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Application News No.G334A In an oil-filled transformer, sulfur-containing compounds in insulating oil are known to cause sulfide corrosion of the transformer. Specifically, dibenzyl disulfide (DBDS), an additive of insulating oil as a metal deactivator, has been reported as a cause of sulfide corrosion. The International Electrotechnical Commission (IEC) has issued the analytical standard for DBDS in insulating oil as IEC62697-1. A sulfur chemiluminescence detector (SCD) that can be used as one of gas chromatographs can selectively analyze sulfur- containing compounds with a high sensitivity. This detector has a high selectivity and avoids the effects of contaminants and enables accurate quantification of sulfur-containing compounds. This article introduces an analysis of DBDS in insulating oil using an SCD in accordance with IEC 62697-1, and it also reports on analysis of the quantity of total sulfur in insulating oil using the equimolar response of SCD. Y. Takemori Sample Preparation [Standard samples] [1] Dibenzyl disulfide (DBDS) was dissolved in toluene to make a concentration of 100 g/kg. [2] Diphenyl disulfide (DPDS) was dissolved in toluene to make a concentration of 500 mg/kg. [3] [1] was added to mineral oil to make concentrations of 0.1 - 100 mg/kg. [4] 0.25 g of each of the DBDS samples prepared in [3] was weighed and dissolved in 5 ml of isooctane. [5] 0.1 ml of [2] was added as an internal standard to each of the DBDS samples prepared in [4], and analyzed as standard samples. [Insulating oil samples] [6] 0.25 g of each of 5 types of insulating oil was weighed and dissolved in 5 ml of isooctane. [7] 0.1 ml of [2] was added as an internal standard to each of solutions prepared in [6] and analyzed as insulating oil samples. Chromatogram and Calibration Curve of Standard Samples The chromatogram and calibration curve of standard samples are shown in Fig. 1 and Fig. 2, respectively. Concentrations as low as 0.1 mg/kg could be detected. Gas Chromatography Analysis of Dibenzyl Disulfide and Total Sulfur in Insulating Oil Using SCD Table 1 Conditions for Quantitative Analysis of DBDS and Separation Analysis of Other Sulfur-Containing Compounds Analytical Method/Conditions The conditions for quantitative analysis of DBDS and conditions for separation analysis of other sulfur-containing compounds are shown in Table 1. The conditions for analysis of total sulfur in insulating oil which is not separated by a column are shown in Table 2. Model : Nexis™ GC-2030 / SCD-2030 Injection Volume : 1 µL Injection : SPL Injection Temp. : 275 °C Injection Mode : Split Split Ratio : 1:5 Carrier Gas : He Carrier Gas Control : Linear velocity (45.0 cm/s) Column : SH-5 (30 m×0.32 mm I.D., 0.25 µm) *1 Column Temp. : 90 °C-10 °C/min–275 °C (20 min) Interface Temp. : 250 °C Electric Furnace Temp. : 850 °C Detector Gas : H 2 100.0 mL/min N 2 10.0 mL/min O 2 12.0 mL/min O 3 25.0 mL/min Table 2 Conditions for Analysis of Total Sulfur in Insulating Oil Not Separated by Column Model : Nexis GC-2030 / SCD-2030 Injection Volume : 0.5 µL Injection : SPL Injection Temp. : 280 °C Injection Mode : Split Split Ratio : 1:50 Carrier Gas : He Carrier Gas Control : Pressure (10 kPa) Column : Deactivated fused silica tube (15 m × 0.2 mm I.D.) Column Temp. : 280 °C (hold time: 10 minutes) Interface Temp. : 250 °C Electric Furnace Temp. : 850 °C Detector Gas : H 2 100.0 mL/min N 2 10.0 mL/min O 2 12.0 mL/min O 3 25.0 mL/min 9.0 10.0 11.0 12.0 13.0 14.0 min DBDS DPDS（IS） DBDS 0.1 mg/kg Fig. 1 Chromatogram of Standard Samples (0.1 - 100 mg/kg) R 2 = 0.9999 0 10 20 30 40 50 60 70 80 90 濃度比 0.0 0.1 0.2 0.3 0.4 0.5 0.6 面積比 1 2 3 4 Fig. 2 Calibration Curve Area ratio Concentration ratio *1 P/N: 221-75703-30
