1.5% (Sm) and 7.4% (Nd) (c = 20 ng/L, n = 7). The proposed method was successfully applied to the analysis of trace/ultratrace rare earth elements in human urine and serum samples, and the recoveries for the spiked samples were in the range of 82–105%. The developed method was simple, rapid, sensitive, and favorable for the analysis of trace/ultratrace rare earth elements in biological samples with limited sample volume.     

MPTS-silica coated capillary microextraction on line hyphenated with inductively coupled plasma atomic emission spectrometry for the determination of Cu, Hg and Pb in biological samples

A novel sol-gel 3-mercaptopropyltrimethoxysilane (MPTS) modified silica coating was developed for capillary microextraction (CME) of trace Cu, Hg and Pb prior to their on line determination by inductively coupled plasma-atomic emission spectrometry (ICP-AES). This organic-inorganic hybrid coating was in situ created on the inner walls of fused silica capillary using a sol solution containing TMOS (tetramethoxysilane) as a precursor, MPTS as a co-precursor, ethanol as the solvent and hydrochloric acid as a catalyst. The structure of the capillary coating was characterized by FT-IR spectroscopy, Raman spectroscopy, SEM and TEM. The factors affecting on the capillary microextraction of analytes such as pH, sample flow rate and volume, elution solution and interfering ions had been investigated, and the optimized experimental parameters were obtained. Under the optimized conditions, the absorption capacity of MPTS-silica coated capillary was found to be 1.17, 1.96 and 1.19 μg m⁻¹ for Cu, Hg and Pb, and the limits of detection were as low as 0.17 0.22 and 0.52 ng mL⁻¹, respectively. With a sampling frequency of 12 h⁻¹, the relative standard deviations (R.S.D.s) were 4.2, 2.6 and 3.8% (C=4 ng mL⁻¹, n = 7, sample volume = 1 mL) for Cu, Hg and Pb, respectively. The proposed method had been successfully applied to the determination of Cu, Hg and Pb in human urine, human serum and preserved egg. To validate the proposed method, certified reference materials of BCR151 milk powder, GBW07601 (GSH-1) human hair, GSBZ 50016-90 and GSB 07-1183-2000 water samples were analyzed and the determined values were in a good agreement with the certified values.     

Dual‐column capillary microextraction (CME) combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV‐ICP‐MS) for the speciation of arsenic in human hair extracts

In this work, dual‐column capillary microextraction (CME) system consisting of N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane (AAPTS)‐silica coated capillary (C1) and 3‐mercaptopropyl trimethoxysilane (MPTS)‐silica coated capillary (C2) was developed for sequential separation/preconcentration of arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] in the extracts of human hair followed by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV‐ICP‐MS) detection with iridium as permanent modifier. Various experimental parameters affecting the dual‐column microextraction of different As species had been investigated in detail. It was found that at pH 9, As(V) and MMA could be quantitatively retained by C1 and only As(III) could be quantitatively retained by C2. With the aid of valve switching, As(V)/MMA(V) retained on C1 and As(III) retained on C2 could be sequentially desorbed by 10 µl of 0.01 mol l^?1 HNO₃ [for As(V)], 0.1 mol l^?1 HNO₃ [for MMA(V)] and 0.2 mol l^?1 HNO₃‐3% thiourea (m/v) [for As(III)], respectively, the eluents were immediately introduced into the Ir‐coated graphite tubes for further ETV‐ICP‐MS detection. With two‐step ETV pyrolysis program, Cl^? in the sample matrix could be in situ removed, and the total As in the human hair extracts or digested solution could be interference‐free, determined by ETV‐ICP‐MS. DMA(V) in the human hair extracts was obtained by subtraction of total As in the human hair extracts from other three As species. Under the optimized conditions, the detection limits (3 σ) of the method were 3.9 pg ml^?1 for As(III), 2.7 pg ml^?1 for As(V), 2.6 pg ml^?1 for MMA(V) and 124 pg ml^?1 for total As with the relative standard deviations less than 7.0% (C = 0.1 ng ml^?1, n = 7), and the enrichment factor was 286, 262 and 260 for As(III), As(V) and MMA(V), respectively. The developed method was successfully applied for the speciation of arsenic in the extracts of human hair. Copyright © 2009 John Wiley & Sons, Ltd.