Determination of Docosahexaenoic Acid and n-3 Fatty Acids in Refined Fish Oils by H-NMR Spectroscopy: IUPAC Interlaboratory Study

A high-resolution proton nuclear magnetic resonance (NMR) method for determining the concentration (mg/g) of docosahexaenoic acid (DHA), the molar proportion (mol%) of DHA, and the molar proportion of total n-3 fatty acids in fish oils was validated by an IUPAC interlaboratory study (the Commission VI-6 on Oils, Fats, and Derivatives WG 3/98). Thirteen laboratories from 5 countries tested 6 pairs of blind duplicate fish oils: a refined tuna oil, 2 extracted tuna oils, an extracted bonito oil, an extracted salmon oil, and an extracted sardine oil ranging from 9 to 30 mol% DHA and from 20 to 35 mol% n-3 fatty acids. Before 1D-proton NMR measurements with 300–500 MHz instruments, oil samples were weighed and diluted with deuterochloroform solution containing ethylene glycol dimethyl ether as internal standard. To achieve precise performance, a detailed procedure for signal area measurement was described in the protocol, and all participants were instructed about the critical importance of following the protocol. Statistical performances with invalid and outlier data removed were as follows: repeatability relative standard deviations (RSDr) ranged from 0.91 to 2.62% and reproducibility relative standard deviation (RSDR) ranged from 1.73 to 4.27% for DHA concentration (mg/g); RSDr ranged from 0.39 to 2.06%, and RSDR ranged from 0.59 to 3.46% for mol% DHA; RSDr ranged from 0.23 to 0.90% and RSDR ranged from 0.85 to 2.01% for mol% total n-3 fatty acids. The method is expected to be recommended by IUPAC.

Parathyroid surgery in Scandinavia

A review of the organization and practice of parathyroid surgery in Scandinavia indicated that it was undertaken in about half of the surgical clinics. About half of these clinics treated only primary hyperparathyroidism (HPT), and in the great majority all parathyroid operations were done by one or two surgeons. The results of surgical treatment were compared in two large Scandinavian series of primary HPT, one based on a general survey of parathyroid surgery in 1975, and the other on results obtained during 1971-1980 in centres specializing in endocrine surgery (Bergen, Stockholm, Uppsala). In the latter series 90% of the patients were normocalcaemic at follow-up averaging 4.4 years after parathyroid surgery whereas in the general survey the rate of normocalcaemia was 76%. At hospitals performing less than ten parathyroid operations per year it was only 70% and there was high incidence of persistent HPT (15%) and presumed permanent hypoparathyroidism (14%). The findings strongly advocate special training and interest in parathyroid surgery in order to ensure success.