An ink composition comprising a dye or a pigment, dissolved or dispersed in an aqueous medium, and having nitrates and nitrites in a total content less than 5 ppm.

An aqueous ink composition containing urea, an azo dye colorant, and water, with dissolved ammonium ion and nitrogen contents lower than 200 ppm and 5 ppm, respectively. The composition is highly stable to elevated temperatures and extended storage times, and gives excellent printing quality. Methods for making the inventive ink compositions, and methods of using the compositions in ink jet recording are also disclosed.

A water-based ink includes coloring agents, polyvalent alcohol, polyvalent alcohol monoalkyl ether, and water. The polyvalent alcohol monoalkyl ether preferably has a vapor pressure not greater than 0.1 mm Hg at 20.degree. C. The ink exhibits superior recording properties (signal responsiveness, stability in liquid form, discharge stability, continuous recording ability over long periods of time, and ink discharge stability after use has been suspended for long periods of time), fluid stability, preservation stability, adherence to recording materials, quick drying, printing quality and low odor, thus being an excellent ink for various types of ink jet recording.

The present invention provides a gas-permeable hollow fiber membrane having an inner diameter of 50 to 500 .mu.m and a membrane thickness of 10 to 150 .mu.m, which is, preferably a composite hollow fiber membrane having a three-layer structure consisting of a nonporous layer having porous layers disposed on both sides thereof. Dissolved gases present in an ink can be removed by passing the ink through the bores of hollow fibers comprising such a hollow fiber membrane, and evacuating the outer surface side of the hollow fibers. This method makes it possible not only to degas inks with a slight pressure loss, but also to degas inks stably even if pressure changes occur during degassing.

An inlet system is used in conjunction with a standard gas chromatograph/mass spectrometer to facilitate the analysis of volatile components of substances fired from inkjet pens. The system allows for the investigation of changes in the ink resulting from resistor firing. In addition, the system can be used as a diagnostic tool to detect failures in individual firing chamber. After a block is cooled with liquid nitrogen, an analyte sample of ink is deposited on a stage in a chamber in the block and the chamber is then sealed. The stage is then heated vaporizing a portion of the analyte sample. A transfer gas passes over the stage and mixes with vaporized analyte. The mixture then enters a gas chromatography mass spectrometer which determines the analyte sample's components and relative amounts thereof.