Ibuprofen is one of the most popular analgesic and antipyretic drugs. An isotope dilution mass spectrometry method based on LC/MS was developed as a candidate reference method for the accurate determination of ibuprofen in pharmaceutical tablets. Isotope labelled ibuprofen, ibuprofen-d 3 , was added as an internal standard into sample extracts. Ibuprofen and ibupro-fen-d 3 , was analysed by LC/MS in a selected ion monitoring (SIM) mode to detect ions at m/z 205 and 208, respectively. The repeatability and reproducibility of the developed ID-LC/MS method were tested for the validation and assessment of metrolog-ical quality of the method.
Glycated hemoglobin (HbA 1c ) has been commonly used to screen and diagnose for patients with diabetes mellitus. Here the accelerated procedure of microwave-assisted sample treatment from acid hydrolysis to enzyme digestion followed by isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) was optimized and applied to measure HbA 1c in an effort to speed up analysis time. First, two signature peptides of HbA 1c and hemoglobin A 0 were certified with amino acid analysis by setting optimized acid hydrolysis conditions to 150 o C, 1.5 h and 10 µM sample concentration in 8 M hydrochloric acid. Consequently, the accurate certified peptides above were used as calibration standards to implement the pro-teolytic procedure with endoproteinase Glu-C at 37 o C, 700 W for 6 h. Compared to the traditional method, the microwave heat-ing not only shortened dramatically sample preparation time, but also afforded comparable recovery yields. The optimized protocol and analytical conditions in this study are suitable for a primary reference method of HbA 1c quantification with full SI-traceability and other similar proteins in complex biological samples.
In clinical diagnosis, it’s well known that the abnormal level of uric acid (UA) in human body is implicated in diverse human diseases, for instance, chronic heart failure, gouty arthritis, diabetes, and so on. As a primary method, an isotope dilution mass spectrometry (IDMS) has been used to obtain the accurate quantity of UA in blood or serum and also develop the certifi-cated reference material (CRM) so as to provide a SI-traceability to clinical laboratories. Due to the low solubility of UA in water, an ammonium hydroxide (NH 4 OH) has been considered as a promising solvent to increase the solubility of UA that enables the preparation of both UA and its isotope standard solution for next IDMS-based absolute quantification. But, because of using this NH 4 OH solvent, it gives rise to the unwanted degradation of UA. In this study, we sought to optimize condition for the stability of UA in NH 4 OH solution by varying the mole ratios of UA to NH 4 OH, followed by ID-LC-MRM analysis. In addi-tion, we also inspected minutely the effect of the storage temperatures. Additionally, we also performed the quantitative analysis of UA in the KRISS serum certificated reference material (CRM, 111-01-02A) with diverse mixing ratios of UA to NH 4 OH and then compared those values to its certification value. Based on our experiments, adjusting the mole ratio of 1/2 (UA/NH 4 OH) with the storage temperature of -20 o C is an effective way to secure both the solubility and stability of UA in NH 4 OH solution for next IDMS-based quantification of UA in serum.
Thiamethoxam is one of the main suspect in honeybee colony collapse disorder (CCD). Due to this reason, thiamethoxam including imidacloprid and clothianidin has been banned for two years in some Europe countries. The CCD phe-nomenon has also been reported in Korea. Regarding this issue and needs, a new project has started to develop the method for the quatitation of thiamethoxam using isotope dilution mass spectrometry (IDMS). In the process of optimization for the IDMS method with thiamethoxam and thiamethoxam-d 3 , we observed that the fragment peaks did not correspond to the fragmentation pathway as published elsewhere. Here, we proposed a candidate fragmentation pathway. To validate the proposed fragmentation pathway, another isotope analogue, thiamethoxam-d 4 , was introduced and the MS/MS spectra of both isotope analogues were compared. In addition, the MS/MS/MS spectra of thiamethoxam were inspected for more evidence of the candidate pathway. Those spectra indicated that the proposed fragmentation pathway could be used to assign the fragment peaks of thiamethoxam.