an introduction to liquid chromatography mass spectrometry · • liquid chromatography-mass...

An Introduction to Liquid Chromatography Mass Spectrometry

Dr Kersti Karu email: [email protected]

Office number: Room LG11

Recommended Textbook:

“Analytical Chemistry”, G. D. Christian, P. K. Dasgupta, K.A. Schug, Wiley, 7th Edition

“Trace Quantitative Analysis by Mass Spectrometry”, R.K. Boyd, C.Basic, R.A. Bethem, Wiley

mailto:[email protected]

Applications

Qualitative and quantitative measurements for many

fields:- clinical, environmental, food, geographical

regions, forensic and etc.

Lecture Overview

• Rate theory of HPLC van Deemter equation

• Principle of LC analysis

– HPLC subclasses

– Stationary phases in HPLC

– LC columns

• Liquid chromatography-mass spectrometry (LC-MS)

– Separation process in reversed-phase liquid chromatography

– Electrospray ionisation (ESI) source

– Taylor cone formation occurs both at the end of the ESI tube and

as the droplets disintegrate to release ions.

– Quadrupole ion trap (QIT) analyser

– Injection of ions into an orthogonal TOF analyser

– Principle of orthogonal TOF analysers with V and W geometries

– Orbitrap analyser

– Tandem mass spectrometry

• LC-MS application sterolomics analysis

• Brief introduction to phytosterol analysis

Principles of LC-MS analysis

• HPLC flow rate 1-2 mL/min, 4.6 mm ID

column, 3-or 5-µm silica-based particles,

5-30 µL injection.

• Capillary LC flow rate 200 µL/min, 1 mm ID

column, 1.5- to 3-µm silica-based particles,

1-5 µL injection

• Nano LC flow rate 200 nL/min, 0.1 mm ID

column, 3-µm silica-based particles, 0.1-2

µL injection

• UHPLC systems (ultra-high-pressure liquid

chromatography) 0.3 - 1 mL/min, 1.5- to 3-

µm silica-based particles capable of

pumping at 15,000 psi.

Basic components of an HPLC system

Principle of separation in HPLC

In HPLC, analytes are

separated based on their

differential affinity between a

solid stationary phase and a

liquid mobile phase. The

kinetics of distribution of

analytes between the

stationary and the mobile

phase is largely diffusion-

controlled.

To minimise the time required for the interaction of the analytes between the mobile

phase and the stationary phase two criteria should be met. (1) the packing material

should be small and as uniformly and densely packed as possible. This criterion is

met by uniformly sized spherical particles and results in a smaller A value in the van

Deemter equation. (2) the stationary phase should be effectively a thin uniform film

with no stagnant pools and provide a small C value. Because molecular diffusion in

liquids is small, the B term is small.

Rate theory of chromatography – the van Deemter equation

The C-term in the van Deemter equation contains both mobile-phase and

stationary phase contributions (Cm and Cs)

The plate height H = A + B/𝑢 + Cm 𝑢 + Cs 𝑢

Except at very low mobile-phase velocities, the longitudinal diffusion term B is

negligible because the diffusional coefficient is very small in the LC. With present

uniform spherical particles of very small particle size (<5 µm) that are tightly and

uniformly packed, the contribution of A term is also very small.

H = Cm 𝑢 + Cs 𝑢

The term Cs is relatively constant at a given k (the retention factor); and Cm

includes stagnant mobile-phase transfer (in the pores of the particles).

Column efficiency is related to

particle size. For well-packed HPLC

columns, H is about two to three

times the mean particle diameter.

H = (2 to 3) x dp

Normal phase chromatography utilises a polar stationary phase and relatively non-polar to

intermediate polarity solvents such as hexane, tetrahydrofuran.

Reversed phase chromatography utilises non-polar stationary phase C18 and polar hydroorganic

solvents, ACN, MeOH, water

Hydrophilic interaction chromatography (HILIC) water is adsorbed on a hydrophilic surface to

provide the partitioning process. This mode of separation suited for highly polar water soluble

analytes. ACN-water is commonly used as the eluent system, in which water is the strong eluent.

