Steps to detect acetonitrile content in surface water

  Acetonitrile in surface water, groundwater, domestic sewage and other water bodies can be determined by gas chromatography. The principle of this method is as follows.

  Direct injection method: The acetonitrile sample is directly injected into the gas chromatograph after filtration, separated by capillary column, detected by NPD detector, qualitative by relative retention time, and quantified by chromatographic peak area (peak height).
  Purge and trap method: The sample is purged with nitrogen, the purged target is enriched through the trap tube, and then the trap tube is rapidly heated to desorb the acetonitrile adsorbed in the trap tube and enter into the gas chromatography Instrument, separated by capillary column, detected by FID or NPD detector, qualitative by relative retention time, quantitative by chromatographic peak area (peak height).

Reagents required for testing

1. Acetonitrile standard stock solution: 1.00×104 mg/L.
  Commercially available certified standard products, generally using water as the solvent; or using chromatographically pure standard products to prepare, first weigh a 10ml volumetric flask containing some pure water, and then drop a few drops of chromatographically pure acetonitrile 100mg (accurate to 0.1mg) , weighed. Make up to volume and mix with pure water, the concentration is about 1.00×104mg/L (accurate to 10mg/L), as the standard stock solution of acetonitrile. Stock solutions are stored in vials with Teflon screw caps and are stable for 3 months at 20-25°C.
2. Acetonitrile standard solution: 100mg/L.
  Pipette a certain volume of acetonitrile standard stock solution into a 100ml volumetric flask containing some pure water, dilute to volume with pure water, and mix to obtain 100mg/L acetonitrile standard solution. The standard use liquid is ready to use.
3. High-purity nitrogen: 99.999% purity.
4. Hydrogen: purity 99.99%.

Instruments required for testing

1. Purge and trap device: The purge device can be directly connected to the chromatographic part and should have a 5ml purge tube. The trap tube generally uses 1/3 Tenax, 1/3 silica gel, 1/3 activated carbon mixed adsorbent or other equivalent adsorbents.
2. Gas chromatograph: It has a capillary column split/splitless injection port, which can electronically control the carrier gas pressure. Equipped with FID or NPD detector.
3. Chromatographic column: Quartz capillary column, 30m×0.32mm×1.0μm, the stationary phase is polyethylene glycol (PEG-20M), or a chromatographic column with similar performance.
4. Air-tight syringe: 5ml.
5. Micro syringe: 5ul, 10ul, 50ul, 100ul, 500ul, 1000ul.
6. Sampling bottle: 40ml brown wide mouth sampling bottle with Teflon liner screw cap.
7. Brown glass bottles: 1ml and 2ml, with teflon-lined screw caps.
8. Balance: 1/10,000 balance.
9. Volumetric flask: Grade A, 10ml and 100ml.

water sample collection

  In accordance with the regulations, parallel double samples are collected for all water samples, and each batch of samples should include a full program blank and a shipping blank. When collecting water samples, the water samples should overflow in the water sample bottle without leaving space.
water sample preservation
  The water sample should be placed in a refrigerator at about 4°C immediately after collection, and sent to the laboratory for analysis as soon as possible. If it cannot be analyzed in time, it can be stored in a refrigerator at about 4°C. There is no organic interference in the water sample storage area, and the water sample should be completed within 7 days. analyze.

Detection steps

Analysis conditions of direct injection method
Reference chromatographic conditions:
Injection volume: 1.0 μl;
Injection port: splitless, temperature 220℃;
Column temperature: constant temperature 50℃;
Analysis time: 15min;
Column flow: constant flow 7.0ml/min (nitrogen);
NPD detector: temperature 330°C, hydrogen 3.5ml/min, air 80ml/min.

Reference Purge and Trap Conditions

Reference chromatographic conditions:

Drawing of the standard curve

  NPD direct injection method: Take 6 100ml volumetric flasks and prepare 6 standard series with concentrations of 0.10, 0.50, 1.00, 2.00, 5.00, 10.0 mg/L with acetonitrile standard solution (5.3) in turn. Accurately take 1.0 μl for gas chromatography analysis, take the peak area (peak height) as the ordinate and the concentration of acetonitrile as the abscissa to draw a standard curve.
  FID purge and trap method: Take five 40ml brown VOC tubes, and sequentially prepare five standard series with concentrations of 0.5, 1.0, 2.0, 3.0, and 5.0 mg/L with acetonitrile standard solution (5.3). Accurately take 5.0ml to the purging tube for purging, and then analyze by gas chromatography. Take the peak area (peak height) as the ordinate and the concentration of acetonitrile as the abscissa to draw a standard curve.
  NPD purge and trap method: Take five 40ml brown VOC tubes, and sequentially prepare five standard series with concentrations of 0.025, 0.050, 0.100, 0.200, and 0.500 mg/L with acetonitrile standard solution (5.3). Accurately take 5.0ml to the purging tube for purging, and then analyze by gas chromatography. Take the peak area (peak height) as the ordinate and the concentration of acetonitrile as the abscissa to draw a standard curve. The standard chromatogram of acetonitrile is shown below.

Steps

direct injection

Purge and trap

Blank test

Qualitative Analysis of Acetonitrile

Quantitative Analysis of Acetonitrile