Larry S. Simeral

Improved Analysis of Minor Species in Mixtures Using Carbon-13 Decoupling in One-Dimensional Proton NMR

Proton nuclear magnetic resonance (NMR) is a useful tool to identify and to quantitate species in mixtures of organic chemicals. However, carbon-13 satellites often interfere with the identification and integration of resonances from species at low concentrations (<2%) in such mixtures. Carbon-13 satellites arise from proton coupling to carbon-13 (spin 1/2, 1.1% isotope abundance). Each satellite is 0.55% of the area of the proton resonance for protons bound to carbon-12. The interferences become particularly troublesome when the principal component of the mixture has many or overlapping resonances.

Determination of Urea, Nitrate, and Ammonium in Aqueous Solution Using Nitrogen-14 Nuclear Magnatic Resonance

The quantitative determination of nitrogen-containing species in aqueous solution is important in biological, chemical, and agricultural analysis. For example, the nitrogen content of aqueous fertilizers is an important speci® cation, process control, and analytical parameter. The standard methods for determination of nitrogen content are based on the Kjeldahl total nitrogen analysis and usually involve three steps: (1) conversion of the nitrogencontaining species to ammonia using sulfuric acid and a catalyst; (2) neutralization of the solution from step 1 and distillation of the ammonia; and (3) ® nish with a titration.1± 5 Analysis of blanks is always included in these methods. These related classical wet chemical methods are very labor intensive, require careful standardization of multiple reagents, and do not provide unequivocal identi® cation of the nitrogen-containing species in a single method. Further, wet chemical methods for nitrogen often suffer interferences from common species present in aqueous solution or in fertilizer, such as nitrite, phosphate, or sulfate. Yet, Kjeldahl-related techniques are widely used. Nitrogen-14 nuclear magnatic resonance (NMR) represents a new approach to quantitative analysis of nitrogen species in solution. Nitrogen-14 NMR is often overlooked because broad resonances are expected to result from the nitrogen-14 quadrupole moment. However, nitrate and ammonium, important aqueous solution species, have narrow resonances, and the nitrogen-14 NMRchemical shift range is large.6 Several recent reports indicate

Determination of Water in Zeolite a Using Low-Resolution NMR:

The water content of zeolites is an important parameter in determining zeolite properties and for zeolite manufacturing quality control. Zeolite A has important uses as a detergent builder. 2 The target moisture content of zeolite A is typically 18±22 wt % water. A drier material tends to have an altered zeolite structure and reduced cation exchange properties. Wetter zeolite A tends to lump and show poor ̄ ow characteristics, making solids handling dif® cult in manufacturing. The standard method for water determination in zeolites is loss on drying (LOD). The LOD is typically determined as the weight loss from treatment at 600±900 8 C in a muf ̄ e furnace for one to two hours. Highly wet material may require pre-drying for additional time at 110 8 C and longer muf ̄ e furnace times. Although LOD is a very simple method to implement, two hours or longer may be an unacceptably long time for analysis turnaround in many applications. Further, most of the other quality control and process control analyses, such as cation exchange capacity, depend on a knowledge of the wt % water in the zeolite; therefore, the LOD determination is often a bottleneck in rapid turnaround of product analysis. Bench-top, low-resolution proton NMR has signi® cant uses in the rapid, accurate, and precise analysis of water and of oil and fat content in food products. The ease of the analysis allows it to be routinely performed at-line and on-line in a manufacturing facility. This note describes the low-resolution proton NMR determination of water in zeolite A with the use of a bench-top NMR

Elemental Analysis Using NMR: Simultaneous Determination of Aluminum and Sodium in Zeolite A Using Low-Field NMR

The standard methods for elemental analysis of aluminum and sodium in zeolites typically require significant sample and reagent preparation before the final titrimetric or atomic spectroscopic measurement. Low-resolution, bench top nuclear magnetic resonance (NMR) has shown important applications for rapid quantitative analysis of hydrogen and/or fluorine containing materials without sample preparation in the food, chemical, and polymer industries. Here we demonstrate the determination of aluminum and sodium in zeolite A without sample preparation by using multinuclear, low-field NMR. The simultaneous determination of aluminum and sodium can be performed in under five minutes with a precision of ∼ 1% relative. The method, calibration, data collection, and significant other applications are discussed.