Size exclusion chromatography molecules are separated based on their size. The stationary phase

is largely occupied by pores. Molecules that are larger than the largest pores cannot enter any pores

and hence are “excluded” from the pores and come out in the void volume. Molecules that are smaller

than the smallest pores, in contrast, can explore the entire space in the stationary phase and come

out last.

Ion exchange chromatography -ion exchange particles carry fixed positive or negative charges, a

sulfonic acid type resin, for example, has SO3-H+ groups where H+ groups can be exchange for other

cations (cation exchange resin). The electrostatic interaction is governing factor in ion exchange

affinities and hydrophobic interactions play also significant role.

Ion exclusion chromatography like SEC, depends on principles of exclusion to accomplish

separation, all analytes elute within a finite retention window. Weak electrolytes can be separated by

this technique, the dominant application area being the separation of organic acids that can be

separated from strong acids and further separate according to their pKa. For example column with a -

SO3H cation exchange resin. The sulfonate group is fully ionised and the resin matrix is negatively

charged. If consider a weak acid HA, the anion A- will be excluded from the interior of the resin, but no

such penetration barrier exists toward a neutral molecule. The fully ionised elute in the void volume

and other elute in the order of increasing pKa; acids that are largely unionised elute last.

HPLC subclasses

Stationary phases in HPLC

High-purity silica particles, low in trace metal content, <10 µm to <2 µm diameter

particles. Smaller diameter particles create higher back pressure, but they exhibit

very little loss of efficiency at higher flow rates, permitting faster separation.

For analysis of small molecules, polypetides and many proteins, and for very high

molecular weight proteins, particles with respective pore sizes of 60 -150 A°; 200 -

300 A°; and 1,000 - 4,000 A° are usedto allow the analyte to penetrate the pores.

Most HPLC is performed in the liquid-liquid partition mode, the stationary phase is

bonded to the support particles. Microporous particles are commonly used, the

pores being permeable to the analytes and the eluting solvent (c). Most of the

mobile phase moves around the particles. The solute diffuses into the stagnant

mobile phase within the pores to interact with the stationary phase, and then

diffuses out into the bulk mobile phase. The use of small particles minimises the

pathlenght for diffusion and hence band broadening.

• (c) Silica particles have surface silanol groups, SiOH. Silanol groups provide polar

interaction sites. The reaction with monochlorosilane R(CH3)2SiCl, where R

=CH3(CH2)16-CH2- will lead to “C18 silica” stationary phase. The extent to which

silanol groups are functionalised depends on the chain length of the functionalising

agent. The extent of functionalisation is expressed in terms of wt %C (as obtained

by elemental analysis).

• Macroporous-micro/mesoporous structures packings. Pores smaller then

~100A° are referred to as micropores while those larger than ~1000 A° are regarded

as macropores. Pores of intermediate size are mesopores (d). Mostly used for

analysis of large molecules.

• Nonporous packings (b) silica in very small particle size (1.5 µm) as there is no

pores, the pore diffusion and longitudinal diffusion limitations disappear. With very

small particles, the diffusion distance from the mobile to the stationary phase is short;

column efficiency is virtually flow rate independent. However, the pressure needed to

attain a certain flow rate thorough a given column varies inversely as the square of

the particle diameter (the pressure is 1000% higher when the column is packed with

1.5 µm than with 5 µm particles). Nonporous packings have a lower surface area,

limiting how much sample can be injected on column and exhibit lower RT.

• Bonded phases (a) the packing material is composed of an inner fused or non

porous particle core and a porous outer particle shell. Analytes interact with the outer

shell, reducing resistance to mass transfer and providing superior separation

efficiency. Particle size as small as 1.3 µm used.

A monolithic column constitutes of a single solid rod that is

thoroughly permeated by interconnecting pores. As with perfusion

packings, they have a bimodal pore structure. Macropores, which

act as flow-through pores, are about 2 µm in diameter. The silica

skeleton contains mesopores with diameters of about 130 A°. It

can be surface modified with stationary phase like C18. The rod is

shrink-wrapped in a polyetheretherketone (PEEK) plastic holder.

