Direct atomic absorption mercury determination (without any pre-treatment procedures) in the samples with complex matrix (foods, vegetation, oil and its products, soils, sediments, various biological materials) is complicated by presence of organic compounds. When such samples are atomized much smoke is produced and practically in all cases the total absorption in the cell is out of the working range of the spectrometer. Using a spectrometer with background correction - Zeeman atomic absorption mercury spectrometer RA-915+ and a developed two-chamber catalyst atomizer (PYRO-915), the direct mercury determination problem is solved.
After inserting the sample in the first chamber of the atomizer it is heated up to 800 C (all mercury compounds are known to be dissociated at such temperatures). Less volatile mercury compounds are dissociated but more volatile species, e.g. mercury organic compounds, can leave the first chamber as compounds during warming up of the chamber. In addition presented organic compounds of the matrix originate much smoke and variously compounds, which are able to produce strong background absorption in the analytical cell. All products are transported from the first chamber to the second one by the carried gas (in our case it is air). The second chamber is continuously heated about 800 C. There, all mercury compounds are dissociated and smoke and interference compounds are burst producing mostly carbon dioxide and water. Zeeman corrector of the spectrometer eliminates the rest background absorption. The catalyst improves the efficiency of oxidation and dissociation in the second chamber.
- Unique direct mercury determination (no pretreatment procedures required) in organic samples at the level of few mg/kg which allows assaying practically all substances with the detection limit much lower than mercury background content
- Mercury determination without its preliminary accumulation on a gold trap
- Broad dynamic measurement range: 3 orders of magnitude without diluting the test.
- Large optical length of analytical cell (40 cm)
- Heated windows of the analytical cell which rules out its contamination even for a sample with a high content of organic substances
- Monitoring the background absorption during measurement allows effective selection of the permissible weight of oil and petrol hydrocarbon samples of any composition, thereby avoiding analysis errors.
- There are no cold sections in the gas duct between the atomizer and analytical cell
- Possible use of oxygen along with air for afterburning organic substances
- No need for compressed oxygen or other gas cylinders
- Visualization of mercury output from the sample, user-friendly computer interface
- Time-stable calibration coefficient after system heating
- Calibration coefficient is set using standard mercury-containing sample of any composition
The validity of the method is proved by the agreement between the measured and certified concentrations in various standard complex-matrix samples (see the table below). Note the excellent consistency of the method: the discrepancies between concurrent measurements do not exceed 10% for different sample weights.
| Reference material | Iass, mg | Measured value, ppb | Certificate value, ppb | Deviation, % |
|---|---|---|---|---|
| NIST 1630a (Coal) |
60
140 |
99
92 |
105±23 | -9 |
| DOLT-2 (Fish liver) |
50
110 |
1860
2070 |
2140±240 | -8 |
| DORM-1 (Fish) |
50
100 |
860
780 |
798±74 | +4 |
| IAEA 140 (Sea plant) |
80
170 |
28
32 |
29±7 | 0 |
| BCR-150(Dry milk) |
52
96 109 |
8.4
7.9 7.9 |
9.4±1.7 | -14 |
| BCR-184(Beef) |
29
59 100 |
2.3
2.5 3.1 |
2.6±0.6 | 0 |
| A table shows analytical features of the developed system for biological samples. It is seen from the table that the detection limit (DL) is lower than the Threshold Limit Value (TLV) of mercury contents accepted in Russia (e.g. for fish the DL is lower than AL in a factor of 30). In this case, a representative sample weight of more than 100 mg is ensured. This Method has also a wide dynamic range from 0.5 to 10 000 ppb | |||
| Samples | TLV, ppb | DL, ppb | SW, mg |
|---|---|---|---|
| Blood | 50 | 0,5 | 300 |
| Hair | 5000 | 2 | 120 |
| Nail | 2 | 120 | |
| Urine | 10 | 0,5 | 300 |
| Fish | 300-700 | 300 | 0,5 |
| Bread | 10 | >300 | 0,5 |
| Cheese | 30 | 120 | 2 |
| Sausages | 30 | 300 | 0,5 |
| Tea | 100 | 100 | 2 |
| Sugar | 10 | 40 | 5 |
| Chocolate | 100 | 100 | 2 |
| Vegetables, (fruits) | 20 | >300 | 0,5 |
| Sample weight | 50-300 mg |
| Upper limit of the measurement range of concentration for a 20 mg sample | 3-5 mg/kg |
| Time for one measurement with air pumping rate 1 l/m | 50-70 c |
| Dimensions and weight of analyzer | 460x210x110 mm, 7.5 kg |
| Dimensions and weight of PYRO-915 (without power supply unit ) | 350x300x150 mm, 5 kg |
| Power requirements for analyzer | 220 Vac, 15 W |
| Power requirements for PYRO-915 | 220 Vac, 300 W |
- RA-915+ mercury analyzer
- PYRO-915 unit
- A PC with OS Windows-95 or higher version with the dedicated software
- standard sample set
- installation and commissioning
Upon request installation and commissioning of LUMEX instruments can be carried out on Customer's site by our service engineers. Consultations and initial training of attendance personnel with due account of Customer's specific needs are performed. Spare parts are delivered and repair is made upon Customer's request (free within the warranty period).