Automatic analytical methods for environmental monitoring and control

Q_A= 0.23 mL min^-1; Q_B= 0.15 mL min^-1; gas flow rate=1 L min^-1 and 70 % relative humidity. Calibration over the range 0 -112 mg mL^-1. The dynamic range in not linear as usual in enzymatic reactions. The calculated deviation was 6.5 % (c = 44 mg mL^-1, n = 5) and the required time per sample 2.3 min.

In environmental air monitoring the level of analytes should be very low and the sample cannot be analyzed as is it in the environment, which obliges to include an on-line sample pre-treatment to obtain a continuous and automated procedure. The so-called chromato-membrane cell, CMC, has been used in different FIA systems for the on-line sample pre-concentration and separation (gas-liquid, liquid-liquid heterogeneous systems, etc.). It is a continuously working device in which the membrane performs a kind of “chromatographic separation”; when two different phases (polar and organic solvent or air) are forced through the membrane the transfer of analytes between tow phases occurs. This device is included in the FIA assembly.

The selected example to illustrate this is the determination of nitrogen dioxide in air so in field as in the laboratory. The analytical method is the “universal” for nitrite; first the nitrogen dioxide should be converted into nitrite. For this conversion is proposed the reported "chromato-membrane cell concentration-distribution device made of a PTFE block with micro- and macropores.

The steps of the flow determination are as follows (see Figure III.2.32.):

1. 
   The absorbing solution of triethanolamine is forced to the CMC at a flow-rate of 0.5 mL min^-1 up to filling, and then the pump is stopped. A second pump is used to force the sample air (20 L) into the cell at 7 mL min^-1. The NO₂ is transferred from the air to the absorbing reagent and transformed into nitrite ions.
   
2. 
   Turning the valve 2 the resulting solution is inserted into the FIA system and merges with the mixture of sulfanilamide and NED (Saltzman reagent) developing the corresponding color to be monitored in the flow-cell of the spectrophotometer.
   
3. 
   By starting again in the reverse direction the free NO₂ air enters into CMC cell to by renewed and start again the cycle.
   

F
igure III.2.32.

The authors do not clearly recommend a reagent; several were tested. They prepared an empirical set-up for a hanging droplet and a film-reaction and tested over 70 chemiluminescent reagents for ozone; the azine dyes phenosafranine, methylene blue and safranin O resulted in the higher light emission.

The main parts of the ozone analyzer are the detection zone:

1. 
   The hanging droplet is formed by a PTFE capillary 3 cm long and 200 nm internal diameter. The accurate and reproducible volume of solution is provided by the peristaltic pump; and the droplet is eliminated by the valve which presses briefly the pumping flexible tubing.
   
2. 
   the film-reagent is a smooth glass surface, 80 x 6 mm, provided with a triangular distributing device to avoid irregularities of the liquid film over the whole surface. Analytical applications are only studied in the film-reactor mode.
   
3. 
   The reactor consists of a 35 x 200 mm chamber build in black PVC. The ozone flowing at 2 L min^-1 reacts with the suitable reagent (according to the operator choice).
   
4. 
   The chemiluminescent reagent is pumped to the detector device placed at about 20 mm of the entrance window of the Photon Counting Module.
   

It is one of the relevant polluting compounds to be controlled to test the air quality and many efforts and procedures have been proposed for its determination in air analyses. Most of these methods lack the required selectivity and suitable sensitivity. A pre-concentration step is the usual sample pre-treatment, which in the next selected example is performed with the aid of a gas permeation device. These devices have been extensively proposed in FIA procedures.

A spectrophotometric monitoring assembly provided with on-line sampling and pre-concentration and able to be field applied is reported.

A micro-pore hydrophobic membrane made of poly(vinyldene) difluoride, sandwiched between two perspex blocks serves for pre-concentration. Air circulates at one side of the membrane at a flow-rate of 0.9 L min^-1; at the other side, the absorbing solution at 0.8 mL min^-1 containing 5 10^-4 mol L^-1 5,5´-dithiobis(2,2´-dinitrobenzoic acid) (DTNB) in 0.025 mol L^-1 phosphate buffer. For a 5 – 8 minutes interval the flow is stopped to allow the pre-concentration process.

