Wei Guang Lan

Orthogonal array design as a chemometric method for the optimization of analytical procedures. Part 4. Mixed-level design and its application to the high-performance liquid chromatographic determination of polycyclic aromatic hydrocarbons

The theory and methodology of a mixed-level orthogonal array design for the optimization of analytical procedures is described. Firstly, the method of construction of a mixed-level orthogonal array design is discussed in detail, followed by the assignment of experiments and the data analysis strategy in the design. The optimization of the parameters involved in the high-performance liquid chromatographic determination of polycyclic aromatic hydrocarbons is then employed to demonstrate the practical application of the proposed mixed-level orthogonal array design in the area of analytical chemistry.

Effect of combined copper, zinc, chromium and selenium by orthogonal array design on alkaline phosphatase activity in liver of the red sea bream, Chrysophrys major

Abstract Red sea bream, Chrysophrys major , were obtained from a marine fish cage-culture farm located in Hoshao Island near Xiamen, Peoples Republic of China, in August, (1990) Orthogonal array design was used to investigate the activating and inhibitory effects of the combination of waterborne Cu, Zn, Cr(VI) and Se(VI) on alkaline phosphatase (APase) activity in liver of C. major . The results obtained demonstrated that (1) the APase activity was significantly increased when Zn was at the level of 100 μg/1 whereas no change was found when Zn was at 500 μg/1; (2) Cu at 20 μg/1 increased APase activity whereas Cu at 100 μg/1 significantly inhibited APase activity; (3) the effect of Se(VI) on APase activity was minimal. However, Se(VI) could suppress the action of Cu on APase activity; and (4) Cr(VI) at concentrations of 0–500 μg/1 had little effect on APase activity. In addition, the results also showed that the duration of exposure was independent of the effects of the combination of waterborne metals on APase activity and no interactive effects of Zn × Se(VI) or Cu × Zn on APase activity were observed.

Orthogonal array design as a chemometric method for the optimization of analytical procedures. Part 3. Five-level design and its application in a polarographic reaction system for selenium determination

The theory and methodology of a five-level orthogonal array design for the optimization of analytical procedures were developed. In the theoretical section, the construction and characteristics of the OA25(56) matrix are described in detail while orthogonality is proved by means of a fourth-order polynomial model. Next, the assignment of experiments in the OA25(56) matrix is illustrated, followed by the data analysis strategy, in which significant/non-significant influence for each factor is quantitatively evaluated by the analysis of variance (ANOVA) technique including the percentage contribution, and the differences among five levels for each factor that has a significant influence are determined by Duncans multiple F-test. Finally, the response surface methodology for the OA25(56) matrix is developed by using the equations obtained from the proof on orthogonality. In the application section, the reaction system for selenium determination by differential-pulse polarography, as a practical example, is employed to demonstrate the application of the OA25(56) matrix in the area of analytical chemistry.

Four-level orthogonal array design as a chemometric approach to the optimization of polarographic reaction system for phosphorus determination.

It is the purpose of the present work to provide information on the four-level orthogonal array design and data analysis for the optimization of analytical procedures. In the theoretical part, the construction and characteristics of the OA(16)(4(5)) matrix is described in detail, followed by the data analysis strategy, in which the significance of the different factors is quantitatively evaluated by an analysis of variance (ANOVA) method including per cent contribution, and the difference among four levels for each factor is determined by Duncans multiple F test. Furthermore, a third-order polynomial model representing response surface is established to estimate the effects for the factors with significant influences. In the application part, the proposed four-level orthogonal array design and data analysis method were applied to optimize polarographic reaction system for phosphorus determination. By conducting 16 preplanned experiments that span the maximum working range of the system, the best experimental conditions for achieving the largest response can be obtained. The expected value for each experimental trial calculated by the third-order regression equation established is in good agreement with the corresponding experimental value. To confirm the validity of the optimization procedure, additional experiments using the recommended conditions were performed. The results demonstrate that satisfactory results can be acquired. Therefore, the proposed four-level orthogonal array design as a chemometric approach to optimize the polarographic reaction system for phosphorus determination is rather efficient and effective.

