Abstract: An extendable sample capture element for use in a sampling device designed to extract samples, such as reaction/reactant samples, from vessels such as reactor vessels. A sample capture element of the present invention includes one or more concave sample pockets that may be of various shape and volume. A sample capture pocket is adapted to capture a known volume of material when the sample capture element is extended into said material. The material sample remains trapped in the sample capture pocket upon sample capture element retraction. When multiple pockets are present, at least one pocket may function as a mixing pocket. Ports in the sample pocket(s) may be placed in communication with corresponding material transfer channels extending through or along the sample capture element to allow for quenching, dilution and discharge of a captured material sample, such as discharge to an analyzer or another downstream location.