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Losses of chlorophylls and carotenoids in aqueous acetone and methanol extracts prepared for RP- HPLC analysis of pigments Dr. K. van Lenning Institute.

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Presentation on theme: "Losses of chlorophylls and carotenoids in aqueous acetone and methanol extracts prepared for RP- HPLC analysis of pigments Dr. K. van Lenning Institute."— Presentation transcript:

1 Losses of chlorophylls and carotenoids in aqueous acetone and methanol extracts prepared for RP- HPLC analysis of pigments Dr. K. van Lenning Institute of Marine Science ICM-CSIC, Barcelona published in Chromatographia - April 2001 M. Latasa, K. van Lenning, J. L. Garrido, R. Scharek, M. Estrada, F. Rodríguez and M. Zapata

2 2 4: Extraction (acetone or methanol) 1: Sample collection at sea (volume usually limited) 2: Filtration on board (25 or 47 mm GF/F) 3: Storage until extraction (liquid N 2 or fridge) 5: Pigment analyses (RP-HPLC procedures) 4: Extraction (is methanol really the best option?)

3 3 Minimum solvent volume wanted to achieve high concentrations - determined by filter size Large injection volumes wanted.... May cause peak distortion May cause peak distortion 4: Extraction (is methanol really the best option?)

4 4 Peak distortion; solutions and consequences Related to differences between extraction solvent and initial mobile phase composition; strength, viscosity,... ? We do not know Two solutions 1: Reduce injection volume and/or 2: Dilute sample with water Dilute sample with water: risky!

5 Solvent- and time dependant losses of individual compounds 1: Maximum sample dilution permitted 2: Best solvent for storage and injection 5 Dilute sample with water Pigments dissolve in organic solvents, but not in water “Critical dilution rate” expected (polar- and nonpolar pigments) Higher dilution rates: larger injection volumes in HPLC (frequently 1: :1)

6 6 1 Influence of dilution rates on pigment losses in acetone and methanol extracts. a: Extract Emiliania huxleyi and Dunaliella tertiolecta in 100% organic solvent and inject small volume. b: Dilute extracts (to 90%, 80%,....) and inject directly in HPLC. c: Keep diluted extracts in refrigerated autosampler (4ºC) and reinject entire range after 24 and 48 hours. d: Establish critical dilution rate and maximum storage time in autosampler. Experiment consisted of 1 main and 2 additional parts: Experiments with E. Hux and D. tertiolecta in acetone or methanol were performed individually under subdued light conditions

7 7 2 Check if the observed anomalies in first injection of diluted samples were induced by losses in the 100% extracts prior to water addition. a: Prepare new extracts of E. huxleyi and D. tertiolecta (first 100% acetone, than methanol). b: Inject fresh extracts directly in HPLC. c: Fill 23 additional vials, keep them in autosampler at 4ºC, and inject as time series.

8 8 3 Check if observed anomalies of diluted samples were related to chromatographic problems. a: Prepare new extracts of E. huxleyi and D. tertiolecta (first 100% acetone, than methanol). b: Measure absorption of red (mainly Chls a and b) and blue light (all pigments) using a spectrophotometer. c: Dilute to same range employed for HPLC experiment and measure red and blue absorption directly. d: Keep samples at 4ºC, and repeat readings after 30, 75, 180, 360 min (6 h), 24 h and 48 h. This quick approach confirmed losses observed by HPLC and results will not be presented.

9 Chlorophyll a Carotenes Total Chl c 3 19’Hex-fucoxanthin Chlorophyll c 2 Time (hours) - symbols indicate injections Differences time zero (%) Time series Emiliania huxleyi extracted in 100% acetone 9 Deviations  5% were attributed to equipment and sample treatment

10 10 First injection: t = 0 Emiliania huxleyi extracted in acetone, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences

11 11 Emiliania huxleyi extracted in acetone, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences Second injection: t = 24 hours

12 12 Emiliania huxleyi extracted in acetone, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences Third injection: t = 48 hours

13 Differences time zero (%) Time (hours) Chlorophyll a Carotenes Chlorophyll b Violaxanthin Lutein Time series Dunaliella tertiolecta extracted in 100% acetone 13

14 14 = Differences larger than 5% 123 = Dilution rate with maximum differences Dunaliella tertiolecta extracted in acetone, diluted with water First injection: t = 0 hours

15 15 Dunaliella tertiolecta extracted in acetone, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences Second injection: t = 24 hours

16 16 Dunaliella tertiolecta extracted in acetone, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences Third injection: t = 48 hours

17 Differences time zero (%) Time (hours) Chlorophyll a Carotenes Chlorophyll b Violaxanthin Lutein Time series Dunaliella tertiolecta extracted in 100% methanol 17

18 18 Dunaliella tertiolecta extracted in methanol, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences First injection: t = 0 hours

19 19 Dunaliella tertiolecta extracted in methanol, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences Second injection: t = 24 hours

20 20 Dunaliella tertiolecta extracted in methanol, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences Third injection: t = 48 hours

21 Time series Emiliania huxleyi extracted in 100% methanol Chlorophyll a Carotenes Total Chl c 3 19’Hex-fucoxanthin Chlorophyll c 2 Differences time zero (%) Time (hours) 21

22 22 First injection: t = 0 Emiliania huxleyi extracted in methanol, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences

23 23 Emiliania huxleyi extracted in methanol, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences Second injection: t = 24

24 24 Emiliania huxleyi extracted in methanol, diluted with water = Differences larger than 5% 123 = Dilution rate with maximum differences Third injection: t = 48

25 Conclusions: 1: Concentrations of pigments only remain stable for at least 24 h in 80% and 90% acetone. This obviously excludes the use of methanol when *normal autoinjectors are involved. 2: The acetone range can be extended to 70% and 100% when injecting fresh extracts immediately after dilution step. Such procedures also allow the use of methanol ( % range). 3: Extended ranges are valid for up to 24 h when concentrations of ,  - and ,  -carotenes are not considered to be important. 4: Amount of pigment losses due to degradation or precipitation may vary between experiments, but tendencies always hold true and can be observed directly or within a few hours. *no automatic sample dilution prior to injection possible

26 Recommendations: 1: The established limits of the “safe” dilution rates are critical and seawater volumes retained by the filters are thus very important. Individuals should check their own limits for which they may (initially) employ a spectrophotometric approach. 2: An HPLC setup should preferably include a refrigerated auto- injector capable of sample dilution prior to injection. 3: In this case it is safe to use a final concentration of % acetone for sample storage at 4ºC (reliable up to at least 48 h), diluted to 70% before injection (maximum injection volume in HPLC without risk of pigment losses at t=0).

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