BOILING POINT DISTRIBUTION OF

HYDROCARBONS BY GAS CHROMATOGRAPHY

UOP Method 621-98

SCOPE

This method is for analyzing by gas chromatography mixtures of liquid hydrocarbons in the range of C5
through C20, using a column that separates components by boiling points. Procedures are provided for
several applications, depending on the calibration used. These include, but are not limited to, (a) component
distribution as defined by boiling points and corresponding carbon numbers, (b) determination of individual
components resolved from a mixture of other components, and (c) analysis of a total sample wherein the
identities of the major components or groups of components are known. Variations may be made as
required, such as grouping of specific components by boiling ranges or extending the application to other
ranges. The range of quantitation for a single component (or group of components) is 0.05 to 99.9 mass-%.

OUTLINE OF METHOD
The sample is injected into a gas chromatograph that is equipped with a flame ionization detector (FID)
and a fused silica capillary column internally coated with cross-linked methyl silicone. One of the following
is analyzed under identical conditions:
a) A quantitative blend composed of n-paraffins whose boiling points extend throughout the boiling range
of the sample to be analyzed. The “calibration chromatogram” obtained is used to determine the various
boiling points or ranges by comparing the retention times of the n-paraffins to the observed retention
times of the sample components.
b) A quantitative blend containing the individual components of interest in a mixture similar in
composition to the sample.
c) A quantitative blend of a wide boiling range mixture wherein all the major components are known.

The mass-% composition of the sample is obtained by the internal normalization technique of
quantitation wherein component areas are first corrected for response differences and then normalized to
100%. Since hydrocarbon components have essentially the same detector response on a mass basis in an
FID, a relative response factor of 1.000 may be used for all components or groups, except when greater
accuracy is desired or the samples contain a significant amount of benzene, toluene or mixed xylenes.

IT IS THE USER'S RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TO

DETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH AND
SAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS
PROCEDURE IN THE MANNER PRESCRIBED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS
(MSDS) OR EXPERIMENTAL MATERIAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED IN
THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION
EQUIPMENT (PPE).

© COPYRIGHT 1965, 1980, 1998 UOP LLC

ALL RIGHTS RESERVED

UOP Methods are available through ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken PA 19428-2959,
United States. The Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at
service@astm.org, 610.832.9555 FAX, or 610.832.9585 PHONE.
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APPARATUS
References to catalog numbers and suppliers are included as a convenience to the method user. Other
suppliers may be used.

Balance, readability 0.1-mg

Chromatographic column, 50 m of 0.2-mm ID fused silica capillary, internally coated to a film thickness
of 0.5-µm with cross-linked methyl silicone, Hewlett Packard, Cat. No. 19091S-001

Gas chromatograph, capable of constant pressure mode and multiple temperature ramping, built for
capillary column chromatography, utilizing a split injection system, having a glass injection port insert,
and equipped with a FID that will give a minimum peak height response of 10 times the background
noise for 0.05 mass-% of n-decane, when operated at the recommended conditions, Hewlett Packard,
Model 6890

Gas purifier, hydrogen, used to remove oxygen from the carrier gas, UOP Mat/Sen, Cat. No. P-200-1

Integrator, electronic, for obtaining peak areas. This device must integrate areas at a sufficiently fast rate
so that the narrow peaks typically resulting from use of a capillary column can be accurately measured.

Leak detector, gas, Alltech Associates, Cat. No. 21-250

Recorder (optional), used to supplement integrator plot

Regulator, air, two-stage, high purity, Matheson Gas Products, Model 3122-590

Regulator, hydrogen, two-stage, high purity, Matheson Gas Products, Model 3122-350

Regulator, nitrogen, two-stage, high purity, Matheson Gas Products, Model 3122-580

Sample injector, syringe or injector capable of introducing a 1.0-µL volume of sample, such as a SGE
Universal Syringe, Fisher Scientific, Cat. No. SG-001105. An autoinjector may be used.

REAGENTS AND MATERIALS

All reagents shall conform to the specifications established by the Committee on Analytical Reagents of
the American Chemical Society, when such specifications are available, unless otherwise specified.

References to catalog numbers and suppliers are included as a convenience to the method user. Other
suppliers may be used.

Air, total hydrocarbons less than 2 ppm as methane

Benzene, 99.9% purity, Aldrich Chemical, Cat. No. 27,070-9. CAUTION: Benzene is a known
carcinogen. All operations involving its use must be performed in a properly ventilated area, while
wearing appropriate personal protective equipment.

