Application Note
Energy and chemicals

Determination of Chloride in Crude
Oils using an Agilent 8900 ICP-QQQ
Fast, accurate analysis of crude oils following
direct dilution in an o-xylene-based diluent

AuthorIntroduction

Jenny Nelson

As stated in a recent study, chlorinated compounds are often removed fromcrude oil refinery streams (1). To avoid corrosion and fouling during distillation,
the concentration of chlorides in crude oil should be less than 1 mg/L. Despite its
sensitivity, there are no ASTM standard test methods that use inductively coupledplasma mass spectrometry (ICP-MS) for the measurement of chloride in crude oils.
However, ASTM D8110–17 test method specifies ICP-MS for the rapid determinationof seven elements in distillate petroleum products (2). Because of its multi-element
capabilities, ICP-MS is increasingly used to test petrochemical-based samples
for a wide range of elements. It would be convenient to also use ICP-MS for themeasurement of chloride.

Agilent Technologies Inc.,
Santa Clara, California, USA
Laura Poirier and Francisco
Lopez-Linares
Chevron Energy TechnologyCompany, Richmond,
California, USAThe determination of chloride in complex matrices is challenging by conventional
single quadrupole ICP-QMS. Petroleum crude oil and derivatives may contain sulfur(S), nitrogen (N), and oxygen (O) at variable concentrations, which could promotemultiple interferences in the plasma. The 35Cl isotope (75.8%natural abundance) suffers polyatomic interferences from
16 18 1 +O O H and 34S1H+. Also, Cl is poorly ionized in the plasma
because of its high first ionization potential of 12.967 eV,
which affects the sensitivity of measurements by ICP-MS.
Collision/reaction cells (CRCs) are used successfully tocontrol many common polyatomic interferences in ICP-QMS.
However, ICP-QMS cannot reduce the 34S1H+ interference
sufficiently to allow the accurate determination of Cl at
trace levels in samples that contain a high level of S (1).

Experimental
Calibration standard and crude oil sample preparation

Based on the findings of previous studies, hydrogen wasused as a reactive cell gas for the determination of 35Cl+(4, 5). Cl+ reacts exothermically with H2 to form HCl+, HCl+ thencontinues to react via a chain reaction to form ClH2+. This
allows the use of the “mass-shift” approach, where the analyte
reacts with a reaction gas in the cell to form a product ion,shifting it away from the interference. In this study, Q1 was
set to m/z 35 to allow 35Cl+ ions to enter the CRC. The analyteions then reacted with H2 in the cell to form 35Cl1H1H+, while
the polyatomic interference ions (16O18O1H+ and 34S1H+) did notreact with H2. Q2 was set to m/z 37, allowing the product ofion 35ClH2+ to pass to the detector, free of interference.
ICP-QQQ instrument operating parameters are detailedin Table 1. For comparison purposes, chlorine was alsomeasured using Instrumental Neutron Activation Analysis(INAA), which was carried out by EAI-Elemental Analysis, Inc,an elemental testing facility located in Lexington, KY, USA.

The calibration standards were prepared using different
concentrations of a Cl organic solvent standard (Conostan,Quebec, Canada) prepared in a diluent. The diluent comprised
90 parts o-xylene (Fisher Scientific, NJ, USA) to 10 parts
matrix modifier. The matrix modifier was made from mineraloil (80%, Fisher Scientific), a dispersant (20%, Chevron
Oronite), and scandium (Sc) and yttrium (Y) spiked at
0.1 mg/kg as internal standards (Conostan, Quebec, Canada).
Multiple calibration standards, ranging from 1 to 1000 mg/kg, were prepared by weight. The diluent (90% o-xylene to 10%
matrix modifier) was run as a blank.

Table 1. ICP-QQQ operating conditions.

Direct dilution
The composition of the 12 crude oil samples used in thisstudy ranged from C (84 to 89 wt.%), H (10 to 14 wt.%), S (0.3to 2.5 wt.%), and N (400 to 2500 mg/kg). The samples werediluted 1:5 or 1:10 (using diluent) to allow all Cl concentrations
to fit within the calibration range. Standard Reference Material(SRM) NIST 1634c trace elements in fuel oil (Gaithersburg,MD, USA) was prepared at 1:5 and 1:10 dilution. All samples
were shaken for two hours in a mechanical shaker. If any
residue was seen on the vial walls, a vortex shaker was used
to improve sample homogenization.

