food& flavors
Applications
note
Restek Corporation • (800) 356-1688 • (814) 353-1300 •
#59358
food& flavors
Determining sulfur impurities in beverage-grade carbon dioxide using the
Rt-XLSulfur
™
micropacked column
ASulfinert
™
-treated sampling system designed to provide
sensitive analysis of trace-level sulfur compounds.
Figure 1
International Society of Beverage Technologists (ISBT)
targets themost commonVSCs.
Table I
The taste and aroma of a carbonated beverage can be affected by
trace impurities from the carbonation process. Therefore, gas
producers go to great lengths to purify carbon dioxide (CO
2
).
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 beverage industry has spentmuch
research time and dollarsmonitoring the impurities inCO
2
.
Themost common impurities inCO
2
are hydrocarbons, alcohols,
permanent gases, and sulfur compounds. Sulfur impurities are
the predominant problem, adding unwanted taste and odor to
beverages. Themost common volatile sulfur compound (VSC)
impurities, listed inTable I, are targeted formonitoring by the
International Society of BeverageTechnologists (ISBT). Of this
group, hydrogen sulfide, carbonyl sulfide, sulfur dioxide,
dimethyl sulfide, andmethylmercaptan are the onesmost com-
monly found in beverage-gradeCO
2
. ISBTguidelines specify
Total Sulfur Content* (TSC) as 0.1ppm (v/v)maximum, exclud-
ing sulfur dioxide; themaximum level of sulfur dioxidemust not
exceed 1ppm (v/v)maximum.
The ability tomeasure reactive sulfur compounds at these levels
requires a highly inert chromatographic system. TheRestekRt-
XLSulfur
™
micropacked column is a powerful analytical tool that
can detect sulfurs inCO
2
at levels of 20ppbv, far below the ISBT
guideline for TSC. This column also achieves the critical separa-
tion of hydrogen sulfide, carbonyl sulfide, and sulfur dioxide as
defined in ISBTProcedure 14.0. TheRt-XLSulfur
™
micropacked
column contains amodified divinyl benzene polymer packed into
Sulfinert
™
tubing, which is ametal tubing specially deactivated
formonitoring ppb levels of active sulfur compounds. Other fea-
tures of theRt-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 introduced onto the column using aValco
®
six-port
sampling valve, fittedwith a 1mLsampling loop (cat. #22845).
When the valve, sample loop, and all other surfaces in the sam-
ple pathway are deactivated using the Sulfinert
™
process, the ana-
lyst will see improved response compared to systems using con-
ventional deactivations (Figure 1). The specialized inertness of
the Sulfinert
™
process is critical for the system to achieve detec-
tion limits of 50ppbv for sulfur dioxide and the other target sulfur
impurities.
We evaluated the effectiveness of theRt-XLSulfur
™
column and
Sulfinert
™
sampling system by analyzing bulkCO
2
andCO
2
spikedwith a sulfur standard (Figure 2). Notice how even low
ppbv levels of sulfur compounds can be detected.We also sam-
pled andmeasured theTSC* of two top brands of cola and a
domestic beer (Figures 3 and 4). The colas show no sulfur con-
tent, ensuring that theCO
2
used for carbonationwas clean. The
beer shows sulfurs that naturally occur during the fermentation
process.
This system is sensitive enough tomonitor the levels of sulfur in
CO
2
during the carbonation process, or in the headspace of the
beverage after carbonation. TheTSC* generated from headspace
sampling of these products demonstrates the ability of theRt-
XLSulfur
™
column and the Sulfinert
™
-deactivatedGC system to
easily detect sulfur compounds at the 20ppbv level. The combina-
tion of theRt-XLSulfur
™
micropacked column and a Sulfinert
™
-
deactivated sample introduction system provides a state-of-the-
art, robust sampling and analysis technique for ppbv levels of
VSCs in beverage-gradeCO
2
.
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
dimethyl disulfide
isobutyl mercaptan
carbon disulfide
n
-butyl mercaptan
tert
-amyl mercaptan
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
IDmicropacked
Rt-XLSulfur
™
column
*TSC iswithout SO
2
.
