share:
delim
delim
delim
delim
Detailed Hydrocarbon Analysis (DHA) Featuring Rtx-DHA Columns-PCSS1007D-UNV

Detailed Hydrocarbon Analysis
Featuring Rtx-DHA Columns

  • Individually tested to meet DHA method criteria; guaranteed column-to-column reproducibility.
  • Improved resolution between oxygenates and hydrocarbons for more accurate reporting.
  • Use of hydrogen carrier gas yields 50% faster run times.

Accurate DHA Analysis, Including Alcohols,
Using Rtx-DHA Columns

  • Individually tested to meet DHA method criteria; guaranteed column-to-column reproducibility.
  • Improved resolution between oxygenates and hydrocarbons for more accurate reporting.
  • Use of hydrogen carrier gas yields 50% faster run times.

Gasolines are complex mixtures of hundreds of compounds. Information about concentrations of the individual components is important for evaluating raw materials and for controlling refinery processes. A high-resolution GC method for detailed hydrocarbon analysis (DHA) of gasolines is outlined in American Society of Testing and Materials (ASTM) Method D6730-01. ASTM D6730-01 is specific for the analysis of hydrocarbon components, plus oxygenated additives such as methanol, ethanol, tert-butanol, methyl tert-butyl ether (MTBE), and tert-amyl methyl ether (TAME) in spark-ignition engine fuels.

To maximize resolution of these complex mixtures, the ASTM method recommends a 100 m x 0.25 mm ID capillary column coated with 0.5 μm of 100% dimethyl polysiloxane stationary phase and sets minimum resolution criteria for several critical pairs of closely eluting compounds. To retain the aromatics and accomplish the separations, a short tuning column, approximately 2–3 m long, coated with 5% diphenyl/95% dimethyl polysiloxane polymer, is connected to the inlet of the 100 m analytical column. Through a series of trial analyses, the length of the tuning column is adjusted to ensure the critical resolutions are achieved. Rtx-DHA-100 columns are ideal for DHA methods and easily meet or exceed performance requirements.

Quality & Consistency

Analytical columns used for DHA applications must exhibit high efficiency and exceptional inertness, especially for polar oxygenates in gasoline. Figure 1 illustrates a column efficiency of 613,600 total theoretical plates, measured on C5, and shows excellent peak symmetry for the oxygenated additives, including ethanol and tert-butanol (tert-butanol skewness = 1.25). We test every Rtx-DHA-100 column for retention (k'), efficiency (n), stationary phase selectivity (α), and bleed, according to ASTM D6730. Data are shown on each test report, assuring that your Rtx-DHA column will meet method specifications.

Figure 1: Rtx-DHA-100 columns meet or exceed ASTM D6730 specifications.

Sharp, symmetric
oxygenate peaks!

Peaks
1.Ethanol
2.C5
3.tert-Butanol
4.2-Methylbutene-2
Detailed Hydrocarbon Analysis on Rtx-DHA-100/Rtx-5 DHA Tuning Column
GC_PC00743A
ColumnRtx-DHA-100, 100 m, 0.25 mm ID, 0.50 µm (cat.# 10148)
using Rtx-5 DHA tuning column, 2.62 m, 0.25 mm ID, 1.0 μm
SampleCustom detailed hydrocarbon analysis (DHA) mix
Conc.: Neat
Injection
Inj. Vol.:0.1 µL split (split ratio 150:1)
Liner:4 mm cup splitter inlet liner with Siltek deactivation
Inj. Temp.:200 °C
Oven
Oven Temp.:35 °C
Carrier GasHe, constant flow
Flow Rate:2.3 mL/min
Linear Velocity:28 cm/sec
DetectorFID @ 250 °C
NotesC5 efficiency: 613,596 total theoretical plates
k' (C5): 0.489
tert-Butanol skewness: 1.25
Resolution (tert-butanol/2-methylbutene-2): 5.60

catalog number 20709-214.1 Cup splitter with Siltek® deactivation obsolete, recommend catalog number 20709

Resolution of Critical Pairs

There are a number of critical compound pairs that must be resolved as measured by an oxy set up blend mix. An Rtx-DHA-100 column meets all ASTM D6730-01 requirements for critical pair resolution, as demonstrated in Figure 2. A tuning column was used to achieve the highlighted resolutions based on retention of the aromatics (e.g., resolution for 1-methylcyclopentene/benzene = 1.5). In addition to qualifying for the ASTM D6730-01 analysis, Rtx-DHA-100 columns meet the similarly stringent Canadian General Standards Board CAN/CGSB 3.0 No. 14.3-99 requirements.

