Adlard E.R. (ed.) Chromatography in the Petroleum Industry

Подождите немного. Документ загружается.

342

aU.l

Chapter

4.w

Fig.

11.19.

Supercritical fluid chromatogram

(FID)

two diesel fuels, CEN 17 and

20,

obtained

with the coupled system. Columns: fused silica (25

0.25

ID), packed with Deltabond-

SFC.

cyano-bonded,

5pm;

fused silica

(290

nun

0.25

nun

ID),

packed with Superspher Si

60,

4pm; fused silica

(100

0.250 mm

ID),

packed with Nucleosil 5

and impregnated

situ

with

AgN03.

Mobile phase, carbon dioxide at 75°C and 375 am. Peaks:

MA,

monoaromatics;

DA,

diaromatics; TA, triaromatics;

polar compounds;

saturated compounds;

alkenes. Switching

points are indicated by

sw.

high column pressures, in forward elution mode only. The saturate fraction con-

tained no aromatics but some alkanedalkenes eluted with the mono-aromatic

fraction. Di Sanzo and Yoder found that SFC-FID gave high aromatic content

values when analysing low aromatic diesel blends

[63].

Comparison with

IP391

(HPLC

with refractive index detection) data shows lower mono-aromatics

(trapped with olefins

the SFC method) and higher di-aromatics (FID response

Supercritical fluid chromatography

343

factor) by

SFC;

PAH

contents are in reasonable agreement although the scatter is

high.

11.4

REFERENCES

S.T. Sie and G.W.A. Rijnders, Anal. Chim. Acta.,

38 (1967) 31.

E. Klesper, A.H. Convin and D.A. Turner, J. Org. Chem.,

27 (1962) 700.

S.T.

Sie, W. van Beersum and G.W.A. Rijnders, Sep. Sci.,

(1966) 459.

S.T.

Sie and G. W.A. Rijnders, Sep. Sci.,

967) 755.

R.E. Jentoft and T.H. Gouw, J. Polym. Sci. Polym. Lett.,

969) 8

R.E. Jentoft and T.H. Gouw, J. Chromatogr. Sci.,

(1970) 138.

T.H.

Gouw and R.E. Jentoft, Adv. Chromatogr.,

13 (1975)

T.H. Gouw and R.E. Jentoft, Chromatography in Petroleum Analysis (K.H. Altgelt and T.H.

Gouw, Eds.), Marcel Dekker, New York

(1979),

Ch.

13,

ISBN

0-8247-6790-X.

M. Novotny, S.R. Springston, P.A. Peaden, J.C. Fjeldsted and M.L. Lee, Anal. Chem.,

(1981) 407A.

D.E. Martire and R.E. Boehm, J. Phys. Chem.,

91 (1987) 2433.

M.G. Rawdon, Anal. Chem.,

984) 83

ASTM D

5186-91,

Standard Test Method for Determination of Aromatic Content of Diesel

Fuels by Supercritical Fluid Chromatography, first published in

1991,

Annual Book of ASTM

Standards, Vol.

05.01.

R. Kornfield,

Am.

Lab.,

24( 14)

992) 25.

N.L. Porter, B.E. Richter, D.J. Bornhop, D.W. Later and F.H. Beyerlein, J. High Resolut.

Chromatogr.,

10 (1987) 477.

M.L. Lee and K.E. Markides (Eds.), Analytical Supercritical Fluid Chromatography and Ex-

traction, Chromatography Conferences, Provo, UT

(1990),

ISBN

0-8425-2394-4.

C.R. Yonker, D.G. McGinn, B. W. Wright and R.D. Smith, J. Chromatogr.,

396

987)

19.

D.E. Raynie, S.M. Fields, N.M. Djordjevic, K.E. Markides and M.L. Lee, J. High Resolut.

Chromatogr.,

12 (1989)

51.

T. Greibrokk, Applications of Supercritical Fluids in Industrial Analysis (J.R. Dean Ed.),

Blackie Academic

Professional, Glasgow

(1993),

Ch.

ISBN

0-8493-71 08-2.

B.E. Richter, D.J. Bomhop, J.T. Swanson,

J.G.

Wangsgaard and M.R. Andersen,

Chroma-

tog. Sci.,

27 (1989) 303.

L.A. Pekay and

V. Olesik, Anal. Chem.,

61 (1989) 2616.

T.A. Norris and M.G. Rawdon, Anal. Chem.,

56 (1984) 1767.

