In situ Rb-Sr dating of mica by LA-ICP-MS/MS

Mica exhibits a relatively high Rb/Sr ratio and possesses a closure temperature for the Rb-Sr isotope system that is higher than the ore-forming temperature range of low-to medium-temperature deposits.Consequently,utilizing the laser ablation(LA)technique for in situ Rb-Sr dating in mica constitutes a significant methodology for resolving the mineralization chronology of low-to medium-temperature hydrothermal ore deposits.In this study,we employed a combination of a triple quadrupole inductively coupled plasma mass spectrometer(ICP-MS/MS)and 193 nm LA system with SF_6as the reaction gas to achieve interference removal of~(87)Rb~+on~(87)Sr~+.We then developed an in situ Rb-Sr dating method for mica.In addition,an investigation was conducted to identify the factors that could influence the analytical accuracy of the method.Subsequently,we applied the developed method to carry out in situ Rb-Sr dating for the ZBH-25 biotite,a national primary reference material(GBW04439)for K-Ar dating,and yielded a younger age(ca.12%,relative standard deviation,RSD)than the reference K-Ar age when using NIST SRM 610 as the reference material for external calibration.This finding indicated that in the process of determining Rb-Sr ages for mica by LA-ICP-MS/MS,there are significant matrix effects between the NIST SRM 610 and the mica samples,resulting in inaccurate Rb-Sr ages.In response to this issue,a two-step calibration method is proposed here.Based on external calibration using NIST SRM 610,ZBH-25 biotite is employed as a second external reference material to perform a second calibration of the sample data to correct the matrix effect between the glass standards and the natural mica samples,thereby improving the accuracy of Rb-Sr dating by LA-ICP-MS/MS.Using the proposed method,in situ Rb-Sr dating by LA-ICP-MS/MS was performed on mica samples from monzonite exposed in Mt.Dromedary,New South Wales,Australia,porphyritic granodiorite in Fangshan pluton and albionite granite in the Gyirong area of Tibet.The obtained Rb-Sr age results show agreement with the recommended values within the analytical uncertainty,which serves to validate the accuracy and effectiveness of the proposed method.

Characterization and quantitation of aristolochic acid analogs in different parts of Aristolochiae Fructus, using UHPLC-Q/TOF-MS and UHPLC-Qq Q-MS

Aristolochiae Fructus, a Chinese herbal medicine derived from the fruit of Aristolochia contorta Bge., contains nephrotoxic aristolochic acid analogues(AAAs). According to ancient medical texts, various medicinal parts of the fruit of A. contorta were ever used. In order to reveal which part could be safely and effectively used, it is necessary to analyze the chemical profiles of different medicinal parts. Herein we compared the chemical compositions and determined aristolochic acid I(AA-I) and aristolochic acid II(AA-II) in the four parts viz. outer pericarp, inner pericarp, septum, and seed. Ultra-high performance liquid chromatography equipped with quadrupole time-of-flight mass spectrometry(UHPLC-QTOF-MS) was applied for chemical profiling. Ultra-high performance liquid coupled with triple quadrupole mass spectrometry(UHPLC-Qq Q-MS) was employed to quantify AA-I and AA-II in different parts. It was found that the chemical compositions of the four parts varied both qualitatively and quantitatively. A total of 10 AAAs, including 5 aristolochic acids and 5 aristolactams, together with 3 alkaloids, were unambiguously or tentatively identified by UHPLC-QTOF-MS. The quantitatively analytical results obtained by UHPLC-Qq Q-MS showed that AA-I and AA-II exclusively accumulate in the seeds of A. contorta. These findings provide supporting data for the rational selection of medicinal parts.