28 Comparing the MICROLAB® 600 to Volumetric Glassware and Air Displacement Pipettes
Introduction Analytical sample preparation is used in many industries such as forensics, environmental, mining, food and beverage, and many others. Concentrated samples are diluted and analyzed via HPLC, GC, Atomic Absorption, and/or Inductively Coupled Plasma Spectroscopy to name a few. Traditionally these samples are prepared using volumetric glassware, syringes, and/or pipettes. These manual techniques are effective but leave room for improvement. Use of volumetric glassware is time consuming and often results in waste due to large preparation volumes. Traditional air displacement pipettes are prone to fluctuations in accuracy resulting from user to user variation, sample vapor pressure, viscosity, and atmospheric pressure. Use of a positive displacement automated pipetting device like the MICROLAB®
600 (ML600) can reduce sample preparation time, reduce waste, and improve consistence of results. Experimental Design
The goal of this experiment is to compare the costs and results of preparing a standard curve using the MICROLAB 600, volumetric glassware, and air displacement pipettes. A 60 mg/mL stock solution of phenol was prepared in 100% acetronitrile. The following series of six dilutions were prepared using each technique; 1:1, 1:4, 1:9, 1:49, 1:99, 1:199. For the MICROLAB 600 and the pipettes the dilutions were made directly into an autosampler vial with a final volume of 1 mL. For the volumetric glassware a 10 mL volumetric flask was used and 1mL was transferred to the autosampler vial. Each dilution series was prepared five times and the results below were averaged. The samples were analyzed on an Agilent 1100 HPLC instrument with a Hamilton PRP-1, 5µM, 2.1 x 150 mm column.
Results The phenol peak areas for all five replicates of the six dilutions were averaged and scatter plotted for each technique in Figure 1. A best fit line and R2 value was determined for each technique. The R2 value indicates the statistical correlation of the best fit line. All techniques showed a high correlation but the MICROLAB 600 was the highest with a value of 0.9992.
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Figure 1. Six point phenol standard curve A 60 mg/mL stock solution of phenol was prepared and diluted 1:1, 1:4, 1:9, 1:49, 1:99, & 1:199. The dilution series was repeated 5 times and then analyzed by HPLC. The resulting peak areas were averaged and plotted to determine the standard curve.
In addition to having the highest R2 value the MICROLAB 600 completed the task almost twice as fast as pipettes and more than 4 times faster than volumetric glassware. The table
below shows that in addition to being slow volumetric glassware consumes approximately 10 times the buffer used by either the MICROLAB 600 or Pipettes. The running cost of the MICROLAB 600 relative to volumetric glassware is 85% less and relative to pipettes not including pipette tips is 40% less.
Table 1. Analysis of Time and Costs for Preparing Dilutions Using Each Technique
a – this is an estimated cost for labour b – this cost came from Sigma for part number 34851-4L
Conclusion
Preparation of samples using the MICROLAB 600 provides more consistent dilutions using less time and buffer. The MICROLAB 600 saves up to 85% in labour and reagent costs for basic dilutions. The inert fluid path and the positive displacement syringe drives make it compatible with virtually any solvent. Unlike disposable pipette tips the fluid path does not leach chemicals making it ideal for even the most sensitive detection methods.
Circle no. 381
LAB ASIA - MAY/JUNE 2011 - ADVERTORIAL
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