Hydrocarbon Processing - December 2021 - 18

Process Controls, Instrumentation
and Automation
D. KUTSCHER, Thermo Fisher
Scientific, Bremen, Germany
Improved methods for trace element analysis
of challenging petrochemical samples
There is no doubt that the purpose of refining crude oils
into natural raw materials is crucial to produce a vast array of
fuels and products used in our daily lives. However, impurities
can often enter the refinement process and reduce the quality
grades of crude oil extracts, intermediates and final products.
Typical impurities, such as metals (e.g., vanadium, mercury or
lead), are known as catalyst poisons. These can severely impact
the performance and value of the final product and have
detrimental effects on the petroleum refining processes. These
metallic impurities can affect products even at very low levels
and have the potential to cause interruptions in the production
cycle by causing equipment corrosion, catalyst poisoning and
build-up in deposits in engines.
Other elements like arsenic or sulfur are released as toxic
emissions when fuels are combusted. Sulfur is a common impurity
in crude oil. Sour crude oils with high quantities of sulfur
compounds must have sulfur extracted to improve the quality
of the oil, as well as to adhere to air quality requirements.
To help reduce the presence of impurities in petrochemical
products, more stringent industry and environmental standards
mean oil samples must be analyzed with high accuracy from
crude, intermediate and final product stages of refinement.
Considering these challenges that impurities cause to the
petrochemical industry, it is critical for laboratories to monitor
the levels of impurities (e.g., metals and sulfur) in common
petrochemical products with highly sensitive methods. This
article will discuss how advances in elemental mass spectrometry
systems are enabling rapid and accurate element analysis of
impurities, and how small changes in the sample introduction
system-such as the use of ceramic torches-are further boosting
operational capacities.
The challenges of trace element analysis. In many laboratories,
the analysis of crude, intermediates and final products
for trace elements is accomplished by using inductively coupled
plasma optical emissions spectrometry (ICP-OES) or mass
spectrometry (ICP-MS). ICP-OES is a highly flexible technique
that can perform fast and robust analyses of samples. ICPMS
is less commonly used, although it offers detection limits
improved by several orders of magnitude and enables identification
and subsequent quantification of sulfur containing compounds
when it is coupled with a suitable separation technique,
such as gas chromatography (GC).
Testing laboratories face several challenges when monitoring
petrochemical impurities. First, the variability of physicochemical
properties of petrochemical products means dedicated
method workflows for each sample type are often required.
18 DECEMBER 2021 | HydrocarbonProcessing.com
Different viscosities of petroleum and many of its derivatives
make it difficult to analyze multiple sample types directly by
ICP-OES or ICP-MS using a single method.
For example, organic samples must be aspirated into plasma
for analysis, and several steps must be taken to prevent carbon
build-up and minimize background interferences. High carbon
is problematic for analysis, as it may deposit on the system
and can cause interferences on analytes, such as chromium
and vanadium. Combustible organic samples (e.g., naphtha or
aviation turbine fuel) have particularly high carbon content, an
issue that increases the potential for carbon deposition in the
torch and interface region of mass spectrometer systems.
A major challenge faced by using ICP-OES is the limit of detection
(LOD) possible for impurities. ICP-OES usually has a
LOD in the parts per billion (ppb) range, whereas ICP-MS can
achieve parts per trillion (ppt) when detecting analytes. While
this higher sensitivity of ICP-MS is beneficial, the method can
have challenges in measuring key elements, such as phosphorus
and sulfur at low levels because they are strongly interfered.
Improving testing quality and efficiency with triple
quadrupole ICP-MS workflows. New advances in ICP-MS
technologies are helping laboratories to overcome many of
these challenges in petrochemical analysis. Advanced ICP-MS
technologies are greatly improving detection limits and lowering
interference levels for elements, like phosphorus and sulfur.
ICP-MS systems also rapidly decrease analysis times, allowing
higher throughput analysis of multiple samples. ICP-MS-based
methodologies are also easy to learn, with straightforward
method set-up and clear data visualization, meaning that laboratories
can train scientists quicker for petrochemical analysis.
Single quadrupole ICP-MS provides collision cell technology
with helium gas and kinetic energy discrimination (KED),
which enables many argon- and carbon-based polyatomic interferences
to be removed. While single quadrupole ICP-MS
systems generally fulfil the requirements in terms of sensitivity
and selectivity, they often have problems analyzing sulfur and
phosphorus due to high levels of interference.
Triple quadrupole ICP-MS systems provide improved accuracy
and detection limits for elements challenged by severe
interferences. The solution lies with an alternate method of
interference removal. With single quadrupole systems, interferences
with sulfur are not fully removable using helium and
KED. However, triple quadrupole ICP-MS uses oxygen (O2
the cell gas to convert sulfur to 32S16
from the very large 16
) as
O+, thereby, moving it away
O2
+ interference and leading to dramatically
improved detection limits.
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