Differential Mobility Detector (DMD) is a type of microelectromechanical system, radio frequency modulated IMS (MEMS RF-IMS) device.
Due its small size, it easily fits into portable units, such as transferable gas chromatographs or drug/explosives sensors. For instance, it was incorporated by Varian in its CP-4900 DMD MicroGC, and by Thermo Fisher in its EGIS Defender system, designed to detect narcotics and explosives in transportation or other homeland security applications.
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However, independent researchers[3] report that RSD for such compounds as hydrogen sulfide, methyl mercaptan, and ethyl mercaptan is from 4 to 11%.
| Type of source | Sealed source (capsule in holder) |
| Capsule Type | Rolled Foil 6.3 mm x 1.3 mm x 5 μm |
| Holder Type | Manifold |
| Isotope (radio nuclide) | Ni – 63 (also written as 63Ni or Nickel 63) |
| Source Manufacturer | |
| Amount of activity per source | 185 MBq (equal to 5 mCi) |
| Physical State of Source | Solid (deposited on one face of the foil) |
| Half life Ni – 63 | 100.1 years |
| Energy of beta for Ni – 63 (average / max) | 17 keV / 67 keV |
| Minimum Specific Activity | 555 GBq per gram |
| Type of decay | β (beta) |
| Progeny (Ni – 63 decays to) | Cu – 63 (stable, not radioactive) |
| ISO – 2919 : 1999 Testing Classification | C32211 |
| Maximum temperature of the source | 180°C |
| ISO – 2919 : 1999 Radio Toxicity Classification Group | B, subgroup B2 |
DMD is able to analyze the substances which can be ionized by the β particles emitted from 63Ni. In this, it is very similar to the ECD. Varian has given the following specifications:[5]
| Analyzer | Application | Detection Limit DMD | Why | Markets |
|---|---|---|---|---|
| Sulfur odorants in Natural Gas | THT | 0.5 mg/m3 (100 ppb) | Safety | Gas transportation |
| TBM | Environmental | Gas Distribution | ||
| MES | City gates | |||
| Fuel cells | ||||
| Sulfur-free odorants in Natural Gas | Methyl Acrylate | 0.35 mg/m3 (100 ppb) | Catalysts | |
| 0.45 mg/m3 (100 ppb) | ||||
| Ethyl Acrylate | ||||
| Anesthetic gases in air | Halotane | 100 ppb | Safety | Operating Theaters |
| Enflurane | Anesthetic gas companies | |||
| Isoflurane | Recovery rooms | |||
| Desflurane | ||||
| Sevoflurane | ||||
| Sulfur hydrocarbons in HC matrices | Hydrogen Sulfide | 200 ppb | Safety | Petro-chemical processes |
| Carbonyl sulfide | Environmental | Catalysts | ||
| Methyl Mercaptan | Corrosion | Fuel cells | ||
| De-sulfurisation companies | ||||
| Mercaptanes C1-C4 in gas | Methyl Mercaptan | 100 ppb | ||
| Ethyl Mercaptan | ||||
| iso-Propyl Mercaptan | ||||
| n-Propyl Mercaptan | ||||
| TBM, tert-Butyl Mercaptan | ||||
| CFC’s & HCFC’s in air | For example | 100 ppb | Safety | Personal monitoring |
| CFC-11 | Environmental | Environmental companies | ||
| CFC-12 | Emission control companies | |||
| CFC-113 | CFC & HCFC Producers | |||
| CFC-114 | ||||
| CFC-115 |