Accurate quantification of oleanolic acid and ursolic acid in traditional chinese medicine

Transcription

1 pplication Note Small Molecule Pharmaceuticals, Generics ccurate quantification of oleanolic acid and ursolic acid in traditional chinese medicine igh-resolution sampling D-LC uthors Rongjie Fu and Xinlei Yang gilent Technologies, Inc. bstract Quality control is one of the most important tasks within the Traditional Chinese Medicine (TCM) industry. It is required that levels of the main compounds in TCMs are determined using PLC methods. Due to the complexity of TCM samples, the target compounds are likely to be coeluted with other minor compounds within an PLC separation. D-LC system could be a powerful method to separate complex samples using orthogonal column chemistries and mobile phases. This pplication Note details the development of a high-resolution sampling D-LC method for the quantitative analysis of oleanolic acid and ursolic acid in Pterocephali erbra.

2 Introduction Traditional Chinese Medicine (TCM) analysis is a challenging task due to the complexity of the components in a single herbal medicine or combined preparation. To control the quality of TCMs, the amounts of main compounds are required to be determined using PLC methods according to China Pharmacopeia (CP) regulations. Often, other compounds will coelute with the target compounds, influencing the accuracy of their quantification. Pterocephali erbra is one of the CP examples that requires the amounts of two target compounds, oleanolic acid and ursolic acid (Figure ), to be determined by PLC. This study found that several other compounds coelute with oleanolic acid and ursolic acid, making the existing method inadequate for the quantification of these compounds. O O Oleanolic acid C 8 O CS: 8-- Ursolic acid C 8 O CS: 77-- Figure. Target compounds separated in this study. O O O O To achieve orthogonal separation, this pplication Note used two gilent InfinityLab Poroshell columns with different selectivities (EC-C8 and Phenyl-exyl) and different mobile phase conditions in high resolution sampling D-LC. The two target compounds were determined by collecting several small fractions over a selected time range, covering the entire area of a peak from a D chromatogram. Each cut was parked in a sampling loop, and all cuts were consecutively analyzed in the second dimension. This mode ensured that all the selected compounds were transferred to, and analyzed in the second dimension. Thus, selected coeluting compounds were subjected to the high-resolution sampling process for analysis in the second dimension. This enabled a reliable quantification, as shown in a previously issued Technical Overview. LC LC Figure. Illustration of high-resolution sampling D-LC. Experimental Chemicals and samples ll reagents and solvents were PLC grade. cetonitrile and methanol were purchased from JT Baker, US. mmonium acetate was purchased from J and K, Beijing China. Fresh ultrapure water was obtained from an ELG water purification system, Lane End, UK. The extracts of Pterocephali erbra and standards of oleanolic acid and ursolic acid were provided by a local pharmaceutical company in China. To achieve a concentration of. mg/ml and. mg/ml respectively, the stock standard solutions were made by dissolving oleanolic acid and ursolic acid together in methanol. Instrument The gilent 9 Infinity II D-LC was composed of the following modules: Two gilent 9 Infinity II high speed pumps (G7) gilent 9 Infinity II multisampler (G767B) with sample cooler (Option #) Two gilent 9 Infinity II MCTs (G76B) Two gilent 9 Infinity II DDs (G77B) with a -mm Max-Light cartridge cell (G-68) and a 6 mm Max Light cartridge cell (G 67) gilent 9 Infinity valve drive (G7) with -position/-port duo valve (D-LC valve head, G6) Two gilent 9 Infinity valve drives (G7) with multiple heart-cutting valves (G-6) equipped with -µl loops

3 Method setup for high-resolution sampling The method setup for high-resolution sampling referred to the previously issued Technical Overview. Figure shows the high-resolution sampling configuration of the gilent 9 Infinity II D-LC system, consisting of a -position/ port duo valve connected to two multiple heart cutting valves holding sampling loops. With this setup, up to consecutive cuts can be sampled and stored until analysis. For high resolution sampling, a maximum loop filling of 8 % is recommended to prevent any loss of sample. Figure shows the method setup used for the D pump. First, a D LC separation of the sample was run, and the chromatogram was loaded as the reference signal preview window. igh-resolution sampling was time based, according to the peak of interest, with eight cuts covering the entire peak width. Under the given D conditions, a sampling time of 8.6 seconds equals a loop filling of 7 %. Waste 6 IN ¹D-Column 6 OUT 6 Figure. Setup of the gilent 9 Infinity II D-LC system, holding sampling loops IN 6 ²D-Pump ²D-Column OUT Figure. Method setup for the D pump.

