On the Widespread Adoption of Photoelectric Colorimetry in Sanitary and Hygienic Investigations
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On the Widespread Adoption of Photoelectric Colorimetry in Sanitary and Hygienic Investigations
Candidate of Medical Sciences A. V. Fedoreyeva
From the Department of Hygiene, Leningrad Pediatric Medical Institute
Photocolorimetric methods of analysis are characterized by great simplicity, speed, and accuracy. They are free from individual errors and require smaller quantities of reagents. These methods occupy an intermediate position between conventional colorimetry and absorption spectrophotometry and are, in essence, closer to the latter, which is the most accurate method of modern analysis. Photocolorimetric methods can be used both in stationary facilities and in the field.
To increase the sensitivity of photocolorimetric methods of investigation, appropriate light filters must be used.
The table presents the results of our investigations to identify the optimal light filters required for the photocolorimetric determination of certain
Absorption maxima and optimal light filters for colorimetric reactions used in water analysis
| Constituent determined in water | Reactions and their products | Optimal light filter (transmission maximum, mµ) | Factor of increase in determination sensitivity |
|---|---|---|---|
| pH 5.2–7.0 | Indicators: bromocresol purple | 570–610 | — |
| pH 7.2–8.8 | Indicator: cresol red | 560–590 | — |
| Dissolved oxygen in water | Aqueous iodine solution | 400–430 | 2.2–5.8 |
| Free chlorine | — | ||
| Sulfates | |||
| Oxidizability | Iodine extract in carbon tetrachloride | 520–560 | |
| Calcium and magnesium salts | |||
| Ammonia | Mercurammonium iodide | 400–450 | 1.6–2.1 |
| Nitrites | Griess reaction | 500–530 | 4.5–6.5 |
| Nitrites | Metaphenylenediamine reaction | 420–430 | 2–6 |
| Nitrates | Brucine reaction (Noll) | 400–500 | — |
| Iron | Ferric thiocyanate | 430–450; 480–500 | 2.4–3 |
| Manganese | Permanganic acid | 500–550 | 2.1–3.2 |
| Free chlorine | Orthotolidine reaction | 420–435 | 6–7.5 |
constituents in water, as well as data on their effectiveness compared with conventional methods.
As the table shows, compared with the methods in current use, photocolorimetry increases the sensitivity of determinations of dissolved oxygen, free chlorine, sulfates, oxidizability, and calcium and magnesium salts in water by 2.2–5.8 times; ammonia by 1.6–2.1 times; nitrites by 4.5–6.5 times with Griess reagent and by 2–6 times with m-phenylenediamine; iron by 2.4–3 times; manganese by 2.1–3.2 times; and free chlorine by 6–7.5 times with o-tolidine.
This increase in sensitivity is observed when optimal light filters are used in photocolorimetric testing; their characteristics for water analysis are given in the table. The filters are selected on the basis of the maximum spectral sensitivity of the colorimetric reactions used in the analysis.
The use of photocolorimetric methods of analysis therefore requires: 1) knowledge of the spectral sensitivity of the colorimetric reactions used in the analysis; 2) identification of the regions of the spectrum that are absorbed most strongly by the substance being determined; and 3) selection of optimal light filters that transmit most fully those regions of the spectrum absorbed most strongly by the substance being determined.
Received June 8, 1954.