F
igure III.2.34.

The application range and detection limits rely on the pre-concentration time and the reference signal; e. g., for 5 min and reference the carrier DNTB solution, 0-4 mg m^-3 and 50 g m^-3, respectively. However, for 8 min of pre-concentration and reference output pure air, the analytical figures of merit are 0-3.2 mg m^-3 and 35 g m^-3. Sample throughput clearly linked to the pre-concentration interval, are 8.5 and 6 h^-1 respectively.

The pollution of underground waters by the extensive use of pesticides is a new anthropogenic problem affecting the health of the population. Pesticides are in the environment as a consequence of being used in agricultural works but also as being used in other activities as domestic use, airports, golf fields, roadsides, etc.

The massive use of pesticides (last two decades) is a new challenge in water treatment plants. Herbicides are the most used pesticides. The manufacturer’s numerical figures give an idea of the size of the problem. In Europe, more than 500 tons/year are fabricated of about 40 pesticides; the manufactured amount of pesticides in USA in 1993 is represented in the Table III.2.3.
Table III.2.3. Amount of pesticides produced in USA in 1993.

Pesticide	Tones	Pesticide	Tones
Atrazine	31,500-33,750	Chlorpyrifos	4,500-6,750
Metalachlor	27,000-29,250	Chlorothalonil	4,500-6,750
Alachlor	20,250-22,500	Propanil	3,150-5,400
Methyl bromide	13,500-15,750	Dicamba	2,700-4,500
Cyanazine	13,500-15,750	Terbufos	22,250-3,600
Dichloropropene	13,500-15,750	Bentazone	1,800-3,150
2,4-D	11,250-13,500	Mancozeb	1,800-3,150
Metam Sodium	11,250-13,500	Parathion	1,800-3,150
Trifluralin	9,000-11,250	Simazine	1,350-2,700
Glyphosate	6,750-9,000	Butylate	1,350-2,700

A pesticide is formulated with additives and co-adjuvant to facilitate its actuation. They are fumigated from air and its concentration in the environment is continuously changing due to dispersion, volatilization, chemical and biological degradation and lixiviation. How these processes are performed is due to the physic-chemical characteristics of each pesticide, but also from the characteristics of waters, soil and atmosphere.

There are many flow methods for pesticide determination. The selected example is based on a new strategy by means of the multi-commutation methodology; with the aid of the chemiluminescence detection and photo-degradation to form the detectable compound. The aqueous solution of the pesticide is irradiated with an UV lamp in the suitable medium. The formed photo-fragments merge with the oxidant, potassium permanganate in a sulfuric medium before the chemiluminescence-based detection of the resulting photoproducts. The use of solenoid valves results in substantial reagent savings and constitutes a further extension of clean chemistry procedures.

T
he pesticide asulam (methyl-4-aminobenzenesulphonyl carbamate), presents a broad spectrum of biological activity. It is used as an insecticide, herbicide and fungicide; and, most often, it is used as a post-emergency herbicide for controlling deciduous and perennial grasses. Asulam acts by stopping cell division and growth of plant tissues. It remains in soil for more than one season. However, it exhibits a high mobility by virtue of the high water solubility of its sodium salt and is therefore a potential water pollutant.

Q2: photodegradation medium (glycine buffer at pH 8.3); Q1: Aqueous solution of asulam; Q4: Carrier (water); Q3: Oxidant (K₃Fe(CN)₆ 0.1 molL^-1 in NaOH 1 molL^-1 or KMnO₄ 10^-4 molL^-1 in H₂SO₄ 1.2 molL^-1). Flow-rate: 9 and 10 mLmin^-1 for Fe(CN)₆^3- and MnO₄^- system, respectively. P: peristaltic pump; PMT: photomultiplier tube; V: Solenoid valve; FC: spiral flow cell; PR: photoreactor consisted of a 173 cm length and 0.8 mm i.d. PTFE tubing helically coiled around a 15 W low-pressure mercury lamp (Sylvania) for germicidal use.

