juānzèng yǐqián yào xiān xiāodú.

The structure is:

捐赠以前 + 要 + 先 + 消毒

A very literal breakdown is:

• 捐赠以前 = before donating / before the donation
• 要 = need to / must
• 先 = first
• 消毒 = disinfect / sterilize / sanitize

So the sentence follows a common Chinese pattern:

time phrase + modal verb + sequence word + main verb

In natural English, it comes out as something like:

Before donating, you need to disinfect first.

The word order feels different from English, but it is very normal in Chinese to put the time phrase near the beginning.

Here, 要 does not mean want to. It means:

• need to
• must
• have to

So in this sentence, 要先消毒 means:

need to disinfect first

This is a very common point of confusion because 要 can mean different things depending on context:

• 我要喝水。 = I want to drink water.
• 去医院以前要预约。 = Before going to the hospital, you need to make an appointment.

In your sentence, because it is giving a requirement or procedure, 要 means must / need to, not want to.

They are related, but they do different jobs.

• 以前 sets the time frame: before donating
• 先 shows the order of actions: first disinfect

So:

• 捐赠以前 = before the donation happens
• 先消毒 = disinfect first

Together, they mean something like:

Before the donation happens, the first thing you should do is disinfect.

If you remove 先, the sentence still works:

• 捐赠以前要消毒。

That means You need to disinfect before donating.

Adding 先 makes the sequence more explicit and natural, especially for instructions or procedures.

以前 has a few related meanings, and the exact meaning depends on what comes before it.

1. After a time or event, it means before

• 捐赠以前 = before donating
• 吃饭以前 = before eating
• 三点以前 = before 3 o’clock

2. By itself, it can mean formerly / previously / in the past

• 我以前住在北京。 = I used to live in Beijing.

So in your sentence, because 以前 comes after 捐赠, it means:

before the act of donating

It does not mean in the past here.

In Chinese, words like 以前, 以后, 之前, and 之后 usually come after the time or event they refer to.

So Chinese says:

• 捐赠以前 = before donating
• 吃饭以后 = after eating
• 上课之前 = before class

This is different from English, where before usually comes first:

• before donating
• after eating

You can think of Chinese as building the phrase like this:

[event] + before

So 捐赠以前 is literally something like:

donating + before

which naturally means before donating.

Chinese often leaves out the subject when it is obvious from context.

So 捐赠以前要先消毒。 does not explicitly say:

• you
• one
• they
• the patient
• the donor
• the skin / equipment

The subject is understood from the situation.

Depending on the context, the meaning could be:

• Before donating, you need to disinfect.
• Before the donation, one must disinfect.
• Before donation, it is necessary to disinfect.

This kind of omission is very common in Chinese, especially in:

• instructions
• signs
• procedures
• medical contexts

English usually wants a subject, but Chinese often does not need one.

Grammatically, 消毒 can be used without stating the object if the object is already understood from context.

For example, in a medical or donation setting, the missing object might be:

• the skin
• the needle
• the area
• the equipment

So 先消毒 can mean:

• disinfect first
• sterilize first
• sanitize first

If you want to be more specific, you can add an object:

• 先给皮肤消毒。 = First disinfect the skin.
• 先把器械消毒。 = First sterilize the equipment.

In the original sentence, the object is omitted because the focus is on the procedure, not on naming the exact thing being disinfected.

Yes, all of these can work:

• 捐赠以前
• 捐赠之前
• 捐赠前

They all mean before donating / before the donation, but there are slight style differences.

Common alternatives

• 捐赠前要先消毒。
• 在捐赠之前，要先消毒。

Notes

• 前 is shorter and often very natural in instructions.
• 之前 and 以前 are both fine; 之前 often feels a bit more straightforward in modern spoken Chinese.
• 在捐赠之前 sounds slightly more complete or formal.

So your sentence is understandable and grammatical, but depending on context, many speakers might prefer a shorter version like:

捐赠前要先消毒。

A comma is optional here.

You may see both:

• 捐赠以前要先消毒。
• 捐赠以前，要先消毒。

Because 捐赠以前 is a time phrase at the beginning, adding a comma can make the pause clearer. But in a short sentence like this, leaving it out is also normal.

So both are acceptable.

A comma is more likely when:

• the sentence is longer
• the writer wants a clearer pause
• the style is more formal

For a short instruction, no comma is perfectly fine.