Analytical methods which extract aqueous samples require that the initial volume of the sample be determined, as it is necessary to calculate the concentration of the analytes in the sample. Typically, this is done by marking the sample meniscus on the side of the sample bottle before the sample is extracted. Once the sample has been decanted, the sample bottle is filled with water up to the meniscus and decanted into a graduated cylinder, where the sample volume is then recorded. The acts of measuring a meniscus, transferring, and decanting are all very subjective, and can lead to a propagation of errors in the final reported values. The SmartPrep SPE Cartridge System utilizes an optical liquid sensor and sophisticated software, to automatically calculate the volume of sample that has been processed.

Instrumentation
• Horizon Technology
- SmartPrep™ SPE Cartridge System
- 6 mL Cartridge Configuration
- 20 mL VOA Vial Tray

Method Summary
1. Condition a 6 mL SPE C-18 cartridge with 2 mL of Reagent Water.
2. Attach a Sip Tube to the sample container and start the method. The optical liquid sensor will determine when the entire volume of water sample has been processed.
3. Clean the sample line with Vent and nitrogen, in preparation for the next sample run.
4. The sample report will display each samples estimated volume.

The SmartPrep software uses an optical liquid sensor to monitor the presence of the water sample, and determines when the water sample has finished processing. By knowing certain values, which are entered in the Utilities window, the total volume of the sample may be calculated. For this work, a value of 0.9 seconds was used for the Overhead Time per syringe stroke. This is the time in seconds for the two 12 port valves to rotate between the SPE cartridge port and the sample bottle port. A value of 36 seconds was used for the Overhead Time for the Load step. This is the time it takes to purge the sample line and a 10 inch Sip Tube of residual air pockets by delivering reagent water down them. A value of -13 was used for the Calibration Offset, and a volume of 2.85mL was used for the Tubing Dead Volume (Volume between sample line inlet and V1).


The Horizon Technology SmartPrep™ Extraction System.

Results
A total of 7 replicates were run over a 7 day period for five different amounts of water (100, 250, 500, 750, and 1000 mL). These volumes were precisely weighed out and processed using the above values through the SmartPrep. The SmartPrep automatically calculated the volumes shown in Table 1. The SmartPrep consistently and accurately measured the volume every time for each volume set with a maximum error of 2.3 %. This error is less than most Class A graduated cylinders which typically have 3 % error.

Conclusions
The results clearly indicate the SmartPrep consistently and accurately measures the volume every time for a wide range of volumes to within 2.3 % error or less. This automated feature eliminates the subjective process of the operator marking and refilling a sample bottle, and transferring to a graduated cylinder and replaces it with an absolute process containing less error. The automated volume feature will not only streamline aqueous extraction methods, but will provide more accurate and precise volumes leading to a higher confidence in results.

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