Ethylbenzene, 99.8% purity, Aldrich Chemical, Cat. No. 29,684-8

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Hydrogen, zero-gas, 99.95% minimum purity, total hydrocarbons less than 0.5 ppm as methane

Nitrogen, zero-gas, 99.99% minimum purity, total hydrocarbons less than 0.5 ppm as methane

n-Paraffins, carbon nos. 5 through 20, for blending purposes, 99% minimum purity, Aldrich Chemical.
Additional hydrocarbons may be required for calibration purposes.

n-Paraffin Cat. No. n-Paraffin Cat. No.

C5 27,041-5 C13 T5,740-1
C6 13,938-6 C14 17,245-6
C7 27,051-2 C15 P340-6
C8 41,223-6 C16 H670-3
C9 N2,940-6 C17 12,850-3
C10 D90-1 C18 O-65-2
C11 U40-7 C19 N2,890-6
C12 D22,110-4 C20 21,927-4
Toluene, 99.8% purity, Aldrich Chemical, Cat. No. 27,037-7

m-Xylene, 99% minimum purity, Aldrich Chemical, Cat. 18-556-6

o-Xylene, 97% minimum purity, Aldrich Chemical, Cat. No. X104-0

p-Xylene, 99% minimum purity, Aldrich Chemical, Cat. No. 13,444-9

PROCEDURE

Chromatographic Technique

1. Install the gas purifier in the supply line between the carrier gas source and the carrier gas inlet on the
gas chromatograph.
• Column life is significantly reduced if the gas purifier is not used.

2. Install the fused silica capillary column in the gas chromatograph, according to the column and gas
chromatograph manufacturers instructions.
• CAUTION: Hydrogen gas leakage into the confined volume of the column oven can cause a violent
explosion. It is, therefore, mandatory to check for leaks each time a connection is made and periodically
thereafter.

3. Establish the recommended operating conditions as given in Table 1.

• Other conditions may be used provided they produce the required sensitivity and chromatographic
separations equivalent to those shown in the Typical Chromatograms (Figs. 1, 2, and 3).

4. Program the column oven to 300°C and maintain this temperature until a stable baseline has been
obtained at the required sensitivity.

5. Cool the column oven to a stabilized 100°C.

6. Mix the sample thoroughly by shaking it vigorously.

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7. Inject 1.0 µL of sample into the gas chromatograph and immediately start the recorder, the integrator
and the column oven programming sequence.

8. Identify the components of interest by comparing the resultant chromatogram to the corresponding
Typical Chromatogram, Fig. 1, Fig. 2 or Fig. 3. In determining the composite area of the components
within a given carbon number boiling point value (Fig. 1), start area measurements immediately after
the n-paraffin peak of the previous carbon number; that is, one carbon less, and continue up to the end
of the n-paraffin peak of the boiling point value under consideration. In this manner, a distribution by
boiling point, or by approximate carbon number, is determined. All material thus measured should be
considered as the higher of the two n-paraffin carbon numbers for approximate carbon number
identification.
• Single ring aromatics elute one carbon number later than n-paraffins of the same carbon number (Fig. 3).
• Two ring aromatics elute approximately two carbon numbers later than n-paraffins of the same carbon
number (Fig. 3).

Table 1
Recommended Operating Conditions
Carrier gas hydrogen
Column head pressure @ 100°C,
constant pressure mode 105 kPa gauge (15 psig)
Equivalent flow 0.6 mL/min
Equivalent linear velocity 24 cm/sec
Split flow 150 mL/min
Injection port temperature 250°C
Column temperature program
Initial temperature 100°C
Initial time 1.5 min
Programming rate 6°C/min
Final temperature 300°C
Final time 10.5 min
Detector FID
Temperature 275°C
Hydrogen flow rate* 30 mL/min
Air flow rate* 400 mL/min
Makeup nitrogen flow rate* 30 mL/min
Sample size 1.0 µL
* Consult the manufacturer’s instrument manual for suggested flow rates.

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Calibration

This analysis uses internal normalization of the entire sample to quantitate the desired components in any
given mixture. Since hydrocarbons, except C6 to C8 aromatics, respond almost equally in the FID on a mass
basis, a relative response factor of 1.000 may be used for all components unless the sample contains a
significant amount of identified C6 to C8 aromatics, or when greater accuracy is desired.

1. Prepare a calibration blend as described in ASTM Method D 4307 to contain a representative

composition of the sample to be analyzed.

2. Run the calibration blend three times as described in Steps 7 through 8 under Chromatographic
Technique.
• A calibration blend is run when the method is initially set up and thereafter when changes have been made
to the equipment, or periodically to verify proper calibration or peak identification.

