[콘텐츠로 건너뛰기](https://www.sigmaaldrich.com#main-content) [![Merck](https://www.sigmaaldrich.com/static/logos/purple/merck.svg)](https://www.sigmaaldrich.com/KR/ko) 제품 장바구니0 KRKO 제품 제품애플리케이션서비스리소스지원 [로그인 / 등록](https://www.sigmaaldrich.com/oidc-sign-in) [주문 조회](https://www.sigmaaldrich.com/KR/ko/order-lookup) [빠른 주문](https://www.sigmaaldrich.com/KR/ko/quick-order) 장바구니0 [Home](https://www.sigmaaldrich.com/KR/en)[Solid Phase Extraction (SPE)](https://www.sigmaaldrich.com/KR/en/applications/analytical-chemistry/sample-preparation/solid-phase-extraction)Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma # Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma __Xiaoning, Lu, David, S Bell__ *Reporter US Volume 33.3* Using a Simple Procedure for Simultaneous Cleanup of Phospholipids and Proteins __Section Overview__ - [Introduction](https://www.sigmaaldrich.com#introduction) - [Experimental](https://www.sigmaaldrich.com#experimental) - [Results and Discussion](https://www.sigmaaldrich.com#results-and-discussion) - [Summary](https://www.sigmaaldrich.com#summary) - [Related Materials](https://www.sigmaaldrich.com#related-materials) ## [](https://www.sigmaaldrich.com)Introduction Digitoxin and digoxin are cardiac glycosides derived from the *digitalis purpurea* (Foxglove) plant. They have been in use for centuries for treatment of various heart conditions. Because of their narrow therapeutic range and high toxicity, their levels in patients taking digitoxin or digoxin are monitored1-2. Immunoassay- based methods for digitoxin or digoxin exist, but are both time consuming and labor intensive. Moreover, the reported immunoassay methods are not selective toward digitoxin or digoxin due to the similarities in their chemical structures, which differ from each other in only one hydroxyl group (__Figure 1__). The present work was aimed at developing a rapid and selective LC/MS/MS method for the determination of digoxin and digitoxin in biological fluids. In addition, a simple sample cleanup technique for simultaneous removal of proteins and phospholipids using a zirconia-based sorbent, HybridSPE®-PLus, was explored. ![Structures of Digitoxin and Digoxin](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/protocols/analytical-chemistry/solid-phase-extraction/t215003-digitoxin-digoxin-fig-1.gif "Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma") __Figure 1.__Structures of Digitoxin and Digoxin ## [](https://www.sigmaaldrich.com)Experimental A 100 µL sample of spiked rat plasma was added to the well of a HybridSPE-PLus 96-well plate followed by 300 µL of 1% formic acid in acetonitrile to precipitate the proteins. The plate was sealed with plastic film and agitated by vibration at 1,000 rpm for 2 minutes on a digital shaker. The plate was transferred to a vacuum manifold and the seal was removed. Vacuum (10 in. Hg) was applied for 4 minutes. The flow-through eluate was analyzed by LC/MS/MS. A Titan™ C18 column packed with 1.9 µm monodisperse, totally porous silica particles was chosen for the UHPLC separation of digitoxin and digoxin. Different mobile phase systems were studied. LC/MS/MS Conditions  sample prep: column: mobile phase: flow rate: detector: instrument:HybridSPE-PLus 96-well plate Titan C18, 10 cm × 2.1 mm I.D., 1.9 µm particles 10 mM ammonium formate in water:methanol (20:80) 0.2 mL/min MS, ESI(+), MRM Shimadzu™ LCMS-8030 Triple Quadrupole Mass Spectrometer ## [](https://www.sigmaaldrich.com)Results and Discussion ### Effect of Mobile Phase Composition on MS Spectra The effect of mobile phase composition was dramatic. __Figure 2A__ shows digitoxin and digoxin are ionized primarily as sodium adducts in the 0.1% formic acid in acetonitrile: water (50:50) mobile phase. Because sodium ions have much higher affinity to digoxin and digitoxin in the gas phase than protons (H+), the sodium adducts are the primary ion in the 0.1% formic acid in acetonitrile-water mobile phase. Further experiments showed the sodium adduct ions are scarcely fragmented in MS/MS regardless of collision energy and gas pressure, thus not amenable to being monitored in MS/MS mode. This issue of forming sodium adducts can be overcome by replacing the mobile phase with water: methanol containing ammonium formate. Digitoxin and digoxin generate primarily ammonium adducts when ammonium formate replaces the formic acid in the mobile phase (__Figure 2B__). The ammonium adducts of digitoxin and digoxin are shown to be readily fragmented under mild collision conditions (__Figure 3__). The MRM transitions 782.5/635.5 and 798.5/651.5 were chosen for LC/MS/MS quantification of digitoxin and digoxin, respectively. ![A comparison of mass spectrometry graphs for Digitoxin (top) and Digoxin (bottom). Both graphs display intensity on the y-axis (in ×100,000) and mass-to-charge ratio (m/z) on the x-axis, ranging from 600 to 950. Key peaks are labeled in red, indicating the \[M+Na\]+ ion, with specific m/z values noted for each compound. The Digitoxin graph shows prominent peaks around 787.5 and 788.5, while the Digoxin graph highlights peaks around 803.5.](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/protocols/analytical-chemistry/solid-phase-extraction/t215003-digitoxin-digoxin-fig-2a.gif "Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma") __Figure 2A.