Gravimetric Methods of Analysis

Two other types of analytical methods are based on mass. In gravimetric titrimetry, which is described in Section 13D, the mass of a reagent, of known concentration, required to react completely with the analyte provides the information needed to determine the analyte concentration. Atomic mass spectrometry uses a ma.ss. spectrometer to separate the gaseous ions formed from the elements making up a sample of matter. The concentration of the resulting ions is then determined by measuring the electrical current produced when they fall on the suiface of an ion detector. This technique is described briefly in Chapter 28. 

For an extensive treatment of gravimetric methods, see C. L. Rulfs. in Treatise on Analvtical Chemisuy, I. M. Kolthoffand P. J. Hiving, Eds.. Part I. Vol. 11. Chapter 1.3. New York  

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In the previous section we used four examples to illustrate the different ways that mass can serve as an analytical signal. These examples also illustrate the four gravimetric methods of analysis. When the signal is the mass of a precipitate, we call the method precipitation gravimetry. The indirect determination of by precipi-... 

Compare Figure 3.1 with Figure 1.1. What is special about the gravimetric method of analysis ... 

The frozen-drop and the wax methods eliminate the tedious and time-consuming operations of microscopic counting of the larger droplets, and sampling errors are less likely because all of a large increment of spray can be collected and handled by employing screens and gravimetric methods of analysis. The chief limitation is that screens are not available to obtain data on particles smaller than 75 microns. Some form of microscopic count or air elutriation procedure is necessary for the smaller droplets. 

Gravimetric methods of analysis are based on mass measurements made with an analytical balance, an instrument that yields highly accurate and precise data. In fact, if you perform a gravimetric chloride determination in the laboratory, you may make some of the most accurate and precise measurements of your life. 

PART III Classical Methods of Analysis 311 Chapter 12 Gravimetric Methods of Analysis 314 Chapter 13 Titrimetric Methods Precipitation Titrimetry 337 Chapter 14 Principles of Neutralization Titrations 368 Chapter 15 Titration Curves for Complex Acid/Base Systems 395 Chapter 16 Applications of Neutralization Titrations 428 Chapter 17 Complexation Reactions and Titrations 449... 

Although accurate volume measurements of solutions can be avoided in gravimetric methods of analysis, they are required for almost any other type of analysis involving solutions. 

The gravimetric methods of analysis with perchlorate or tetraphenyl boro-sodium, frequently used in the past, are rarely used today. 

A crystalline precipitate of magnesium ammonium phosphate hexahydrate (struvite) is produced when other magnesium salts are added with ammonia to weakly basic or neutral phosphate solutions (5.39). The ignition of this salt to give the pyrophosphate forms the basis of a gravimetric method of analysis for P (Chapter 14.1). 

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