4 This pplication Note used the following LC columns: gilent InfinityLab Poroshell Phenyl-exyl,. mm,.9 µm (p/n ) gilent InfinityLab Poroshell EC-C8,. mm,.7 µm (p/n ) Software used for system control and data analysis included: gilent OpenLab CDS ChemStation Edition Rev. C..7 SR [] with gilent D-LC Software add-on, Product Version.. []. Results and discussion Separation Figure shows a typical chromatogram for oleanolic acid and ursolic acid analysis in Pterocephali erbra using an optimized method according to a CP method. While this method, using the InfinityLab Poroshell µm, provided good resolution for the standards, the extreme complexity of the sample did not allow adequate separation of the target analytes from interfering compounds. Therefore, the target analytes were not able to be quantitated using a traditional D-LC separation. To properly quantify these two target compounds, high-resolution sampling D-LC was used to separate them from interfering compounds. This was achieved using column chemistries that differed from one another in their selectivity. The introduction of many chemistries for.7 and.9 µm superficially porous particles makes InfinityLab Poroshell columns ideal for achieving the separation orthogonality required in D PLC separations. This work used a Phenyl exyl column for the first dimension. The two target compounds, oleanolic acid and ursolic acid, were baseline separated on an gilent InfinityLab Poroshell Table. igh-resolution sampling D-LC method for the analysis of oleanolic acid and ursolic acid. Columns First dimension gilent InfinityLab Poroshell Phenyl-exyl,. mm,.9 µm Second dimension gilent InfinityLab Poroshell EC-C8,. mm,.7 µm Solvent Solvent B Flow rate Gradient Solvent Solvent B Flow rate Gradient D Gradient stop time D Cycle time Stop time Time based Sampling time Number of cuts 8 D Pump mm ammonium acetate in water Methanol. ml/min 7 %B at minutes 7 %B at 8 minutes %B at 8. minutes %B at. minutes 7 %B at. minutes. % PO in water cetonitrile ml/min First dimension C Second dimension C Injection volume µl %B at minutes 9 %B at minutes. minutes. minutes minutes.8 minutes 8.6 seconds D Pump igh-resolution sampling Multicolumn thermostat Multisampler Needle wash seconds in methanol: water : Wavelength Data rate Flow cell Wavelength Data rate Flow cell nm/ nm z D Diode array detector -mm Max-Light cartridge cell nm/ nm 8 z D Diode array detector 6-mm Max-Light cartridge cell Phenyl exyl,. mm,.9 µm column, shown in Figure 6. The sub- µm superficially porous particle Poroshell column gave high efficiency and good resolution for the two compounds with narrow peak widths, making it easy for D separation sampling. The second dimension separation used an gilent InfinityLab Poroshell EC C8,. mm,.7 µm column. The low backpressure of these columns allows the use of a higher flow rate to achieve a quick separation of coeluted compounds away from target compounds. Using high-resolution sampling, eight cuts in the time range of the peak containing oleanolic acid and ursolic acid were sampled (Figure 6) and injected to the second dimension for analysis (Figure 6D).

