Depending on what you want to spend or buy:
1) long term purchase - get a portable alloy analyzer (NITON, SpectroAnalytical, etc.) - be prepared to spend some money though (in excess of $30,000 usually) - reason to purchase is frequent checks, fast results.
2) short term purchase - alloy spot checking kit (wet chemistry) - inexpensive, usually under $1000 - reason to purchase is infrequent checks, budget prohibits larger purchase.
3) no purchase - hire a metallurgical or NDE analysis company to provide the service on a contractural or per need basis.
We use a NITON II (portable, handheld, looks like a phaser from Star Trek) where I work. It has been fairly reliable and provides a good quick analysis (from power up to results usually in less than 2 or 3 minutes). The only drawback is distinguishing between the same type of metal that has differing carbon or sulfur contents.
~NiM