RU2218563C2 - Technique and indicator for detection of lead, process of manufacture of indicator - Google Patents

Abstract

FIELD: analytical chemistry, manufacture of indication means. SUBSTANCE: technique detecting lead includes operation of bringing of tested object in contact with indicator plate. Aqueous solution of 4-(2- pyridylazo)resorcin in concentration of 0.08-0.20 per cent by mass with aqueous solution of ammonium acetate in concentration of 20.0-40.0 per cent by mass is utilized in the capacity of indicator composition. Indicator is made of indicator plate comprising carrier with high capillary properties with indicator composition applied to it. Plate is placed in wetted state into sealed package. Package comes in the form of pack one side of which is double-layer side. Inner layer is clear and has central indicator hole. Process of manufacture of indicator includes impregnation of carrier plate with indicator composition. Carrier plate is put into pack made of water and gas impermeable material with hole in one side of pack. Impregnation is carried out with the aid of dropping method through central hole, then package is sealed by covering this side of pack with hole with second layer of water and gas impermeable material. EFFECT: simplified and reliable technique, expanded application field of technique. 5 cl, 2 dwg, 1 tbl

Description

 The invention relates to analytical chemistry, in particular to methods for determining lead and the manufacture of indicators.

There is a method for determining the mass concentration of lead in gasoline, which consists in extracting lead compounds from gasoline with a solution of iodine monochloride, destroying the excess of iodine monochloride with solutions of ammonia and sodium sulfate and subsequent spectrophotometric determination of lead in the form of a complex with 4- (2-pyridylazo) resorcinol or sulfarsazene. The method provides a fairly accurate and reliable quantitative result when the lead content in gasoline in a concentration of from 0.005 to 3.0 g / dm ³ (0,0007-0.4 wt.%) [GOST 28828-90]. However, this method is quite time-consuming, time-consuming and not suitable for rapid analysis.

 Another known method allows to qualitatively determine the presence of tetraethyl lead in gasoline solvents. The essence of the method consists in the decomposition of tetraethyl lead by iodine when they are boiled together and in the subsequent determination of lead using a color reaction with sodium rhodisonate. The sensitivity of the method for tetraethyl lead is 0.0001 wt.% [GOST 7978-74].

The disadvantage of this method is the relatively long analysis time (~ 1.5 h) and an excessively high sensitivity to the presence of traces of lead, which prevents the differentiation of the ranges of acceptable lead content in unleaded and leaded gasolines: for the first <0.01 g / dm ³ (~ 0.002 wt.%), and for the second> 0.01 g / dm ³ .

 There is also known a method consisting in the fact that a sample of the test gasoline is burned in an open vessel, the residue is dissolved in a slightly acidic solvent and then the presence of lead is determined by color reaction using special indicator paper [US Pat. Germany 3618842, MKI G 01 N 33/22, publ. 12/10/87].

 The disadvantage of this method is the relatively high threshold sensitivity to the presence of lead, corresponding to 50 ppm (0.005 wt.%).

 The closest analogue of the proposed method is a method for determining lead in gasoline, including burning a sample in an open vessel, treating the residue with a 30% aqueous solution of acetic acid and bringing into contact with paper coated with an indicator composition, and before bringing into contact a freshly prepared indicator composition is applied to paper contacting is carried out by applying an acetic acid solution to the indicator composition, and an aqueous solution of sodium rhodizonate with a concentration of a fraction of 0.10-0.25 wt.% or a solution of dithizone in acetone with a concentration of 0.025-0.10 wt.% (RF patent 2058548 C1, CL G 01 N 33/22, 04/20/96).

The method allows to determine the concentration of lead in gasoline more than 0.01 g / DM ³ .

 The disadvantage of this method is its limited use only for gasoline, the need for special devices and several reagents, requires the burning of gasoline, which makes it difficult to use in unequipped rooms, for example, at gas stations.

 The indicator paper used in this method with the indicator composition of sodium rhodisonic acid or a solution of digotizone in acetone applied to it, taken as the closest analogue, is inconvenient to use, since it requires application to it immediately before determining the freshly prepared composition.

The closest analogue of the proposed indicator is the indicator "Plumbtesto" company Macherey Nagel Ltd, Düren, Germany (1992), containing a paper carrier with an indicator composition deposited on it, including sodium rhodisonate (Rd ₃ Na), a buffering agent that creates acidity pH 2.8 and an indifferent substance.

 Indicators with dried indicator composition are packaged in 5 pieces in sealed bags. Before use, the package is opened, one indicator strip is taken, moistened with distilled water and pressed for 2 minutes to the test surface.

 The disadvantage of the Plumbtesto indicators is the need to wet them before using distilled water, and also has a limited shelf life of no more than 3 months, a quick loss of sensitivity (less than 2 hours) when moisture gets in and the effect of the following elements on the reaction: tellurium, silver, cadmium, barium, strontium.