__MS Spectra of Digoxin and Digitoxin in Formic Acid Mobile Phase __Conditions__ __mobile phase__: 0.1% formic acid in water: acetonitrile (50:50) ![A comparison of mass spectrometry graphs for Digitoxin (top) and Digoxin (bottom). The graphs display intensity on the y-axis (in ×100,000) and mass-to-charge ratio (m/z) on the x-axis, ranging from 500 to 950. Key peaks are labeled in red, indicating the \[M+NH\]+ and \[M+Na\]+ ions, with specific m/z values noted for each compound. The Digitoxin graph shows significant peaks at 782.7 and 787.6, while the Digoxin graph features prominent peaks at 798.6 and 825.7.](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/protocols/analytical-chemistry/solid-phase-extraction/t215003-digitoxin-digoxin-fig-2b.gif "Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma") __Figure 2B.__ MS Spectra of Digoxin and Digitoxin in Ammonium Formate Mobile Phase __Conditions__ __mobile phase:__ 10 mM ammonium formate in water:methanol (50:50) ![A comparison of mass spectrometry graphs for Digitoxin (top) and Digoxin (bottom). The graphs display intensity on the y-axis (in ×10,000) and mass-to-charge ratio (m/z) on the x-axis, ranging from 100 to 800. The Digitoxin graph, labeled with the precursor ion at 782.5 m/z, shows significant peaks at 243.3 and 782.7. The Digoxin graph, labeled with the precursor ion at 798.5 m/z, highlights peaks at 260.9 and 651.5. Key peaks are marked in red with specific m/z values noted.](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/protocols/analytical-chemistry/solid-phase-extraction/t215003-digitoxin-digoxin-fig-3.gif "Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma") __Figure 3.__MS/MS Spectra of Digitoxin and Digoxin (Ammonium Adducts) __Conditions__ __mobile phase:__ 10 mM ammonium formate in water:methanol (50:50) __Linearity and LOD of the LC Method__ __Figure 4__ shows the two analytes are well resolved by the Titan C18 column within four minutes. The limit of detection of the LC/MS/MS method was approximately 0.01 ng/mL of the analyte standard. The calibration curve of the method is linear over a range of three orders of magnitude, with a linearity (r2) >0.999 (__Figure 5__). ![A graph displaying the intensity of two peaks over time, labeled as "Blank" on the left in blue and "Spike 10 ng/mL" in red on the right. The x-axis represents time in minutes, ranging from 0 to 5, while the y-axis shows intensity in counts per second (cps), ranging up to 3500. The first peak (1) corresponds to Digoxin with an MRM of 798.5/651.5 m/z, and the second peak (2) corresponds to Digitoxin with an MRM of 782.5/635.5 m/z, both occurring around 3.3 minutes.](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/protocols/analytical-chemistry/solid-phase-extraction/t215003-digitoxin-digoxin-fig-4.gif "Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma") __Figure 4.__MS Spectra of Digoxin and Digitoxin in Ammonium Formate __Conditions__ __column:__ Titan C18, 10 cm x 2.1 mm I.D., 1.9 µm particles (Product No. [577124-U](https://www.sigmaaldrich.com/KR/en/product/supelco/577124U)); __mobile phase:__ 10 mM ammonium formate in water:methanol (20:80); __flow rate:__ 0.2 mL/min; __pressure:__ 4550 psi; __column temp.:__ 35 °C; __detector:__ MS, ESI(+), MRM; __injection:__ 2 µL; __sample:__ rat plasma, blank and spiked at 10 ng/mL, extracted with HybridSPE-PLus; __instrument:__ Shimadzu LCMS-8030 ![A split graph comparing the calibration curves for Digitoxin (left) and Digoxin (right). Each graph plots concentration in ng/mL on the x-axis against count on the y-axis, with both axes labeled accordingly. The Digitoxin graph shows a linear relationship with an r² value of 0.9996, while the Digoxin graph displays a similarly strong linear relationship with an r² value of 0.9991. Both graphs feature data points represented by blue dots connected by a red line, indicating the correlation between concentration and count.](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/protocols/analytical-chemistry/solid-phase-extraction/t215003-digitoxin-digoxin-fig-5.gif "Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma") __Figure 5.