Investigation of unknowns

From time to time it happens that problems arise in most manufacturing processes and cable manufacture is no exception. Faults in cables are not acceptable, owing to the long service life and reliability requirements, and therefore these must be investigated so that the cause of the fault can be remedied. Various analytical strategies are employed in such investigations, often in combination, since this gives better confidence in interpretation. DSC is a valuable tool for this type of work, either alone or in conjunction with other techniques, particularly where the fault is caused by a contaminant. 

---

Standardisation of EPDM characterisation tests (molecular composition, stabiliser and oil content) for QC and specification purposes was reported [64,65]. Infrared spectroscopy (rather than HPLC or photometry) is recommended for the determination of the stabiliser content (hindered phenol type) of EP(D)M [65]. Determination of the oil content of oil-extended EPDM is best carried out by Soxhlet extraction using MEK as a solvent [66], A round robin test was reported that evaluated the various techniques currently used in the investigation of unknown rubber compounds (passenger tyre tread stock formulations) [67]. 

Size exclusion (gel filtration or permeation) chromatography (SEC) is suitable for solutes with molecular weights of 2000 or more and is also useful for the preliminary investigation of unknown samples. Separated fractions can then be subjected to one of the other modes of HPLC. Exclusion chromatography is discussed in section 4.3.6. 

An extensive study of the infra-red absorption spectra of nitro compounds was reported recently by Pristera, Halik, Castelli and Fredericks [37a], The following are bands which are valuable in the structural investigation of unknown nitro compounds and their mixtures (Table 25). 

Ofrier soft ionisation techniques include field desorption, field ionisation, atmospheric pressure ionisation, and fast atom bombardment and each increases the rmolecular weight but because of the production of cluster ions such as (M + Na), (M + 2Na), 2M, etc., they are not used in the investigation of unknowns. 

As a practical matter the following sequence of solvents is recommended in an investigation of unknown mixtures elute first with petroleum ether then ligroin, followed by ligroin containing 1%, 2%, 5%, 10%, 25%, and 50% ether pure ether ether and dichloromethane mixtures, followed by dichloromethane and methanol mixtures. A sudden change in solvent polarity will cause heat evolution as the alumina or silica gel adsorbs the new solvent. This will cause undesirable vapor pockets and cracks in the column. 

The reliability of these two-dimensional connectivity experiments is now well enough established that they can be used with confidence in the investigation of unknown structures in conjunction with diffraction studies. In a first step in this direction, a study of the three-dimensional bonding connectivities in ZSM-11 in both its high- and low-temperature forms has been reported [86]. As described earlier these are related to each other by a temperature-induced phase transition. The high-temperature form is known to have tetragonal symmetry with space... 

Self-Contained Breathing Apparatus (SCBA) used during emergencies (e.g., major chemical spills, toxic gas releases /air monitoring alarm conditions, or investigation of unknown... 

In this way the student s knowledge of the organic reactions is consolidated as he proceeds through the sections, his experience of the general method of identification steadily increases, and the investigation of the unknown compounds forms a welcome break from the systematic pursuit of the sectional work. 

Pancreas Oral cholecysto-graphic agent iopanoate ( ) experimental Unknown excretion into pancreatic duct Schmiedl U etal (1994) Imaging of exocrine pancreatic function investigation of the bioavailability of weak organic acids as potential pancreatic contrast agents for computed tomography. Invest Radiol 29 689-694... 

In summary, this work has shown that superlattices are promising systems for investigation of quantum control in the solid state. The examples presented here show that the dynamics of charge carriers can be controlled using relatively simple, experimentally laser fields. Superlattices are ideal candidates for quantum control precisely because their complexity does not allow for simple, intuition-guided experiments, and because their dynamics are largely unknown. 

---