| Abstract: | Previously an acceptable precision (coefficient of variation less than 10%) could be obtained only part of the time for the peak areas of derivatized iodothyronine standards, even relative to that of a structurally close internal standard, 3,4-diiodo-3′,5′-dibromothyronine, when these compounds were analyzed at the low picogram level by capillary gas chromatography with electron-capture detection. This problem has now been ovecome, primarily by introducing a new design, material and conditioning of a direct vapor-injector insert. An extensive analysis under practical operating conditions of derivatized 3,5-di-, 3,5,3′-tri and 3,5,3′,5′-tetraiodothyronine at the 5-10-pg level, involving several changes in the injection equipment and several days of injections, now gives within-day coefficients of variation ranging from 2.7 to 7.7%, 1.5 to 5.3% and 1.8 to 5.2%, respectively, for the relative peak areas of these compounds. |
