The purpose of this project is to demonstrate that accuracy, recovery and precision criteria in standard methods such as ASTM D 51843, IP 3774 and IP 5015 can be met by using borate fusion as a dissolution method for inductively coupled plasma emission spectroscopy (ICP-OES) analysis. This preparation step will be facilitated by using LeNeo fusion instrument. A lithium metaborate with 1.5% lithium bromide integrated (LiM/1.5% LiBr) flux is used instead of the lithium tetraborate blended with 10% lithium fluoride (LiT/LiF 90/10) flux suggested in the standards. This avoids the loss of silicon ensued by the reaction with fluoride and increases the solubility of the analytes found in fuel oil.
Fuel oil is one of the main by-products of petroleum refining. It is used as fuel for ocean liners and cargo ships engines. It is also used in power plants and industrial plants. Fluid catalytic cracking (FCC) is often found in the petroleum refining process to maximize the distillation of hydrocarbon with a high octane rate1. Some contaminants such as nickel, iron, vanadium, silicon, aluminium, sodium and calcium are found in FCC and are transferred in fuel oil during the refining process. It is important to find the concentration of these elements because they are adhesive at certain temperatures and they cause corrosion on the reheater tube surfaces of boilers as well as on the combustion chamber and components of fuel oil engines2. Corrosion should be avoided as much as possible because it causes wear and entails additional costs for maintenance or replacement.
The purpose of this project is to demonstrate that accuracy, recovery and precision criteria in standard methods such as ASTM D 51843, IP 3774 and IP 5015 can be met by using borate fusion as a dissolution method for inductively coupled plasma emission spectroscopy (ICP-OES) analysis. This preparation step will be facilitated by using LeNeo® fusion instrument. A lithium metaborate with 1.5% lithium bromide integrated (LiM/1.5% LiBr) flux is used instead of the lithium tetraborate blended with 10% lithium fluoride (LiT/LiF 90/10) flux suggested in the standards. This avoids the loss of silicon ensued by the reaction with fluoride and increases the solubility of the analytes found in fuel oil.
An automatic Claisse® LeNeo fusion instrument was used to create borate-based solutions. Its resistance-based electric system, excellent insulation properties and preset fusion programs allow a uniform heating, thus providing repeatable and reproducible fusion conditions as well as a perfect retention of volatile elements.
A Fisher Scientific™ Isotemp™ muffle furnace was used to ignite the samples.
A PerkinElmer® Optima® 7300 DV ICP-OES spectrometer was used to collect the data. The operating parameters used on the spectrometer are shown in Table 1.
| Nebulizer | GemTipTM Cross-Flow | Argon flow | Plasma: 16 L/min
Nebulizer: 0.8 L/min Auxiliary: 0.4 L/min |
| Spray chamber | Scott | ||
| Injector | Alumina 2 mm i.d. | ||
| RF | 1500 W | Sample flow rate | 1.0 mL/min |
Each sample was prepared according to the following steps before being submitted to the fusion process.
The sample was then mixed with 0.4 g of LiM/1.5% LiBr flux in a Pt/Au crucible. A fully automatic LeNeo instrument was used to fuse the sample. LeNeo fusion instrument automatically poured the melt into 80 mL of a 10% hydrochloric acid (HCl) solution and magnetically agitated the solution to obtain a complete dissolution.
The whole fusion and dissolution process took less than 15 minutes. The resulting solutios were then completed up to 100 mL in 10% HCl for subsequent analyses on a PerkinElmer Optima 7300 DV ICP-OES.
A matrix with a high content of easily ionizable elements (lithium in this case) can cause signal suppression or signal increase for some elements. Matrix matching and internal standards were used to counteract this effect. The dilution of the sample prevented any clogging caused by a matrix with a high salt content. The calibration solutions of all elements were done in a LiM/1.5% LiBr matrix, just like the sample. Calibration curves were made using a concentration range close to the sample concentrations. Sample concentrations are within the calibration range. Five points including the calibration blank were used for each element. The correlation of each curve was higher than 0.999.
Method detection limits (MDLs) were based on 10 replicate measurements of a series of diluted sample solutions. The MDL was calculated by multiplying the standard deviation of the 10 replicate measurements (S10) by 3 (see Table 2).
MDL = 3 x S10
The ICP-OES analysis method was validated for the determination of the analytes with the concentration ranges shown in Table 2.
| Elements
| Wavelength (nm)
| View
| Concentration range (mg/kg)
| MDL (mg/kg)
| |
|---|---|---|---|---|---|
| Minimum
| Maximum
| ||||
| Al
| 396.153
| Axial
| 5
| 150
| 0.01
|
| Ca
| 396.847
| Radial
| 3
| 100
| 0.3
|
| Fe
| 259.939
| Radial | 2
| 100
| 0.03
|
| Na
| 589.592
| Radial | 1
| 100
| 0.3
|
| Ni
| 227.022
| Axial | 1
| 100
| 0.02
|
| P
| 177.434
| Axial | 1
| 60
| 0.2
|
| Si
| 251.611
| Radial | 10
| 250
| 0.2
|
| V
| 270.093
| Axial | 1
| 400
| 0.04
|
| Zn | 202.548 | Axial | 1 | 70 | 0.02 |
The following table shows the accuracy obtained on 10 replicates of 4 fuel oil samples. These samples come from the round robin entitled 'Committee D2 Proficiency Testing Program # 6 Fuel Oil'. The accuracy is the proximity of results to the true value. True values were calculated on the mean values of each round robin samples.
