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The taste and aroma of a carbonated beverage can
be affected by trace impurities from the carbona-
tion process. Therefore, gas producers go to great
lengths to purify carbon dioxide (CO2). Carbon
dioxide, a by-product of oil refining, fermentation,
and power generating facilities, must be extremely
pure to be suitable for a beverage additive. The bev-
erage industry has spent much research time and
money monitoring the impurities in CO2.
The most common impurities in CO2 are hydrocar-
bons, alcohols, permanent gases, and sulfur com-
pounds. Sulfur impurities are the predominant
problem, adding unwanted taste and odor to bever-
ages. The most common volatile sulfur compounds
(VSC) impurities are targeted for monitoring by the
International Society of Beverage Technologists
(ISBT) (Table I). Of this group, hydrogen sulfide,
carbonyl sulfide, sulfur dioxide, dimethyl sulfide,
and methyl mercaptan are the ones most commonly
found in beverage-grade CO 2. ISBT guidelines spec-
ify Total Sulfur Content* (TSC) as 0.1ppm (v/v)
maximum, excluding sulfur dioxide; the maximum
level of sulfur dioxide must not exceed 1ppm v/v
maximum.
The ability to measure reactive sulfur compounds at
these levels requires a highly inert chromatography
system. The Restek Rt-XLSulfur™ micropacked col-
umn is a powerful analytical tool that can detect
by Neil Mosesman, GC Columns Product Marketing Manager,
and Barry Burger, Innovations Chemist
Analyzing Trace Sulfur
Compounds in CO2
Rt-XLSulfur™ Packed Column and
Sulfinert™ System
✔ Detects sulfur compounds at low ppbv levels.
✔ Thermal stability to 300°C for longer column lifetime.
Table I
Sulfur compounds can affect the taste and
aroma of beer.
hydrogen sulfide isopropyl mercaptan
carbonyl sulfide methyl ethyl sulfide
methyl mercaptan n-propyl mercaptan
ethyl mercaptan tert-butyl mercaptan
sulfur dioxide sec-butyl mercaptan
dimethyl sulfide diethyl sulfide
dimethy disulfide isobutyl mercaptan
carbon disulfide n-butyl mercaptan
tert-amyl mercaptan
sulfurs in CO 2 at levels of 20ppbv, far below the
ISBT guideline for total sulfur content. This column
also achieves the critical separation of hydrogen
sulfide, carbonyl sulfide, and sulfur dioxide as
defined in ISBT Procedure 14.0. The Rt-XLSulfur™
micropacked column contains a modified divinyl
benzene polymer packed into Sulfinert™ tubing,
which is a metal tubing specially deactivated for
monitoring ppbv levels of active sulfur compounds.
Other features of the Rt-XLSulfur ™ column include
low bleed and thermal stability up to 300°C.
Sample introduction into the column is another
critical aspect of obtaining accurate analytical
results for sulfur compounds. The sample is intro-
duced onto the column using a Valco ® six-port
sampling valve, fitted with a 1mL sampling loop
*Total Sulfur Content seen with an asterisk indicates it is without SO2 .
Figure 1
A sampling system was designed to optimize trace-level sulfur analysis without adsorption.
Sulfinert™
1mL
sample
loop
bulk CO 2
cylinder
Sulfinert™
6-port Valco®
valve
orifice=0.0060"
rotor composition:
polyimide/PTFE/carbon
composite
Sievers
Chemiluminescence
Detector
1m x
0.75mm ID
micropacked
Rt-XLSulfur™
column
(cat. #22845). When the valve, sample loop, and
all other surfaces in the sample pathway are deacti-
vated using the Sulfinert™ process, the analyst will
see improved response compared to systems using
conventional deactivations. We suggest connecting
your bulk CO2 via this system (Figure 1). The spe-
cialized inertness of the Sulfinert™ process is criti-
cal for the system to achieve detection limits of
50ppbv for sulfur dioxide and the other target sul-
fur impurities.
We evaluated the effectiveness of the RT-XLSulfur™
column and Sulfinert™ sampling system by analyz-
ing bulk CO 2 and CO 2 spiked with a sulfur standard
(Figure 2). Notice how even low ppbv of sulfurs
can be detected. We also sampled and measured
the TSC* of two top brands of cola and a domestic
beer (Figures 3 and 4). The colas show no sulfur
content, verifying that the CO 2 used for carbonation
was clean. The beer sample shows sulfur com-
pounds that naturally occur during the fermentation
process.
This system is sensitive enough to monitor the lev-
els of sulfur in CO2 during the carbonation process,
or in the headspace of the beverage after carbona-
tion. The TSC* generated from headspace sampling
of these products demonstrates the ability of the
RT-XLSulfur™ column and the Sulfinert™ -deactivated
GC system to easily detect sulfur compounds at the
20ppbv level. The combination of the Rt-XLSulfur™
micropacked column and a Sulfinert™ -deactivated
sample introduction system provide a state-of-the-
art, robust sampling and analysis technique for ppb
levels of VSCs in beverage-grade CO 2.