Introduction
Heavy metal pollution remains a major concern in environmental and food safety due to its persistence, bioaccumulation, and high toxicity. Lead, cadmium, mercury, chromium, arsenic, and copper ions are harmful to human health even at trace concentrations. While atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS) enable ultra-trace analysis, these instruments are expensive. UV-Vis spectrophotometry, through selective chromogenic reactions, offers an economical and simple approach for heavy metal detection.
STON Technologies' NanoQuant series UV-Vis spectrophotometers provide reliable platforms for heavy metal testing with excellent photometric accuracy and stable optical performance.
Determination of Common Heavy Metals
Hexavalent Chromium (Cr⁶⁺): DPCA Method
In acidic solution, hexavalent chromium reacts with 1,5-diphenylcarbazide (DPC) to form a violet-red complex measured at 540nm. This method achieves a detection limit of 0.004mg/L and is the standard method per GB 7467-87 and EPA Method 7196A. The NanoQuant series delivers photometric accuracy of ±0.002A at 540nm for reliable low-level determination.
Copper (Cu²⁺): DDTC Method
In ammoniacal solution (pH 8-10), copper reacts with sodium diethyldithiocarbamate to form a yellow-brown colloidal complex measured at 440nm.
Iron (Fe²⁺/Fe³⁺): 1,10-Phenanthroline Method
Ferrous iron forms a stable orange-red complex with 1,10-phenanthroline in the pH range 3-9, measured at 510nm. Molar absorptivity reaches 1.1×10⁴ L·mol⁻¹·cm⁻¹. This is the standard method for total iron determination (GB/T 3049-2006).
Nickel (Ni²⁺): Dimethylglyoxime Method
In the presence of an oxidizing agent, nickel reacts with dimethylglyoxime in alkaline solution to form a red-brown complex measured at 530nm.
Manganese (Mn²⁺/Mn⁷⁺): Periodate Oxidation Method
Under acidic conditions, Mn²⁺ is oxidized by potassium periodate to purple permanganate ions, measured at 525nm.
Lead (Pb²⁺): Dithizone Method
Under alkaline conditions, lead reacts with dithizone to form a red complex, extractable in carbon tetrachloride and measured at 520nm.
Arsenic (As³⁺/As⁵⁺): Ag-DDC Method
Arsine reacts with silver diethyldithiocarbamate to form red colloidal silver, measured at 525nm. This is the standard method for total arsenic determination (GB/T 7485-87).
Simultaneous Multi-Element Determination
UV-Vis spectrophotometry can simultaneously determine multiple heavy metals through multi-wavelength analysis and chemometric methods. The NanoQuant1920's variable slit design (0.5/1/2/4/5nm) optimizes spectral resolution as needed.
Advantages and Limitations
Advantages:
- Low instrument cost (1/10 to 1/100 of AAS/ICP-MS)
- Simple operation, no complex sample preparation
- Low maintenance, stable and reliable operation
- Ideal for small laboratories and field testing
Limitations:
- Lower sensitivity than AAS/ICP-MS
- Potential interference from complex matrices
- Generally measures total metal content
STON Solutions for Heavy Metal Analysis
- NanoQuant756: Wavelength accuracy ±0.5nm, stray light ≤0.1%T, cost-effective for routine screening
- NanoQuant1810: Ratio dual-beam system eliminates source fluctuations, photometric accuracy ±0.002A
- NanoQuant1920: Double beam, baseline flatness ±0.0005A, photometric noise ±0.0003A, ideal for demanding trace analysis
Conclusion
UV-Vis spectrophotometry remains irreplaceable for heavy metal detection in routine screening, field testing, and resource-limited laboratories. STON NanoQuant series spectrophotometers offer reliable, cost-effective solutions for heavy metal analysis.
