E largest peak areas when the mass of anhydrous sodium sulfate

E largest peak areas when the mass of anhydrous sodium sulfate

E largest peak areas when the mass of anhydrous sodium sulfate used was 4 g. doi:10.1371/journal.pone.0060858.gmeans of a Doehlert design, while the other parameters of the derivatization process (concentration and volume of Na2SO4 solution and acidic methanol, volume of saturated NaHCO3 solution) were optimized using two sequential experimental designs: a fractional factorial 25 design involving 32 experiments was applied to establish the relative influence of the factors and a Doehlert experimental design was developed to study the most significant factors. The volume of organic solvent (MTBE) was optimized by a single factor with three-level statistical analysis.Derivatization Temperature and TimeDerivatization temperature and time were two critical factors affecting derivatization efficiency and one study suggested that an increase of these two factors could increase the derivatization efficiency of HAA9, especially trihaloacetic acids (TXAAs) [25]. However, an unlimited increase of derivatization temperature andtime leads to lengthening the operation time and excessively high temperature may result in the loss of the derivatives because of the volatility of MTBE. Moreover, previous research did not consider IAA detection and the conditions may not be suitable for IAA determination. In this study, a Doehlert design was used to optimize derivatization temperature and time, with the peak area of each analyte being the response variable (Y). P values of all the models and coefficients were less than 0.05 and P values of the lack of fit were greater than 0.05, which meant that the models and coefficients in this experiment were statistically significant. A 3D response surface figure obtained from the software demonstrated that the impact of the derivatization temperature on the efficiency of IAA derivatization was significantly greater than the impact of derivatization time (Fig. 1). There was a small interaction between derivatization time and temperature and these two factors had negative effects onFigure 4.Ketoconazole 3D response surface of IAA for optimization of extraction time and mass of anhydrous sodium sulfate.SPP1 Protein, Human (HEK 293, His) X1 was the mass of anhydrous sodium sulfate (g), X2 was extraction time (min) and Y was the peak area of IAA. doi:10.1371/journal.pone.0060858.gPLOS ONE | www.plosone.orgDetecting IAA, IF, THM4, and HAA9 in WaterFigure 5. Chromatogram of IF and THM4. The concentration of each THM was 10 mg/L and that of IF was 1.0 mg/L. 1 stood for CF, 2 was BDCM, 3 was CDBM, 4 was BF, 5 was the internal standard (bromofluorobenzene) and 6 was IF. doi:10.1371/journal.pone.0060858.gderivatization efficiency. Low temperature and short time enhanced the generation of IAA derivative. On the basis of these responses (peak area counts), a second-order model suitable for predicting the responses in all experimental regions was obtained: Y = +5166.PMID:25105126 962496.62X125773.62X2+337.05X1X2+2131.56X12 where Y was the IAA peak area, and X1 and X2 corresponded to derivatization time and temperature, respectively. However, decreasing the derivatization time and temperature affects the derivatization efficiency of dihaloacetic acids (DXAAs) and trihaloacetic acids (TXAAs). The models and 3D response surfaces (Table S5) indicated that the derivatization efficiency of CAA and BAA decreased with increasing temperature while that of DXAAs and TXAAs exhibited a bell-shaped curve in relation to temperature. DXAAs and TXAAs had the highest derivatization efficiency between 40uC.

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