Instrumentation
An Agilent 8900 ICP-QQQ (#100 for advanced applications)
was used. The instrument was equipped with platinum
sampling and skimmer cones, a concentric glass nebulizer,quartz spray chamber, and quartz torch with 1 mm injector.
The diluted samples were introduced directly into theICP-QQQ via a peristaltic pump fitted with solvent-resistanttubing (0.89 mm i.d., bought from Cole Parmer). Other parts
were from the Agilent Organic Solvent Introduction kit (p/nG3280-60580). An optional gas ﬂow of 20% O2 in Ar wasadded to the carrier gas to prevent carbon building up on
the interface cones. An o-xylene rinse was used between
each sample to eliminate any carry-over from the sample
introduction system.

2ParameterValue

RF power (W)1500

Nebulizer gas flow rate (L/min)

0.4

Sampling depth (mm)8Spray chamber temp (°C)

–2Option gas flow rate (mL/min);
Ar 80%, O2 20%

0.35 (35%)

Make up gas flow rate (L/min)

0.1

Nebulizer pump speed (rps)

0.1

H2 cell gas flow rate (mL/min)

4.6

Octopole bias (V)–18

Octopole RF (V)180

Energy discrimination (V)0Monitored masses

Q1:35, Q2:37

Integration time (s)3Results and discussion
The calibration plot for 35Cl is shown in Figure 1. Threesigma detection limits (DL), limits of quantification (LOQ),and background concentration (BEC) for 35Cl were determinedby measuring a blank solution (o-xylene diluent containing amatrix modifier and internal standard) ten times. The results
are shown in Table 2.

Table 3. Determination of Cl concentration in NIST 1634c SRM in o-xylene
diluent using ICP-QQQ.
Dilution Factor 5Cl35

Dilution Factor 10

Concentration(mg/kg)*Recovery(%)

Concentration(mg/kg)*Recovery(%)

44.33 ± 1.00

9948.28 ± 1.89107*NIST reference value for Cl = 45 mg/kg, S = 2 wt%

Quantitative analysis of crude oil samples
Twelve petroleum crude oil samples with a sulfur content
spanning from 0.38 up to 2.01 wt.% and hydrogen to carbon(H/C) ratio from 1.68 to 1.88 were analyzed by ICP-QQQ.
The H/C provides an insight to the aromatic/paraffinic natureof the crude samples, which has implications for trading,
processing, and stability of crude. The quantitative resultsfor Cl measurements are given in Table 4.
Figure 1. Calibration plot of Cl in o-xylene. Units: mg/kg (ppm).

Table 4. Determination of the Cl concentrations in 12 petroleum crude oilsamples in o-xylene diluent using ICP-QQQ operating in H2 mass-shift mode.
Dilution factor 1:5. n = 3.

Table 2. DL, LOQ, and BEC of 35Cl in a blank solution determined by
ICP-QQQ in H2 mass-shift mode.

SampleS(%)

H/C

S10.381.84

22.32 ± 0.36

S20.38

1.85

S30.38

S4Cl35Detection Limit(mg/kg)

LOQ(mg/kg)BEC(mg/kg)0.01

0.040.24

Reference material analysis
Chlorine was determined in the petroleum feedstock SRM
using the 8900 ICP-QQQ operating in H2 mass-shift mode.
The reference value for chlorine in NIST 1634c is 45 mg/kg.
The SRM was diluted in o-xylene at two different dilution
factors. Other than carbon and hydrogen, real petroleum
samples contain heteroatoms, S, N, and O, and metals suchas V and Ni, among others. The sulfur content of NIST 1634c
is around 2 wt.%, so the SRM is a useful test sample forICP-QQQ given the likely interference on 35Cl by 34S1H+.
As can be seen from the results presented in Table 3,excellent recoveries were obtained for 35Cl, irrespective ofthe dilution factor (100 ± 10%). Since H2 effectively reacts
with Cl+ to form ClH2+, the interferences on 35Cl can beavoided by measuring the product ion 35ClH2+ at m/z 37.

35
Cl Measured Sample
Concentration(mg/kg)

S(%)

H/C35
Cl Measured
Concentration(mg/kg)

S7

1.19

1.78

24.80 ± 1.04

12.80 ± 0.07

S81.191.78

20.78 ± 0.08

1.86

22.84 ± 0.16

S91.97

1.71

48.33 ± 2.38

0.38

1.88

6.15 ± 0.05

S101.99

1.68

18.25 ± 0.24S50.50

1.85

33.89 ± 0.31

S112.01

1.70

50.35 ± 3.00

S60.591.87

24.87 ± 0.15

S122.01

1.71

17.68 ± 0.55

Comparison of results
To further evaluate the accuracy of the ICP-QQQ method,quantitative results for Cl were compared with the results
obtained by INAA. The results obtained for three crude samples
are shown in Table 5.
Table 5. Comparison of measured Cl concentrations in crude oil samples
obtained by ICP-QQQ (dilution factor 1:5) and INAA.
Measured Cl Concentration (mg/kg)
SampleICP-QQQ