 In addition, the color of the indicator changed under the influence of lead remains only for 15 minutes after application, which excludes the use of the indicator as evidence in the future.

 The Congo indicator paper is also known.

There is also a known method of manufacturing indicator papers, which includes sequentially moistening the carrier tape with a 5-10-fold diluted solution of reactive substances to obtain a degree of retention of 10%, then saturating a 2-5-fold diluted solution of reactive substances to obtain a degree of retention of 10-50% relative to a given final the content of these substances in the indicator paper, and then saturation with reactive solutions of the appropriate concentration until a given amount of reactive substances is obtained in in the indicator paper. The saturated carrier tape is dried at a temperature of 70-150 ^o C and a blown air speed of 1-50 m / min, which provides retention of the carrier tape on an air cushion without contact with the base, and is subjected to further processing (see application NDP 263663, MKI G 01 N, published on September 15, 88).

 The disadvantage of this method is the applicability for the manufacture of only dry indicator paper, the need for sophisticated equipment for its implementation and constant step-by-step control.

The closest analogue of the proposed method is a method of manufacturing indicator paper by impregnating filter paper with an aqueous solution of the azo compound, drying, impregnating with a solution of salt, subsequent drying (see ed. St. USSR 1567975, MKI G 01 N 31/22, publ. 30.05.90, )
This method is only suitable for the manufacture of dry indicator paper, which can only be used to control liquid substances and solutions.

 The single technical result achieved in the implementation of the claimed group of inventions is to ensure simplicity and reliability of determination and expansion of the scope by determining lead in unequipped rooms, field conditions without the use of special equipment for a wide variety of objects in aviation and motor gasoline, wastewater, solutions, exhaust gases, as well as on any surfaces in contact with lead.

 This technical result is provided by the claimed method of determination, as well as the design and method of manufacturing the indicator.

 In the inventive method, comprising bringing the test object into contact with an indicator plate consisting of a carrier coated with an indicator composition, according to the invention, an aqueous solution of 4- (2-pyridylazo) resorcinol (PAR) with a concentration of 0.08-0 is used as an indicator composition. 20 wt.% With an aqueous solution of ammonium acetate in a concentration of 20-40 wt.%.

 The determination of lead can be carried out on any object under investigation that comes into contact with lead: gasoline, sewage, on the nozzle of a gas station pistol, in the exhaust gases and on the exhaust pipe of a car, in a printing house and in printing publications, x-ray offices, etc.

 The inventive indicator contains an indicator plate consisting of a carrier with high capillary properties with an indicator composition deposited on it. The difference of the claimed indicator is that the indicator plate in a wet state is placed in a sealed package. In this case, one of the sides of the package is made of two layers, the inner layer of which is made transparent and has a central indicator hole.

 A manufacturing method includes impregnating a carrier plate with high capillary properties with an indicator composition.

 The difference between the method is that before impregnation, the plate is placed in a package of water-impermeable material with a central hole on one side of the package, the impregnation is carried out by the drip method, dropping an indicator compound into the opening of the package, and then the package is sealed, closing the side of the package with the opening with a second - additional layer of water-gas impermeable material.

 The inventive objects form a group of inventions united by a single inventive concept, because aimed at solving the same problem, achieving a joint technical result - to provide simplicity, reliability and speed of determining the presence of lead without the use of special equipment and to expand the scope.

 Figure 1 shows an indicator for determining lead (general view); in FIG. 2 - indicator details.

 The indicator consists of an indicator plate 1 in the form of a carrier with high capillary properties, for example filter paper, impregnated with an indicator composition and in a wet state, placed in a bag 2 of a water-impermeable material. The package contains the lower side 3 and the upper side 4, consisting of two layers. First, the inner layer 5 is made of a transparent (water and gas impermeable) material with a central hole 6, which is located near the center of the indicator plate and acts as an indicator window. The second - the outer layer 7 covers the inner layer. The lower side of the package, it is advisable to perform with a white inner surface, or to make transparent and provide a white substrate (not shown).

 The lower side and both layers of the upper side are hermetically connected to each other, for example, glued around the perimeter (zones 8, 9, 10). The lower side and the outer layer of the upper side are equipped with valves 11, 12 for the convenience of separating the outer layer of the upper side when using the indicator, as well as to accommodate the necessary inscriptions.

 The inventive indicator with an indicator plate in the wet state can be used to determine not only lead, but also other substances, depending on the use of various indicator compounds that respond to certain substances.

 For example, to determine cadmium, an indicator plate is impregnated with UREA cadion, hydrogen sulfide with lead nitrate, nickel with dimethylglyoxime, and mercury vapor with iodine copper.

