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Low Level Detection

Trace Detection of Benzene in a Hydrocarbon
Trace Detection of Sulfate in a Aqueous Solution
Toluene added to Benzene
Nitrate added to Aqueous Solution

(click the picture for a high quality version)

Trace Detection of Benzene in a Hydrocarbon (top)

The spectral response from trace concentrations of benzene in isopropyl alcohol are displayed to the right, and the observed spectral responses were initially background corrected.  A PI-200 spectrograph containing high performance lenses was used for the benzene monitroing.  Lower detection limits, down to the 5 ppm range, could be easily obtained by using our high performance CCD, increasing laser power, or increasing the sample integration time.
The figure to the right displays the linear relationship between the benzene peak intensity and the benzene’s concentration in a hydrocarbon.  The linear relationship has a correlation coefficient of 0.9987
Trace Detection of Sulfate in a Aqueous Solution (top)

The spectral response from trace concentrations of sulfate in an aqueous solution are displayed to the right, and the observed spectral responses were initially background corrected.  A PI-200-L spectrograph containing high performance lenses was used for this study.
The figure to the right displays the linear relationship between the sulfate peak intensity and the sulfate’s concentration in an aqueous solution.  The linear relationship has a correlation coefficient of 0.9934.
Sulfate monitoring stability measurements were also conducted on a PI-200-L-HP.  The Laboratory High Performance instrument utilized a deep depleted CCD that has a higher quantum efficiency and a laser with ~ 3 ½ times more power when compared to the standard PI-200-L instrument.  One can notice that the high performance system has an improved signal to noise ratio.
Comparisons between the actual and predicted sulfate concentrations in an aqueous solution are displayed on the right.  The standard deviation from the (actual – predicted) concentrations was 0.82 ppm and the linear relationship had a correlation coefficient of 0.976.
Toluene added to Benzene (top)

Spectra of benzene with incremental additions of toluene. The left y-axis shows the intensity of the 990 cm-1 peak. The right y-axis shows the intensity of the smaller benzene peaks including the toluene peak at 784 cm-1. The spectra were obtained with an Andor CCD camera. toluene and benzene
Closeup view of the 784 cm-1 toluene peak and the adjacent benzene peak. The spectra were normalized to the intensity of the 830 cm-1 benzene peak also shown. toluene added to benzene
Closeup view of the 784 cm-1 toluene peak. The change in the peak intensity is easily seen. toluene and benzene 0 to 500 PPM
Nitrate added to Aqueous Solution (top)

Spectra of a nitrate peak in an aqueous solution. The change in the peak intensity is easily distinguishable. nitrate in aqueous solution
Plot of the nitrate peak intensity showing the linear change with concentration of nitrate in the aqueous solution plot of peak height