Altex injection system

Apparatus. The major components in the HPLC system (Figure 2) include a Varian HPLC pump (model 5000, Varian Assoc., Walnut Creek, CA), Altex injection valve (model 210, Beckman Inst., Fullerton,... 

Apparatus Pumping systems used in these studies for high-performance columns were a Varian 8500 syringe pump and a Varian 5000 isocratic pump. An Altex IlOA was employed for the con-trolled-pore glass (CPG) columns. Waters Associates model 401 refractometers were used on all instruments. Stagnant mobile phase was kept in the reference side of the refractometer. Samples were injected with a Rheodyne 70-10 injection valve using a 20yl loop (lOOyl for CPG columns). 

The trend toward automatic injection will become predominant with increasing routine application. Currently, satisfactory injection devices are only available for GC septum injection from Hewlett-Packard, Varian, etc. These have been adapted to HPLC with good results [6] within the general limitations of septum injection. Automatic injection usually results in better reproducibility with relative standard deviations of less than 1% and external standardization can be used [6]. Automatic systems based on loop injection have been announced by several manufacturers, e.g. DuPont, Varian, Altex. 

Figure 3 shows a schematic of the FIA system and details the thin-layer transducer cell, which contains the poly(3-methylthiophene) anion sensor electrode(s). Electrochemical detection in the amperometric mode was employed for the FIA/EC (flow injection analysis with electrochemical detection) studies. A typical potential used was +1.00 volts vs. Ag/AgCl reference electrode. The FIA-EC system consisted of an Altex lOOA double reciprocation pump and a Rheodyne injector (Cotai, CA) with either a 20 or 50 microliter sample loop. Constant potentials were applied using the herein described DWEP, which is software controlled. The electronically transduced signals are converted from analog to digital by use of A/D and D/A converter circuits. The option exists to automatically save the data on the computer or print the results as the experiment progresses. 

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