 The specified indicator is used in the method for determining lead in various environments, for example in gasoline. For this purpose, an aqueous solution of 4- (2-pyridylazo) resorcinol (PAR) with an aqueous solution of ammonium acetate was used as an indicator composition.

 The method is as follows.

 Take an indicator with an indicator plate, for example, in the form of a circle with a diameter of 32 mm from a carrier with high capillary properties, for example, filter paper according to TU 6-09-1678-86, impregnated with one of the indicator compositions in examples 1-10 shown in the table.

 The outer layer 7 of the upper side 4 is separated from the packet and through the hole 6 in the inner layer a test plate 1 is applied for 5-10 s to the test object: either solutions containing from 0.05 mg / ml to 1.0 mg / ml Pb (11 ), or to surfaces moistened with this solution.

 The result of the study appears after 2-5 minutes.

 Examples 3-5 are given for the concentration of the test solution of 0.2 mg / ml, which is critical for the determination of leaded gasoline.

Lead is usually present in polluted environments, studied objects, gasoline in the composition of various salts and oxides in the form of doubly charged lead ions Pb (II). When wet test paper is brought into contact with the test object (surface), a reaction occurs with an aqueous solution of ammonium acetate to form an acetate complex of lead and ammonia
Pb ²⁺ + 4CH ₃ COOH ₄ -> Pb (CH ₃ COO) ₄ ^2- + 4NH ₄ ⁺ ,
and then a complex compound of lead and PAR is formed, which changes the color of the indicator plate.

 The presence of an aqueous solution of ammonium acetate in the indicator composition allows you to dissolve any lead compounds, even insoluble in water, which increases the sensitivity of the method.

 The color change of the indicator paper in the hole from light yellow to red-orange indicates the presence of lead in the test object.

 An indicator is made as follows.

 As a carrier with high capillary properties, for example, filter paper, fabric, a polyethylene terephthalate film treated with potassium dichloride in concentrated sulfuric acid and then diluted with sulfuric acid can be used (see auth. St. USSR 1719985, MKI G 01 N 31 / 22, publ. March 15, 1992). A plate is cut out of the carrier material, for example, in the form of a circle 1. From the blank of the lower side of the packet 3 with the valve 11 and the inner layer of the upper side of the packet 5 with the hole 6, the packet is folded, the carrier plate 1 is laid between side 3 and layer 5 and the sides of the packet are hermetically connected around the perimeter, for example, by welding, leaving the valve 11 free.

 The plate is impregnated through the central hole with an indicator composition, applying, for example, 2-3 drops of an aqueous solution of PAR at a concentration of 0.1 wt.% And an aqueous solution of ammonium acetate at a concentration of 30 wt.% And hermetically close the bag using the outer layer 7 the upper side, sticking it over the entire area of the inner layer, leaving the valve 12 free.

 The sealed packaging keeps the indicator in a wet state, i.e. workable up to 12 months.

Claims (5)

1. The method of determining lead, including bringing the test object into contact with an indicator containing an indicator plate, consisting of a carrier with high capillary properties with an indicator composition deposited on it, characterized in that an aqueous solution of 4- (2-pyridylazo is used as an indicator composition) ) resorcinol with a concentration of 0.08-0.20 wt.% with an aqueous solution of ammonium acetate in a concentration of 20-40 wt.%, the indicator plate in a wet state is placed in a sealed package, the packaging is made in the form of a package, one and from the sides of the package is made two-layer, and the inner layer is made transparent with a Central indicator hole. 2. An indicator for determining lead containing an indicator plate, consisting of a carrier with high capillary properties, with an indicator composition deposited on it, characterized in that the indicator plate is placed in a sealed package when wet, the package is made in the form of a package, one of the sides of the package made of two layers, with the inner layer made transparent with a central indicator hole, and as an indicator composition, the indicator includes an aqueous solution of 4- (2-pyridylazo) resorcinol with concent tion 0,08-0,20 wt.% of the aqueous solution of ammonium acetate at a concentration of 20-40 wt.%. 3. The indicator according to claim 2, characterized in that the carrier with high capillary properties is made in the form of filter paper. 4. A method of manufacturing an indicator for determining lead, including impregnating the carrier in the form of a plate with high capillary properties by an indicator composition, characterized in that before the impregnation, the carrier is placed in a bag of water-impermeable material with a central hole on one side of the bag, the impregnation is carried out by the drip method through the central hole, and then seal the package, closing the side of the bag with the hole with a second layer of water-impermeable material, as an indicator composition using comfort an aqueous solution of 4- (2-pyridylazo) resorcinol with a concentration of 0.08-0.20 wt.% with an aqueous solution of ammonium acetate and a concentration of 20-40 wt.%. 5. The method according to claim 4, characterized in that filter paper is used as a carrier with high capillary properties.

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