Reversed-phase Chromatography-tandem Mass Research Articles

Analysis of perfluoroalkyl compounds in marine fish muscle samples by liquid chromatography tandem mass spectrometry

ABSTRACT In this work, a reversed phase chromatography tandem mass spectrometry has been used for analysis of 23 perfluoroalkyl substances in marine fish muscle samples. Fish samples was collected, codded and dried via freeze-dried and homogenised, and poly/perfluoroalkyl substances (PFASs) were extracted by ultrasonic assisted ion pair liquid-liquid extraction. The extractant was then cleaned up with solid phase extraction with different absorbents. To avoid carry-over, contamination/losing target analytes during SPE step, a simple one-step centrifugal SPE was used. All parameters of the analytical method such as linearity range, stability of analytical signal, LOD, and LOQ of the analytical method have been investigated and presented. Limit of quantification of the method was from 0.04 µg kg−1 to 0.45 µg kg−1 for the wet weight sample. Matrix effect was investigated and eliminated by solid phase extraction. Overall recovery of the PFASs in range of 44%−132% was achieved. Excellent repeatability of analytical signal in both short-term and long-term were below 9.0% and 16%, respectively. The analytical method has been validated by using certified reference material, NIST 1947. The validated analytical method was then used for analysis of PFASs in edible fish samples that collected in several coastal sites in Vietnam. The results showed that the main compounds in marine fish samples were perfluorooctanesulfonate (PFOS) and 2:6-FT. However, concentration of PFOS and its derivatives in all analysed marine fish samples was below European Union maximum allowable concentration.

Red blood cell folate concentrations and polyglutamate distribution in juvenile arthritis

Methotrexate (MTX) has several enzymatic targets in the folate pathway. To better understand the variability in response to MTX, we characterized the interindividual variability of intracellular folate pools in children with juvenile arthritis (JA) and determined clinical and genetic contributors to this variability. This exploratory single-center cross-sectional study evaluated 93 patients with JA not currently receiving MTX. Whole blood, plasma, and erythrocyte folate concentrations were determined after deconjugation and analyzed through reversed-phase separation and stable isotope dilution tandem mass spectrometry. Folate polyglutamates were measured in red blood cell lysates using an ion-pair reversed phase chromatography tandem mass spectrometry method. Intracellular concentrations of 5-methyl-tetrahydrofolate (5-CH3-THF) and 5,10-methenyl-tetrahydrofolate varied approximately 20-fold and 80-fold, respectively. The polyglutamated forms of 5-CH3-THF as a percentage of total 5-CH3-THF (5-CH3-THFGlun) were also measured. Hierarchical clustering of 5-CH3-THFGlun revealed two groups, each with two distinct clusters. There was an inverse relationship between 5-CH3-THFGlun chain length and plasma 5-CH3-THF concentrations. A subgroup of patients with a historical intolerance to MTX had significantly lower cellular folate concentrations (P<0.0001). In univariate analyses, clinical variables including sex, age, and folate supplementation in addition to variations in MTHFR, MTR, and SLC25A32 were associated with differential intracellular folate redox concentrations. Multivariate analysis further supported the association of single nucleotide polymorphisms in SLC25A32, MTHFR, and MTR with variability in intracellular 5-CH3-THF and 5,10-methenyl-tetrahydrofolate concentrations, respectively. Measurement of intracellular folate isoforms may contribute toward a better understanding of individual MTX effects in JA. Clinical variables in addition to genotypic differences beyond MTHFR may additionally explain differential intracellular folate concentrations and variable responses to MTX.