1. Mike Rusak and Laura Fairburn CURRENT OBSTACLES ON THE APPLICATION OF AMBIENT IONIZATION MS IN FORENSICS

2. SUMMARY OF THE DRAWBACKS Cost Professional experience is needed Lack of comparable data Ionization is affected by spray, chemical, and surface parameters. Problems with portability

3. SUMMARY OF THE DRAWBACKS Utilization of standards Problems with quantitative analysis Lack of research on matrix effects Lack of field testing Information obtained is not yet applicable to current standards

4. COST Cost of the operator and the equipment can’t be afforded by police departments The knowledge for just the calibration and operation is very specialized, increasing one’s expected salary Not a very practical purchase for a small police department Right now, the prototypes of the portable MS machines can only be afforded by the US military

5. EXPERIENCE NEEDED Need to have a lot of experience and education You can’t just walk off the street, be given basic training and then be allowed to operate the equipment and deemed an expert Most evidence requiring MS is outsourced to specialized forensic labs

6. LACK OF COMPARABLE DATA WHEN WORKING WITH UNKNOWNS Since this technique is still in the prototype phase, there aren’t many successful standard cases to compare one’s results as few labs use this technique All results need to be confirmed with other techniques such as IR and NMR, or GC-MS

7. PARAMETERS THAT AFFECT IONIZATION All of the following parameters can be very difficult to control in the field 1. Geometric parameters 2. Spray parameters 3. Chemical parameters 4. Surface parameters

8. PORTABILITY The large volume and power supply needed reduces the portability of the machine Currently, portable machines are very rare and experimental Compromises sensitivity and accuracy of readings

9. UTILIZATION OF STANDARDS Standards are used to quantify and identify the analyte of interest There’s a dependence of the ion signal on the type of substrate present Eg) Thermal conductivity of substrate/matrix can influence the signal Roughness of substrate Hard to quantify an analyte  use a conventional MS apparatus instead

10. UTILIZATION OF STANDARDS If it isn’t possible to mix in a standard, an intrinsic compound of known concentration can be used, which isn’t ideal. Not very quantitative

11. MATRIX EFFECTS Matrix: the material the analyte of interest is mixed with Influences desorption and ionization of the analyte Eg) cream, fillers (in the case of medicinal tablets), dirt, carpet, etc. Systematic matrix studies are rare

12. MATRIX EFFECTS The matrix can cause overlap in the spectra due to unwanted compounds Can also cause ion suppression Less volatile compounds in the matrix disrupt droplet formation or evaporation, suppressing the amount of ions reaching the detector Can react with analyte during desorption or ion formation

13. MATRIX STUDIES Yu et al. studied the effect of different biological matrices on the observed signal via DART analysis Showed that verapimil analyte signal can be reduced to 50% in bile, and 3% in brain tissue homogenate, compared to verapimil in neat solvent Also showed that matrix effects are compound dependent.

15. MATRIX STUDIES Jecklin et al. showed how the limit of detection (LOD) varies when analyzing pesticides in different fruit juice matrices The authors noted that background intensities were not responsible for the observed changes

17. LACK OF FIELD TESTING Explosives, toxic industrial compounds, chemical warfare agents, etc., have been explored by a variety of methods Analysis of these compounds is limited for that fact that the experiments are very controlled. Either done from standard solutions or complex matrices doped with standards

18. LACK OF FIELD TESTING For drug analysis, pure chemicals are usually spiked onto food, skin, or other surfaces. More research needs to be done with real evidence and analytes in a non-standardized environment.

19. APPLICABILITY Yield a type of information which may not be applicable to current standards Eg) Food policy requires that pesticide levels be measured in concentration (wt/wt), which requires homogenizing the fruit/veggies of concern. Sample preparation still needs to be done in some cases Eg) To reduce ion suppression, especially for analytes in a low concentration in complex matrices

20. REFERENCES Alberici, Rosana M. et al. Ambient mass spectrometry: bringing MS into the “real world”. Anal Bioanal Chem. 2010, 398: 265–294 Cooks et al., Forensic Applications of Ambient Mass Spectrometry. Anal Bioanal Chem (2009) 394, 1995-2008 Chen et al., What Can We Learn From Ambient Ionization Techniques? J Am Soc Mass Spectrom (2009) 20, 1947-1963 Gamez et al., Atmospheric pressure glow discharge desorption mass spectrometry for rapid screening of pesticides in food. Rapid Commun Mass Spectrom. (2008) 22, 2791- 2798 Takats, Zoltan et al. Ambient mass spectrometry using desorption electrospray ionization (DESI): instrumentation, mechanisms and applications in forensics, chemistry, and biology. J. Mass Spectrom. 2005, 40: 1261–1275 Yu et al., Bioanalysis without Sample Cleanup or Chromatography: The Evaluation and Initial Implementation of Direct Analysis in Real Time Ionization Mass Spectrometry for the Quantification of Drugs in Biological Matrixes. Anal Chem. (2009) 81,193-202