J.M. Levy and W.M. Ritchie, J. Chromatogr. Sci.,

24 (1986) 242.

Greibrokk,

B.E.

Berg, A.L. Blilie, J. Doehl, A. Farbrot and E. Lundanes, J. Chromatogr.,

394 (1987) 429.

M, Lafosse, M. Dreux and L. Morin-Allory, J. Chromatogr.,

404 (1987) 95.

Hof€inann and

Greibrokk, J. Microcol. Sep., 1

(1989) 35.

Tong, K.D. Bartle, R.E. Robinson and P. Altham,

Chromatogr. Sci.,

(1993) 77.

J.C. Kuei, K.E. Markides and M.L. Lee, J. High Resolut. Chromatogr. Chromatogr. Commun.,

(1987) 257.

J.P. Chervet, M. Ursem,

J.P.

Salzmann and R.W. Vannoort, J. High Resolut. Chromatogr.,

(1989) 278.

Jinno, T. Hoshino,

Hondo,

Saito and M. Senda, Anal. Chem.,

58 (1986) 2696.

3 44

Chapter

J.E. France and K.J. Voorhees, J. High Resolut. Chromatogr. Chromatogr. Commun., I1

(1988) 692.

S.R.

Weinberger and D.J. Bornhop,

Microcol. Sep., 1 (1989) 90.

J.C. Fjeldsted, B.E. Richter, W.P. Jackson and M.L. Lee, J. Chromatogr., 279 (1 983) 423.

J.K. Simons, C.H. Sin, N.A. Zabriskie, S.M. Fields, M.L. Lee and S.R. Goates, J. Microcol.

Sep., 1

989) 200.

M.A. Healy, T.J. Jenkins and M. Poliakoff, Trends Anal. Chem.,

(1991) 92.

Sheu, G. Lavigne, H. Sandhu, M. Koenig, G. Moebus and J.F. Johnson, Fuel Sci. Technol.

lnt., 10 (1992) 825.

K.D. Bartle, A.A. Clifford and M.W. Raynor, J. Chromatogr. Libr., 53 (Hyphenated Tech.

Supercritical Fluid Chromatogr Extr), Elsevier, Amsterdam, 1992, pp. 103-127.

L.A. Allen, T.E. Glass and H.C. Dom, Anal. Chem.,

(1 988) 390.

W.R. West and M.L. Lee, J. High Resolut. Chrornatogr. Chromatogr. Commun., 9 (1986) 161.

J.C. Fjeldsted, R.C. Kong and M.L. Lee, J. Chromatogr., 279 (1983) 449; P.A. David and M.

Novotny,

Chromatogr., 461 (1989)

11;

Ashrof-Khorassani and J.M. Levy, Fresenius J.

Anal. Chem., 342 (1992) 688491.

L. Mathiasson, J.A. Jonsson and

Karlsson, J. Chromatogr., 467 (1989) 61.

K.E. Markides, E.D. Lee,

Bolick and M.L. Lee, Anal. Chem., 58 (1986) 740.

(a) H.-C.

Chang and L.T. Taylor, J. Chromatogr., 517 (1990) 491;

(b)

L.A.

Pekay and

S.V.

Olesik, J. Microcol. Sep.,

(1990) 270; (c) A.L. Howard and L.T. Taylor, Anal. Chem., 65

(1993) 724-729.

B.W. Wright and R.D. Smith, in: Modem Supercritical Fluid Chromatography (C.M. White

Ed.), Huethig, Heidelberg (1988)

189.

D.R. Gere, R. Boord and D. McManigill, Anal Chem., 54 (1982) 736.

M. Saito,

Yamauchi, H. Kashiwazaki and M. Sugawara, Chromatographia, 25 (1988) 801.

M.A. Morrissey et al., J. Chromatogr. Sci., 29 (1991) 237.

Trestianu, G. Zilioli, A. Sironi, C. Saravalle,

Munari, M. Galli, G. Gasper, J.M. Colin

and J.L. Lovelin,

High Resolut. Chromatogr. Chromatogr. Commun.,

(1985) 771.

H.E. Schwartz, R.G. Brownlee, M.M. Boduszynski and F.

Su,

Anal. Chem., 59 (1987) 1393.

J. Curvers and P. van den Engel, J. High Resolut. Chromatogr. Chromatogr. Commun., 12

(1989) 16.

