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Frozen samples, can it affect my analysis?

 

We have been asked recently by customers what possible effects could be seen with samples freezing in extreme conditons.

The first thing we should say is that in the 10 years that we have been testing we have never had a sample arrive at the lab frozen, that's not to say of course that it can't happen.

We prepared a solution for testing that we spiked with trace elements as we felt that just testing a standard seawater sample would be pointless, for many of the trace elements are at such low levels or do not appear it would not be possible to observe them. We have taken three samples from this solution, Sample A001 which will be left at normal temperature (22°C), Sample A002 which will be frozen in liquid nitrogen at -198°C, and A003 which will be frozen to -10°C. The two frozen samples will then be viewed against the A001 Blank for comparrison.

 

 

 

Sample 1

A001

Blank

Sample 2

A002

-198

Sample 3

A003 

-10

Observed change 

A001-A002

Observed change 

A001-A003

Sodium (mg/l)

10734

10729

10731

-5

-3

Magnesium (mg/l)

1359

1357

1364

-2

5

Calcium (mg/l)

429

433

429

4

0

Potassium (mg/l)

379

382

378

3

-1

Bromide (mg/l)

57

59

59

2

2

Strontium (mg/l)

8.087

8.262

8.039

0.175

-0.048

Boron (mg/l)

3.856

3.987

3.933

0.131

0.077

Sulphur (mg/l)

937

931

932

-6

-5

Lithium (µg/l)

425

424

425

-1

0

Beryllium (µg/l)

73

72

71

-1

-2

Barium (µg/l)

90

92

92

2

2

Titanium (µg/l)

23

22

21

-1

-2

Vanadium (µg/l)

66

66

65

0

-1

Chromium (µg/l)

23

21

22

-2

-1

Manganese (µg/l)

67

73

72

6

5

Iron (µg/l)

19

16

16

-3

-3

Cobalt (µg/l)

72

75

74

3

2

Nickel (µg/l)

72

74

74

2

2

Copper (µg/l)

49

52

49

3

0

Zinc (µg/l)

94

99

98

5

4

Aluminium (µg/l)

52

48

49

-4

-3

Silicon (µg/l)

506

523

511

17

5

Arsenic (µg/l)

72

76

74

4

2

Antimony (µg/l)

73

75

73

2

0

Tin (µg/l)

40

50

46

10

6

Cadmium (µg/l)

67

68

67

1

0

Selenium (µg/l)

62

72

64

10

2

Molybdenum (µg/l)

89

89

88

0

-1

Mercury (µg/l)

89

94

88

5

-1

Phosphorus (µg/l)

49

51

48

2

-1

Lead (µg/l)

31

34

30

3

-1

Iodine (µg/l)

62

62

61

0

-1

Tungsten (µg/l)*

0

0

0

0

0

Lanthanum (µg/l)*

0

0

0

0

0

Scandium (µg/l)*

0

0

0

0

0

*Elements unable to be spiked in the sample solution

 

Simple conclusion

Even freezing samples lower than -40°C and shock freezed with liquid nitrogen did not show any significant effect on our testing method and it’s usability in reef aquariums.

Tested for macro elements and as many trace elements as possible in seawater. 

Some of the elements that normally tend to decrease in a sample over time, for example Mercury, Tin, Selenium, and Manganese show possible better recovery. Further testing is needed to asses a real benefit of freezing samples prior to analysis. For this reason we will redo this testing with the samples A002 and A003 remaining in a frozen state for two weeks.

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So in simple terms, no, samples being exposed to freezing conditions does not significatly change your analysis.