Design and Use of Background-Reduced 27 Al NMR Probes for the Study of Dilute Samples from the Environment

Abstract

Development of methods for the detection and measurement of aluminum (Al) is crucial for our understanding of Al(III) chemistry and toxicity in natural waters, soil solutions, and environmental samples. Traditional colorimetric assays, by their very nature, alter solution Al(III) chemistry, potentially biasing measurements. Methods based on ²⁷Al NMR spectroscopy have the advantage of being nondestructive and of not altering the chemistry of the solution. Standard commercial NMR probes and sample tubes, unfortunately, are constructed from aluminum-containing components. These materials give substantial background signal, which is detected as a large, broad hump, overwhelming signals from dilute samples. We describe here the construction of two novel NMR probes and a sample container built from a variety of materials with low Al content. The designs feature the use of transversely mounted solenoid coils with aluminum-free sample holders. The sample container features a second chamber which can be filled with an external reference solution. These novel ²⁷Al NMR probes are being used for the NMR spectroscopic investigation and quantitation of natural, dilute (10⁻⁶ M) Al(III) samples from the environment.