Doehlert matrix for optimisation of procedure for determination of nickel in saline oil-refinery effluents by use of flame atomic absorption spectrometry after preconcentration by cloud-point extraction

Abstract

This paper proposes a preconcentration procedure for determination of nickel in saline aqueous waste samples by flame atomic absorption spectrometry (FAAS). It is based on cloud-point extraction of nickel(II) ions as 2-(5-bromo-2-pyridylazo)-5-diethilaminophenol (Br-PADAP) complexes using octylphenoxypolyethoxyethanol (Triton X-114) as surfactant. The optimisation step was performed using a four-variable Doehlert design, involving the factors centrifugation time (CT) of system after addition of surfactant, solution pH, methanol volume (MV) added at micellar phase, and buffer concentration (BC). The analytical response used was absorbance, after volume correction. Using the established experimental conditions in the optimisation step the procedure enables nickel determination with a detection limit (3 delta/ S) of 0.2 microg L(-1), quantification limit (10 delta/ S) of 0.7 microg L(-1), and precision, calculated as relative standard deviation ( RSD) of 4.7 ( n=8) and 3.5% ( n=8) for nickel concentration of 1 and 5 microg L(-1), respectively. The preconcentration factor, determined from the ratio of the slopes of the analytical curves with and without preconcentration, is 74. The recovery achieved for nickel determination in the presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The robustness was checked by using saturated fractional factorial designs, centred on the established experimental conditions in the optimisation step. The results of these tests demonstrated that the variables centrifugation time and buffer concentration are robust for modification by 10% and that solution pH and methanol volume are robust for 5%. Accuracy was evaluated by using the certified material reference SLEW-3 estuarine water for trace metals. The procedure was used for determination of nickel in saline effluents from oil refinery samples. Recovery results (95-104%) indicate that the procedure has satisfactory accuracy for nickel determination in these samples.

Optimization of mesoporous titanosilicate catalysts for cyclohexene epoxidation via statistically guided synthesis

“…Hence, the DM approach has been widely utilized in analytical sciences, as an optimization tool and as a simple alternative to orthogonal design [47]. The method has been utilized successfully in oil refining, homogeneous catalysis, heavy metal analysis and food science, for optimization of experimental and analytical parameters [54][55][56][57][58][59]. ESI, Sects.…”

Determination of cadmium in rice and water by tungsten coil electrothermal vaporization-atomic fluorescence spectrometry and tungsten coil electrothermal atomic absorption spectrometry after cloud point extraction

“…The small volume of the surfactant-rich phase obtained from CPE permits the design of extraction schemes of simplicity, high efficiency, rapidness and environmental friendliness, compared with conventional liquid-liquid extraction using organic solvents [2][3][4]. The application of CPE as sample preparation method has been well-documented in the literature for a variety of instrumental methods, such as flame atomic absorption spectrometry (FAAS) [5,6], inductively coupled plasma optical emission spectrometry (ICP-OES) [7,8], inductively coupled plasma mass spectrometry (ICP-MS) [9,10], gas chromatography (GC) [11], high-performance liquid chromatography (HPLC) [12,13], capillary electrophoresis (CE) [14][15][16], and chemiluminescence (CL) [17]. Apart from analyte preconcentration, CPE can also effectively eliminate the matrix effect encountered in ultrasensitive detection schemes, for example, ICP-MS [18] and graphite furnace atomic absorption spectrometry (GF-AAS) [19,20].…”

Determination of trace nickel in water samples by cloud point extraction preconcentration coupled with graphite furnace atomic absorption spectrometry

“…CPE as a preconcentration step in conjunction with detection by spectrophotometry, FIA-spectrofluorimetry, FAAS, ICP-AES and HPLC for the determination of various metal ions has been widely studied [19][20][21][22][23][24][25][26]. CPE combination with FAAS for the determination of nickel has also been reported [27][28][29][30][31].…”