No. G334A Application News www.shimadzu.com/an/ Shimadzu Corporation © Shimadzu Corporation, 2020 For Research Use Only. Not for use in diagnostic procedures. This publication may contain references to products that are not available in your country. Please contact us to check the availability of these products in your country. The content of this publication shall not be reproduced, altered or sold for any commercial purpose without the written approval of Shimadzu. See http://www.shimadzu.com/about/trademarks/index.html for details. Third party trademarks and trade names may be used in this publication to refer to either the entities or their products/services, whether or not they are used with trademark symbol “TM” or “”. Shimadzu disclaims any proprietary interest in trademarks and trade names other than its own. The information contained herein is provided to you "as is" without warranty of any kind including without limitation warranties as to its accuracy or completeness. Shimadzu does not assume any responsibility or liability for any damage, whether direct or indirect, relating to the use of this publication. This publication is based upon the information available to Shimadzu on or before the date of publication, and subject to change without notice. Quantitative Results of DBDS Fig. 3 shows the chromatogram of 5 types of insulating oil samples. Table 3 shows the results of DBDS quantification based on the calibration curve using the internal standard method. Fig. 3 Chromatograms of Insulating Oil Samples 0.0 5.0 10.0 15.0 20.0 min ・絶縁油5 ・絶縁油4 ・絶縁油3 ・絶縁油2 ・絶縁油1 DPDS（IS） DBDS 溶出位置 Insulating oil 1 Insulating oil 2 Insulating oil 3 Insulating oil 4 Insulating oil 5 Elution position of DBDS Table 3 Quantitative Results of DBDS Insulating oil sample DBDS concentration (mg/kg) Insulating oil 1 0.1 Insulating oil 2 2.6 Insulating oil 3 92.2 Insulating oil 4 0.8 Insulating oil 5 0.5 Analysis of Quantity of Total Sulfur Using the Characteristics of SCD As shown in Fig. 3, many sulfur-containing compounds were detected from the insulating oil samples. In this analysis, the quantities of total sulfur in insulating oil samples were determined by and compared between the following two methods. Similar quantities of total sulfur in the samples separated or unseparated were obtained. [ 1] Analysis of the quantity of total sulfur in the normally separated samples (analytical conditions: Table 1) SCD exhibits the same sensitivity (equimolar sensitivity*), regardless of sulfur-containing compound structure, when the same number of sulfur atoms is introduced into the SCD. This characteristic of SCD allows the use of a calibration curve as shown in Fig. 2 to quantify and aggregate all detected peaks of sulfur-containing compounds and determine the quantity of total sulfur in each sample, as shown in Fig. 4 (*For the details of equimolar sensitivity, refer to G330). [ 2] Analysis of the quantity of total sulfur in the unseparated samples (analytical conditions: Table 2) SCD, in principle, has no sensitivity to compounds other than those containing sulfur. Using this characteristic, the sample injection was connected to SCD with a deactivated fused silica tube, and the unseparated insulating oil samples were introduced into the SCD. Fig. 5 compares the peaks of each of the samples as the quantity of total sulfur. 絶縁油1 絶縁油2 絶縁油3 絶縁油4 絶縁油5 0 100 200 300 400 500 600 700 800 総硫黄量(mgS/kg) 絶縁油4 絶縁油1 絶縁油3 絶縁油2 0.9 1.0 1.1 1.2 min 絶縁油5 Quantity of total sulfur (mgS/kg) Insulating oil 1 Insulating oil 2 Insulating oil 3 Insulating oil 4 Insulating oil 5 Insulating oil 1 Insulating oil 5 Insulating oil 3 Insulating oil 4 Insulating oil 2 Fig. 4 Comparison of Quantity of Total Sulfur in Separated Samples Calculated Using Calibration Curve of DBDS Fig. 5 Comparison of Unseparated Insulating Oil Samples Conclusion SCD could determine the quantity of DBDS in insulating oil with a high sensitivity. The use of the characteristics of SCD also enables the quantity of total sulfur to be determined. Nexis is a trademark of Shimadzu Corporation or its affiliated companies in Japan and/or other countries. First Edition: Aug. 2020 Revision A: Mar. 2023
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