Full Text Article - Millipore

More documents

Recommendations

Info

2 Additionally, technical hints are given as to how to ensure reproducible high quality ultrapure water, including after each consumable change. One of the most widely trusted parameters used to track ultrapure water quality is resistivity monitoring. Previous studies: traditional HPLC profiles The quality of purified water is often questioned, when poor baselines are obtained (especially at 214 nm, a wavelength which most organic contaminants absorb). To illustrate this, a blank gradient (no sample injected) was run by pumping for 4 minutes at initial conditions (100% water), then ramping up to final conditions (100% acetonitrile) over a period of 20 minutes. Next, suspecting water as the contributor of the contaminant peaks, the same procedure was run except that initial conditions were kept for 36 minutes, before running the gradient. Since the size of the peaks increased, one can be certain they came from the water and not from the acetonitrile (Figure 1). If any of the peaks of interest were eluted at the same time as these contaminating peaks, there would be quantitation errors. There is also a possibility that the contaminating peaks could be confused with desired compounds. 1.0 A.U. 0 10 20 Figure 1: Blank analysis profiles at 214 nm. Time (minutes) 36 minute delay 4 minute delay Typical chromatograms obtained with different purified water types are given below. The first one is a gradient analysis of 50 ml of lab water that is not ultrapure, concentrated on the head of a C18 column. A gradient was then run, up to 100% acetonitrile, and the output was monitored at two different wavelengths at a moderately sensitive setting. Clearly, as shown in Figure 2 this water source is not acceptable for HPLC, be it the isocratic or the gradient method. Peaks due to the water occur throughout the chromatogram. Two peaks come from the acetonitrile. 1.0 A.U. 0 contaminants from water 10 20 Figure 2: Poor baseline profiles at 214 and 254 nm. contaminants from acetonitrile Time (minutes) The R&D Notebook: From tap to ultrapure water: tracking organic contaminants This value, however, does not measure the possible organic contaminants that may be present in water. Significant organic contamination will still give an 18.2MΩ.cm resistivity reading 7 . The second one is a gradient analysis of 50 ml of triple distilled water, concentrated on the head of a C18 column. A gradient was then run, up to 100% acetonitrile, and the output monitored at two different wavelengths at a moderately sensitive setting. Clearly, this water source is not acceptable for HPLC. The early peaks are due to the water, the last two peaks come from the acetonitrile (see Figure 3). 1.0 A.U. 0 For reverse osmosis water, gradient analysis of 50 ml concentrated on the head of a C18 column is shown in Figure 4. A gradient was run, up to 100% acetonitrile, and the output monitored at two different wavelengths at a moderately sensitive setting . Clearly, this water source is not acceptable for HPLC, neither isocratic nor gradient. The early peaks are due to the water, two of the last peaks come from the acetonitrile. Moreover, with this type of purified water, the residual background is very high. A.U. 0 contaminants from water Figure 3: Triple distilled water. 10 20 contaminants from water 10 20 contaminants from acetonitrile contaminants from acetonitrile Time (minutes) 1.0 214 nm Figure 4: RO water. 254 nm Time (minutes) In order to get the ultrapure water quality required to perform organic chromatography analysis, a water purification chain combining various technologies is therefore necessary. In order to highlight the efficiency in removing organics from tap water, organic studies are performed on the water delivered after the main purification steps.
Experimental Water Purification System A combination of technologies is necessary to produce ultrapure water. Methods for tracing classes of organic matter at different points in a water purification system were first described in 1987 8 . Combination techniques were also used to obtain meaningful information about contamination in the DI water process 9 . The configuration used during this qualitative study is made up of two new water purification systems. The first one combines reverse Chromatographic conditions Equipment RO reject RO permeate EDI Product Reservoir The following equipment was used throughout the experiment: HPLC pumps delivering a gradient eluent at 2.0 ml/min Computer for data acquisition and system control Injector for 100 µL injection with 250 µL loop, 200 µL syringe, and appropriate vials. Detectors: Dual detectors operated at 214 nm and 254 nm (Waters Corp, Milford, Mass, USA). Column Type: Waters µBondapak ® C-18 column, 3.9 x 300 mm (#27324). Precolumn Type (optional): C18 (Waters µBondapak C-18 Guard-Pak TM (#T33552)) Elution solvents: Water (fresh Milli-Q ® system water (<strong>Millipore</strong>)) Acetonitrile (HPLC grade: J.T. Baker JT9017 or equivalent). The bottles were rinsed in 10% nitric acid, washed extensively with fresh Milli-Q system water before sampling. Figure 5: The water purification chain studied. osmosis and electrodeionization techniques. This purified water is stored in a 60 l reservoir. This high purity water tank is specifically designed for the optimization of high purity water storage 10 . A second system combining activated carbon, ion exchange resins and UV treatment is fed by this pretreated water. Sampling ports are ensured throughout the process (see arrows in Figure 5) HPLC gradient Ultrapure water The following elution gradient was used throughout the experiment. 50 ml of each water sample were injected (except for tap water and RO reject water where 1 ml was used) in order to concentrate trace impurities on the column. Time [minutes] Flow [ml/min.] Water % Acetonitrile % 0.0 2.0 100 0 2.0 2.0 100 0 12.0 2.0 0 100 15.0 2.0 0 100 19.0 2.0 100 0 25.0 2.0 100 0 The acquisition time was fixed at 14 minutes with a 4 point/second acquisition rate and a resolution over 20 bit. Chromatograms were compared at different maintenance conditions and during the different water purification stages. The R&D Notebook: From tap to ultrapure water: tracking organic contaminants 3
Page 1: The R&D Notebook From tap to ultrap
Page 5 and 6: UV absorbance UV absorbance From ta

Full Text Article - Millipore

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?