3. Identify the peaks and average the individual peak areas from the triplicate runs.

4. Use the average peak areas to calculate the relative response factor for each component of interest to
three decimal places, using one of the components as a reference (1.000), and Eq. 1.

AB
F= (1)
CD

where:
A = concentration of the component of interest (or group) in the blend, mass-%
B = average peak area of the reference component
C = concentration of the reference component in the blend, mass-%
D = average peak area for the component of interest
F = relative response factor for component of interest

A blend of n-paraffins, in about equal proportions, is used for designating specific boiling points over a
wide range. The boiling points of n-paraffins, from C5 through C20, are listed in Table 2.

Table 2
Boiling Points of Normal Paraffins

n-Paraffin Boiling Point, oC n-Paraffin Boiling Point, oC

C5 36.1 C13 235.4
C6 68.7 C14 253.6
C7 98.4 C15 270.6
C8 125.7 C16 286.8
C9 150.8 C17 301.8
C10 174.1 C18 316.1
C11 195.9 C19 329.7
C12 216.3 C20 342.7

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CALCULATIONS
Calculate the concentration of each component (or group) using Eq. 2.

 GF 
Component (or group), mass- % = 100   (2)
 N 

where:
F = relative response factor for component (or group), Eq. 1 or 1.000, if appropriate
G = peak area of individual component (or group) in the sample
N = sum of the products GF of all the components in the sample
100 = factor to convert to mass-%

Report to one significant digit below 0.1 mass-%, two significant digits from 0.1 to 1 mass-%, and three
significant digits above 1 mass-%.

PRECISION

ASTM Repeatability

A nested design was carried out for boiling point distribution of hydrocarbons analysis with four analysts.
Each analyst carried out tests on two separate days, performing two tests each day. The total number of tests
performed was 16. Using a stepwise analysis of variance procedure, the within-day estimated standard
deviations (esds) were calculated for the components listed in Table 3. Two analyses performed in one
laboratory by the same analyst on the same day should not differ by more than the ASTM allowable
differences shown in Table 3 at the concentrations listed with 95% confidence.

UOP Repeatability

A nested design was carried out for boiling point distribution of hydrocarbons analysis by four analysts,
with each analyst carrying out tests on two separate days and performing two tests each day. The number of
analyses performed was 16. Using a stepwise analysis of variance procedure, the within-lab estimated
standard deviations (esds) were calculated for the components listed in Table 3. Two analyses performed in
one laboratory by different analysts on different days should not differ by more than the UOP allowable
differences shown in Table 3 at the concentrations listed with 95% confidence.

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Table 3
ASTM and UOP Repeatability, mass-%

ASTM Repeatability UOP Repeatability

Within-Day Allowable Within-Lab Allowable
Component Concentration esd Difference esd Difference

C5 Non-aromatics 0.23 0.004 0.01 0.01 0.03

Benzene 26.5 0.03 0.1 0.05 0.2
Toluene 40.7 0.06 0.2 0.10 0.3
C8 Aromatics 14.9 0.03 0.1 0.05 0.2
C10 Aromatics 1.05 0.006 0.02 0.005 0.02
Naphthalene 3.13 0.013 0.04 0.015 0.05
C12 Aromatics 0.05 0.003 0.01 0.003 0.01
The data in Table 3 were obtained using an autoinjector and are a short-term estimate of repeatability.
When the test is run routinely in the field, a control standard and chart should be used to develop a better
estimate of the long-term repeatability.

Reproducibility

There is insufficient data to calculate the reproducibility of the test at this time.

TIME FOR ANALYSIS

The elapsed time for one analysis is one hour. The labor requirement is 0.25 hour.

REFERENCE
ASTM Method D 4307, www.astm.org

SUGGESTED SUPPLIERS
Aldrich Chemical Co., Inc., P.O. Box 355, Milwaukee, WI 53201 (414-273-3850)
Alltech Associates, Inc., 2051 Waukegan Rd., Deerfield, IL 60015 (847-948-8600)
Fisher Scientific, 711 Forbes Ave., Pittsburgh, PA 15219 (412-562-8300)
Hewlett Packard Co., 2850 Centerville Rd., Wilmington, DE 19808-1610 (302-633-8000)
Matheson Gas Products, Inc., P.O. Box 96, Joliet, IL 60434 (815-727-4848)
UOP Mat/Sen, 4509 Golden Foothill Pkwy., El Dorado Hills, CA 95762 (916-939-8800)

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Figure 1
Typical Chromatogram
n-Paraffins and Components by Carbon Number

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Figure 2
Typical Chromatogram
Molex Sample with Desorbent

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Figure 3
Typical Chromatogram
n-Paraffins and Aromatics

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