Figure 2: Critical pairs of gasoline components resolved per ASTM specifications, using an Rtx-DHA-100 column.

Resolve all critical pairs!

Peaks
1.Ethanol
2.C5 (n-pentane)
3.tert-Butanol
4.2-Methylbutene-2
5.2,3-Dimethylbutane
6.Methyl tert-butyl ether (MTBE)
7.C6 (n-hexane)
8.1-Methylcyclopentene
9.Benzene
10.Cyclohexane
11.3-Ethylpentane
12.trans-1,2-Dimethylcyclopentane
13.C7 (n-heptane)
14.2,3,3-Trimethylpentane
Peaks
15.Toluene
16.C8 (n-octane)
17.Ethylbenzene
18.p-Xylene
19.2,3-Dimethylheptane
20.C9 (n-nonane)
21.5-Methylnonane
22.1-Methyl-2-ethylbenzene
23.C10 (n-decane)
24.C11 (undecane)
25.1,2,3,5-Tetramethylbenzene
26.Naphthalene
27.C12 (dodecane)
28.1-Methylnaphthalene
29.C13 (tridecane)
Detailed Hydrocarbon Analysis (DHA) on  Rtx-DHA-100
GC_PC1284
ColumnRtx-DHA-100, 100 m, 0.25 mm ID, 0.50 µm (cat.# 10148)
using Rtx-5 DHA tuning column 2-5 m, 0.25 mm ID (cat.# 10165)
with universal Press-Tight connectors (cat.# 20429)
SampleOxy setup blend (cat.# 33034)
Injection
Inj. Vol.:0.1 µL split (split ratio 150:1)
Liner:Premium 4 mm Precision liner w/wool (cat.# 23305.1)
Inj. Temp.:250 °C
Oven
Oven Temp.:5 °C (hold 10 min) to 49 °C at 5 °C/min (hold 50 min) to 200 °C at 1.5 °C/min (hold 10 min)
Carrier GasHe, constant flow
Flow Rate:2.2 mL/min
DetectorFID @ 275 °C
Make-up Gas Flow Rate:30 mL/min
Make-up Gas Type:N2
Hydrogen flow:40 mL/min
Air flow:368 mL/min
InstrumentAgilent 7890B GC
NotesRestek's Rtx-DHA-100 column has the required selectivity to deliver adequate resolution between the critical pairs in ASTM Method D6730. Excellent column inertness provides peak shapes for oxygenated compounds that meet or exceed ASTM method criteria.

Chromatogram was obtained using 2.5 m of Rtx-5 DHA tuning column.

Speed Up Analysis Time Using Hydrogen

Rtx-DHA-100 columns easily meet all ASTM and CGSB method requirements when using helium as the carrier gas. However, analysis times can be improved significantly—with no loss in chromatographic performance—by switching to hydrogen as the carrier gas. Rtx-DHA-100 columns meet or exceed all criteria in these standardized methods in up to 50% less time when using hydrogen (Figure 3).

Figure 3: Achieve up to 50% faster analysis times using hydrogen instead of helium.

Optimized D6730
with hydrogen*

Optimized D6730
with helium*

Standard D6730
conditions

Approximate analysis time

72 min.

98 min.

146 min.

% Time savings (relative to standard method conditions)

51% faster

33% faster

* Optimized conditions and chromatographic results for hydrogen shown below; for helium, see Figure 2.


Peaks
1.Ethanol
2.Pentane (C5)
3.tert-Butanol
4.2-Methylbutene-2
5.2,3-Dimethylbutane
6.Methyl tert-butyl ether (MTBE)
7.Hexane (C6)
8.1-Methylcyclopentene
9.Benzene
10.Cyclohexane
11.3-Ethylpentane
12.1,2-Dimethylcyclopentane
13.Heptane (C7)
14.2,2,3-Trimethylpentane
15.2,3,3-Trimethylpentane
Peaks
16.Toluene
17.Octane (C8)
18.Ethylbenzene
19.p-Xylene
20.2,3-Dimethylheptane
21.Nonane (C9)
22.5-Methylnonane
23.1,2-Methylethylbenzene
24.Decane (C10)
25.Undecane (C11)
26.1,2,3,5-Tetramethylbenzene
27.Naphthalene
28.n-Dodecane (C12)
29.1-Methylnaphthalene
30.Tridecane (C13)
Fast Detailed Hydrocarbons Analysis (DHA) on Rtx-DHA-100/Rtx-5 DHA
GC_PC00774
ColumnRtx-DHA-100, 100 m, 0.25 mm ID, 0.50 µm (cat.# 10148)
using Rtx-5 DHA tuning column* 2-5 m, 0.25 mm ID,
SampleDHA/oxygenates setup blend
Injection
Inj. Vol.:0.1 µL split (split ratio 150:1)
Liner:4 mm ID deactivated cup inlet liner (cat.# 20835 [replaced by 20836])
Inj. Temp.:250 °C
Oven
Carrier GasH2, constant flow
Flow Rate:3.62 mL/min
Linear Velocity:55 cm/sec
DetectorFID @ 300 °C
Notes
*Note that the exact length of the tuning column was determined experimentally based on the resolution of critical pairs as per method D6730-01 (reapproved 2011).

