London-based Alterian has purchased Techrigy, which sells social media monitoring and analytics tools. Financial terms were not disclosed. Techrigy’s online software is used by marketing professionals to track discussions about their clients on social media sites, while Alterian offers an integrated platform to help marketers manage their work, featuring e-mail, web content management, and analytics services. Alterian said the acquisition represented a “unique opportunity to enter a young technology market,” adding that a push into the interactive marketing space was a key goal. Last year, Alterian purchased online content manager Mediasurface. Release.