Reduction of the extra-column band dispersion by a slow transport and splitting of a sample band in isocratic reversed-phase liquid chromatography.

Sample introduction method was studied to reduce the extra-column effect in reversed-phase HPLC. Slow transport of a sample band (SToSB) in the pre-column space followed by the introduction of the band into the column at a near-optimum flow rate resulted in larger plate counts for a 1.0 mmID, 5 cm long column as much as 1.4-1.6 times for solutes with a retention factor (k) of 0.5-1.8 compared to a conventional elution method. Further reduction of the extra-column effect was possible by orthogonally splitting the sample band (SplSB) by flow switching during its slow transport followed by the introduction of the leading part of the band into the column. In this case, increased plate counts of up to 2-3 times for solutes with k of 0.5-1.8 were observed for a 1.0 mmID, 5 cm column. The sample introduction method, SToSB in the injector and the pre-column tube of a few µL, was found to reduce the extra-column band variance by 0.4-0.5 µL2 for an UHPLC system with the extra-column volume (Vextra) of ca. 4.6 µL and the system variance (σextra2) of 1.1 µL2 at flow rate of 100 µL/min, while SToSB and subsequent SplSB were found to be more effective, reducing σextra2 by about 0.8 µL2. With an UHPLC instrument with Vextra of about 10 µL and σextra2 of ca. 3.6 µL2 at flow rate of 300 µL/min, 1.4-2.1 times as many plate counts were observed with SToSB and SplSB compared to the normal elution method for early-eluting solutes with k=0.25-1.7 for a column, 2.1 mmID, 5 cm long. With this UHPLC instrument, SToSB and/or SplSB resulted in the reduction of σextra2 by 1.2-2.2 µL2.

A new method for the measurement of trace amounts of HONO in the atmosphere using an air-dragged aqua-membrane-type denuder and fluorescence detection.

A new method for the measurement of trace amounts of HONO has been developed. Nitrous acid in the ambient air is absorbed in an aqueous solution by an air-dragged aqua-membrane-type denuder. The absorbed nitrite is reacted with 2,3-diaminonaphthalene, and the formed 1-naphthotriazol is measured using a fluorescence method. The calibration curve of HONO shows a straight line from 0 to 4000 ppt, and the detection limit is estimated to be 8.1 ppt calculated as being three times of the base line noise. The time resolution, which is defined as the time required to become a constant value by changing from 0 to ca. 1000 ppt was 2 min. The present method is not affected by NO(2), NO, SO(2), O(3) NH(3) or mixtures of these gases and organic nitrate, organic carboxylic acids, alcohols and aldehydes. The determination results of HONO concentrations in the ambient air by the present method are in good agreement with those by the annular denuder system and the differential optical absorption method.