Oven Temp.
A: 35 °C
B: 5 °C (hold 8.32 min) (elute C5) to 48 °C at 22 °C/min (hold 26.32 min) (elute ethylbenzene) to 141 °C at 3.20 °C/min (elute C12) to 300 °C at 1 °C/min


A: Front end of DHA/oxygenates setup blend
C5 Efficiency: 586,825 plates
C5 k': 0.476
tert-Butanol skew: 2.10
Resolution: tert-Butanol/2-methylbutene-2: 5.39


AcknowledgementChromatogram courtesy of Neil Johansen, Inc., Aztec, New Mexico, in association with Envantage Analytical Software, Inc., Cleveland, Ohio.

Superior Performance for DHA Analysis

A comparison of DHA columns (also referred to as PIANO, PIONA, or PONA columns by other manufacturers) shows that the Rtx-DHA-100 column is the best overall DHA column for peak shape, theoretical plates, and required resolution. Figure 4 shows that, at 35 °C, as specified in the ASTM methods, the Competitor A and Competitor B PONA columns did not meet ASTM D6730 method specifications. The Competitor C and Competitor D PONA columns performed within specifications, but column efficiency was less than ideal. In contrast, the performance of the Rtx-DHA-100 column at
35 °C was well within ASTM D6730 method specifications, and column efficiency exceeded the specification. The column also performed well at sub-ambient temperature. [Additional evidence of Rtx-DHA-100 column performance is available at www.restek.com/DHAreport, which shows processed data from Neil Johansen identifying more than 400 individual components in finished gasoline.]

Figure 4: Rtx-DHA-100 columns outperform competitor columns for detailed hydrocarbon analysis.

PONA Test Mix

ASTM D6730 guidelines

Rtx-DHA-100

Competitor A

Competitor B

Competitor C

Competitor D

Minimum C5 Efficiency*

400,000-550,000 plates

613,596

522,974

466,089

489,991

483,449

k' (C5)

0.45-0.50

0.49

0.46

0.51**

0.47

0.46

tert-butanol skewness

>1.00-<5.00

1.25

>5.00**

3.60

1.71

1.59

Resolution (tert-butanol/2-methylbutene-2)*

3.25-5.25

5.60

1.00**

4.32

5.01

5.07

* Minimum values; criteria may be exceeded for these parameters.

** Fails method criteria (results based on analyses at 35 °C).




Column
Sample
Injection

Inj. Vol.:
Inj. temp.:
Oven
Oven temp.:
Carrier gas
Linear velocity:
Detector
Notes

Column A:
Column B:
Column C:
Column D:
Rtx-DHA-100:

     Peaks
1. Ethanol
2. Pentane (C5)
3. tert-Butanol
4. 2-Methylbutene-2

100 m, 0.25 mm ID, 0.50 μm
DHA Oxy-Setup mix (Transition Labs #94100)

0.01 μL split (split ratio 150:1)
275 °C

35 °C and Method D 6730 temperature profile
hydrogen
Linear velocity: 48 cm/sec.
FID @ 300 °C
Temperature Profile
5 °C > 8.23 min. > 22 °C/min. > 48 min.
5 °C > 8.84 min. > 22 °C/min. > 48 min.
5 °C > 8.87 min. > 22 °C/min. > 48 min.
5 °C > 8.19 min. > 22 °C/min. > 48 min.
5 °C > 8.20 min. > 22 °C/min. > 48 min.

Conclusion

Rtx-DHA-100 columns offer the best overall value and performance for detailed hydrocarbon analysis. These columns meet or exceed all ASTM D6730-01 and Canadian General Standards Board method requirements and outperform other commercially available columns. Make your next DHA column an Rtx-DHA-100 column—individually tested to meet DHA method criteria, assuring outstanding performance and column-to-column reproducibility.