I.D. Singh,

V. Ramaswamy,

Kothiyal, D. Severin and

Kollmeier, Fuel Sci. Technol. Int.

990) 467.

M.M. Boduszynski, Energy Fuels,

(1987)

D.E. Raynie, K.E. Markides and M.L. Lee, J. Microcol. Sep, 3 (1991) 423.

K.D.

Bartle, M. Burke, D.G. Mills,

Pape and

Lu, Fuel Sci. Technol. Int. 10 (1992) 1071.

J.M. Levy, A.C. Rosselli,

Storozynsky,

R. Ravey, L.A. Dolata and M Ashraf-Khorassani,

F. Mellor, W. Ecknig, K. Richter and

Just, Chromatographia., 35 (1993) 97.

J.S. Thompson and A.F. Rynaski, J. High Resolut. Chromatogr. 15 (1992) 227.

Macleod, Processing, January 23-24 (1992).

F.A. Barbour and J.F. Branthaver, Fuel Sci. Technol. Int., 10 (1992) 979.

M.P. Stadler, M.D. Deo and F.M.

Orr,

Proc. SPE 1993 Int. Oilfield Chemistry Symp., New

Orleans (1993) 413-420.

Hewlett Packard Application Note 228-169, published May (1992).

P.E. Andersson, Thesis, Stockholm University (1993).

S.E.W. Lee, B.J. Fuhr, L.R. Holloway and C. Reichert, Energy Fuels, 80 (1989).

F.P. Di Sanzo and R.E. Yoder, J. Chromatogr. Sci., 29 (1991) 4.

LC-GC, lO(5) (1992) 386.

Supercritical

fluid

chromatography

345

B.J. Fuhr, L.L. Klein, C. Reichert and

S.W.

Lee, LC-GC,

S(10) (1990)

800;

LC-GC Int.,

4(1)

(199?) 36.

T.A. Norris and M.G. Rawdon, Anal. Chem.,

56 (1984) 1767.

H.E. Schwartz and R.G. Brownlee,

Chromatogr.,

353 (1986) 77.

R.M. Campbell, Thesis, Brighan Young University

(1987).

R.M. Campbell, N.M. Djordjevic, K.E. Markides and M.L. Lee,

Anal.

Chem.,

60 (1988) 356.

P.E. Anderson,

Demirbuker and L.G. Blomberg.

Chromatogr.,

595 (1992) 301.

W.W.

Schulz and M.W. Genowitz, Pittsburgh Conf. on Analytical Chemistry, New York

990),

Paper No

133.

M. Ashraf-Khorassani, J.M. Levy and L.A. Dolata,

Am.

Lab.,

24(8) (1992) 29.

R. Fraile and

Sanchez,

High Resolut. Chromatogr.,

16 (1993) 169.

T.P. Lynch, unpublished results.

IP391/90

Aromatic Hydrocarbon Types in Diesel Fuels and Petroleum Distillates by HPLC

with Refractive Index Detection.

Hewlett Packard Application note

228-167,

May

(1992).

P.E. Anderson, M. Demirbuker and L.G. Blomberg,

Chromatogr.,

641 (1993) 347.

This Page Intentionally Left Blank

E.R.

Adlard Fd.),

Chromatography

the Petroleum Industry

Journal

Chromatography

Library

Series,

Vol.

1995 Elsevier Science

B.V.

All

rib&

reserved

347

CHAPTER

HPLC

and column liquid chromatography

A.C.

Neal

Esso

Research Centre, Milton Hill,

Abingdon,

Oxfordshire

OX13

6AE,

12.1

INTRODUCTION

The development of high performance liquid chromatography (HPLC) was

predicted in

1941

by Martin and Synge

[l].

In addition to pioneering liquid-

liquid chromatography and the theoretical plate model of chromatography, these

authors predicted that HPLC would be achieved by using “very small particles

and a high pressure difference across the column”. In fact, the origins of such

columns can be traced back to the work of Tswett in

1903 [2]

and their use was

further extended by Kuhn and Lederer in

193

[3].

The advance of gas chromatography (GC) in the petroleum industry in the

1950s

was such that liquid chromatography was effectively overlooked through-

out that decade. This rapid exploration and application of GC rekindled interest

in liquid chromatography as a complementary technique which could open up

regions of solute polarity, molecular weight and bulk separation alien to GC.