The surface area of the mesopores is about 300 m2/g, and the

total porosity is 80%. The column exhibits a van Deemter curve

close to that for 3.5-µm packed particles, but with a pressure drop

~40% of the packed column run at the same flow rate. Polymeric

monoliths are available in capillary formats from 0.1 to 1 mm in

diameter and up to 250 mm in length.

Stationary phases for hydrophilic interaction chromatography (HILIC) three types

of HILIC phases:- neutral, charged and zwitterionic. The neutral HILIC phase contains

amide or diol functionalities bonded to porous silica. A charged phase exhibits strong

electrostatic interactions and may consist of bare silica or amino, aminoalkyl or

sulfonate functionalities bonded to porous silica. The separation selectivity between

different analytes can be favoured by the electrostatic interactions that are contributing

to the retention with the charged HILIC stationary phases. A zwitterionic bonded phase,

a -O3S(CH2)3-N+(CH3)2CH2- zwitterionic group is the functional entity bonded to a

porous silica support, or a polymeric support for greater pH range.

Monolithic column and HILIC

Sample injection system

LC Columns

Liquid chromatography – mass spectrometry (LC-MS)

A reversed phase LC column contains porous particles coated with an organic stationary phase,

e.g., a C18 hydrocarbon chain. The mobile phase carries analytes around and through the

particles. The order of elution is determined by the length of time individual analytes partitioned in

the stationary phase.

Compounds elute in reverse order of their polarity, the most polar compounds elute earlier.

S1 S1 S2

Separation process in reversed-phase liquid chromatography

analyser

Electrospray ionisation (ESI) source

Two concentric steel tubes carry the liquid and nebulising gas. After nebulisation, additional gas

is used to dry the droplets. As the droplets shrink the charge density increases to the point at

which the droplets are no longer stable and ions are released from the liquid matrix into the

vapour phase. Ions enter the mass analyser at an angle to reduce the entrainment of neutral

molecules.

At low flow rates, such as in nanospray ESI, spontaneous evaporation is sufficient to eliminate

the need for the drying gas.

Stable nebulisation of the liquid flow occurs when a Taylor cone is established at the

tip of the ESI source.

As the droplets are dried the charge density increases resulting in droplet

disintegration either because of Coulombic forces or by distortion to form a Taylor

cone from which ions are released.

Taylor cone formation occurs both at the end of the ESI tube and as the

droplets disintegrate to release ions.

electrode

Ions injected into the trap are held by rf and dc voltages placed on the hyperbolic ring

electrode and end caps. Ions move in a complex sinusoidal path where there are crossover

points. Space-charge effects occur at the crossover points of the ion paths when too many

ions are present. By changing the voltages progressively ions with different m/z values are

ejected sequentially onto the detector, generating spectra. MSMS fragmentation takes place

when a specific m/z is isolated in the trap and excited in the presence of a neutral gas,

providing MS/MS data. The isolation/fragmentation cycle can be repeated to obtain MSn data.

Quadrupole ion trap (QIT) analyser

API focusing pusher

ion source region (pulsed voltage) part of ion beam

direction of ions in the analyser is

composed of horizontal and vertical

components imparted by the source

and pusher voltages.

Ions are generated continuously in API sources, thus, the individual packets of ions required in

TOF analysis must be excised from the ion beam, and accelerated orthogonally into the analyser

using a pulsed pusher voltage. Only part of the continuous ion beam can be sampled as the

excised ion packet must traverses the analyser before another set of ions can be introduced. The

duty cycle of the orthogonal injection process limits the sensitivity of orthogonal TOF instruments.

Injection of ions into an orthogonal TOF analyser

The basic principle of TOF analyser:- pulses of ions are accelerated from the ion source into the

analyser tube, and the time for an ion to travel through a field-free region to the detector is

measured. The time-of-flight for the passage of an ion in a TOF analyser is a function of

momentum, and therefore its m/z. The acceleration voltage and (consequently) the kinetic energy

(momentum), is the same for all ions. Thus those with the lowest m/z will travel fastest and arrive at

the detector first, followed by the sequential arrival of ions with successively higher m/z.

