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A Kaiser Aerospace & Electronics Company

Sample Report	September 9, 1999

To:	Jill Pasteris (Washington University in St. Louis)

CC:	Mike Pelletier (KOSI)

From:	Jeremy Shaver

Re:	Seawater Samples

Dear Dr. Pasteris,

We have run some spectra on the seawater samples you sent to us in July. Attached are three figures derived from those spectra. Initially, we measured all the samples in their Nalgene bottles and simply subtracted the minor Nalgene background. We also measured spectra of sample 990527A (subsequently called #27) in a glass vial, as you requested. The difference between spectra taken in the glass vial and those taken in the bottle and subsequently background subtracted were negligible so the remainder of the spectra were simply measured in the Nalgene bottles and corrected accordingly.

The unit used to measure these spectra was a HoloLab 5000 base unit with a 50 mW, 532 nm Nd:YAG laser. Equipped with an immersion optic, the system delivered around 20 mW to the sample. This is lower than what one can usually expect from a normally tuned system which should give around 30 mW. All spectra were taken using cosmic filtering which averages two spectra together, removing cosmic spikes; as a result, the total integration time is actually twice the time we entered into the program (e.g. 10 sec exposure was comprised of two, 5 second exposures, averaged together.)

Figure 1 shows the entire low frequency spectra for all three samples, labeled with the final two digits of your sample number. All spectra shown were taken using 240 seconds of total acquisition time. Although the original spectra have very similar intensities, their exact maxima and minima have been scaled to allow you to compare them side by side. As you expected, the primary features from the dissolved ions appear in the 900 to 1500 cm-1 range. This range is shown expanded in Figure 2 after normalizing to the HOH bend at 1650 cm-1.

Because of the normalization used in Figure 2, we can now safely compare intensities between the three samples. It is clear from the sulfate band around 980 cm-1 that sample #29 has the highest concentration followed by #26 and then #27. Sample #27 also shows at least two additional features around 1013 cm-1 and 1360 cm-1. I have not attempted to exhaustively assign the various bands not knowing all of the various species in solution (counter ions, metals, pH, etc.) but there appear to be several other consistent spectral features throughout this region in all three samples.

The final figure shows three spectra taken of sample #27 in the glass vial at different integration times. The spectra have been min/max scaled and offset for clarity. These spectra are included for you to compare the signal to noise obtained at various times. You can also infer the signal to noise available by doubling the laser power and halving the exposure time. That is, for most experiments with this equipment, it is safe to say that a 240 sec exposure with 20 mW is equivalent to 120 sec with 40 mW.

I hope these results give you some idea of the potential use of Raman to measure these samples. If you want me to try any other experiments or wish to discuss these results with me further, please do not hesitate to call or e-mail me at the numbers or address below.

Best regards,

Jeremy Shaver

Applications Scientist

phone: 734-214-3659

fax: 734-665-8199

e-mail: shaver@kosi.com