API system

The overall system for safety described above can be called the API System. It is based on a series of API Standards and Recommended Practices which can be summarized as a four step system with each succeeding step encompassing the preceding steps ... 

In the API system the least demanding classification for a petrol engine was originally designated SA. The most demanding is, at present, SG. (The S stands for Service... 

Station.) Constant development of both engines and oils means that from time to time the highest ratings are superseded by even higher ratings. The API system also classifies diesel engine oils by their severity of service. Here the categories have the prefix C, which stands for Commercial. 

Reproducible and consistent performance (direct transfer of methods between API systems without re-optimisation)... 

These problems have largely been solved by the development of a wide variety of powerful LC-MS interfaces (reviewed in Refs. [1-3]). In the following paragraphs, the two most widely used atmospheric pressure ionisation (API) systems, namely atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI), are briefly described, along with the older technique of thermospray ionisation... 

Fig. 16. Time difference using tagged alpha in API system. Distances in centimeters and times in nanoseconds.

We find that for a resolving time of 1 ns, this results in an accidental rate of 5 x 106 x 105 x 10-9, or 500 cps, compared with a true rate of lOcps. Because the accidental rate is proportional to S2, the API systems generally run at source strengths of 107 neutrons/s or less, and consequently, the true count rates are low resulting in long inspection times. Whether this is a problem will depend on the inspection scenario and the amount of explosive to be detected. 

A wide variety of API source designs have been available from the various instrament manufacturers. The various designs are briefly discussed below, in combination with some recent developments in API interfacing and laboratory-modified commercial systems. The discussion is illustrated with systematic diagrams of a variety of commercial API systems. 

Four types of ion-samphng orifices are used in commercial API systems ... 

A flat ion-sampling orifice (in the API systems from Sciex, Fignre 5.6). 

An ion-sampling cone (in the API systems from Waters, Figure 5.7, and in the aQa-sonrce from Finnigan, Fignre 5.9). 

A two- or four-sprayer device to spray one solution through a number of needles was described to study the dynamic range and the flow-rate limitations of an API system [58]. The device allowed flow-rates up to 1 ml/min and provided improved signal stability at higher flow-rates. 

The use of rapid systems, such as the API system, relies on a series of biochemical tests carried out simultaneously. The results of these tests are pooled... 

Substrate test kits include those of the Enterotube, API, BioLog, and other related systems. They can be used to determine biochemical reactions of bacteria, yeasts, and molds within 1-3 days and thus aid in their identification. Some API system kits can be used to characterize organisms at the subspecies level by their capacity to utilize up to 100 substrates. The Biolog systems use carbon source metabolic fingerprints to identify microorganisms. 

In the early API systems, the ion sampling aperture consisted of a 25-200 p,m i.d. pinhole in a metal plate. The size of the pinhole is limited by the pumping capacity of the vacuum system of the MS. 

The observation of multiple charging of proteins in electrospray ionization attracted much attention all major instrument manufacturers introduced an API system to be used in combination with an electrospray interface. At the same time, it was found that electrospray ionization is not only suitable for the mass analysis of large molecules, but is also a very efficient ionization technique of small polar or ionic molecules, e.g. drugs and their metabolites. In the past few years, hundreds of dedicated API-MS systems equipped with electrospray and APCI interfaces have found their way into many different laboratories, especially within pharmaceutical companies and biochemistry/biotechnology laboratories. 

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