# Comparison of Automated Extraction Techniques for Volatile Analysis of Whole Milk Powder
## 3 Results and Discussion
### The Percentage of Each Chemical Class Extracted from Whole Milk Powder by Each Technique  
Figure 1a is histogram highlighting the breakdown of the percentage of each chemical class extracted by each of the four techniques using the non-polar GC column with and without salting out. Figure 1b is the corresponding figure for the polar GC column. It is immediately apparent that significant differences existed in relation to the type and percentage of each chemical class extracted by each technique, influenced by GC column polarity and, to a lesser extent, salting out. All DI-HiSorb techniques (DI-HiSorb S and DI-HiSorb NS), independent of GC column polarity, were characterized by the large volume of lactones extracted (>82%), which differs considerably to all of the other extraction techniques. A similar result was found for SBSE, which is a comparable technique to DI-HiSorb that also used PDMS as the sorbent phase [19]. The only other significant number of chemical classes extracted by DI-HiSorb NS were aldehydes, ketones, and furans, but DI-HiSorb NS did not extract any alcohols, sulphur compounds, acids, terpenes, or esters with the non-polar GC column (but did extract low levels, from 0.5-0.63%, with the polar GC column). The DI-HiSorb S slightly modified the percentage recovery of some chemical classes in comparison to the DI-HiSorb NS. The percentages of chemical classes extracted by DI-HiSorb (DI-HiSorb S and DI-HiSorb NS) using the non-polar GC column were similar independent of salting out (although slightly more alcohols were extracted with salting out). The percentage of each chemical class extracted by HS-HiSorb (HS-HiSorb S and HS-HiSorb NS) for each GC column polarity differed considerably to that attained by DI-HiSorb. This same trend was also apparent when comparing HSSE (similar to HS-HiSorb) and SBSE (similar to DI-HiSorb) [19]. HS-HiSorb S and HS-HiSorb NS attained a much lower percentage of lactones on the polar GC column (~14-20%) and with the non-polar GC column (~5-6%) than DI-HiSorb S and DI-HiSorb NS. HS-HiSorb S and HS-HiSorb NS had a much higher percentage recovery of aldehydes (~42-48%) than DI-HiSorb S and DI-HiSorb NS across both GC column polarities. The percentage of ketones extracted by HS-HiSorb S and HS-HiSorb NS varied considerably depending upon GC column polarity with levels at ~32-35% with the non-polar GC column, and ~14-19% with the polar GC column. The greatest difference in the percentage recovery of chemical classes between HS-HiSorb S and HS-HiSorb NS in relation to GC column polarity, apart from lactones, was for the recovery of furans, with only 1-2% recovered using the non-polar GC column, but \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & & \multicolumn{4}{c}{**NON-POLAR GC COLUM**} \\
**Extraction Technique** & **HS-SPME S** & **TD S** & **Di-HiSorb S** & **HS-HiSorb S** & **HS-SPME NS** & **TD NS** & **Di-HiSorb NS** & **HS-HiSorb NS** \\ \hline No of VOCs & 28 & 34 & 49 & 46 & 25 & 36 & 51 & 42 \\ Abundance \% & 1.7 & 1.3 & 34.2 & 7.5 & 3.9 & 2.2 & 100 & 11.6 \\ Average RSD \% & 39.3 & 33.7 & 45.3 & 33.5 & 38.3 & 38.1 & 40.5 & 35.2 \\ \hline \multicolumn{8}{c}{**POLAR GC COLUM**} \\
**Extraction Technique** & **HS-SPME S** & **TD S** & **Di-HiSorb S** & **HS-HiSorb S** & **HS-SPME NS** & **TD NS** & **Di-HiSorb NS** & **HS-HiSorb NS** \\ \hline No of VOCs & 23 & 28 & 23 & 19 & 17 & 25 & 22 & 16 \\ Abundance \% & 1.2 & 2.5 & 39.7 & 4 & 1.3 & 3.1 & 100 & 7.7 \\ Average RSD \% & 37.4 & 39.1 & 37.6 & 71.1 & 63.8 & 32.5 & 34.6 & 90 \\ \hline \end{tabular}  
* No. of VOCs (number of volatile organic compounds). Abundance %, (the greatest abundance achieved by a single extraction technique equated to 100% and the remaining extraction techniques were expressed as a percentage thereof). Average RSD % (the average percentage relative standard deviation of all VOCs for extraction technique).  
\end{table}