Trace-mixture analysis

From a medicinal chemist s perspective, nuclear magnetic resonance (NMR) was still the analytical tool of choice, whereas mass spectrometry, infrared (IR), and elemental analyses completed the necessary ensemble of analytical structure confirmation. Synthesis routines were capable of generating several milligrams of product, which is more than adequate for proton and carbon NMR experiments. For analyses that involved natural products, metabolites, or synthetic impurities, time-consuming and often painstaking isolation methods were necessary, followed by expensive scale-up procedures, to obtain the necessary amount of material for an NMR experiment. In situations that involved trace-mixture analysis, radiolabeling approaches were often used in conjunction with various formats of chromatographic separation. 

The understanding and application of MS in the pharmaceutical industry has experienced tremendous growth due to unprecedented sample requirements (i.e.,trace mixture analysis) and commercial pressure (i.e.,faster development time-lines). Today, MS is an essential component of the modern pharmaceutical laboratory as well as an important complement to traditional methods of analysis. 

The evolution of mass spectrometry has been both dramatic and fascinating. Trace analytical measurement, specifically the demand for trace mixture analysis, has created an increased demand for this powerful tool. In many cases, the preference for the trace mixture sample type has transformed the mass spectrometer into a gold standard platform for qualitative and quantitative assays. 

There is a need for increased chromatography-FTIR sensitivity to extend IR analysis to trace mixture components. GC-FTIR-MS was prospected as the method of choice for volatile complex mixture analysis [167]. HPLC-FT1R, SFC-FTIR and TLC-FTIR are not as sensitive as GC-FTIR, but are more appropriate for analyses involving nonvolatile mixture components. Although GC-FTIR is one of the most developed and practised techniques which combine chromatography (GC, SFC, HPLC, SEC, TLC) and FUR, it does not find wide use for polymer/additive analysis, in contrast to HPLC-FTIR. 

Two methods were examined for digestion of biological samples prior to trace element analysis. In the first one a nitric acid-hydrogen peroxide-hydrofluoric acid mixture was used in an open system, and in the second one nitric acid in a closed Teflon bomb. The latter method was superior for Ge determination, however, germanium was lost whenever hydrogen fluoride had to be added for disolving sihcious material. End analysis by ICP-AES was used for Ge concentrations in the Xg/g range13. 

Liquid chromatography/mass spectrometry (LC/MS)-based techniques provide unique capabilities for pharmaceutical analysis. LC/MS methods are applicable to a wide range of compounds of pharmaceutical interest, and they feature powerful analytical figures of merit (sensitivity, selectivity, speed of analysis, and cost-effectiveness). These analytical features have continually improved, resulting in easier-to-use and more reliable instruments. These developments coincided with the pharmaceutical industry s focus on describing the collective properties of novel compounds in a rapid, precise, and quantitative way. As a result, the predominant pharmaceutical sample type shifted from nontrace/pure samples to trace mixtures (i.e., protein digests, natural products, automated synthesis, bile, plasma, urine). The results of these developments have been sig-... 

Figure 1.1 Structure analysis matrix that illustrates pharmaceutical analysis preferences for four specific sample types nontrace/pure nontrace/ mixture trace/pure and trace/mixture. (Courtesy of Milestone Development Services, Newtown, Pa., USA.)...

As described above, individual packaging components will invariably contain complex mixtures of chemical entities (e.g., additives and oligomers), many if not most of which are at relatively trace levels (i.e., pg/g and lower). The principles of Trace Organic Analysis, as developed in the environmental, geochemical, and bioanalytical fields, can be applied to the problem of identification and quantification of these individual chemical entities, whether as extractables or as leachables.f The general process is as follows ... 

Solutions or mixtures of one or more substances mainly for trace element analysis, more rarely for organic traces, but often for alloys and gases. If they are certified on the basis of primary methods, e.g. gravimetry, and do not present risk of degradation they can also be called PRMs. Sets of materials of mixtures of pure substances are used for WDXRF calibration and in general for calibration of comparative methods (see section 2,1.3)... 

The fast pace and highly interdisciplinary nature of drug discovery research further requires that these trace/mixture methods accommodate high-throughput analysis formats. Thus, there exists a balance between simplicity and complexity to provide methods that generate data and inspire confidence while maintaining speed. 

Solid samples can be a bulk material such as a polymer or a raw material, they can be a surface coating such as varnish buildup on a piston or a particle on a semiconductor wafer. Liquids can be pure or as a solution or mixture. Gases can be pure or a mixture, such as in stack gases they may also be very dilute, down to mg 1 (parts per million) level for trace gas analysis such as for atmospheric monitoring or breathing gas for divers. In addition to these possibilities, it may be necessary to carry out the analysis at temperature and pressure conditions well removed from ambient. A final complication is that pure samples are rarely encountered much more common are mixtures, often with the material of interest present as the minor component. 

SPLS is very sensitive and selective for organic trace analysis. Detection limits of a nanogram or even a picogram can be obtained. The methodology is simple, inexpensive, relatively precise (2-20%), relatively rapid, can handle small samples, and can be very selective in mixture analysis when solid-phase fluorescence (SPF) and solid-phase phosphorescence (SPP) are combined or when using derivative, synchronous, or time-resolved SPLS. Additionally, SPLS is well suited to being combined directly with both thin-layer and paper planar chromatography. 

Detection with MS is particularly important for the isolation of compounds that lack useful chromophores or are found only in complicated mixtures such as lactose [56]. The lack of a UV-absorbing chromophore in the saccharide structure limits the mode of detection. Refractive index detection requires precise control of the mobile phase and often does not meet the demands of trace-level analysis needed concerning sensitivity and selectivity. Even chemical derivatization, for example, postcolumn derivatization and enzymatic derivatization, which greatly improves the selectivity and sensitivity of a chromatographic detection systan, does not meet the needed trace levels for the detection of the fine particle dose of lactose. The reason... 

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