14. Methods for monitoring nitrate concentration

Monitoring food quality is carried out by:

• manufacturer;

• special official establishments - sanitary-epidemic stations;

• public organizations.

For detection of nitrates there is a whole arsenal of research tests:

We’ll focus in POTENTIOMETER method for nitrate contents determining applied in this work.

Let’s take two vessels and fill them with any solutions of potassium niter having different concentrations then connect them with thin pipe which have ion-selective membrane and capable to pass only ions through (fig. 5).

Dipping into solutions two electrodes connected to milli-voltmeter it’ll indicate an electromotive force (EMF). This is electrochemical circuit, which work as a battery.

If to leave concentration of a saline solution in the first vessel unchanged and to change concentration of solution only in second one, the magnitude of EMF will be changed accordingly. It is possible to build a calibration curve giving EMF dependence on concentration of saline solution in the second vessel.

Fig. 5 The scheme for nitrates concentration determining by potentiometer method:

1,2 - vessels with saline solutions, 3 - pipe with ion-selective membrane, 4,5 - electrodes (metallic wire), 6 - milli-voltmeter.

That curve can be described by the equation

, (6)

where E - magnitude of electromotive force, mV; E₀ - constant, mV; s - constant coefficient (slope of a curve); C - saline concentration in the second vessel, mg/l.

Obtained graph can be further applied for determining concentration of potassium niter in solution (in the second vessel) with unknown concentration.

Solving equation (6) for C we’ll get the following equation for concentration determination:

. (7)

Instrument and equipment applied in laboratory analysis are shown in fig. 6.

Fig. 6 Nitrate-meter «HM-002»:

1 - transducer; 2 - indicator; 3 - switch; 4 - mode switch; 5 - knobs of variable resistance; 6 - auxiliary electrode; 7 - measuring electrode; 8 - vessel with solution.

The method of potentiometry described above is the basic for the device operation.

The device is purposed for the express analysis of nitrates in water solutions of ground, water, agricultural products.

It consists from two parts: transducer and electrode system. The transducer 1 provides the output of concentration value on indicator 2, not the value of electromotive force what’s measured. That makes device more convenient in use.

Instrument should be calibrated before use. To do that use 3 solutions with known concentration of potassium niter KNO₃: C₁ = 10 mg/l, C₁ = 1000 mg/l, C₃ = 100 mg/l for device calibration. Dip the electrodes washed out in distil water and wiped by filter paper into solution with concentration of ions C₁ = 10 mg/l. After 1.5 .. 2 min press the button « > 0 < » and set on the device indicator «0.00 m».

15. Meteorological conditioning

Microclimate (meteorological conditions) is assumed a climate of internal environment of work area that is introduced as common action of the following parameters: air temperature, air humidity, air circulation and radiant heat.

The environment outside the human’s body is able to accept the heat, which is worked out by the human. That heat transfers into environment due to temperature conductivity through the cloth, convection while air contacts open skin areas, radiant heat, vaporizing of water from the skin surface and heating of air on respiration. The balance between the heat extracted by body and the absorbed by environment maintains normal thermal and functional condition of the human.

Imbalance of heat exchange causes over heating or overcooling, then loss of consciousness or even thermal death. Heat extraction depends on physical exertion and makes from 85 J/s (easy work) to 500 J/s (heavy work).

Human organism keeps its temperature stable in wide range of environmental parameters. Body maintains temperature at about 36.6 deg С when air temperature changes from -40 deg С to +40 deg С. However some parts of the body may have temperature varying from +24 deg С to +37.1 deg С.

The intensive heat-exchange runs in liver – its temperature equals to 38.0..38.5 deg C. It’s also known the biological cycle of the skin temperature: maximal (37.0..37.1 deg C) at 4.00 - 7.00 p.m., minimal (36.0..36.2 deg C) at 2.0 - 4.00 a.m.

Lung ventilation is volume of the air inhaled per one hour. It depends on physical exertion, air humidity, and air temperature.

Thermal condition of person depends on physical exertion, temperature of surrounding objects and microclimate parameters (air temperature, air circulation, air humidity and atmospheric pressure).

Low air temperature causes rising heat emission through convection and radiation and may lead to overcooling of organism.

High air temperature causes opposite process. It’s in fact that work capacity of a person descents at air temperature over 30 deg C. Insufficient air humidity causes intensive vaporizing from mucous membranes, their drying and chapping and consequently infecting. Water and saline removed by sweating should be made up cause their loss brings to blood clotting and effects cardio-vascular system.

6 % dehydration of organism violates brain activity and worsens vision. 15 - 20% dehydration may be fatal. Low saline concentration deprives blood of ability to hold water and violates cardio-vascular system. At high air temperature organism loses carbohydrate, fat, protein.

Longtime being at high air temperature and humidity may cause heat accumulation in organism and its hyperthermia, when body temperature rises to 38 - 40 deg C. Headache, dizziness, wrong color perception, weakness, mouth dryness, vomiting, sweating are symptoms of hyperthermia. Increasing heart rate and respiration riches blood with residual nitrogen and carbon dioxide, what exhibits as paleness, blue color of skin, wide pupils, sometimes cramps, loss of consciousness.

Lowering temperature causes overcooling (hypothermia). Decreasing frequency of respiration follows hypothermia, inhale takes more volume. Then it comes muscle tremor, which is body reaction that transfers muscles contraction into heat. That allows holding up lowering temperate for a while. Cold injury is consequence of low temperature.

Appropriate air circulation makes normal occupational condition also. Human organism is already sensitive to airflow at 0.15 mps. Air flow temperature up to 36 deg C makes it feel chilling, and over 40 deg C has inhibiting effect.

Heat transfer from hot or melted surface goes through convection, heat conductivity and heat radiation. Convection is the process of heat transfer through a fluid (steam flow, air, liquid), caused by movement of molecules from cool regions to warmer regions of lower density; heat conductivity is the property of transmitting heat in solid body; radiant heat is heat transferred in the form of electromagnetic radiation rather than by conduction or convection (infrared radiation), infrared radiation transfers into thermal energy only being incident to a surface.

Radiant energy may cause burns like after direct contact with hot surfaces. Burns are classified according to the depth of tissue affected:

1. first-degree burn: skin surface painful and red;

2. second-degree burn: blisters appear on the skin;

3. third-degree burn: destruction of both epidermis and dermis.

Heat regulation is called ability of organism to regulate heat exchange with environment and keep body temperature constantly at normal level independent on outer conditions and physical activity.

Basic factor of heat regulation is ability to extend or contract blood flow in peripheral vascular system. Overheating makes vascular system extend and heat transfers outside more intensive. Overcooling causes contraction of the vascular system.