This papre describes a simple method of carbon disulphide determination in the air of working environment in the chemical companies and plants after its absorption into aprotic N,N-dimethylformamide solvent. Carbon disulphide absorbed into aprotic solvent was transformed by using ammonium hydroxide on sulphides which were determined by spectrophotometry. 5,
Carbon disulphide (CS2) is a strong neurotic poison with broad toxic influence on the human organism [
Recently series of strongly powerful instrumental techniques have been applied in analytics using chromatographic separation methods [
Determination methods of CS2 in the air are based mostly on its consumption of solid sorbent [
The following chemicals were used for experiments: carbon disulphide (Riedel-de Haën), 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB, Ellman’s reagent), blue tetrazolium chloride (BTC), that is, 3,3′-(3,3′-dimethoxy-4,4′-biphenylene)-bis(2,5-diphenyl-2H-tetrazolium chloride), N,N-dimethylformamide (DMFA), ammonium hydroxide 28%, and ethanol anhydrous (all from Sigma-Aldrich-Fluka). All chemicals were analytically pure. Water was distilled twice.
Two analytical reagents (A and B) were prepared. Analytical reagent A was prepared in the 100 mL volumetric flask by weighing 0.01 g of DTNB, then 0.2 mL ammonium hydroxide (28%) was added using pipette, and DMFA was added up to the mark. Analytical reagent B was prepared by solving 0.1 BTC in the mixture which contained 2 mL of ammonium hydroxide (28%) and 2 mL anhydrous ethanol and DMFA was added to the volume of 100 mL. Reagents must be fresh (8 hours). Under alkaline conditions, DTNB or BTC is already transformed into the colour product without any reactant. Measurements of absorbance were done on UV-VIS spectrophotometer Helios Alpha (Thermo Electron). The pump AirCheck 2000 (SKC) with flow meter was used for the air sampling.
Working solution was prepared by dissolving 0.1 mL CS2 in DMFA to a total volume of 100 mL. Cleanliness of CS2 was controlled by iodine-metric titration [
Steam-air mixture with CS2 prepared in testing chamber was absorbed into 15 mL of DMFA in the washing apparatus. Speed of air flow was 200 mL·min−1. After sampling, 4 mL of analytical reagent (A or B) was added to the absorbed substance and levelled with DMFA to 20 mL. Absorbance values were measured against pure DMFA after 30 minutes of reaction time.
Concentration of CS2 in the air (
In the presence of ammonium hydroxide, CS2 reacts with ammonium dithiocarbamate, which with excess ammonium hydroxide is transformed into ammonium sulphide and ammonium thiocyanate. Sulphides reduced DTNB or BTC to coloured products suitable for spectrophotometric measurements. The course of chemical reaction for the case of DTNB reagent is displayed in Figure
Scheme of analytical reaction (with DTNB).
Reduction of BTC.
Simple absorption spectra; 1: DTNB method, 2: BTC method.
Ammonium hydroxide was used for transformation of CS2 to sulphides, but other compounds with ammonium ions (e.g., ammonium acetate) are suitable also. Reaction is progressing in the significant surplus of ammonium ions. Dependence of absorbance on concentration of ammonium ions, described as ratio of molar concentration of
Dependence of absorbance on the ratio of molar concentrations of
Transformation of CS2 to sulphides is progressing very quickly and with a good yield in aprotic solvents. This report describes application of DMFA, but it is also possible to use dimethyl sulfoxide (DMSO). Since DMSO solidifies at the temperature of 18°C, in the field and unfavourable climate conditions it is advantageous to use the mixture of DMFA/DMSO (1 : 1).
Stability of reaction balance is achieved for both methods within 30 minutes. The start of colouring is quicker with the DTNB method. One-half of the maximal absorbance at wavelength
One of the limiting factors of CS2 determination in the air is the effectiveness of its absorption in aprotic solvent. Effectiveness of absorption is mainly dependent on the speed of air flow during sampling. It is valid that the lower the speed of air flow, the higher the effectiveness of absorption. In practice the optimal time of the air sampling must also be taken into account, as not to exceed the acceptable limit. Air sampling with the speed of air flow 200 mL·min−1 for 50 minutes seems to be optimal. It corresponds with air sampling with the total volume of 10 L.
Basic parameters of determination of CS2 in the absorbed substance (molar absorptivity, detection limit, determination limit, Sandell’s sensitivity, and parameters of linear regression) are presented in Table
Base parameters of CS2 determination (in the absorbed substance).
Parameter | Method A | Method B |
(DTNB) | (BTC) | |
Molar absorptivity (L | 2.4 | 2.0 |
Detection limit ( | 0.1 | 0.2 |
Determination limit ( | 0.2 | 0.6 |
Sandell’s sensitivity ( | 0.002 | 0.004 |
Standard deviation | 0.007 | 0.015 |
Linear regression ( | ||
Slope | 0.3138 | −0.2639 |
Intercept | 0.2318 | −0.1435 |
Correlation coefficient | 0.9884 | 0.9983 |
Calibration line (Figure
Verifying of correctness of CS2 determination in the air.
CS2 inserted, mg | CS2 found, mg | |
Method A (DTNB) | Method B (BTC) | |
1 | ||
5 | ||
10 | ||
25 | ||
50 |
Calibration curves obtained for the determination of CS2 in the air by the DTNB method (1) and BTC method (2).
Reducing components present in the controlled air disturb determination of CS2 by the proposed method. Hydrogen sulphide reacts mostly with DTNB or BTC, which can originate for instance like a byproduct of synthesis of CS2 with methane and sulphur. To eliminate hydrogen sulphide, we can use filtration insert produced by impregnation of filtration paper or filtration materials from glass fibres by the solution of salts from certain heavy metals, for instance, lead, copper, or bismuth. This filtration insert is placed in the form of tube in front of the container with absorptive liquid. Sulphur dioxide (a result of pyrolysis of CS2) and volatile aliphatic triplets have significant disturbing influence. Overview of the selected the disturbing influences, which with DTNB and BTC produce the coloured reduction products, is in Table
Concentration limit of foreign components which with reagents produce coloured products.
Component | Concentration limit, mg | |
Method A (DTNB) | Method B (BTC) | |
Hydrogen sulphide | 0.2 | 0.2 |
Sulphur dioxide | 2.0 | — |
Hydrogen cyanide | 0.4 | — |
2-Sulfanylethane-1-ol | 0.2 | 0.2 |
The proposed method allows spectrophotometric determination of CS2 in the workplace air of chemical companies and plants. This method is based on transfer of CS2 with the help of ammonium ions to sulphides, which react further with DTNB or BTC to the characteristically coloured reaction products. Reactions are in progress in the medium of aprotic solvent, with advantage in DMFA. The method is simple and easy to instrumentation and technique. The sensitivity method, detection limits, and the range of use are comparable with other spectrophotometric methods described in the literature [
The advantage of the proposed analytical process (based on transfer of CS2 to sulphides) is in the opening of new development possibilities of colorimetric and spectrophotometric methods for CS2 determination. Interconnection of CS2 and sulphides analysis allows using and modifying a relatively significant number of standard methods for determination of sulphides (hydrogen sulphide) with regard to concrete conditions and determined objectives.
This work was prepared as part of a research project supported by the Ministry of Interior of the Czech Republic (Project VG20102013048).