The MnO₄^–/H₂SO₄ system proved more selective. Especially strong was the interference of calcium with the Fe(CN)₆^3-/NaOH system and the photo-degradation of nitrate to nitrite which reacted with the permanganate. Copper gave a strong chemiluminescent signal, even at low concentrations. This may require the prior removal of copper from some types of sample with a solid-phase reactor filled with an appropriate ion-exchange resin. The limit of detection was 40 g L^–1 asulam; the equation relating the two was I = 110.42 [mg L^–1] – 214.84 (r² = 0.9926). The overall analysis time was 120 s.

1. 
   Field-portable flow-injection analysers for monitoring of air and water pollution. P. W. Alexander, L. T. Di Benedetto, T. Dimitrakopoulos, D. B. Hibbert, J. C. Ngila, M. Sequeira and D. Shiels, Talanta, 1996, 43(6), 915 – 925.
   
2. 
   B. Karlberg, B. Pacey, Flow Injection Analysis, a practical guide, Elsevier, New York, 1989.
   
3. 
   Miniature flow injection analyser for laboratory, shipboard and in situ monitoring of nitrate in estuarine and coastal waters. P. C. F. C. Gardolinski, A. R. J. David and P. J. Worsfold, Talanta, 2002, 58(6), 1015 – 1027.
   
4. 
   A reverse-flow injection analysis method for the determination of dissolved oxygen in fresh and marine waters. S. Muangkaew, I. D. MaKelvie, M. R. Grace, M. Rayanakorn, K. Grudpan, J. Jakmunce and D. Nacapricha, Talanta, 2002, 58(6), 1285 – 1291.
   
5. 
   Flow-injection system with enzyme reactor for differential amperometric determination of hydrogen peroxide in rain water, R. Camargo Matos, J.J. Pedrotti and L. Angnes, Anal. Chim. Acta, 2001, 441(1), 73-79.
   
6. 
   Amperometric flow-injection technique for determination of hydrogen peroxide and sulphur(IV) in atmospheric liquid water, I.G.R. Gutz and D. Klockow, Fresenius' Z. Anal. Chem. 1989, 335(8), 919-923.
   
7. 
   Application of flowing stream techniques and related compounds to water analysis. Part I. Ionic species: dissolved inorganic carbon, nutrients, M. Miró, J. M. Estela and V. Cerdá, Talanta, 2003, 60(5), 867 – 886
   
8. 
   An enzymic-fluorimetric method for monitoring of ethanol in ambient air. M. Schilling, G. Voigt, T. Tavares and D. Klockow, Fresenius' J. Anal. Chem., 1999, 364(1-2), 100-105.
   
9. 
   Absorption, concentration and determination of trace amounts of air pollutants by flow injection method coupled with a chromatomembrane cell system: application to nitrogen dioxide determination. Y. L. Wei, M. Oshima, J. Simon, L.N. Moskvin and S. Motomizu, Talanta, 2002, 58(6), 1343-1355.
   
10. 
    Determination of ozone in ambient air with a chemiluminescence reagent film detector. C. Eipel, P. Jeroschewski and I. Steinke, Anal. Chim. Acta, 2003, 491(2), 145-153.
    
11. 
    Flow injection determination of gaseous sulfur dioxide with gas permeation denuder-based online sampling and preconcentration. Z.X. Guo, Y.Z. Li, X.X. Zhang, W.B. Chang and Y.X. Ci, Anal. Bioanal. Chem., 2002, 374(6), 1141-1146.
    
12. 
    A new flow-multicommutation method for the photo- chemiluminometric determination of the carbamate pesticide asulam. A. Chivulescu, M. Catalá-Icardo, J. V. García-Mateo and J. Martínez-Calatayud, Anal. Chim.Acta 2004, in print.