API atmospheric

pressure ionisation

secondary

ion mirror

V geometry W geometry

Ion path

pusher

Ions arriving from the source are accelerated orthogonally into the analyser by a

pulsed voltage from the pusher. Ions separate based on their momenta. As they

travel through the analyser the lightest, fastest, ions (lowest m/z) will arrive at the

detector first.

Some horizontal momentum imparted in the source remains so that ions travel at

an angle into and out of the reflectron thus attaining a characteristic ‘V’ trajectory.

Increasing the distance that the ions travel improves mass resolution, e.g., by

using ‘W’ geometry.

Principle of orthogonal TOF analysers with V and W geometries

induced transient ion input is off center

and oscillate along, the

specially shaped inner

electrode creating a

complex ion path.

Ions, typically from ESI and APCI, are collected in a specialised component

called the C-trap and them injected into the orbitrap as high-speed pulses. Ions

are injected at an angle and offset from the centre of the trap. The momentum of

the ions causes them to orbit around, and oscillate along, the central spindle-like

electrode. The lateral oscillation of the ions along the inner electrode induces a

transient (image) current in the split outer electrode. The recorded image current

is interpreted using Fourier transform analysis to provide m/z values and

intensities.

Orbitrap analyzer

API CID

Principle of a QTOF MS/MS instrument

Ions are produced in an atmospheric pressure ionisation (API) source.

The quadrupole can be used in broad bandpass (q) mode, to pass all ions to the

time-of-flight (TOF) analyser, or in narrow band pass (Q) mode to select an ion with a

specific m/z for collision induced dissociation (CID). The CID cell also has a q

function by which the fragments formed are constrained and transferred to the TOF

analyser. CID fragment ions are separated and collected in the TOF analyser.

Quadrupoles as ion guide (q) the rf voltages can be applied to the quadrupole, but

without being combined with a dc field. Under these conditions all ions, e.g. those

emerging from the ion source that enter the q are transmitted, regardless of their m/z

values.

second

(b) ICR cell

superconducting magnet

The LIT-orbitrap combination can be used for both MS and MSn experiments because the LIT has its own

detector. Additional fragmentation at a different collision energy can be undertaken in a second collision cell.

Products from either collision cell are injected, via the C trap, into the orbitrap where transients are collected for

subsequent FT analysis.

In the LIT-ICRMS, ions from the LIT traverse a set of extended optics into the ICR cell located within a

superconducting magnet. A ramped rf voltage pulse is used to coalesce different m/z values and move them

close to the receiver plates where transients are collected for subsequent FT analysis.

Schematic of a hybrid linear ion trap with an orbitrap or ion

cyclotron resonance (ICR) cell as the second analyzer

High resolution improves accurate mass measurement

Cyclopentanoperhydrophenanthrene skeleton

Natural steroids have

two methyls

5α-Cholestane structure with

IUPAC numbering showing four

fused-ring isoprene structure

STEROIDS

Steroids in Brain

• 25% body’s cholesterol is present in brain

• Cholesterol formed de novo

• 1st step of cholesterol metabolism formation of an

oxysterol

HOOH

Lütjohann Acta Neurol Scand 2006 114 33

24S-Hydroxycholesterol

Cholesterol

Oxysterols in brain

(S)

(R)

HO

(R)

(Z)

(S)

OH

ng/mg ng-pg/mg

(S)

(R)

HO

(S)

(Z)

(R)

OH

(S)

(R)

HO

(R)

(Z)

OH

(S)

(R)

HO

(S)

(R)

(Z) OH

• Transport forms of cholesterol

• Oxysterols are ligands for LXR

• Oxysterols implicated in neurodegenerative

disease (AD)

