Analytical Methods
Supporting Analytical Chemists for nearly a century, GFS Chemicals continues to provide high quality laboratory chemicals for use in qualitative and quantitative methodologies including: spectroscopy, chromatography, titrimetry, sample preparation and wet chemical analysis.
pH Reference Buffers and Primary Standards
pH Reference Buffers
GFS Chemicals’ pH Buffers are manufactured from the finest high-purity water and reagent grade chemicals. They are standardized at 25°C against NIST reference materials to a tolerance of 0.01 on Buffers 4.00, 7.00, and 10.00 and to a tolerance of 0.02 on all other buffer ranges.
Our buffers are used with confidence for all applications because standardization is performed using the most trusted instruments in the business – Orion, Beckman-Coulter, and Hanna, to name a few. For simplicity, all common buffers are the same price regardless of pH or if color coded. This catalog features not only new products but also many new unit sizes, including bulk containers, and case pricing. Certificates of Analysis are provided with every shipment and include NIST Traceability.
Primary Standards
Even with the automation of so many lab methods, it remains essential to verify analytical standard solutions. For over 75 years, GFS Chemicals has provided primary standards to support analytical chemists worldwide with traceability and confidence their results are accurate.
GFS continues to support chemists performing such titrations as acid-base, redox, complexometric, and many others. Following is a list of many common primary standards manufactured by GFS. Throughout the catalog, many others are listed and we welcome inquiries for your unique standards.
For acid-base: diphenylguanidine, constant boiling perchloric acid, potassium acid phthalate, potassium bi-iodate, sulfamic acid, and tris-hydroxymethylaminomethane.
For redox titrimetry the following are listed as primary standards: ceric ammonium nitrate, ferrous ethylenediammonium sulfate, electrolytic iron, potassium bi-iodate, potassium dichromate, and sodium oxalate.
For complexation titrimetry (EDTA): calcium carbonate, di-sodium dihydrogen ethylenediaminetetraacetate dihydrate, and magnesium iodate tetrahydrate.
Other specially prepared primary standards include sodium chloride for argentimetric titrations; acetanilide for checking microchemical analyses for carbon, hydrogen, and nitrogen; and cobalt sulfate for volumetric and colorimetric analyses.
Find these items by name in the alphabetical listing in this catalog. For more information, request GFS Chemicals publication No. 497, Standard Substances and Solutions.
Complexometric Titration Reagents
A spectacular advance in analytical chemistry was the introduction of ethylenediaminetetraacetate as a standard solution in titrations involving the formation of complex ions. Of several substances which can be used as standard solutions in such analyses, sodium ethylenediaminetetraacetate (EDTA) is one of the most satisfactory in that it forms highly stable complex ions with calcium, magnesium and numerous other metals. A solution of disodium dihydrogen ethylenediaminetetraacetate (pH 5.5) is usually used as the standard solution. The most common of such titrations is the determination of calcium and magnesium, as in analysis of waters for hardness, or of limestone. The end-point may be detected in various ways, the most common utilizing the dyestuff Eriochrome Black T. This dyestuff has the unique property of itself forming a complex ion with magnesium. On titration, the EDTA first unites with the calcium and magnesium ions in solution and then pulls the magnesium away from the dyestuff-magnesium complex resulting in a color change from red to blue. The titration is carried out at a pH of 10 and yields the sum of the calcium and the magnesium present.
Aqueous solutions of Eriochrome Black T do not keep and another indicator, Calmagite, was introduced for the EDTA titration of calcium plus magnesium. The color change of Calmagite at the end-point is also from red to blue but the colors are clearer and the end-point sharper. Aqueous solutions of this indicator are stable indefinitely. Carried out under slightly different conditions, pH 12, and with the indicator Calcein, calcium alone may be determined in the presence of even large amounts of magnesium. This procedure may be applied to the determination of calcium in water and in limestone. Calcein modified by the addition of certain blue dyes, thymolphthalein or bromthymol blue, gives a somewhat more satisfying color change at the end-point. The end-point with Calcein may be detected also by the disappearance of the fluorescence under ultraviolet illumination of the calcium salt.
Calcein is prepared by the action of formaldehyde and iminodiacetic acid on fluorescein. It is typical of a class of indicators known at "metalfluorochromic" indicators. Another indicator of this class in Calcein Blue (β-methyl-umbelliferonemethyleneiminodiacetic acid) which is useful in the titration of copper, cobalt and other metals with EDTA.
Three primary standard materials are available for titrimetric work with EDTA. Ordinary reagent grade calcium carbonate contains sufficient magnesium to make it unacceptable as a primary standard but a special, low-magnesium grade is available, No. 337. About the only good primary standard magnesium compound is magnesium iodate tetrahydrate, described in 1962 by Lindstrom and Stevens; this material is available as No. 348. Disodium Dihydrogen Ethylenediaminetetraacetate Dihydrate, the reagent used to prepare EDTA solutions, is itself a good primary standard when properly prepared, item #365.
