🌿 Manganese and its compounds in workplace air — flame AAS

Environment PN-Z-04472

Overview

Manganese is used in metallurgy for the manufacture of ferrous and non-ferrous alloys and of steel; manganese dioxide — in galvanic cells, as an oxidising agent and as an additive to paints; other compounds — in fertilisers, feeds, wood preservatives and in the pharmaceutical, glass and ceramic industries. Occupational exposure is connected with the extraction and the processing of ores, with the manufacture and the casting of alloys and with welding with electrodes containing manganese. Chronic exposure damages the nervous, the respiratory and the reproductive systems; poisoning with manganese clinically resembles Parkinson's disease and is irreversible. The NDS values: 0.2 mg/m³ for the inhalable fraction and 0.05 mg/m³ for the respirable fraction — the assessment of the exposure is carried out separately for the two fractions.

The method of flame atomic absorption spectrometry worked out at CIOP-PIB constitutes a revision of the standard PN-79/Z-04125.02 and has been embodied in the standard PN-Z-04472:2015-10; the limit of determination is 0.02 mg/m³ for the inhalable fraction and 0.005 mg/m³ for the respirable fraction (air volume 600–720 l, final volume of the sample 10 ml). The CIOP-PIB procedure of 2021 determines manganese together with nickel and iron in a single analytical run; its measuring range for manganese of 0.30–8.0 µg/ml corresponds to 0.017–0.44 mg/m³ in the inhalable fraction (dilution 4) and to 0.0042–0.11 mg/m³ in the respirable fraction (without dilution), that is 0.085–2.2 NDS.

Method principle

A known volume of air (up to 720 l) is drawn through cellulose ester membrane filters (0.85 µm): for the inhalable fraction a filter in a holder with a flow rate of not more than 2 l/min, for the respirable fraction, in parallel, a filter in the upper part of a microcyclone with the flow rate proper to the separation of that fraction. Each filter is mineralised in a 50 ml beaker with 2 ml of concentrated HNO₃ on a hot plate (about 140 °C) until the filter has dissolved and the contents have evaporated almost to dryness (several times), 2 ml of 10 % HNO₃ is added, after 30 min it is transferred into a 10 ml flask and made up with 0.1 mol/l HNO₃. The solution of the inhalable fraction is diluted (2.5 ml + 1.5 ml of 10 % HNO₃ + 0.5 ml of lanthanum chloride to 10 ml, k = 4); the solution of the respirable fraction is prepared without dilution with the addition of 0.5 ml of lanthanum chloride. Manganese is determined at 279.5 nm in an oxidising acetylene–air flame, against a calibration curve of 0.30–6.00 µg/ml and with a blank from a clean filter; the concentration X = (c − c0)·V1·k/V [mg/m³], separately for each fraction.

Applications

• Assessment of the exposure of welders and of workers in metallurgy, in foundries, in the manufacture of alloys and in the processing of manganese ores
• Plants using manganese compounds: manufacture of cells, paints, fertilisers, glass, ceramics, wood preservatives
• Periodic measurements under the regulation of the Minister of Health — comparison with the NDS of 0.2 mg/m³ (inhalable fraction) and 0.05 mg/m³ (respirable fraction)
• Personal sampling with parallel sampling of the two fractions of the aerosol
• Determination of Mn together with Ni and Fe from one series of samples (the CIOP-PIB procedure 2021)

Key parameters

Standard

Standard number

PN-Z-04472:2015-10 + Ap1:2015-12

Title (PL)

Ochrona czystości powietrza — Oznaczanie manganu i jego związków na stanowiskach pracy metodą płomieniowej absorpcyjnej spektrometrii atomowej

Title (EN)

Air purity protection — Determination of manganese and its compounds at workplaces by flame atomic absorption spectrometry

Step-by-step procedure

1. Sampling

   In accordance with the principles of PN-Z-04008-7 take two samples in parallel in the breathing zone: the inhalable fraction through a filter in a holder (up to 720 l, flow rate ≤ 2 l/min) and the respirable fraction through a filter in the upper part of a microcyclone (up to 720 l, the flow rate proper to the microcyclone).

2. Mineralisation

   Place each filter in a 50 ml beaker, add 2 ml of concentrated HNO₃ and heat it on the hot plate (about 140 °C) until the filter has dissolved and the contents have evaporated almost to dryness; repeat until the sample has completely dissolved. Add 2 ml of 10 % HNO₃, wait about 30 min, transfer it quantitatively with 5–6 portions of 0.1 mol/l HNO₃ into a 10 ml flask and make up to the mark. In parallel mineralise clean filters (the blanks No 1 and No 2).

3. Solutions for the test

   Inhalable fraction (No 1): into a 10 ml flask transfer 2.5 ml of the solution after the mineralisation, add 1.5 ml of 10 % HNO₃ and 0.5 ml of lanthanum chloride and make up with 0.1 mol/l HNO₃ (k = 4). Respirable fraction (No 2): into the 10 ml flask with the residue after the mineralisation add 0.5 ml of lanthanum chloride and make up with 0.1 mol/l HNO₃ (without dilution).

4. Calibration curve

   On the day of the analysis prepare six working solutions of 0.30–6.00 µg/ml Mn (0.5 ml of lanthanum chloride and 2 ml of 10 % HNO₃ per 10 ml) and a zero sample. Make three measurements of the absorbance at 279.5 nm in an oxidising acetylene–air flame, zeroing with 0.1 mol/l HNO₃; automatic calibration of the instrument is permitted.

5. Measurement

   Measure the absorbance of the solutions No 1 and No 2 and of the blanks under the conditions as for the calibration and read the concentrations from the curve. Where the range is exceeded repeat the determination with a smaller volume of the solution, taking the dilution factor into account.

6. Calculation and assessment

   For each fraction calculate X = (c − c0)·V1·k/V [mg/m³] (V1 = 10 ml; k = 4 for the inhalable fraction, 1 for the respirable one; V — the volume of air in l). Compare it separately with the NDS of 0.2 mg/m³ (inhalable) and 0.05 mg/m³ (respirable).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Operations with concentrated nitric acid — in protective clothing and under an efficient fume cupboard; the hot mineralisation evolves nitrogen oxides
• Operate the acetylene and the AAS burner according to the instructions of the manufacturer; check the leak-tightness of the gas installation
• Collect the residues of the solutions of the reagents and of the standards in containers and hand them over for disposal to authorised institutions

Frequently asked questions