• Oxysterols formed by reaction with O3 or

ROS as a result of inflammation

HOOH

Björkhem et al Curr Opin Lipidol 2002 13 247

Analytical Strategy

• Extraction: 1st C2H5OH, 2nd CH3OH/CH2Cl2

• Separation: Straight phase

• Derivatisation:

• LC-ES-MSn

HOOH

•Specificity for 3b-OH

•Enhance Solubility

•Enhance Sensitivity

•x 100

Wang et al Anal Chem 2006 78 164

Smith & Brooks J Chromatogr 1974 101 373

360 400 440 480 520 0

20

40

60

80

100 534

385 367

m/z

Rela

tive A

bu

nd

an

ce,

%

Ion Current: 8x107

OH

OH

[M+H]+

m/z 403

[M]+

[M+H-H2O]+

[M+H-2xH2O]+

nano-ESI Mass Spectrum

C5-3β,24S-diol

C4-24S-ol-3-one GP hydrazone

N

N+NH

O

OH

[M]+

m/z 534

Oxysterols in rat brain

300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700m/z0

100

%

518

333

373

534

550

665

100 mg brain

Inject ~ 0.1 mg cholesterol

hydroxycholesterol

dihydroxycholesterol dehydrocholesterol

Direct infusion ESI into the QTOF

m/z 534 [M]+MS2

[M-79-CO]+

[M-79]+

150 200 250 300 350 400 450

m/z

Re

lative A

bu

ndance, %

455

427

437 409 353 163 394 325 231

100

[M-79-H2O]+

C4-24S-ol-3-one GP hydrazone

[M]+ [M-79]+

N

OH

HNN

O

m/z 534 N

OH

HN

O

m/z 455

[M-79-CO]+

N

OH

NH

m/z 427

[M-79-H20]+

N

HN

O

m/z 437

m/z 534 [M]+m/z 455 [M-79]+

MS3

‘*f

‘*e

*b3-C2H4

*b1-12

[M-107]+

*b2

150 200 250 300 350 400

m/z

Rela

tive A

bu

nd

an

ce,

%

437

163

427

151

353

409

394 177 367 325 231 135

[M-79-H2O]+ C4-24S-ol-3-one

GP hydrazone

N

OH

HN

O

m/z 455

-H

'*e

-H'*f

N

HN

O

m/z 151

*b1-12

[M-79]+

*b1-12

*b2HN

HN

CH2

*b2O

CH3

m/z 177

*b3-C2H4

HN

HN

O

m/z 163

*b3-C2H4

Cap-LC Ion Source

Nano-ES Mass Analyser

Ion trap

Detector

Vacuum

Ions

Computer

Ions Signal

Chromatography

• LC-MSn

• Ultimate 3000 HPLC – LTQduo ion trap MS

• PepMap C18 Column (3 µm particles, 180 µm x 150 mm)

• 800 mL/min

• (A) 50% MeOH, 0.1% FA

• (B) 95% MeOH, 0.1% FA

• 30%(B) 80%(B) (80%) 30%(B) 15min 10min 10min

0 20 40

Time (min)

20

60

100

25.8

22.2

23.1 21.9

19.4

19.6

19.1

18.8

16.5 15.4

11.7

N

NHN

O

C4 -7-one-3-one GP

O

N

NHN

O

C4 -24S-ol-3-one GP

(S)

OH

N

NHN

O

C4 -25-ol-3-one GP

OH

N

NHN

O

CO

OH

BA4 -3-one GP

N

NHN

O

C4 -ol-3-one GP

N

NHN

O

(S)

N

NHN

O

C4 -22S-ol-3-one GP

OH

capLC - MS3

N

N+NH

O

OH

C4 -7ß-ol-3-one GP

N

N+NH

O

OH

OH

C4 -7a,27-diol-3-one GP

Chromatography

• LC-MSn

• Surveyor HPLC – LTQ-Orbitrap

• Hypersil GOLD Column (1.9 mm particles, 50 x 2.1 mm)