__LC/MS/MS Calibration Curves for Digitoxin and Digoxin ### Comparison of Sample Prep Techniques Protein precipitation is widely used for sample preparation of biological matrices prior to LC/MS analysis. The approach is effective in eliminating proteins, but not in removing phospholipids3. Indeed, multiple species of phospholipids were present in high amounts in the rat plasma after protein precipitation as reflected by their intense MS signals (__Figure 6A__). This study exploited HybridSPE-PLus which specifically and effectively eliminated both precipitated proteins and phospholipids from the plasma samples (__Figure 6B__) ![A comparative mass spectrometry analysis displayed in two sections. The top section (A) titled "Protein Precipitation" shows intensity on the y-axis (in ×1,000,000) and mass-to-charge ratio (m/z) on the x-axis, ranging from 200 to 850. Key peaks are labeled with their respective m/z values, including 227.0, 258.1, 280.2, 369.4, 496.4, 524.4, and 758.7, with red asterisks indicating phospholipids confirmed by MS/MS spectra. The bottom section (B) titled "HybridSPE-Plus" also displays intensity on the y-axis and m/z on the x-axis, showing a peak at 229.2, with other peaks appearing minimal.](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/protocols/analytical-chemistry/solid-phase-extraction/t215003-digitoxin-digoxin-fig-6.gif "Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma") __Figure 6.__Improved Recovery of Digitoxin and Digoxin using HybridSPE-PLus Compared to Conventional Protein Precipitation The mechanism behind the effectiveness of HybridSPE-PLus technology is based on the unique Lewis acid/Lewis base interaction between the zirconia and the phosphate group of phospholipids4. __Figure 7__ compares the effectiveness of the two sample preparation techniques, standard protein precipitation and HybridSPE-PLus, on the LC/MS/MS signals. The ion signals of both analytes of the samples prepared by standard protein precipitation were only one-third to one-fourth of those of the samples prepared by HybridSPE-PLus, resulting in low recoveries (__Table 1__). Furthermore, the ion signals of both analytes following standard protein precipitation decreased with increasing number of injections, likely from build-up of phospholipids on the column, leading to irreproducible results and shortened column lifetime. In contrast, the samples prepared by HybridSPE-PLus exhibited high recoveries (>90%) with good reproducibility (<6% RSD). Matrix effects were essentially eliminated by using the HybridSPE-PLus method. ![A dual graph comparing recovery rates for Digitoxin (top) and Digoxin (bottom) across injection numbers. Each graph has the x-axis labeled as "Injection Number" ranging from 0 to 40 and the y-axis labeled as "Recovery" percentage ranging from 0% to 120%. The Digitoxin graph shows a blue line for HybridSPE-Plus maintaining near 100% recovery, while the red line for Protein Precipitation fluctuates around 20-40%. The Digoxin graph similarly shows a stable blue line for HybridSPE-Plus around 100%, while the red line for Protein Precipitation remains consistently below 40%. Both graphs indicate the performance of the two methods over multiple injections.](https://www.sigmaaldrich.com/content/dam/cms-commons/sigmaaldrich/marketing/global/images/technical-documents/protocols/analytical-chemistry/solid-phase-extraction/t215003-digitoxin-digoxin-fig-7.gif "Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma") __Figure 7.__Improved Recovery of Digitoxin and Digoxin using HybridSPE-PLus Compared to Conventional Protein Precipitation. This figure shows the change in LC/MS/MS signal intensity with serial injections of spiked rat serum prepared by using protein precipitation or HybridSPE-PLus. __Conditions__ __Sample:__ 10 ng/mL digitoxin and digoxin spiked in rat plasma. Conditions as in __Figure 4__. | | | | | | | |--------------|-------------------------|------------------|--------------|----------------------------------|---------------------------| | | | | | __Protein Precipitation Method__ | __HybridSPE-PLus Method__ | | __Compound__ | __MRM Quantifier Ions__ | __Recovery (%)__ | __C.V. (%)__ | __Recovery (%)__ | __C.V. (%)__ | | Digitoxin | 782.5/635.5 | 27.0 | 28.8 | 94.7 | 5.8 | | Digoxin | 798.5/651.5 | 35.4 | 12.1 | 95.1 | 4.1 | ## [](https://www.sigmaaldrich.com)Summary A rapid and sensitive LC/MS/MS method has been developed for the determination of digitoxin and digoxin in plasma. A Titan™ C18 UHPLC column with monodisperse particles was employed to resolve the two analytes within four minutes. Severe matrix effects, including ion suppression and irreproducibility, that were observed using standard protein precipitation procedures were overcome by utilizing HybridSPE-PLus, an innovative technique for simple and quick sample cleanup of phospholipids and proteins in biological matrices. ## Related Materials 예기치 못한 오류가 발생했습니다. Response not successful: Received status code 500 1\. Valdes R, Jortani SA, Gheorghiade M. 1998. Standards of laboratory practice: cardiac drug monitoring. 44(5):1096-1109. [https://doi.org/10.1093/clinchem/44.5.1096](https://doi.org/10.1093/clinchem/44.5.1096) 2\. 2010\. Digoxin: serious drug interactions. Prescrire Int. 19 (106), 68-70. 3\. Aurand. Understanding, Visualizing, and Reducing the Impact of Phospholipid-Induced Ion Suppression in LC-MS; Supelco Reporter. Volume 30.2: 10-12 4\. 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