INAA

S212.80 ± 0.07

14.40 ± 0.59

S46.19 ± 0.05

12.90 ± 0.53

S533.89 ± 0.31

25.30 ± 0.91

3

Depending on the sample, the agreement between the results
obtained by ICP-QQQ and INAA was reasonably close. Theagreement for sample S2 was around 89%, whereas it wasslightly higher at 134% for sample S5. A similar observation
was reported recently for these types of samples, using thesame techniques (6). The low bias of the ICP-QQQ result forsample S4 suggests that the sample may contain solids or isheterogeneous. A qualitative XRF analysis of S4 suggested
the presence of solids (most likely NaCl), which would explain
why the ICP-QQQ result was low. It is likely that S4 wasn’t fully
solubilized or well dispersed in the o-xylene diluent.

References
1.

Jenny Nelson, Laura Poirier, and Francisco LopezLinares, Determination of Chloride in Crude Oils by Direct
Dilution using Inductively Coupled Plasma Tandem Mass
Spectrometry (ICP-MS/MS), J. Anal. At. Spectrom., 2019,
Advance Article, DOI 10.1039/C9JA00096H

2.

ASTM D8110–17 Standard Test Method for ElementalAnalysis of Distillate Products by Inductively Coupled
Plasma Mass Spectrometry (ICP-MS). ASTM
International, West Conshohocken, PA, 2017,www.astm.org/Standards/D8110.htm

3.

Handbook of ICP-QQQ Applications using the Agilent
8800 and 8900, Agilent publication, 5991-2802EN

4.

Naoki Sugiyama, Trace level analysis of sulfur,phosphorus, silicon and chlorine in NMP using theAgilent 8800 Triple Quadrupole ICP-MS, Agilent
publication 5991-2303EN

5.

Kazumi Nakano, Ultra low-level determination ofphosphorus, sulfur, silicon, and chlorine using theAgilent 8900 ICP-QQQ, Agilent publication, 5991-6852EN

6.

Adriana Doyle, Alvaro Saavedra, Maria Luiza B. Tristão,Márcio Nele, Ricardo Q. Aucélio, Direct chlorine
determination in crude oils by energy dispersive X-ray
fluorescence spectrometry: An improved method basedon a proper strategy for sample homogenization andcalibration with inorganic standards, Spectrochimica
Acta Part B. 2011, 66, 368–372

Conclusion
The Agilent 8900 ICP-QQQ is suitable for the determinationof chlorine in petroleum crude samples. Despite the complex
matrix, potential interferences on Cl ions originating from thecrude petroleum samples were handled effectively using
MS/MS technology. MS/MS enables more consistentand reliable reaction gas methods to be used for difficult
elements, such as chlorine in complex matrices, than single
quadrupole ICP-MS.
In this study, a BEC of 240 µg/kg was achieved for the mostabundant Cl isotope, 35Cl+, using mass-shift mode and H2 cellgas. Interferences from 16O18O1H+ and 34S1H+ on 35Cl+ were
avoided by measuring the product ion 35ClH2+ at m/z 37.
A NIST trace element in fuel oil SRM and 12 crude oil samples
were prepared for analysis using direct dilution. The speciallyprepared diluent contained o-xylene and a mineral oil matrix
modifier, a dispersant, and internal standards. Excellent
recoveries of Cl (99 and 107%) in the SRM were determinedat two different dilution factors (5 and 10).
The petroleum crude samples were analyzed using
ICP-QQQ, and some of the results were checked using INNA.
The results show the importance of fully solubilized samples
when using direct dilution as the sample preparation techniqueto avoid biased results due to the presence of particles.
Chloride was measured above the potential-corrosion trigger
threshold of 1 mg/L in all 12 crude oil samples, indicating arisk of corrosion at refining facilities from the formation of HCl.

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This information is subject to change without notice.
© Agilent Technologies, Inc. 2019
Printed in the USA, July 9, 20195994-1094EN

More information
For a full account of the method development, see
Jenny Nelson, Laura Poirier, and Francisco LopezLinares, Determination of Chloride in Crude Oils by Direct
Dilution using Inductively Coupled Plasma Tandem Mass
Spectrometry (ICP-MS/MS), J. Anal. At. Spectrom., 2019,
Advance Article, DOI 10.1039/C9JA00096H