ABSTRACT
The determination of inorganic anions and cations in food is of obvious importance from a health-related viewpoint. With respect to cations, the alkali metals Na+ and K+ are essential to the maintenance of a proper electrolyte balance, and excessive levels of Na+ have been linked to high blood pressure. The alkaline earths Mg2+ and Ca2+ are important for bone growth, and concentrations of these cations plus Na+ and K+ in infant formulas are regulated by the U.S. government. Environmental hazards such as arsenic in seafood and transition metals such as Cu2+ and Ni2+ in vegetables are of importance. Certain anions are likewise routinely determined analytically. Halogenated anions such as bromate (BrO3−) added to improve the strength of our and reduce fermentation time as well as I− in table salt are measured in the presence of chloride. Nitrate (NO3−) and nitrite (NO2−) are commonly quantied in meat products since nitrite is added as a preservative and color enhancer. Nitrite is also of concern since it can react with secondary amines to form carcinogenic nitrosamines. The determination of sulte (SO3−) is of utmost importance since it is commonly added to a wide variety of foods such as farm products, seafood, and bakery products
26.1 Introduction ................................................................................................................................. 945 26.2 Ion Exchange Chromatography .................................................................................................. 946
26.2.1 Ion Exchange Equilibria ............................................................................................... 946 26.2.2 Ion Chromatography ..................................................................................................... 947
26.2.2.1 Conductivity Detection ................................................................................ 948 26.2.2.2 Capillary Ion Chromatography .................................................................... 949 26.2.2.3 Indirect Detection Chromatography .............................................................951 26.2.2.4 Chromatography of Inorganic Ions with Different Detectors ..................... 952 26.2.2.5 Ion Exclusion Chromatography ................................................................... 954
26.3 HPLC Applications to Food ....................................................................................................... 954 26.3.1 Anions ........................................................................................................................... 954
26.3.1.1 Halogens ....................................................................................................... 954 26.3.1.2 Nitrogen ....................................................................................................... 956 26.3.1.3 Sulfur ........................................................................................................... 958 26.3.1.4 Phosphorus ................................................................................................... 960 26.3.1.5 Anion Mixtures ............................................................................................ 962 26.3.1.6 Anion and Organic Acid Mixtures .............................................................. 963
26.3.2 Cations .......................................................................................................................... 963 26.3.2.1 Alkali and Alkaline Earth Metals ............................................................... 964 26.3.2.2 Transition Metals ......................................................................................... 966 26.3.2.3 Nonmetals .................................................................................................... 966
26.4 Capillary Electrophoresis for Ions in Food ................................................................................ 967 References .............................................................................................................................................. 969
A variety of analytical methods have been utilized for the analysis of food samples for ions. Atomic spectroscopy is commonly employed for the determination of cations. In particular, atomic absorption spectroscopy (AAS) has been used when one or two cations are of specic interest. Matrix effects such as phosphate in the determination of Ca2+ can be a problem, and standard addition methods may be required. Simple ame emission will permit the easy determination of alkali metals, while inductively coupled plasma (ICP) is well suited for the simultaneous determination of many metals at the trace level. However, the ICP instrument is still quite expensive. A few cations such as Na+, K+, and Ca2+ can be determined using ion selective electrodes (ISEs). In addition, some anions such as the halides (F−, Cl−, Br −, I−) and nitrate can be monitored; however, interferences from other anions are likely. Long-term stability and response are also of concern for some electrodes [1].