• 200 mL/min

• (A) 50% MeOH, 0.1% FA

• (B) 95% MeOH, 0.1% FA

• 20%(B) 80%(B) (80%) 20%(B) 7min 5min 4min

ESI_Unisil2_070206_fr1 03/05/2006 18:23:26

RT: 0.00 - 17.00

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Time (min)

0

50

100

0

50

100

0

50

100

0

50

100

0

50

100

0

50

100

0

50

100

0

50

10012.53

12.38

12.91 13.6511.7311.0510.399.18 14.628.197.792.110.48 6.956.12 15.625.17

7.60

6.85 10.239.797.81 10.42

7.35

7.65

7.87 9.48 10.03 10.87 12.38 12.90 14.57

8.88

9.058.488.34 9.23

5.49

6.17 8.996.26 9.377.22 9.96 10.62

5.454.47

5.064.31 5.91 9.20 9.436.45 8.76

10.03

9.23

5.436.15

8.37

6.597.76

NL: 7.89E5

m/z= 518.4079-518.4131 F: FTMS + p ESI Full ms [ 320.00-600.00] MS ESI_Unisil2_070206_fr1

NL: 8.91E5


NL: 5.29E7


NL: 1.95E4


NL: 2.16E5


NL: 3.30E5


NL: 6.34E5


NL: 7.62E4


Data From LTQ-Orbitrap (Exact Mass RIC ±5ppm)

LC-MSn Strategy (m/z 300 - 600)

RT: 0.00 - 17.00

0 2 4 6 8 10 12 14 16

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100 NL: 5.29E7


7.35

7.65

a

N (Z)

(Z)

HNC

O

N

N (Z)(E)

C34H52N3O2+

Exact Mass: 534.40540

HN

ON

C34H52N3O2+


(S)

OH

(S)

OH

Reconstructed ion chromatogram (RIC) fro m/z 534

24S_OH_C #51 RT: 5.45 AV: 1 NL: 5.99E6F: FTMS + p ESI Full ms2 [email protected] [ 145.00-550.00]

150 200 250 300 350 400 450 500 550

m/z

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

455.3630

427.3685

N

HNC

O

N

N

HNC

O

C34H52N3O2+


C29H47N2O2+


OHOH

534MS2

M-79

M-107

534455MS3

24S_OH_C #67-80 RT: 6.36-7.10 AV: 14 NL: 2.03E6F: FTMS + p ESI Full ms3 [email protected] [email protected] [ 125.00-550.00]

150 200 250 300 350 400 450 500 550

m/z

0

10

20

30

40

50

60

70

80

90

100

Re

lative

Ab

un

da

nce

437.3528

427.3686

409.3580353.2591

163.0865

151.0865

394.3471

193.2107

N

HNC

O C29H47N2O2+


N

HNC

O

C29H45N2O+


*b1-12 *b2

*b3-28N

HNC

O

C23H33N2O+


OH'*f

H

M-79-18

*b1-12

*b3-28

*b2

‘*f

M-107

24(S)-hydroxycholesterol

Lanosterol

HOH

H

H

HOH

H

H

4,4-Dimethylcholesta-8(9),14,24-trien-3b-ol

HOH

H

H

Dihydrolanosterol

CYP51A/

Lanosterol-14--demethylase

(EC 1.14.13.70)

3b-Hydroxysterol 24-reductase/

Desmosterol reductase

(EC:1.3.1.72)

4,4-Dimethylcholesta-8(9),14-dien-3b-ol

HOH

H

H

4,4-Dimethylcholesta-8(9),24-dien-3b-ol

HOH

H

H

4,4-Dimethylcholesta-8(9)-en-3b-ol

HOH

H

H

Sterol C14-reductase/

14-Sterol reductase/

3b-Hydroxysterol-14-reductase

(EC 1.3.1.70)

HOH

H

H

Zymosterol

C-4 Methylsterol oxidase/Methylsterol monoxygenase(EC 1.14.13.72)

C4-Sterol decarboxylase/

Sterol-4-carboxylate 3-dehydrogenase

(decarboxylating)

(EC 1.1.1.170)

