# 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 2a relates to each chemical class with and without salting out using the non-polar GC column. The total level of discrimination was 44.8% (PCA 1 23.6% and PCA 2 20.6%). It is immediately apparent that salting out did not have a major impact on the individual extraction techniques, as with and without salting out (S and NS) for each technique are very closely associated with each other. Both DI-HiSorb S and DI-HiSorb NS were most strongly associated with lactones as previously mentioned, and were separate from HS-HiSorb S and HS-HiSorb NS, which were not strongly associated with any chemical class, but more so with esters and ketones. Although both HS-HiSorb techniques appeared closely associated with the chemical group acids, this was more a reflection of using the overall percentage of each chemical class data, the fact that only one VOC (acetic acid) made up this chemical class, and due to the relationship of this acid with the other extraction techniques. In fact, HS-HiSorb NS did not extract acetic acid. TD (TD S and TD NS) were most strongly associated with aldehydes, benzene/phenols, alcohols, and ketones, while HS-SPME (HS-SPME S and HS-SPME NS) were most closely associated with terpenes and sulphur compounds. Although the HS-SPME techniques did extract a high percentage of ketones and aldehydes, the association was less obvious as the relationship of these chemical classes to the other extraction techniques  
also influenced their position on the PCA (as stated earlier, the overall percentage of each chemical class data was used to generate the PCA rather than individual VOC). Figure 1: (**a**) The percentage of each chemical class extracted by the four extraction techniques using the non-polar GC column with and without salting out, and (**b**) the percentage of each chemical class extracted by the four extraction techniques using the polar GC column with and without salting out. Direct Immersion HiSorb without salting out (DI-HiSorb NS), Direct Immersion HiSorb with salting out (DI-HiSorb S), Headspace HiSorb without salting out (HS-HiSorb NS), Headspace HiSorb with salting out (HS-HiSorb S), Thermal Desorption without salting out (TD-NS), Thermal Desorption with salting out (TD S), Headspace Solid Phase Microextraction without salting out (HS-SPME NS), Headspace Solid Phase Microextraction with salting out (HS-SPME S). Figure 2: (**a**) Principal component analysis of the volatile organic compounds (as per chemical class) per individual extraction technique, with and without salting out, using the non-polar GC column, and (**b**) principal component analysis of the volatile organic compounds (as per chemical class) per individual extraction technique, with and without salting out, using the polar GC column. Direct Immersion HiSorb without salting out (DI-HiSorb NS), Direct Immersion HiSorb with salting out (DI-HiSorb S),Headspace HiSorb without salting out (HS-HiSorb NS), Headspace HiSorb with salting out (HS-HiSorb S), Thermal Desorption without salting out (TD-NS), Thermal Desorption with salting out (TD S), Headspace Solid Phase Microextraction without salting out (HS-SPME NS), Headspace Solid Phase Microextraction with salting out (HS-SPME S). Figure 2b highlights the same associations of chemical classes with each extraction technique with and without salting out, but using the polar GC column. The level of overall discrimination was less, at 39.7% (PCA 1 22.2% and PCA 2 17.5%), than that achieved in Figure 2a. As acetic acid was found using the polar GC column, the acid chemical class is not present. Some similar patterns are evident with the polar GC column as found with the non-polar GC column. It is also evident that the impact of salting out was minimal due to the close association of each individual technique with and without salting out (S and NS). For the polar GC column, both DI-HiSorb (DI-HiSorb S and DI-HiSorb NS) and HS-HiSorb (HS-HiSorb S and HS-HiSorb NS) were much more closely associated with lactones and furans.