Commercialization of HPLC columns, pumps and detectors during the

1960s

and

early

1970s

simplified operation of the technique and allowed potential users to

apply it with relative ease. During this time, various terms were used to describe

the new technique: “modern liquid chromatography”, ”high pressure liquid

chromatography” and “high performance liquid chromatography” and the latter

now universally used although it is not easy to define exactly what is meant by

“high performance”.

comprehensive introduction to HPLC can be found in

Snyder and Kirkland

[4]

although this excellent book is now almost

years old.

More recently, Parris

[5]

and Gilbert

[6]

have written good general reviews on

the subject and the reader is referred to reference

[4]

for detailed and fundamen-

tal information and the latter

two

books for general theory and instrumental de-

scriptions.

References

pp.

372-374

348

Chapter

The applications of HPLC in petroleum analysis has itself been reviewed by

Amos in

1979

[7].

At that time, the number of specific applications in the indus-

try were few and the major uses were in hydrocarbon type analysis and the de-

termination of hindered phenol antioxidants in fuels, most notably aviation

tur-

bine fuel. By comparison with paper chromatography and thin-layer chromatog-

raphy, which had independently competed with HPLC during the earlier years of

development, Amos concluded that “the choice between PC, TLC and HPLC is

now fairly clear cut” and that “HPLC should be used for all routine high-speed

quantitative analysis.

Since that review was written, HPLC pump, column and detector designs have

advanced and expanded markedly, such that a far wider field of applications now

exists. HPLC has also diversified into aqueous/ionic systems (ion chromatogra-

phy) and high performance size exclusion chromatography (gel permeation

chromatography), and been “hyphenated” with spectrometry including induc-

tively coupled plasma emission spectroscopy (ICPES), nuclear magnetic reso-

nance spectroscopy (NMR), Fourier transform infra-red spectroscopy (FTIR)

and most importantly mass spectrometry

(MS).

The numerous attempts to inter-

face HPLC with MS have resulted

a variety

LC-MS systems with each in-

terface type having its own specific limitations and applications.

12.2

APPARATUS

typical HPLC system (Fig.

12.1)

is still composed of a pump, sample injec-

tor, column, detector and data recorder much as described by Amos

[7].

How-

ever, considerable improvement and development of each component has taken

place. Advances in columns and detectors have resulted in a wider range of sepa-

rations and detection strategies being available.

12.2.1

Solvent

reservoirs

Solvent reservoirs consist of purpose built glass bottles with a helium inlet

and filter (for degassing) and a solvent outlet composed of a fritted particulate

filter and PTFE outlet tube. Some systems even allow for a slight helium over-

pressurization of the reservoir to assist pump priming and prevent cavitation in

the solvent inlet tubing.

12.2.2

Pumps

Pumps have progressed from single isocratic systems delivering premixed

solvent, to purpose built binary, tertiary and even quaternary mixing systems

HPLC

and column liquid chromatography

Solvent Reservoirs

349

Detectors

Data

System

Fig.

12.1.

Elements

HPLC

system.

which premix the solvents to the desired composition and deliver them at the

required flow rate, compensating automatically for pressure and viscosity effects

which may occur during the mixing process.

During the early 1980s, much debate took place over the relative merits of

high pressure mixing (after the pump outlet) and low pressure mixing (at the

pump inlet).

High pressure mixing suffers from a number of drawbacks: chief among these

the need for more than one pump with the concomitant expense. In addition,

imprecision in the solvent composition may occur if one or more of the solvents

is present as less than

of the total.

Low pressure mixing requires only one pump with the solvents proportioned

and mixed before the pump head. Control by microprocessor or computer data

systems allows for almost any shape of gradient (and flow) profile to be deliv-

ered. For these reasons, low pressure mixing, under either of the remote control

systems given above, has come to dominate the market for LC gradient systems

but some caution is still necessary in use. Firstly, for complete mixing, some

systems rely on a fairly large volume mixing chamber on the outlet side

the

pump. In certain applications, such as backflushing, a sharp gradient profile

desirable and this may be compromised by the hold-up volume of the chamber.

In other words, if it

necessary to make sudden step changes in the gradient, the

step may actually be a slope. Low volume (10~1) dynamic mixers, such as the

References

pp.

3 72-3 74

350

Chapter

LEE

micromixer, are of considerable use in eliminating this problem. Secondly,

efficient degassing

the solvent used to be a prerequisite for accurate mixing in

order to eliminate cavitation

the mixing system and the detector noise and in-

accurate flow rates that could result.

practice, improvement in the design

the solvent reservoirs and pump head geometry have reduced the occurrence of

these problems, provided that the manufacturers advice is heeded. Gradient elu-

tion may also limit the choice

detector to be used, especially if the detector

depends on changes in a physical property

the mobile phase itself. This issue

is discussed in detail in the section on detectors.