Comparison of four microwave digestion methods for the determination of selenium in fish tissue by using hydride generation atomic absorption spectrometry

Four microwave digestion methods of fish tissue for selenium determination by hydride generation atomic absorption spectrometry were compared, in which potassium hexacyanoferrate(III) was chosen as a masking agent for eliminating matrix interferences. The results showed that the methods employing HNO(3)/H(2)O(2), HNO(3)/K(2)S(2)O(8)/H(2)O(2) and HNO(3)/H(3)PO(4)/H(2)O(2) digestion media were unreliable. However, the decomposition using the digestion media of HNO(3)/H(2)SO(4)/H(2)O(2) enabled adequate digestion of fish tissue and retention of selenium in a state amenable for determination. Therefore, the digestion procedures with HNO(3)/H(2)SO(4)/H(2)O(2) media are proposed for the determination of selenium in fish tissue by hydride generation atomic absorption spectrometry. The recoveries of the spiked samples investigated ranged from 90 to 102%. The result obtained from analyzing the NIES CRM No. 6 mussel was in good agreement with the reference value (reference value: 1.5 mug/g; found: 1.45 +/- 0.05 mug/g). The limit of detection for selenium was 0.03 mug/g dry mass for a 100 mg sample. The contents of selenium in local fish species investigated ranged from 0.49 to 2.90 mug/g, and the relative standard deviation for the determination of selenium was less than 8%.

Optimization of liquid chromatographic parameters for the separation of priority phenols by using mixed-level orthogonal array design

Abstract Mixed-level orthogonal array design (OAD) as a chemometric method has been employed to optimize liquid Chromatographic (LC) conditions for the separation of environmental pollutants. Six parameters were examined by OAD, namely reversed-phase (C18) LC columns from different manufacturers, content of methanol and acetonitrile in the mobile phase, initial time-duration of a fixed mobile phase composition, time-duration of a gradient elution programme, and mobile phase flow rate. The optimization of these parameters for the determination of eleven priority substituted phenols was carried out to demonstrate the applicability of mixed-level OAD in environmental analytical chemistry in which the use of trial-and-error procedures is often unsatisfactory due to sample complexity. The advantages and the disadvantages of mixed-level OAD were discussed.

Microwave digestion of fish tissue for selenium determination by differential pulse polarography

In KIO(3)NH(3)NH(4)Cl medium, the selenium complex Se(O)SO(2-)(3), resulted from the reaction of selenite and sulphite in acid solution, gave a catalytic wave, which was applied to the determination of selenium in fish by differential pulse polarography. The sample was decomposed using the HNO(3)/H(2)SO(4)/H(2)O(2) digestion mixture in a closed PTFE digestion vessel with microwave heating. The detection limit was 0.06 mug/dm(3). The calibration curve was linear up to 8 mug/dm(3). Selenate present was reduced with hot hydrochloric acid to selenite. The recoveries of the selenite and selenate in two spiked samples investigated ranged from 91 to 104%. The NIES CRM No. 6 mussel was analyzed and the results obtained agreed well with the reference value (reference value: 1.5 mug/g; found: 1.43 +/- 0.05 mug/g). The results obtained by differential pulse polarography were in good agreement with those found by hydride generation atomic absorption spectrometry.

In vitro effect of mercuric chloride on ATPase activity in kidney of the fancy carp Cyprinus carpio

Abstract 1. The Na+/K+-ATPase and Mg2+-ATPase activity of fancy carp (Cyprinus carpio) kidney homogenate without the presence of EDTA was significantly inhibited by mercuric chloride in a concentration-dependent manner. 2. The Na+/K+-ATPase and Mg2+-ATPase activity of fancy carp (Cyprinus carpio) kidney homogenate in the presence of EDTA showed no significant change with the increasing concentration of mercuric chloride. 3. The sensitivity of Na+/K+-ATPase to mercuric chloride was greater than that of the Mg2+-ATPase. 4. In conclusion, the use of EDTA in the determination of the effect of heavy metal on the ATPase activity as a toxicological index should be avoided. Using Na+/K +-ATPase activity as a toxicological index in the studies of heavy metal effect is better than using Mg2+-ATPase activity.

Kinetic studies of mercuric chloride on Na+K+-ATPase in the kidney of fancy carp, Cyprinus carpio

Abstract 1. 1. The effect of mercuric chloride on the substrate and ionic activation kinetics of Na + K + -ATPase activity in the kidney of fancy carp ( Cyprinus carpio ) was determined. 2. 2. Mercuric inhibition was shown to be a classical competitive nature with respect to substrate ATP activated Na + K + -ATPase , in that the apparent K m values were increased without a significant change in the apparent V max values. 3. 3. Mercuric inhibition was a mixed noncompetitive nature with respect to Na + -activated Na + K + -ATPase , where the apparent K m values were increased but the apparent V max values were decreased. 4. 4. Mercuric inhibition was a pure noncompetitive nature with respect to Mg 2+ and K + -activated Na + K + -ATPase , in that the apparent V max values were decreased but not the apparent K m values. 5. 5. Based on the above results, we proposed a possible kinetic model for elucidating the biochemical mechanism of inhibition of mercuric chloride on Na + K + -ATPase in the kidney of fancy carp.