| Elements | F61409
(%) | F61501
(%) | F61505
(%) | F61509
(%) |
|---|---|---|---|---|
| Al
| 99
| 91
| 89
| 89
|
| Si
| 97
| 97
| 98
| 97
|
Table 4 shows the recovery values obtained in 4 similar matrixes. Recovery was calculated on 5 replicates for each spiked sample.
| Elements
| F61409
(%) | F61501
(%) | F61505
(%) | F61509
(%) |
|---|---|---|---|---|
| Al
| 107
| 93
| 98
| 101
|
| Ca
| 97
| 95
| 100
| 100
|
| Fe
| 93
| 93
| 94
| 95
|
| Na
| 98
| 93
| 101
| 106
|
| Ni
| 95
| 101
| 97
| 101
|
| P
| 103
| 97
| 98
| 97
|
| Si
| 99
| 99
| 96
| 105
|
| V
| 99
| 95
| 106
| 98
|
| Zn
| 102
| 105
| 105
| 100
|
The experimental repeatability (SD10) was obtained by multiplying the standard deviation on 10 replicates that were prepared and analysed on different days by 2.776. Inside the concentration range, the experimental repeatability should not exceed the expected repeatability (SDstd) calculated in accordance with the standards 3, 4 and 5.
| Elements
| 1 mg/kg
| 2 mg/kg | 3 mg/kg
| 4 mg/kg
| 5 mg/kg
| 6 mg/kg
| 7 mg/kg
| 8 mg/kg
| 9 mg/kg
| 10 mg/kg
| Average
| SD10 mg/kg
| SDstd mg/kg
|
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Al*
| 3.0
| 3.2
| 3.3
| 3.2
| 3.6
| 3.4
| 3.0
| 3.0
| 3.3
| 3.5
| 3.2
| 0.6
| 0.2
|
| Ca
| 9.6
| 10.1
| 9.7
| 9.7
| 10.3
| 9.7
| 10.1
| 10.2
| 10.4
| 96
| 9.9
| 0.8
| 1.7
|
| Fe
| 27
| 29
| 28
| 28
| 28
| 27
| 28
| 27
| 28
| 28
| 28
| 2
| 4
|
| Na
| 19
| 20
| 19
| 19
| 19
| 19
| 18
| 18
| 20
| 19
| 19
| 2
| 3
|
| Ni
| 50
| 53
| 51
| 51
| 54
| 51
| 51
| 50
| 51
| 51
| 51
| 3
| 7
|
| P
| 3.9
| 3.9
| 3.7
| 4.0
| 3.7
| 3.9
| 3.5
| 3.7
| 3.7
| 3.8
| 3.8
| 0.4
| 1.2
|
| Si*
| 6.4
| 6.2
| 6.4
| 6.0
| 6.2
| 6.3
| 6.3
| 6.3
| 6.1
| 6.6
| 6.3
| 0.4
| 0.4
|
| V
| 219
| 226
| 218
| 221
| 218
| 215
| 221
| 219
| 218
| 217
| 219
| 8
| 17
|
| Zn
| 4.6
| 4.7
| 4.8
| 4.7
| 4.7
| 4.7
| 4.5
| 4.7
| 4.6
| 4.7
| 4.7
| 0.2
| 1.0 |
*Values outside the concentration range
The results presented in the previous tables indicate that sample preparation by fusion using a LiM/1.5% LiBr flux and ICP-OES analysis is effective to analyse fuel oil. Sample preparation with LeNeo instrument has interesting benefits for all laboratories. In fact, it is fast (a fusion cycle is completed in less than 15 minutes including dissolution) and simple (total dissolution without heating of acid). The accuracy obtained (higher than 89%) combined with an excellent recovery (between 93 to 107%) show that this method is highly reliable and valid. The good repeatability of the method proves that LeNeo instrument leads to a reproducible sample preparation and that it allows to meet the reproducibility and repeatability expected in the standards ASTM D 5184, IP 377 and IP 501.
[ 1 ] Julius Scherzer. 1989. Octane-Enhancing Zeolitic FCC Catalysts: Scientific and Technical Aspects. Catalysis Reviews: Science and Engineering. Vol. 31 (3). www.tandfonline.com
[ 2 ] International Organization for Standardization. 2010. ISO 8217/10 Petroleum Products – Fuels (class F) – Specifications of Marine Fuels. Fourth Edition. Switzerland. www.iso.org/iso/home.html
[ 3 ] ASTM International. 2012. ASTM D5184-12. Standard Test Methods for Determination of Aluminum and Silicon in Fuel Oils by Ashing, Fusion, Inductively Coupled Plasma Atomic Emission Spectrometry, and Atomic Absorption Spectrometry. West Conshohocken, PA. www.astm.org
[ 4 ] International Organization for Standardization. 2014. IP 377/95. Determination of Aluminium and Silicon in Fuel Oils - Inductively Coupled Plasma Emission and Atomic Absorption Spectroscopy Methods. Switzerland. www.iso.org/iso/home.html
[ 5 ] International Organization for Standardization. 2005. IP 501/05. Determination of Aluminium, Silicon, Vanadium, Nickel, Iron, Sodium, Calcium, Zinc and Phosphorus in Residual Fuel Oil by Ashing, Fusion and Inductively Coupled Plasma Emission Spectrometry. Switzerland. www.iso.org/iso/home.html
[ 6 ] ASTM International. 2008. ASTM E177-08. Standard Practice for Use of Terms Precision and Bias in ASTM Test Methods. West Conshohocken, PA. www.astm.org
Acknowledgments: Sylvain Roy, Lab Technician, Claisse
