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Rationale: Gas chromatography‐combustion‐isotope ratio mass spectrometry (GC/C/IRMS) is widely used for compound‐specific carbon isotopic analysis. However, current isotopic analysis systems utilize the GC IsoLink combustion reactor, and independent reduction furnaces are not implemented. Therefore, whether this limitation in furnace use affects the precision of compound‐specific carbon isotopic analysis needs to be evaluated. Methods: We attempted to add a separate reduction furnace to the GC IsoLink interface and compared the δ13C values of n‐alkanes (including C and H elements), fatty acid methyl ester (including C, H, and O elements), caffeine (USGS61 and USGS62, including C, H, O, and N elements), and 9‐ethylcarbazole (including C, H, and N elements) before and after the addition of the reduction furnace using the GC IsoLink combustion reactor. Results: For n‐alkanes and fatty acid methyl esters, the δ13C differences between the measured values and their standard values were basically falling within 0.5‰ whether or not an independent reduction furnace was added. However, for the nitrogen‐containing compounds (caffeine and 9‐ethylcarbazole), the δ13C differences between the measured values and their standard values were much larger without an independent reduction furnace (1.0–3.71‰ for USGS61, 1.78–2.19‰ for USGS62, and 0.39–1.13‰ for 9‐ethylcarbazole) than with a reduction furnace (−0.31–0.68‰ for USGS61, −0.44–0.06‰ for USGS62, and −0.04–0.25‰ for 9‐ethylcarbazole). Conclusions: The addition of an independent reduction furnace had no significant effect on the δ13C of n‐alkanes and fatty acid methyl esters, but it had a significant effect on the δ13C of nitrogen‐containing compounds. It is suggested that GC IsoLink needs an independent reduction furnace to effectively eliminate the interference of NOx on CO2 isotopic determination to improve the accuracy of δ13C for nitrogen‐containing compounds. [ABSTRACT FROM AUTHOR]

Inactivated variants in CLCNKB gene encoding the basolateral chloride channel ClC-Kb cause classic Bartter syndrome characterized by hypokalemic metabolic alkalosis and hyperreninemic hyperaldosteronism. Here, we identified two cBS siblings presenting hypokalemia in a Chinese family due to novel compound heterozygous CLCNKB mutations (c.848_850delTCT/c.1755A>G). Compound heterozygosity was confirmed by amplifying and sequencing the patient's genomic DNA. The synonymous mutation c.1755A>G (Thr585Thr) was located at +2 bp from the 5' splice donor site in exon 15. Further transcript analysis demonstrated that this single nucleotide mutation causes exclusion of exon 15 in the cDNA from the proband and his mother. Furthermore, we investigated the expression and protein trafficking change of c.848_850delTCT (ΔTCT) and exon 15 deletion (ΔE15) mutation in vitro. The ΔE15 mutation markedly decreased the expression of ClC-Kb and resulted in a low-molecular-weight band (~55 kDa) trapping in the endoplasmic reticulum, while the ΔTCT mutant only decreased the total and plasma membrane ClC-Kb protein expression but did not affect the subcellular localization. Finally, we studied the physiological functions of mutations by using whole cell patch-clamp and found that the ΔE15 or ΔTCT mutation decreased the current of the ClC-Kb/barttin channel. These results suggested that the compound defective mutations of the CLCNKB gene are the molecular mechanism of the two cBS siblings.