Other Principles

The preceding principles do not represent an exhaustive list. Certainly, there are other chemical principles that contribute to the extraction process, but play a more minor role. Some of these are discussed briefly below.

Time A longer extraction time will usually produce better recoveries, but this effect assumes that the

Table 4 Total per cent recovery as a function of ft, D and number of extractions

Phase ratio

D

After 1st

After 2nd

After3rd

After4th

ß=V2lV1

extraction

extraction

extraction

extraction

1/1

1

50

75

88

94

2

67

89

96

10

91

99

100

99

1/4

1

20

36

49

59

2

33

56

70

80

10

71

92

98

99

100

96

99

1/10

1

9

17

25

32

2

17

31

42

52

10

50

75

100

91

99

Reproduced with permission of ACCTA, Inc.

Reproduced with permission of ACCTA, Inc.

analytes, reagents and solvents are nonvolatile, stable and do not react with each other. If these assumptions are not valid, longer extraction times may actually produce poorer recoveries.

Ionic strength The addition of ionic species to an aqueous solution results in a 'salting-out' effect. This procedure often enhances extraction of neutral organic analytes from water by increasing D.

Surface area Reducing the particle size of a solid matrix, thereby increasing contact areas between phases, can cause a dramatic increase in extraction rates.

Stirring/mixing Adequate stirring enhances the rate of procedures that are otherwise limited by diffusion processes.

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