Chemical/Petrochemical Articles

How Good is Your PONA Column?

Data-Based Decisions Help Simplify the Choice

By Barry L. Burger, Innovations Chemist

When tested, most PONA columns do not meet ASTM D-6730 method specifications.
Restek 100-meter PONA column meets all ASTM specifications.
Restek PONA column is compatible with hydrogen carrier gas.

So, you’re ready to purchase a PONA column. But, with all the options available today, which manufacturer do you purchase the column from, and what criteria do you consider in making your selection? Do you select the most expensive column, thinking higher price means quality, and therefore higher performance? Or, do you take the advice of the guy in the laboratory down the hall when he tells you it doesn’t matter whose column you buy — they are all the same? That statement cannot be further from reality. Many variables affect how well a column will perform in the demanding ASTM D-6730 method: column length and ID, polymer deposition, and column deactivation, to name a few. These all vary among manufacturers, and the effects of these variations are substantiated by data.

To assist you in making a data-based decision when selecting a PONA column for use in the ASTM D-6730 method, Restek purchased designated versions of the 100 meter x 0.25mm ID x 0.5df PONA column from four vendors. We evaluated these columns, and our own Rtx®-1PONA column, using the proposed D-6730 method that calls for hydrogen carrier gas, which reduces tridecane retention time from 140 minutes to approximately 70 minutes. (For more advantages of using hydrogen as the carrier gas, see Parker ChromGas® Hydrogen Generators, Is your lab wasting money on bottled gas?)

We performed the comparisons using an Agilent 6890 GC equipped with a flame ionization detector and ChemStation data collection software. In all analyses we used hydrogen carrier gas in the constant flow mode, adjusted the dead time to 3.50 ±0.05 minutes at 35°C, and set a split ratio of 150:1. Data presented here were generated at 35°C, as specified by the ASTM method, to determine if a column is suitable for adding a tuning column and performing the PONA analysis. We used Transition Labs’ (Golden, Colorado) DHA Oxy-Setup mix (Transition Labs part number 94100) for this determination. We evaluated all five columns under the same conditions, and measured each against the specifications for ASTM D-6730, as follows:

Parameter
theoretical plates for C5:
K’ for C5:
peak asymmetry for t-butanol:
resolution of t-butanol/2-methylbutene-2:

ASTM D-6730 Specification
450,000 - 550,000
0.45 - 0.50
>1.00 - <5.00
3.25 - 5.25

On opening the competitor PONA column containers we discovered that only one of the four manufacturers provided QA data pertinent to the ASTM 6730 method — each of the other three provided a chromatogram of a sample unrelated to the method. Further, one column did not meet the ASTM D-6730 minimum efficiency specification of 450,000 theoretical plates.

Figure 1 shows that, at 35°C, the “Vendor A” PONA column did not meet ASTM D-6730 method specifications. Further, at sub-ambient temperature and using hydrogen as the carrier gas, per ASTM D-6730 method, peak asymmetry for the oxygenates was unacceptable, and the elution order for t-butanol and 2-methylbutene-2 was reversed. Similarly, at 35°C, the “Vendor B” PONA column did not meet method specifications. At 35°C, the “Vendor C” and “Vendor D” PONA columns performed well within specifications, but column efficiency was less than ideal.

In contrast, the performance of the Restek PONA column at 35°C was well within ASTM 6730 method specifications, and column efficiency exceeded the specification. The column also performed well at sub-ambient temperature and using hydrogen as the carrier gas.

As these figures show, all PONA columns — or any columns, for that matter — are NOT the same. You the customer, have the final say about which vendor to select for your analytical column needs. If you make data based decisions, you can choose wisely.

Figure 1 An Rtx®-1PONA column offers superior performance for ASTM D-6730 method specifications.

Vendor A Column

efficiency for C5: 522,974 plates K’ for C5: 0.46 peak asymmetry for t-butanol: ;5.00 does not meet ASTM D 6730 specification resolution of t butanol/ 2-methylbutene-2: 1.00 does not meet ASTM D 6730 specification column 2416OU


Vendor B Column

efficiency for C5: 466,089 plates K’ for C5: 0.51 does not meet ASTM D 6730 specification peak asymmetry for t-butanol: 3.60 resolution of t butanol/2-methylbutene-2: 4.32 column 54818


Vendor C Column

efficiency for C5: 489,991 plates K’ for C5: 0.47 peak asymmetry for t-butanol: 1.71 resolution of t butanol/ 2-methylbutene-2: 5.01 column 7530


Vendor D Column

efficiency for C5: 483,449 plates K’ for C5: 0.46 peak asymmetry for t-butanol: 1.59 resolution of t butanol/ 2-methylbutene-2: 5.07 column 19091S004


Rtx®-1PONA Column

efficiency for C5: 551,294 plates K’ for C5: 0.48 peak asymmetry for t-butanol: 1.31 resolution of t butanol/ 2-methylbutene-2: 4.84 ethanol pentane (C5) t-butanol 2-methylbutene-2

Column:	100m, 0.25mm ID, 0.50µm
Sample:	DHA Oxy-Setup mix (Transition Labs #94100)
Inj.:	0.01µL split (split ratio 150:1)
Inj. temp.:	275°C
Carrier gas:	hydrogen
Linear velocity:	48cm/sec.
Oven temp.:	35°C and Method D 6730 temperature profile
Det.:	FID
Det. temp.:	300°C
Temperature Profile
Column A:	5°C > 8.23 min. > 22°C/min. > 48 min.
Column B:	5°C > 8.84 min. > 22°C/min. > 48 min.
Column C:	5°C > 8.87 min. > 22°C/min. > 48 min.
Column D:	5°C > 8.19 min. > 22°C/min. > 48 min.
Rtx®-1PONA:	5°C > 8.20 min. > 22°C/min. > 48 min.