A method for collecting a sample of liquid in a container having a closure and a specific head space comprising: providing a plurality of container assemblies, each of said container assemblies defining a container with a closed bottom, an open top and a sidewall extending between said closed bottom and said open top; providing closures (70, 170) for each of said containers, at least a first of said closures having a first length and being dimensioned to extend a first distance into the open top of the respective container, and at least a second of said closures having a second length which is greater than the first length, the second closure being dimensioned to extend a second distance (h) into the open top of the respective container, wherein the second distance (h) is greater than the first distance so that the second closure defines an inner volume smaller than the container with said first closure; determining a required volume of a liquid sample; selecting an appropriate one of said containers with a volume greater than the required volume by an amount for achieving a specified head space, wherein the head space is defined as the volume between a top of the collected sample and a bottom of the first closure and/or second closure; collecting the selected volume of said liquid in said selected one of said containers; and selecting one of said first closure and said second closure for achieving the specified head space in the container and sealingly engaging the selected one of said first closure and said second closure with the open top of said selected one of said containers, whereby said container with said first closure and said container with said second closure enable collection of first and second differing volumes of liquid samples in the respective container each with substantially identical head spaces. providing a plurality of container assemblies, each of said container assemblies defining a container with a closed bottom, an open top and a sidewall extending between said closed bottom and said open top; providing closures (70, 170) for each of said containers, at least a first of said closures having a first length and being dimensioned to extend a first distance into the open top of the respective container, and at least a second of said closures having a second length which is greater than the first length, the second closure being dimensioned to extend a second distance (h) into the open top of the respective container, wherein the second distance (h) is greater than the first distance so that the second closure defines an inner volume smaller than the container with said first closure; determining a required volume of a liquid sample; selecting an appropriate one of said containers with a volume greater than the required volume by an amount for achieving a specified head space, wherein the head space is defined as the volume between a top of the collected sample and a bottom of the first closure and/or second closure; collecting the selected volume of said liquid in said selected one of said containers; and selecting one of said first closure and said second closure for achieving the specified head space in the container and sealingly engaging the selected one of said first closure and said second closure with the open top of said selected one of said containers, whereby said container with said first closure and said container with said second closure enable collection of first and second differing volumes of liquid samples in the respective container each with substantially identical head spaces.