Rapid In Situ Esterification Method for the Determination of Benzoic Acid in Dairy Milk by GC-FID
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Rapid In Situ Esterification Method for the Determination of Benzoic Acid in Dairy Milk by GC-FID Sana Jawaid & Farah N. Talpur & Shafi M. Nizamani & Nusrat N. Memon & Hassan Imran Afridi & Abid A. Khaskheli
Received: 20 June 2014 / Accepted: 13 October 2014 # Springer Science+Business Media New York 2014
Abstract An efficient and simple in situ ultrasonic assisted esterification method has been developed for gas chromatographic determination of benzoic acid (BA) in raw and processed milk samples. For optimization of variables, chemometric approach was employed using Plackett–Burman design (PBD) and face-centered central composite design (FCCCD). Firstly, major factors affecting benzoic acid methyl ester (BAME) yield, i.e., BA concentration, volume of methanol, sonication time, amount of milk, and sulfuric acid, were studied with PBD. After screening significant factors, further optimization was carried out with FCCCD. Analysis of variance (ANOVA) of the quadratic model demonstrated that BA concentration, interaction factors of BA with sulfuric acid, and methanol volume significantly (p F
The FCCC design contains an entrenched factorial design with center points. It is used to find the best set of values for a set of factors giving an optimal response. In this mathematical approach, the design helps in exploring quadratic surface
Model A2 AC CD Residual Cor total
6394.72 2814.30 964.10 2616.32 878.16 7272.88
3 1 1 1 7 10
2131.57 2814.30 964.10 2616.32 125.45
16.99 22.43 7.69 20.86
0.0014a 0.0021a 0.0276a 0.0026a
Std. Dev. Mean CV % PRESS
1.20 48.18 3.25 2143.17
R2 Adj R2 Pred R2 Adeq precision
Table 1 Variables used in Plackett–Burman design with their corresponding lower and higher levels Variable code Variables
Units
Low (−) High (+)
A B C D E
mg L−1 mL mL mL min
0.05 3 1 3 15
Benzoic acid concentration Amount of milk Amount of sulfuric acid Volume of methanol Sonication time
2.5 10 3 10 60
a
0.8793 0.8275 0.7053 12.17
Significant
A benzoic acid concentration, C amount of sulfuric acid, D amount of methanol
Food Anal. Methods
Fig. 1 Three-dimensional response surface graphs of the interaction between a benzoic acid concentration and sulfuric acid and b amount of sulfuric acid and volume of methanol
Results and Discussion Five factors were used to optimize the %yield of BAME such as BA concentration (A), amount of milk (B), amount of sulfuric acid (C), volume of methanol (D), and sonication time (E) by Plackett–Burman design. These factors and their low (−) and high (+) levels are described in Table 1. The quantitative yield of BAME 13.44–98.12 % was obtained with proposed in situ method, and the standardized effects of variables were visualized by using a Pareto chart that shows the factors A, C, and D imply the significant effect on the %yield of BAME. From inference test, the results produced a minimum t value of 2.45 at 95.0 % confidence interval and we consider that a factor is significant when the t value for a certain factor is higher than 2.45. ANOVA showed that the most signifi
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