Cholesterol / Cholesterylester - ESI-MS/MS - Liebisch et al.
From LipidomicsWiki
Contents |
Sample preparation
- Lipid extraction according to Bligh and Dyer
- internal standards are added prior lipid extraction
- to avoid the loss of lipids, extraction was performed in glassware
- samples are dissolved in methanol containing 10 mM ammonium acetate/chloroform (3/1 = v/v)
Material | Material used | Internal Standard(s) | Internal Standard(s) added |
---|---|---|---|
Cultured cells | 100µg protein | D7-FC, CE 17:0, CE 22:0 | 3000ng D7-FC; 500ng each CE 17:0, CE 22:0 |
Human plasma | 20µl | D7-FC, CE 17:0, CE 22:0 | 10µg each D7-FC, CE 17:0, CE 22:0 |
Instrumentation and method
Pump
- Type: binary high pressure gradient (Agilent 1100)
- Mode: isocratic flow gradient
- Solvent(s): Methanol containing 10 mM ammonium acetate/chloroform (3/1 = v/v)
- Flow gradient:
Time [min] | Flow [ml/min] | % Solvent A | % Solvent B |
---|---|---|---|
0 | 0.05 | 100 | 0 |
0.1 | 0.03 | 100 | 0 |
1.1 | 0.2 | 100 | 0 |
1.3 | 0.05 | 100 | 0 |
Autosampler
- Type: CTC Pal
- Injection volume: 20µl
- Wash solvent: methanol/chloroform = 1/1
Mass spectrometer
- Type: Triple quadrupole (Micromass, Quattro Ultima)
- Ionization mode: ESI positive
- Ionization voltage: 3500 V
- Source temperature: 220°C
- Collision gas: Argon
- Collision gas pressure: 1.0 10-3 Torr
- Collision energy: 13 V
- MS/MS-mode:
- selected reaction monitoring (SRM) for acetylated free cholesterol (FC) and D7-FC
- precursor ion scan m/z 369.3 for cholesteryl ester (CE species)
Analyte | Precursor [m/z] | Precursor [m/z] | Collision energy [eV] |
---|---|---|---|
CE 2:0 (acetylated FC) | 446.4 | 369.3 | 13 V |
D7-CE 2:0 (acetylated D7-FC) (IS) | 453.4 | 376.3 | 13 V |
CE species | Scan 610 - 730 | 369.3 | 13 V |
Data analysis and quantification
Data handling
- combine spectra above half peak height
- smooth combined spectrum (if necessary)
- centroid combined spectrum
- pick peak intensities
Isotope correction
- using Excel Macros correcting the peak intensities in a sequential algorithm starting from low mass species
- five isotope peaks including the monoisotopic were used
- the detailed algorithm is described in the appendix of Liebisch et al. Biochim Biophys Acta. 2004 Nov 8;1686(1-2):108-17.
Calibration and quantification
- calibration type: matrix calibration - addition of naturally occurring species
- species used for calibration
Species | Cultured cells | Human plasma |
---|---|---|
FC | 0 - 3 nmol | 0 - 10 nmol |
CE 16:0 | 0 - 500 pmol | 0 - 10 nmol |
CE 18:0 | 0 - 500 pmol | 0 - 10 nmol |
CE 18:1 | 0 - 500 pmol | 0 - 10 nmol |
CE 18:2 | 0 - 500 pmol | 0 - 10 nmol |
Method validation
Precision
- CV within-run: 3 %(major), 5-10 % (minor)
- CV total: 10 % (major), 15-20 % (minor)
LOD
- 0.5 µM in plasma