The need for in situ chemical analysis in fields such as environmental or security analysis has lead to the development of detection methodologies using lab scale instrumentation. Because of the excellent analytical capabilities of mass spectrometry in terms of speed, sensitivity, specificity, and versatility, this technique has been investigated for achieving needed solutions. The solutions developed using traditional instruments have proven useful on a limited scale due to large instrument size and limitations in sample introduction. The purpose of this thesis is to demonstrate the analytical capabilities of multiple versions of home-built mass spectrometers by analysis of environmentally relevant analytes. The instruments investigated are characterized not only by their portability but by their use of atmospheric pressure inlets, allowing the introduction of externally generated ions. The instruments used are fully functional as indicated by mass ranges up to m/z 450, unit or better) resolution, tandem mass spectrometric capabilities, and limits of detection in the low to sub-ppb range. The instruments also demonstrated the capability for further improvements in analytical parameters and versatility by physical and electronic modifications to the instrument. Ambient ionization methods developed in lab, such as desorption electrospray ionization DESI) and low temperature plasma LTP) ionization have allowed rapid, direct analysis of analyte from an untreated surface. Many highly relevant applications have been developed using these ionization methods on lab scale and handheld instruments. Modification of a handheld instrument has allowed the investigation of security screening experiments, namely the detection of explosives on a large area using ambient ionization methods.