Analytical methods colorimetry

Recommended Analytical Methods Colorimetry using Hach reagents (Hach Company, Handbook of Brine Analysis, 2nd Edition, p. 29). 

Procedures for determining the quaUty of formaldehyde solutions ate outlined by ASTM (120). Analytical methods relevant to Table 5 foUow formaldehyde by the sodium sulfite method (D2194) methanol by specific gravity (D2380) acidity as formic acid by titration with sodium hydroxide (D2379) iron by colorimetry (D2087) and color (APHA) by comparison to platinum—cobalt color standards (D1209). 

The nitroparaftins have been determined by procedures such as fractionation, titration, colorimetry, kifrared spectroscopy, mass spectrometry, and gas chromatography. The early analytical methods and uses of polynitroparaftins as analytical reagents have been reviewed (11). More recent quaHtative and quantitative methods have also been reviewed (83). 

Many biologically interesting molecules, for instance hormones, can be determined using any of a number of analytical methods, such as GC, GC-MS, and RIA. In blood serum and similarly complex matrices, the more traditional methods (colorimetry, titration, TLC) suffer from interference and/or lack of sensitivity. 

Comparative values for several physicochemical analytical methods for establishing stability of the drug solutions and detecting impurities (including colorimetry) was reported [45]. 

The most common analytical methods used were gas chromatography, HPLC, AA spectrophotometry, polarography, colorimetry, and potentiometry with ion-selective electrodes. In this study GC/MS and other more expensive instrumentation were avoided. If sorbent tubes could not be used for gaseous substances, then the less desirable miniature bubblers or impingers were considered. Although these devices are inconvenient they were often used because no better alternatives were available. Bags were used in a few cases where the analyte could not be retained on a sorbent because of volatility and a small tendency to sorb. Filters were used for particulates. Combinations of collection devices were used if we felt that both particulates and vapor might be present in the analyte. 

Visual colorimetry, probably the oldest analytical method, was last used by the Greeks and Romans. This method found its scientific basis in 1729 when Pierre Bouguer theorised that if a given width of glass absorbs half of the light emitted by a source then double the width will reduce the fight by one quarter its initial value . 

Wet chemical methods involve sophisticated sample preparation and standardization with National Bureau of Standards reference materials but are not difficult for the analytical chemist nor necessarily time consuming (Figure 1). The time from sample preparation to final results for various analytical methods, such as GFAA (graphite furnace atomic absorption), ICP (inductively coupled plasma spectroscopy), ICP-MS (ICP-mass spectrometry), and colorimetry, ranges from 0.5 to 5.0 h, depending on the technique used. Colorimetry is the method of choice because of its extreme accuracy. Typical results of the colorimetric analysis of doped oxides are shown in Tables I and II, which show the accuracy and precision of the measurements. 

The biodegradabilities were followed by three analytical methods, i.e. (A) foam height method, (B) cobalt thiocyanate colorimetry (CTAS) and (C) COD (Cr) method. 

Historically, analysis for selenium has been difficult, partly because environmental concentrations are naturally low. Indeed, selenium analysis still remains problematic for many laboratories at concentrations below 0.01 mg a relatively high concentration in many environments (Steinhoff et al., 1999). Hence, selenium has often been omitted from multi-element geochemical surveys despite its importance (Darnley et al., 1995). Analytical methods with limits of detection of <0.01 mgL include colorimetry, total reflectance-XRF, HG-AFS, gas chromatography... 

Ion chromatography has become an indispensable tool for the analytical chemist in the area of anion analysis. In many cases this method has superseded conventional wet chemical methods such as titration, photometry, gravimetry, turbidimetry, and colorimetry, all of which are labor-intensive, time-consuming, and occasionally susceptible to interferences. Publications by Darimont [1] and Schwedt [2] have shown, that ion chromatographic methods yield results comparable to conventional analytical methods, thus dissolving the scepticism with which this analytical method was initially met. In the field of cation analysis, ion chromatography is attractive because of its simultaneous detection and sensitivity. It provides a welcome complement to atomic spectroscopic methods such as AAS and ICP. 

The analytical methods used to verify the between-ampoule homogeneity were potentiometry (pH), flame atomic absorption spectometry (Ca, K, Mg and Na), colorimetry (NH4, NO3, PO4 and SO4) and electrothermal AAS (Fe and Mn). No significant differences were observed between the between-ampoules and method variances and the materials were hence considered to be homogeneous [15]. 

Several classes of analytical methods have been applied to the determination of micromolar concentrations of NH3. These include colorimetry [142— 145], chromatography [146], mass spectroscopy [147-149], and the use of... 

Nonspecific analytical methods, such as colorimetry and titrimetry, for determination of summary parameters were the earliest attempts to analyze surfactants in the environment. The main disadvantage of these methods is that, apart from surfactants, other interfering organic compounds from the environmental matrices are recorded too, resulting in systematic errors. Nevertheless, colorimetric and titrimetric methods are stiU widely used for determination of anionic, nonionic, and cationic surfactants because of their easy handling and the need for relatively simple apparatus. 

Species analysis is performed with various analytical methods, and some examples are described in the following section. Sulfate can be determined depending on the amount in various waters (drinking, surface, waste and saline waters), either colorimetri-cally after reaction with chloranilate in forming the colored acid chloranilate ion, automated as methylthymol blue, as barium sulfate either gravimetrically or nephelometri-cally (turbidimetric) and directly with IC... 

Colorimetric methods Colorimetry, or spectrophotometry, is a chemical analytical method that exploits the link between chemical composition and color intensity for a range of dyes. 

Colorimetry—An analytical method by which the amount of a compound in solution can be determined by measuring the strength of its color by either visual or photometric methods. Combustible— Term used to classify certain liquids that will burn on the basis of flash point NEPA and DOT classify combustible liquids as having a flash point of 100°F (38°C) or higher. Combustible liquids—OSHA defines combustible liquids as any liquid having a flash point at or above 100°E (38°C) but below 200°E (93.3°C). 

One of the results of contamination of bleach with transition metals is the accumulation of oxygen in pipelines and storage tanks. This has become a safety issue for suppliers and utilities. Many utilities have revised their specifications for transition metal ions in bleach into the ppb range. This requires more sensitivity and precision in analytical methods. Pham [81 ] has studied a number of methods and reported results obtained by chloroform extraction colorimetry and ion chromatography. The latter is the preferred analytical method. 

The choice of analytical method is obviously largely dependent upon the availability of instrumentation. There are four techniques, however, which are used far more widely in the analysis of lead in environmental samples than other methods they are XRF, ASV, colorimetry with dithizone and AAS. Because of its versatility, ease of use and the low capital cost of equipment, atomic absorption is by far the most commonly used technique. Comments will be restricted to these four more important methods. Detection limits based upon experience, rather than manufacturer s literature are cited in Table 8.1. Obviously these may be an important determinant of the techniques selected for low-level work. 

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