5 PLC Conditions Parameter Value mu 8 6 Peak ID. Oleanolic acid. Ursolic acid Mobile phase % mm ammonium acetate in water/8 % methanol Flow rate ml/min Injection volume µl Temperature C Detector UV nm Standard mu B 8 6 Sample Figure. Chromatogram of oleanolic acid and ursolic acid analysis in Pterocephali erbra with an gilent InfinityLab Poroshell EC-C8,.6 mm, µm column. B C D E Figure 6. D-LC Viewer. ) D chromatogram with eight consecutive cuts over the entire width of the two peaks. B) Sampling table with eight cuts taken from the first dimension. C) Peak table of the selected cut and its peak area and other parameters. D) Overview of all D chromatograms of eight cuts. E) Chromatogram of each selected cut.

6 Figure 7 shows an overlay of D chromatograms of oleanolic acid standard (from cut to cut ), and Figure 8 shows the ursolic acid standard (from cut to 8). The entire peaks of oleanolic acid and ursolic acid were sampled respectively, then transferred to, and analyzed in, the second dimension. In this manner, possible coeluting compounds in the sample can be separated in the second dimension. Figure 9 shows overlaid D chromatograms of a TCM sample isolating oleanolic acid. The sample showed a good separation of oleanolic acid, and some small peaks. In Figure, the D separation shows that ursolic acid was well separated from several other compounds observed in the D chromatogram of the TCM sample. mu D 6.8 Standards. Oleanolic acid. Ursolic acid 6 8 mu B D Oleanolic acid..... Figure 7. Overlay of D chromatograms of cuts for oleanolic acid standard. mu 8 7 D Standards. Oleanolic acid. Ursolic acid 6 8 mu B D Ursolic acid..... Figure 8. Overlay of D chromatograms of cuts 8 for ursolic acid standard. 6

7 Quantification Standard solutions of oleanolic acid in a concentration range of 7., µg/ml and ursolic acid in a concentration range of, µg/ml were analyzed three times with the above method as well as the sample solutions. For quantification, peaks of one compound were integrated in every D chromatogram by the software, and the sum of peak areas for each compound was calculated for the calibration curve. Figure shows good linearity across the entire calibration range, with R values greater than.999 for both compounds. The amounts (average of three analyses) calculated in the determined samples were 9.6 µg/ml oleanolic acid and 8.9 µg/ml ursolic acid. Repeatability To determine the repeatability of the high-resolution sampling D-LC method, six consecutive analyses of a standard mix containing µg/ml oleanolic acid and µg/ml ursolic acid were performed. Total peak areas of oleanolic acid and ursolic acid were determined from the D chromatograms. Relative standard deviations (RSDs) were.8 % for oleanolic acid and. % for ursolic acid. mu D mu B D Oleanolic acid Figure 9. Overlay of D chromatograms of cuts for oleanolic acid from sample. mu Sample..... D Sample mu B D Ursolic acid..... Figure. Overlay of D chromatograms of cuts 8 for ursolic acid from sample. 7

8 Conclusions This pplication Note demonstrates a high-resolution sampling gilent InfinityLab D LC solution for complex TCM analysis. Interfering compounds in the first dimension can be well separated so that target compounds are reliably quantified over high-resolution sampling D-LC within the same run. To achieve the required separations at each step of the D analysis, the gilent InfinityLab Poroshell columns provide ideal particle sizes. To provide the orthogonal separation required for a successful D-LC separation, these columns also offer wide selectivity options that can be used with different organic phases. The high-resolution sampling D-LC method developed in this pplication Note enables reliable quantification for complex TCMs. rea, Oleanolic acid rea = *mt.987, Rel. Res%(): 7.79,,, Correlation:.9999 mount (µg/ml) rea, B Ursolic acid, rea =.778*mt.667, Rel. Res%():. 8 6 Correlation:.999 mount (µg/ml) Figure. Calibration curves from the sum of D peaks for oleanolic acid and ursolic acid. Reference. Stephan, S. igh-resolution Sampling D-LC with the gilent 9 Infinity II D-LC Solution. gilent Technologies Technical Overview, publication number EN, 6. For Research Use Only. Not for use in diagnostic procedures. This information is subject to change without notice. gilent Technologies, Inc. 8 Printed in the US, March 8, EN