Rapid extraction of total lipids and lipophilic POPs from all EU-regulated foods of animal origin: Smedes’ method revisited and enhanced

Environmental Sciences Europe

Table 2 Sample weight (g), solvent volumes (mL), dispersing and swirl times (s), and expected times for phase separation for various samples of animal origin

	Extraction step	Egg	Egg powder	Fat	Fish	Fish oil^f	Liver	Meat	Milk	Milk powder^g	Milk fat, butter	Infant food
1. Extraction	Sample weight (g)^a	10	2.4^d	1.0	10	1.0	10	15	30	5.0	1.0	20
	Propan-2-ol (mL)^b	32	32	32	32	32	32	48	32	16	32	32
	Cyclohexane (mL)	40	40	40	40	40	40	60	40	20	40	40
	Ultra-Turrax A (s)	10	10	20	10	10	10	20	10	10	10	10
	ddH₂O (mL)	24	24	24	24	24	24	36	22	16	24	24
	Ultra-Turrax B (s)	15	15	30	15	15	15	30	15	15	15	15
	Propan-2-ol (mL)^c	5–10	5–10	5–10	5–10	5–10	5–10	5–10	5–10	–	5–10	5–10
	Circular swirling (s)	5–10	5–10	5–10	15–20^e	5–10	15–20^e	5–10	5–10	5–10	5–10	5–10
	Phase separation (s)	< 30	< 30	< 30	2–3 min	< 30	2–3 min	< 30	< 30	< 30	< 30	< 30
2.-3.(4.) Extraction	Repetitions	2	2	2	2–3	1	2–3	2	2	2	2	2
	Cyclohexane (mL)	20	20	20	20	20	20	30	20	14	20	20
	Ultra-Turrax (s)	10	10	15	10	10	10	15	10	10	10	10
	Propan-2-ol (mL)^c	5–10	5–10	5–10	5–10	5–10	5–10	5–10	5–10	–^h	5–10	5–10
	Circular swirling (s)	5	5	5	5–10	5–10	5–10	5–10	5–10	5–10	5–10	5–10
	Phase separation (s)	< 30	< 30	< 30	1–2 min	< 30	1–2 min	< 30	< 30	< 30	< 30	< 30

^aExample weight, adjust solvent volumes for other sample weights. For sample weights (except fat) < 5 g use volumes as calculated for 5 g
^bBefore adding cyclohexane, mix sample with propan-2-ol by gentle swirling
^cRinse sample remains sticking to the dispersing element back into sample vessel with propan-2-ol (enlarge volume to 10 mL if required)
^dEgg powder (dried): soak in 7.6 mL ddH₂O (for 76% water content) prior to extraction
^eIf, in rare cases, an organic phase (≥ 10 mL) does not separate at the top of the mixture by (repeated) swirling, alternatively the mixture can be centrifuged
^fExtraction is advised only if clean extracts are required for follow-up ultra-trace analysis of POPs
^gWhole milk powder. Adjust sample weight and volumes for semi-skimmed or skimmed milk powders
^hUse 7–10 mL cyclohexane to rinse sample remains sticking to the dispersing element into sample vessel, then add 2–3 mL propan-2-ol for phase separation