HOH

H

H

Cholesta-8(9)-en-3b-ol

HOH

H

H

Cholesta-7,24-dien-3b-ol

3b-Hydroxysterol 8,7-isomerase

(EC 5.3.3.5)

HOH

H

H

Lathosterol/

Cholesta-7-en-3b-ol

HO

H

H

7-DehydrodesmosterolHO

H

H

7-Dehydrocholesterol

Lathosterol 5-desaturase/Sterol-C5-desaturase(EC 1.14.21.6)

HO

H

H

Desmosterol HO

H

H

Cholesterol

Sterol 7-reductase/

3b-Hydroxysterol 7-reductase

(EC 1.3.1.21)

(EC 1.14.13.70)

(EC:1.3.1.72)

(EC:1.3.1.72)

(EC:1.3.1.72)

(EC:1.3.1.72)

(EC:1.3.1.72)

(EC:1.3.1.72)

(EC 1.3.1.70)

(EC 1.14.13.72)

(EC 1.1.1.170)

(EC 5.3.3.5)

(EC 1.14.21.6)

(EC 1.3.1.21)

2,3-Oxidosqualene

O

Squalene Epoxidase(EC 1.14.99.7)

Squalene

Squalene Epoxidase(EC 1.14.99.7)

2,3:22,23-DioxidosqualeneO

O

24S,25-EpoxylanosterolHO

H

H

H

O

(EC 1.14.13.70)

HOH

H

H

Lanosterol synthase/OSC/2,3-Epoxysqualene-Lanosterol Cyclase(EC 5.4.99.7)

(EC 5.4.99.7)

O

(EC 1.3.1.70)

HOH

H

H

O

(EC 1.14.13.72)

(EC 1.1.1.170)

HOH

H

H

O

(EC 5.3.3.5)

HOH

H

H

O

(EC 1.14.21.6)

HO

H

H

O

(EC 1.3.1.21)

HO

H

H

24S,25-Epoxycholesterol

O

The prenatal diagnosis of Smith-Lemli-Opitz syndrome from amniotic fluid

Sterol analysis for the prenatal diagnosis of

Smith-Lemli-Opitz syndrome

0 10 20 30 40

Time (min)

100

100

10025.83

24.46

23.90

Cholesterol518→439

7-DHC516→437

Desmosterol516→437

%RA

%RA

%RA

Ion Count 6.7E6

Ion Count 9.85E4

0 10 20 30 40

Time (min)

100

10025.83

23.90

%RA

%RA

MS2 : 518→439

MS2 : 516→437

(a)

Ion Count 5.58E6

Ion Count 6.27E6

0 10 20 30 40

Time (min)

100

10025.83

23.90

MS2 : 518→439

MS2 : 516→437

%RA

%RA

(b)

0.002-0.01 µL amniotic fluid

injected on-column

Mean ratio of 7/8-DHC to cholesterol for 18 amniotic fluids from SLOS-

affected and non-affected pregnancies. Eighteen samples were subjected to

oxidation/GP-derivatisation reactions in triplicate and were analysed by cap-

LC-MSn.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

31576

30488

30355

31414

32688

32288

34090

33952

33953

34048

29986

34107

34105

34070

34106

34089

34104

30079

β-sitosterol 5-cholesten-24β-ethyl-3β-ol

Stigmasterol 5,22-cholestadien-24β-ethyl-3β-ol

Campesterol 5-cholesten-24α-methyl-3β-ol

Stigmastanol 5-cholestan-24β-ethyl-3β-ol

Cholesterol 5-cholesten-3β-ol

Phytosterol practical

Analytical Strategy

• Extraction of phytosterols : C2H5OH

• Derivatisation with GP hydrazine

• Direct infusion ESI onto the QTOF

• LC-ES-MSn

Direct infusion of a sample into

the mass spectrometer

LC and Mass Spectrometry

• LC-MS: Separate components of interest, giving sharp peaks (10 s – 1 min) away from the solvent front

an introduction to liquid chromatography mass spectrometry · • liquid chromatography-mass...

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