Summary. Citric acid anhydrous (CAS 77-92-9) and citric acid monohydrate (CAS 5949-29-1) are two products with two data sheets, not two names for one. A purchase order that says only 'citric acid' leaves the form, the assay basis, the monograph and the pack open. This guide is a checklist for writing the PO line, reading the Certificate of Analysis and avoiding a substitution mistake.
Why a one-word PO line goes wrong
Citric acid is sold in more than one form and quality, and the word on the invoice rarely settles which. Loose trade names make it worse: sour salt and lemon salt are used for citric acid (general knowledge), and the E330 code on a foreign document tells you only that the substance is citric acid. None of these says whether the powder in the bag is water-free or carries a molecule of water, or which pharmacopoeia the batch was tested against.
The fix costs nothing: write four things on the order line, and ask for the documents that prove them. Supreme Petro Chemicals is a Chennai importer and bulk distributor, and the product pages for citric acid anhydrous and citric acid monohydrate hold the identifiers and data sheets for each form.
Step 1: name the form and the CAS number
Start with the form and the CAS number together. The CAS number is the unambiguous part, because it differs between the two forms. The HSN code does not help here: both forms sit on one tariff line, 2918 14 00, so an invoice carrying that code could describe either.
| Form | CAS number | Water content on the SPC data sheet | HSN code |
|---|---|---|---|
| Citric acid anhydrous | 77-92-9 | 0.5% max (Karl Fischer) | 2918 14 00 |
| Citric acid monohydrate | 5949-29-1 | 7.5-8.8% | 2918 14 00 |
If the water you add through a raw material matters, the form is a process decision, not a purchasing detail. A dry powder blend is the usual case: the water-free form adds no moisture to the mix, which is why a formulator may specify anhydrous. If water in the recipe is unimportant, either form may do the acid job, but the choice should be written down and signed off by QA rather than left to whichever bag arrives.
Do not convert by eye
General knowledge: monohydrate contains roughly 8.6% water by theory (molar masses of about 210.14 and 192.12 g/mol), so about 1.09 kg of monohydrate supplies 1 kg of anhydrous acid. Do not scale a formulation on that number alone. The impurity limits on the two data sheets are not identical, and a trial batch is the proper check.
Step 2: state the assay basis
An assay number means little without its basis. The anhydrous data sheet (SPC-TDS-ACD-015) gives 99.5-100.5% on the anhydrous basis. The monohydrate data sheet (SPC-TDS-ACD-004) gives 99.5-100.5% on the dried basis. Both are ranges, not minimums. General knowledge: a titration result on a dried or water-free basis can read marginally above 100%, which is why monographs state a band.
On the order line, write the basis in words: 'assay 99.5-100.5%, anhydrous basis' for the water-free form. When the CoA arrives, check that the basis is printed. A bare '99.8%' with no basis cannot be compared with the data sheet, and it should be queried before the material is released to production.
Step 3: name the monograph, not the E-number
The E-number identifies the substance. The monograph defines the quality. Our anhydrous data sheet follows the harmonised BP / USP / FCC monograph specification published by the maker, Shandong Ensign. If your QA team works to a specific edition of a pharmacopoeia, name the edition on the order and raise it at the quote stage.
The two data sheets carry different limits, which is the practical reason a monohydrate CoA does not substitute for an anhydrous one. A few examples:
| Test | Anhydrous (SPC-TDS-ACD-015) | Monohydrate (SPC-TDS-ACD-004) |
|---|---|---|
| Oxalate | 100 ppm max | 50 mg/kg max |
| Heavy metals (as Pb) | 10 ppm max | 5 mg/kg max |
| Arsenic | 1 ppm max | 0.1 mg/kg max |
The full impurity table is on the citric acid anhydrous product page.
Technical grade is not food or pharma grade, and that applies here too. If the material is going into a food or pharmaceutical product, name the monograph on the order. Our wider guides cover the labels: food-grade chemicals and FCC standards explains why a food-grade claim is a compliance statement, and IP, BP and USP grades explains what each pharmacopoeial label means.
Step 4: specify pack and documents
The standard pack on the data sheet for the anhydrous powder is the 25 kg HDPE-lined paper bag. If you want a different pack, say so at the enquiry stage; do not assume it from a listing. The anhydrous powder is hygroscopic, so ask that bags arrive sealed and that your store keeps opened bags closed and below 25 C. A bag left open absorbs moisture and cakes, which is a storage problem rather than a defect in the batch.
Then list the documents you need with the delivery:
- The technical data sheet for the form ordered, with its document number.
- The safety data sheet. It classifies citric acid anhydrous as Skin Irrit. 2, Eye Irrit. 2 and STOT SE 3 (H315, H319, H335), signal word WARNING, and restricts its stated use to industrial and professional use. Suitability for food or pharma rests on the TDS monograph and your own qualification.
- The batch Certificate of Analysis, which we supply with every delivery.
Reading the CoA when it arrives
A CoA is only useful if you check it against the order. Work down this list:
- The batch number on the CoA matches the batch number on the bags.
- The product name and form match your order line: anhydrous or monohydrate, not 'citric acid'.
- The assay is a number with a stated basis, inside 99.5-100.5%.
- Water is reported, and for the anhydrous form it is no more than 0.5%.
- Sulphated ash, sulphate, oxalate, heavy metals and arsenic are reported against limits at least as tight as the data sheet.
- The monograph or standard the test followed is named.
- The maker's name is the one on the data sheet.
Do not trust a document because its figures are internally consistent. A certificate that is identical to a producer original except for the year deserves a question. When in doubt, compare it with the producer's original certificate.
A model PO line
The wording below is a template, not a quotation. Fill in the brackets from your own requirement.
| Field | Example entry |
|---|---|
| Product and form | Citric acid anhydrous, CAS 77-92-9 |
| Assay and basis | 99.5-100.5%, anhydrous basis |
| Monograph | [BP / USP / FCC, edition if required] |
| Pack | 25 kg HDPE-lined paper bags |
| Quantity | [your quantity] |
| Delivery location | [Chennai / Tamil Nadu / South India site] |
| Documents | TDS, SDS, batch Certificate of Analysis |
Common mistakes
- Ordering 'citric acid' with no form. The supplier has to guess, and a wrong guess changes both the water in your blend and the limits you are covered by.
- Treating E330 as a quality statement. It names the substance only.
- Assuming the HSN settles the form. Both forms share 2918 14 00.
- Swapping forms mid-contract without QA sign-off. The water content and impurity limits differ.
- Reading the assay without its basis. Anhydrous basis and dried basis are not the same statement as 'as is'.
- Leaving opened bags unsealed. The powder is hygroscopic and cakes.
What to send us for a quote
Send the form and CAS number, the monograph, the quantity, the pack and the delivery location. Call or WhatsApp +91 86087 80096 and we give a quote within 4 working hours. We supply from Chennai (warehouse at Redhills), with a batch Certificate of Analysis supplied with every delivery. Start from the citric acid anhydrous product page for the full specification table, or the monohydrate page if the hydrated form is the one your process needs.
Sources and limits of this guide
SPC figures come from data sheets SPC-TDS-ACD-015 (anhydrous) and SPC-TDS-ACD-004 (monohydrate), the anhydrous safety data sheet (Rev 3.1) and our HSN record. The theoretical water content, the 1.09 conversion factor, the titration remark and the trade names sour salt and lemon salt are general knowledge, not SPC specifications. Nothing here replaces your own QA qualification.