Three main types

pump, reciprocating piston, syringe and diaphragm, were

all applied

the early days but the reciprocating piston pump now dominates

the “standard”

HPLC

market where flow rates are at

above,

ml min-*. Sy-

ringe pumps are best suited to lower flow rates and as such find more use

”microbore”

HPLC

where flow rates are typically well below

ml min-l.

Reciprocating piston pumps operate by means

a rotating eccentric cam

which drives a piston. The piston draws solvent into a cylinder through the inlet

check valve during the return stroke. During the delivery stroke, solvent is ex-

pelled through the outlet check valve and hence ultimately to the column. These

pumps

are relatively inexpensive, simple to maintain, and deliver a constant flow

solvent over a wide range of flow rates. The piston drive is usually controlled

solid state pulsing circuits and a stepper motor. This allows

for

rapid refilling

of the cylinder followed by swift repressurization

the solvent in the pump

head and then a smooth, constant volume delivery until the end of the delivery

stroke. The design of the cam and its eccentricity determine the smoothness of

the flow profile. This

now so well defined that accurate, rapid refilling has

become commonplace and methods

for

smoothing the profile such as large vol-

ume pulse dampers and dual

triple stage pump heads are largely redundant.

Lower volume dampers may still be used and are often an integral part

the

pump,

“invisible” inside the box.

12.2.3

Sample

injectors

Sample injectors are almost exclusively of the six-port valve type, although

on-column syringe injectors were initially used. Injection valves

are

connected

between the pump and the column and as close to the top of the column as prac-

tically possible. An interchangeable sample loop

of discreet volume is connected

to the valve and isolated from the flow

of mobile phase. The loop is filled with

sample solution and the valve

then turned manually

electronically

that

the loop

connected into the flowing mobile phase and the sample is thereby

injected onto the column.

HPLC

and column liquid chromatography

351

Various designs of injectors exist, depending on the volume of sample avail-

able and the physical scale of the

HPLC

system. Internal microlitre-sized loop

injectors are available for microbore applications, whereas for standard and

preparative work, interchangeable sample loops up to

ml in volume can be

used with standard Rheodyne or Valco valves. Loops are filled by a standard

glass syringe with a Luer fitting, with or without a flat-ended needle according to

the design of the sample inlet on the valve.

Remote actuation of injection valves or flow switching valves is usually ac-

complished pneumatically or electrically. Typically the solvent delivery system

or data station allows for timed events, one of which is the activation

the in-

jection valve. In pneumatic actuation, the valve is turned by a supply

high

pressure gas, usually air, in

purpose made pistodcylinder type actuator. The

gas supply is itself delivered to the actuator by a solenoid valve. The solenoid

valve opens or closes under the control of the solvent delivery system or data

station, in order to pressurize or depressurize the actuator and hence operate the

injector.

Electrical actuators tend to be more expensive but are faster than pneumatic

actuators. They use a synchronous, high torque electric motor, directly con-

trolled by a relay closure or TTL switch. The valve may be coupled directly to

the motor, minimizing the number of moving parts. Although faster and poten-

tially more reliable than the pneumatic actuator, the extra capital cost is often the

sole factor which mitigates against their use.

our experience, pneumatic actua-

tors seldom give any cause for concern and the extra cost of electrical actuators

rarely justified.

12.2.4

Columns

Selection of the appropriate column is,

course, entirely dependent on the

particular separation desired. Over the last 15 years, the technology

column

design and manufacture has advanced markedly, as has the range and reliability

of packings available.

the late

1970s,

columns were almost exclusively

250

mm long

316

stainless steel with an internal diameter of

4.6

mm. End fit-

tings were of solid

stainless steel and packings typically amorphous silica or

alumina, or else silica with an octadecyl bonded phase, commonly referred to as

ODS

C18.

At that time, intermediate polarity stationary phases were begin-

ning to excite interest but only amino

(-NH,)

and nitrile

(XN)

phases were

readily available. Since then the range of

HPLC

applications has broadened

considerably and advances in column chemistry and design have been fundamen-

tal to that progress.

HPLC

analysis can be placed in one of four categories largely by virtue of the

column type used.

References pp.

72-3