Bisacodyl is a stimulant laxative primarily used clinically to treat constipation and for bowel preparation before intestinal surgery. In recent years, some unscrupulous businesses have illegally added bisacodyl and its derivatives to products such as weight-loss teas, enzyme foods, and meal replacement powders to enhance their purported "slimming" effects, posing serious health risks to consumers. The State Administration for Market Regulation's current special campaign aims to curb such illegal practices and ensure food safety. Detecting these illegally added substances requires specialized analytical instruments and technical methods. This article systematically introduces the major instruments and techniques applicable for detecting bisacodyl and its derivatives.
High-performance liquid chromatography (HPLC) is currently the most widely used analytical instrument for detecting bisacodyl, offering high sensitivity, excellent selectivity, and rapid analysis.
Instrument Configuration Requirements: Reverse-phase HPLC systems equipped with ultraviolet (UV) or diode array detectors (DAD) are typically employed for bisacodyl detection. A C18 column (250 mm × 4.6 mm, 5 μm) is commonly used, with a mobile phase consisting of methanol-water or acetonitrile-water, often supplemented with 0.1% phosphoric or formic acid to adjust pH and improve separation.
Optimization of Detection Conditions: The optimal detection wavelength for bisacodyl is around 263 nm. Method development requires optimization of parameters such as mobile phase ratio, flow rate (typically 1.0 mL/min), and column temperature (30–40°C). Sample preparation usually involves extraction with methanol or acetonitrile, followed by solid-phase extraction (SPE) purification if necessary.
Method Advantages: HPLC can simultaneously detect bisacodyl and its major metabolites, with a method detection limit (MDL) as low as 0.01 mg/kg, fully meeting the requirements for trace-level detection in food. The State Administration for Market Regulation's published method "Determination of Bisacodyl in Food" (BJS 201905) is based on HPLC technology.
For trace levels of bisacodyl and its derivatives in complex food matrices, liquid chromatography-tandem mass spectrometry (LC-MS/MS) offers superior sensitivity and specificity.
Instrument Configuration: A triple quadrupole mass spectrometer with electrospray ionization (ESI) in positive ion mode is used. The precursor ion for bisacodyl is m/z 361.1 [M+H]+, with characteristic product ions at m/z 233.0 and m/z 91.0. Mass spectrometry parameters, including collision energy and ion source temperature, must be optimized.
Sample Preparation: Compared to HPLC, LC-MS/MS demands more rigorous sample cleanup. Methods such as QuEChERS or solid-phase extraction (SPE) using MCX or HLB cartridges are commonly employed. Isotope-labeled internal standards are recommended for quantification to mitigate matrix effects.
Method Performance: LC-MS/MS achieves a detection limit of 0.001 mg/kg and can simultaneously screen multiple illegally added laxatives. This method has been incorporated into several provincial food safety inspection protocols as the gold standard for confirming positive samples.
Although bisacodyl is more suited to LC-based analysis, gas chromatography-mass spectrometry (GC-MS) can serve as a supplementary detection technique.
Instrument Conditions: GC-MS analysis requires derivatization of the analyte, typically using BSTFA + TMCS (99:1) as a silylating reagent. A DB-5MS column (30 m × 0.25 mm × 0.25 μm) with temperature programming is employed. Mass spectrometry is performed in electron ionization (EI) mode, using full scan or selected ion monitoring (SIM).
Application Scenarios: GC-MS is more suitable for analyzing certain bisacodyl derivatives or degradation products. It can also serve as a preliminary screening tool in grassroots testing facilities lacking LC-MS equipment. However, its sensitivity is lower than LC-MS, with a detection limit of approximately 0.05 mg/kg.
To meet the needs of on-site rapid screening for market supervision, various rapid detection technologies have been applied for preliminary bisacodyl screening.
Enzyme-Linked Immunosorbent Assay (ELISA): This rapid detection method, based on antigen-antibody specific reactions, provides results within 30 minutes. Commercial bisacodyl detection kits are available, suitable for high-throughput sample screening, though false positives may occur.
Surface-Enhanced Raman Spectroscopy (SERS): An emerging rapid detection technology that enables trace-level detection through nanoparticle-enhanced Raman signals. Studies have reported characteristic Raman peaks for bisacodyl at 1585 cm⁻¹ and 1605 cm⁻¹, with simple sample preparation and results available within 5 minutes.
Portable Mass Spectrometers: Recently developed portable mass spectrometers, such as the Mini β, allow on-site qualitative analysis of bisacodyl, though quantitative accuracy requires further improvement.
In practical regulatory work, appropriate method combinations should be selected based on testing objectives and laboratory conditions.
Principles for Method Selection: Routine supervision and sampling recommend HPLC-DAD; for law enforcement and case confirmation, LC-MS/MS should be used; rapid screening may employ ELISA or SERS. Grassroots regulatory offices can use HPLC-UV for preliminary testing, with positive samples sent to higher-level institutions for LC-MS/MS confirmation.
Key Validation Metrics: These include linear range (typically 0.005–0.5 mg/L), limit of detection (LOD), limit of quantification (LOQ), precision (RSD < 15%), recovery rate (80%–110%), and matrix effects. Inter-laboratory comparison and validation are necessary when required.
Quality Control Measures: Each batch of samples should include blank controls, spiked recoveries, and duplicates; certified reference materials should be used periodically for verification; instrument maintenance and calibration protocols must be established; and personnel training and technical exchanges should be strengthened.
As illegal addition methods become more covert, detection technologies continue to evolve.
High-Resolution Mass Spectrometry: Techniques such as LC-QTOF-MS enable non-targeted screening and the establishment of spectral libraries for bisacodyl derivatives, addressing structurally modified illegal additives.
Microfluidic Chip Technology: Integrating sample preparation and detection into microchips allows for on-site rapid detection, potentially leading to dedicated bisacodyl detection devices.
Artificial Intelligence-Assisted Analysis: Combining big data and machine learning algorithms improves the identification efficiency of trace illegal additives in complex matrices and reduces false-negative rates.
The State Administration for Market Regulation will continue to refine detection methodologies and enhance technical capabilities, providing robust support for combating illegal practices such as bisacodyl addition in food and ensuring the safety of consumers' diets.
