RuiXin SJ-LH221 Oxalic Acid Detection Kit for Crab Washing Powder Residue

Overview

The RuiXin SJ-LH221 Oxalic Acid Detection Kit is a field-deployable, rapid immunoassay system engineered for the qualitative and semi-quantitative screening of residual oxalic acid on or in rinse solutions used during post-harvest processing of Chinese mitten crab (*Eriocheir sinensis*). Designed specifically to verify compliance with food safety regulations prohibiting unauthorized use of oxalic acid in crustacean cleaning—particularly for removal of black epidermal stains—the kit leverages a competitive lateral flow immunoassay (LFIA) principle. In this format, free oxalic acid in the sample competes with immobilized oxalate conjugates for binding sites on anti-oxalate monoclonal antibodies labeled with colloidal gold nanoparticles. A visible test line intensity inversely correlates with analyte concentration, enabling visual or densitometric interpretation within 10 minutes. The assay is optimized for aqueous extracts from crab surface swabs or final rinse water, delivering high specificity against structurally related dicarboxylic acids (e.g., malonic, succinic) and negligible cross-reactivity with common organic acids found in aquatic environments.

Key Features

• Rapid analysis: Complete result generation in ≤10 minutes without instrumentation
• High sensitivity: Limit of detection (LOD) of 1 ppm (µg/g or µg/mL), validated per AOAC Official Method guidelines for lateral flow residue screening
• Quantitative capability: Semi-quantitative estimation via calibrated color intensity comparison chart (1–50 ppm range) or optional handheld reader (RuiXin RD-200, sold separately)
• Robust stability: Lyophilized reagents retain activity for ≥18 months at 4–25°C; no cold chain required for transport or storage
• User-friendly workflow: Minimal training required—only three steps: sample extraction, dilution, and lateral flow strip insertion
• Regulatory alignment: Kit design and validation documentation support adherence to GB 2763–2021 (China’s Maximum Residue Limits for Pesticides and Other Chemicals in Food) and general principles of HACCP-based seafood processing controls

Sample Compatibility & Compliance

The SJ-LH221 kit accepts multiple sample matrices relevant to crab processing facilities: (i) 10 mL final rinse water collected after washing; (ii) surface swabs (sterile polyester-tipped) moistened with 1 mL extraction buffer and rubbed across crab carapace/abdomen, then eluted; (iii) homogenized gill or hepatopancreas tissue extracts (≤5% w/v in buffer). All samples require centrifugation (3,000 × g, 5 min) prior to testing. The assay has been verified for matrix tolerance up to 15% total dissolved solids (TDS) and pH 4.0–7.5. While not certified under ISO/IEC 17025, the kit’s performance characteristics—including intra-assay CV <12%, inter-batch CV <15%, and recovery rates of 88–103% in spiked crab rinse water—meet internal validation protocols aligned with ICH Q2(R2) principles for screening methods. It supports GLP-aligned recordkeeping when used with RuiXin’s traceable lot-numbered consumables and logbook templates.

Software & Data Management

This is a non-instrumental assay; no proprietary software is embedded. However, optional digital integration is supported via the RuiXin RD-200 portable densitometer (sold separately), which connects via Bluetooth to the RuiXin LabTrack Mobile App (iOS/Android). The app enables image capture, automatic line-intensity quantification, batch-level reporting, PDF certificate generation (with timestamp, operator ID, and lot traceability), and export to CSV or LIMS-compatible XML. All data are stored locally on-device unless manually synced to cloud-based RuiXin SecureVault (AES-256 encrypted, GDPR-compliant infrastructure). Audit trail functionality complies with FDA 21 CFR Part 11 requirements for electronic records when paired with user authentication and electronic signature modules.

Applications

• Verification of oxalic acid prohibition in certified organic or eco-labeled crab supply chains
• In-process quality control at wholesale crab grading and packing facilities

<liRegulatory inspection support for municipal food safety bureaus conducting unannounced audits

• Supplier qualification testing during procurement of live crab from aquaculture cooperatives
• Root cause analysis during non-conformance investigations following consumer complaints or export rejection
• Training tool for QA/QC personnel on chemical residue risk awareness and rapid response protocols

FAQ

Can this kit detect oxalic acid in cooked or frozen crab meat?
No. The SJ-LH221 is validated exclusively for rinse water and surface swabs from raw, live, or chilled post-harvest crab. Thermal processing alters oxalate speciation and matrix interference invalidates results.
Is cross-reactivity with citric or tartaric acid documented?
Yes. Cross-reactivity testing shows <0.5% signal response at 100 ppm citric acid and <0.3% at 100 ppm tartaric acid—well below the LOD threshold.
Does the kit include extraction buffers and swabs?
Yes. Each 50-test kit contains 50 lateral flow strips, 50 extraction tubes with lyophilized buffer tablets, 50 sterile swabs, 50 pipette tips, and a color reference card.
What is the shelf life after first opening the pouch?
Once opened, strips must be used within 1 hour under ambient humidity <60% RH. Unopened foil pouches retain full performance until the printed expiry date.
Is method validation data available for regulatory submission?
Yes. Certificate of Analysis (CoA), summary validation report (including precision, accuracy, LOD/LOQ, and ruggedness), and SOP template are provided digitally upon request with proof of purchase.