High external standards procedure

The oleoresins were analyzed by high performance liquid chromatography following the standard procedure of the Normalization French Association (AFNOR) (7). The quantification of each component was carried out by using the external standard vanillylnonanamide. 

The external standard method is the simplest one and should therefore only be used for simple analytical problems. The injection must be performed with good reproducibility thus it is recommended that the complete loop filling method be used (see Section 4.6). With multiple-point calibration it is not recommended to inject different volumes from a reference stock solution (e.g. 10, 20, 30, 40 and 50 (xl) because it is well possible that neither accuracy nor precision of these injections are high enough. It is better to prepare a number of calibration solutions with different concentrations and to inject equal volumes of them (with complete loop filling or with exactly the same procedure as is used also for the sample). 

The choice of an internal standard for an analytical procedure is often made in a too cavalier a fashion and may actually provide lower precision than external calibration. The successful use of an internal standard depends on the existence of a high correlation between the peak areas (heights) of the analytes and the internal standard for the complete analytical procedure and their being lower variability in the internal standard area (height) compared to those of the analytes [286-288]. An external standard will generally provide higher precision than an internal standard when the variation of the recovery for analytes and standards is sufficiently different and the standard deviation in the mean for repeated analyses of the internal standard is larger than that for the analytes of interest... 

An LC method for alpha acids is advocated by Analytica-EBC Fourth Edition. It uses, however, the Ganziin procedure to prepare the sample solution. As stated above, this is needlessly complicated and for a number of reasons (10) will give high results. The method also uses an extract of known composition as "External Standard" and furthermore recommends equilibration of the column for 30 minutes, running the external standard twice, before and after the samples and running each sample at least two times. With an analysis time of 35 minutes his means about 3 h analysis time for one sample. We feel that this is too long. The Analytics method mentions also only... 

Measurements of BET nitrogen surface area at 77 K are frequently used as a standard procedure for characterisation of porous materials. Studies suggested that BET surface area correlates with MOE surface areas determined from crystallographic data. However, heterogeneous surfaces are found in MOEs and it is best to describe the BET surface area as an apparent surface area. If a Type I isotherm has a plateau at high relative pressure, the micropore volume is given by the amount adsorbed (converted to a liquid volume) since the mesopore volume and external surface are both relatively small. Porous structure characterisation parameters (Eangmuir and BET surface areas and pore volumes) obtained from gas adsorption studies of MOEs have interrelated correlations. 

The following procedure is carried out in a ventilated hood. Finely powdered dry sodium cyanide (29.4 g., 0.60 mol) and 180 ml. of dimethylformamide (DMF) are placed into a 1-1., three-necked, standard-taper round-bottomed flask equipped with a reflux condenser, dropping funnel, and Hirshberg stirrer connected to a high-speed stirring motor. External cooling is provided by a cold-water or ice-water bath. Carbon disulfide... 

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